IECEN'I' TRENDS AND DEVELOPMENTS II THE CONCRETE FIELD "mi: Io: flu 009m OI I. -S.' MICHIGAN STATE COLLEGE John C. Bullock, Jr. 1949 . ..§.n...,v.a... Smurzaxuu. OWI . 5. . Fwfi 5t;.fli-.. .-1 ... .. . .13 5. .....h.r\0$ma ".411”.- ‘ .. \I RECERT TREKDS AND DEVELOPMENTS IN THE COKCRETE FIELD A Thesis Submitted ta The Faculty of Michigan State College of Agriculture and Applied Science by Jam} Ce Enllaok. Ire “hi-e. Candidate for the Degree of Bachelor of Science fiaroh, 1949 THESIS /‘* " . I. I- v 4 1.“— Dedication The present legieletion of the Civil Engineering De- partment of'Michigan State College requires that thie paper be claeaified an a "theeie." Therefore, it eeemed only fitting that I investigate the aforementioned deno- tation. and aecertain the extent to which thie paper qualifiee as such. The Webeter'e Collegiate Dictionary, 6th Edition, which has been my faithful companion for the past four yeare, can my aource of reference. Without further coir ment. I quote from thin eource, "theeie--l. A proposition: epecif.. a position or propoeition which a pereon advancee and offere to maintain by argument. 2. a dieeertation preeented by a candidate for a degree or diploma-~--." It became apparent when I had read theee linee that my faithful companion had again been my aalvation in a time of need. There in a etory molded within these linee. a story of tyranny and oppression. of bitter atrugglee. climaxed by eucceaeful conquest. In years gone by, a proepective graduate, turning to_hie dictionary for the meaning of the very word which I have Juet defined, found but one defini- tion, 'theeie----e propoeition which a person advancee and offere to maintain by argument." ‘What terrific chagrin it wont have heaped on the many-who were confronted with the titanic tank of approaching thie ineurmountable attainment. 216922 L The irony of eueceaafully facing four yearn of con-tent oppreeeicn only to be struck down with one laet cruehing blow! Fortunately, there are those etaleart Joan-of-Arce who do not shy away from giants, but who fight and fall that othere might eurmount their battered bodice to better atrike the fatal blow. To these martyrs I bow down. How the belle.muet have eounded, and the Joyoue echoes of laughter and hilarity filled all Christendom on the day the gatee were finally felled and the arcade came eurging in. The day the book was again opened and the victor‘e hand firmly wrote the liberation of poeterity, 'theeie--- a dieeertation presented by a etudent for a degree or diploma----." So, to the memory of thoae brave aoule who etruggled, fought, and perished that I might aubmit my theeie an a true fulfillment of the obligation which the word‘ggg rep- reaente, I hereby dedicate this endeavor. Respectfully. W... ll Preface The theeie. an applied to a candidate for a degree. may be thought of as having several different connotatione. One, the material presented by a etudent who has endeavored to offer a new theory or idea, to present a new design or method. or solution to an existing or ficticioue problem. A second, in the report of a student who has eet about to investigate a theory or idea, a design. or a.method. in order to determine its soundness or possible falaciea. A third connotation ie the material that is advanced by a student who has attempted to offer new evidence on a sub- Ject of which there is little information, or possibly a great deal of conflicting information. Thie paper does not qualify in any of these categorise. It was my intention merely to investigate the concrete field. attempt to get eome vague idea of what current pro- greee is being made in the concrete field. to stimulate my own interact, and in general to further my can very vague knowledge of the subject. There has been little effort on my part to attempt any solutione. to formulate any definite opinions, or to determine the eoundneee of any material which has come to my attention in regards to the eubiect. In order to express a worthwhile opinion, a person should be thoroughly familiar with.the subject under contemplation. Thie was not and could not be achieved for such a broad subject in the limited time available. Occasionally. an opinion ie expreeeed, but these are generally for purposes iii OI} ma th 31 am 3011 and hat 1111' neg Bfip her Eve: the of clarity, and in all cases may be subject to considerable alteration. Approximately two hundred issues of about twenty peri- odicals were canvassed for material pertinent to the sub- Jest. In addition, thirty letters were written to Various manufacturers and other possible sources of information with rather gratifying results. There were, however. sev- eral sources of information which could not be exploited for one reason or another in the time afforded. Five weeks were spent in gathering information from current periodicals. and an additional seek in reading the material received by mail. Approximately three weeks were spent in organizing the material and setting it down in the order in which it now appears. The required time of eighteen hours per week to be devoted to the thesis, was amply fulfilled. The manner in which the material is organized warrants some comment. The amount of material under each heading and sub-heading is entirely dependent upon the amount of material found in the periodicals canvassed. This does not infer that the subjects of the greatest importance are necessarily those in which the greatest amount of material appears. Some of the more startling discoveries may be merely mentioned under the "Miscellaneous” heading. How- ever. the tepics moat exploited in the last few years with the greatest amount of success, are necessarily represented by the greater amount of material. It is also very possible iv t! :1 d1 it so or no and We: 03! :65 ‘88 me; 5mg 01a 88‘: B11 that several important recent developments in the concrete field received no mention. again it is only because they did not appear in the current periodicals canvassed. In order to cepe with the size of the subject chosen, it was necessary to provide some limitations, and to make some omissions. Any information dealing with the design of standard sand-gravel mixes or their proportioning was not considered, since it was felt that this material was of a comparatively minor nature. This limitation see also applied to conventional reinforcement design, except in the instances where the novelty was such as to remove the de- sign from its conventional classification. There has been a great deal of work done with.wsterproofing applications, and paints for concrete, in the past few years. These were also omitted because they are extraneous to the actual concrete ingredients and their design. Some topics that 1 had planned to encounter in my reading were found strangely absent. Soil-cement concrete was scarcely mentioned, and there was also very little mention of bituminous-cement combinations, except for the small section herein included. no attempt has been made to credit the material in- cluded to its proper source. However, in the event that several sources covered the same topic with about the same completeness, no reference is listed. Also, some averages were calculated on items from different sources which had slight variance. No references are listed for these figures. V The evaluation of the various materials and methods in- cluded are in many cases those of the manufacturer, and are necessarily quite one sided. It is rather difficult to obtain a clear picture of the exact worth of these materials or make accurate comparisons, by comparing very opinionated reports. A great deal of the so called "facts and figures” of the manufacturer which appeared to be obvious exaggerations or special cases, were omitted; or if included, the source was also given. The enormity of the topic chosen has necessitated a very great degree of incompleteness both in the nature of the material included, and in its organization. However, a great deal of knowledge was acquired.from the endeavor, and my interest was vary greatly stimulated. Therefore, the purpose of the undertaking was fulfilled. Perhaps at some future date the author can present a more compre- hensive and complete report. Concrete is definitely an interesting subject, and one which is certainly worthy of future study. Eedicat Preface Light" Th Tu: Pm m Ob: Roc Dedication . . . PretaQ. s Table of Contents Lightweight Aggregates The lightweight Aggregate Pumice . . Pumicite . Perlite . . Obsidian . Scoria . . Vermiculite Haydite . . Rocklite . Sinterlite .Airox . . . Lite Rook . Celocrete . Concrete Blank O Vegetable Fibers . DuriIOI e e e e e e Coral Concrete Shorts 0 I O . O O O I O Woodéfiool Blocks Sweden's Ytong German By-Product Aggregate in Norway VL\ Page .111 . 16 . 17 . 20 . 21 . 22 . 26 . 83 . 29 . 51 . 32 Preatrel 1111 Hit Pre Pre The Fre Eng 0r] Rodulized Fuller's Earth Hodulized Diatomaceous Shale Eul-Kra ”wonder Block" Porete Concrete Units Preetressed Concrete Introduction to Prestreased Concrete . . . . . H1Itor1°fll Sk.‘0h e s e s e e s e s e e s s e Preetressed Concrete Pipe The Largest Frestressed Concrete Pipe on RIOOTd e e e e e e s e e e e s e e e e PPCGtTCIBOO Tanke e e e s e e s e e e e s e s The'World's Largest Covered Prestressed Tank . Prestressed Digestion Tanks for Los Angeles . England's First Prestressed Cast-inarlace Highway Bridge e e e s s e e e e e e e e e e e Orly Field Runway Hear Paris Prestreesed Concrete Designed by Freyssinet america's First Prestreased Floor . . . . . . Prestress Bond . . . . . . . . . . . . . . . . Precast Concrete Precast Concrete (Introduction) . . . . . . . The Large Structural Units of the Csmentstone Corporation 0! Pittsburgh. e e e e s s e L.r8. Prcoa‘t Slab. e e e e e s e s s e e s e Light'C1Sh‘ PrCGGBt PBDCI. e s e s e s s s e e GonorOtQ'Gyp'um Prcoaat Units 0 e e e e e e e viu 42 45 £9 60 62 53 56 59 61 63 67 69 ihole Rd Re Whole House Casting Pouring Concrete Houses in a Big ; The Le Tourneau House Th. Cullen 80“.. s e e s e s s e Air Entrainment and Cement Dispersion Alt Engrfiinmant e e s e e s s e Cement Dispersion Gunite Gunite (Introduction) . . . . . Steel Panel Gunited Houses . . . Cunited Dry Block Ball . . . . . Miscellaneous Bulld1ng EOODOM10. e e e e e e e The florld‘s Longest Reinforced Concrete Arch new chsite Concrete Testing Rethod . spans 0 I I O O I Comfort Concrete 0 e e s e e e e s e e e Concrete Floors Poured in Reverse Order' . . . Reinforcing Steel in Bundles . . I O I O O O 0 Heat Control of Large Concrete Kansas Using Ice. EIpnnding Concrete s e s e s e 0 Loc e O 70 72 74 76 85 91 93 94 95 96 97 99 100 102 LIGHW EIGHT accama'ras _The Lightweight Aggregate Field The lightweight aggregate field is perhaps the field in which the greatest strides are being made today, and the field that may have the greatest effect on the future design principles of buildings both from an engineering and an architectural standpoint. Lightweight aggregates are not new. They have been known since the time of the Romans. They have been used for construction purposes in southern Germany and other parts of Europe for many years. However, their introduc- tion into this country is relatively new. The concrete masonry industry was the first to realize the advantages of a lightweight aggregate in their products, with the chief saving seen in the ease of handling which could be afforded. In 1946, the production of lightweight block reached 386,389,000 8 x 8 x 16 inch equivalent units, as compared with 553,718,000 of the heavier variety, or approximately 41% of the total block output. Recover, the most recent developments of lightweight aggregates have been in the monlithic field where great success has been achieved, principally on the west coast, where natural aggregate is readily available. So great have been the savings and advantages of lightweight concrete' in projects already completed, that it threatens to super- cede stone and gravel concrete in this part of the country almost entirely. keen and L the Chen as t tlve eBEr GGVe Some Det1 Mini amt Lightweight aggregates, in general, offer the advan- tages of reduced dead load, ease in handling, heat insula- tion, and sound absorption qualities and increased earth quake resistance. 0n the other hand, they present the problems of floating out of the aggregate, bleeding, and an increased cost factor. The advantages have been found to outweigh the disadvantages, except where long haulage sill make the cost factor prohibitive. Specific advantages and disadvantages will be discussed for each aggregate in turn, as there is a side range of characteristics in the different classes and specific aggregates. The lightweight aggregate field promises to offer a keen rivalry between the ingenuities of aggregate producers and processors. Formerly, with stone and gravel aggregates, the local outfit had much the advantage, since the freight charges constituted the only principle difference in price, as the mining and processing of the material was on a rela- . tively standardized basis. Now, with a whole new field of aggregates opening up, and new methods of processing being developed, producing better products, there promises to be some interesting competitive marketing. In fact, this com- petition has already begun. According to Stuart B. Ingram (Pasadena, California mining engineer), "A lightweight aggregate, in order to hold a marketing position, should have these qualifications:" (1) (2) (3) (4) (5) (e) (7) Be sell graded in size Have minimum voids to be filled with mortar Have good compressive strength Be firm, so that particles won't break down in handling Bond sell with cement and be inert must not be affected by weather, time, moisture, insects and fungi Be as light as possible (to be economical, should not be more than 50% of the weight of rock or gravel, or weigh less than 60 pcf.) Lightweight aggregates may be classified into the fol- lowing classes: (1) (2) (3) (4) (5) Aggregates of volcanic origin Micaceous materials EXDBDGOG clays and shales By-products of manufacturing processes Vegetable fibers Each class will be discussed in turn with its various group members. in' fro: hem nevi fie] grea the Pros true t' from 5111: are : Pumice Foremost among the natural lightweight aggregates, now in the process of rapidly increasing production, is pumice. Professor Raymond E. Davis of the civil engineering depart- ment, University of California, has described pumice as having "real potentialities” in the lightweight aggregate field.28 Pumice has proved itself in recent years to be of great value, and the demand has increased tremendously in the past two or three years. Pumice has been defined as an acidic, volcanic glass, produced from s granitic magma during emplosive volcanic eruption.22 Pumice, a glassy froth, honeycombed with e- longated parallel cavities, is formed as gases are released from the lava particles as they cool to solidity.12 Essentially, pumice is composed of complex amorphous 22 silicates of aluminum. A typical analysis of s pumice ore is given in the accompanying table (table 1)1 Silica (dioxide) 72% Alumina . 14; Potassium oxide ’ a Sodium oxide 7% Calcium oxide . a magnesium oxide 2.5% Iron oxide 1.0; Loss on lnition 5.5% Table 1.1 Components of a typical pumice deposit. Pumice is found near the surface of the earth with little or no overburden. Deposits are in layers of varying thickness, which would apparently be governed by the fre- quency, duration, magnitude, and type of volcanic action of the particular volcano from*whieh the deposit has originated. Deposits in Washington vary in depth from 2 feet to ls feet with 6 feet being an average deposit (see Table 2).6 Other states have somewhat larger deposits, with 10 feet to 26 feet being a common deposit in new Nexico. Material De h nche Silty soil 13 Buff colored pumice 25 Sand . 3 Gray pumice 36 (older layer) Silt, sand, and rock fragments 95 Table 2.6 Typical pumice deposit in dashington. Due to its volcanic origin, pumice deposits are con- fined to western states with volcanic or formerly volcanic mountains. Pumice deposits are found in Bishop and Imp yoken, California; Bend, Oregon; Sante Fe and Albuquerque, new nexico: and near Mount St. Helena and Glacier Peak in Washington. Other deposits have also been located. new liexico probably contains 40% of the nation's pumice supply} It is interesting to note that all volcanoe do not have pum ton pumice deposits. mts. Baker, Rainier, and Adams in dashing- ton, for example, are apparently devoid of pumice.6 Pumice has been known since the time of the Romans.22 It has been used for polishing, as an abrasive, and in puzzolanic cements to increase the resistance to penetra- tion and corrosion by fresh or sea water, and provide long continuous age hardening of concrete. However, this has been on a relatively small scale as compared to the huge quantities in use today. The first use of pumice as an aggregate, of any impor- tance, was the building of several concrete ships for florid Ear 1.13 However, it was not until 19e0 that the huge strides in the production and use of this natural volcanic material began to be made. Production has probably doubled in the last five years. California produced 7,170 tons of pumice and pumicite (discussed later) in 1926. This was used almost entirely as an abrasive. In 1946, the same state produced 109,191 tons of pumice and pumicite, with over 90% being used as an aggregate in the building industry.22 The use of pumice in the manufacture of concrete blocks has accounted for the major portion of its utilization in the past. Blocks have been produced from pumice aggregate 58 under a large number of trade names, such as: Pyrolite, Pumalite, 1 White Lava Elock, eta, however, pumice is now being used in place of regular stone mixes in on-the-Job xnonolithic pourings, and in prefabricated panel production, in both cases with great success. Pumice has nearly all of the advantages of an ideal lightweight aggregate. It is light, has high insulation preperties, is of uniform quality, is incombustible, and has a surface texture to which plaster readily adheres. In addition, it requires little processing prior to actual use as an aggregate; it is relatively strong; and it is easily mined. The weight of pumice aggregate ranges from 25 to 68 pounds as found in its natural state of gradation. It is found in sizes up to about one inch, being very nearly of design mix gradation. However, it is usually screened and very often crushed to meet specifieational demands. Pumice is generally white to gray in color, although newer deposits may be of various colors. Pumice absorbs considerable water, and may require as high as five days to become inundated.1 It must, therefore, be saturated before or during mixing. Several methods of pressturating the aggregate have been used, including: spraying the aggregate as it stands in piles; presatura- ting the aggregate in a mixer prior to actual addition of cement; or actual addition of extra water to the mix to compensate for the absorption. Either of the former methods is to be preferred. One of the important advantages of pumice is its very high insulation property. A pumice concrete will have about six times the insulation ability as compared to a concrete using regular stone or gravel as an aggregate. Table saggives a fairly representative idea of the ”X" factor (thermal conductivity factor) of well proportioned pumice mixes. ”X" factor ‘Btu/GQs ft./1n/ F/hr) Compressive strength {psi} Pumige cgngrete Rog; concrete 5500 2.25 13.00 5000 2.20 12.50 2500 2.15 12.00 2000 2.00 11.50 1500 1.95 11.00 1000 1.85 10.50 Table 3.22 Thermal conductivity of typical pumice and rock concrete mixes. The Albequerqus (R.h.) Gravel Products Company has conducted many tests on pumice concrete. They have dis- covered1 that workable mixes can be designed as easily and with the same scientific approach as so-called hard rock concrete: that pumice concrete definitely follows the water- cement ratio law for strength. he is the case with most lightweight aggregates, pumice, because of its lightness, has a tendency to float out of the 1 mix, producing segregation and bleeding. It is recomnsnded, therefore, that the mix be kept as dry as possible (with a slump of 2 inches or less) and that no troweling be done tintil the mix has partially set; even than dusting should precede has has crease Pu strengt eat up: cement address greater in incr the or; added t the etr Btrengt 81'0 le dietanc If flpeoir1 1! 5.5 hard as Ir °ld1ma treatme to IUGr Duniog ! den. 18 precede finished troweling. Pozzolith (discussed later) has been added successfully to prevent bleeding and in~ creaee workability.1 Pumice concrete can be designed for a compressive strength up to about 3500 psi.22 This is largely dependv ent upon the gradation of the aggregate and the water cement ratio, of course. The larger sizes of pumice aggregate have the lighter weight but the fines have the greater strength factor.1 The addition of fine pumice in increasing quantities will give increased strength at the expense of an increase in weight.22 Send has been added to correct for the fineness modulus and increase the strengthfll however, it too sacrifices weight for its strength gain. Addition of fine pumice is said to also give less permeability to water and greater corrosion re- sistance to sea water, fresh water, and organic acids.22 If pumice were melted down, it would have about the specific gravity of granite, or 2.4 to 2.6. The hardness is 5.5 to 6.0, the same as the feldspare and almost as hard as quartz which is 7.0.1 Professor havis, of the University of California, claims that pumices can be improved a great deal by heat treatment, to reduce absorption in pumice concrete, and to increase its strength.28 However, the demand for pumice without this treatment is, at the present time, great enough that the extra expense of this heat treat- ment is not warranted. The Pumice Aggregate Sales Corporation, of Albequerque. 5. h. (most modern and one of the larger producers of pumice) has sponsored the testing of its aggregate at the University of New Mexico, and the Pittsburg Testing Laboratory of San Francisco.1 Tests have also been conducted at the Univer- sities of Texas, Oklahoma and California (to mention a few). These tests have so far indicated, that pumice concrete has equal shear, bond, and tensile strength with that of con~ ventional concrete.1 Table t gives a comparison of the unit weights of stone and pumice concretes for desired strengths, and also a comparison of the cement required to obtain these strengths. In each case a well graded aggregate mix is inferred. Compression Unit weight Cement re uired desired (pcf) (sacksjyd) (psi) pumige rgck pumige ch 3600 110 165 7.8 6.5 3000 102 152 7.0 6.0 2500 90 150 6.6 5.5 2000 87 148 6.0 6.0 1600 75 145 5.0 4.0 1000 66 142 4.5 5.5 Table 4.22 Comparison of unit weights and cement required for pumice and rock concrete mixes That the strength of pumice concrete increases with age is illustrated in tests performed on pumice ships of World war I which have been since broken up. These tests to gave strengths of 8,000 psi, when standard cylinders were cut from the broken hulls.2 This is believed to be due in part to the puzzolsnic action of the pumice aggregate, plus a more complete hydration due to the porous nature of the aggregate. Fire and heat resistant tests have been conducted on pumice products with very good results. as an example,1 the Utah-Idaho Concrete Pipe Company conducted tests ac~ cording to a.S.T.M. Specifications on a concrete block well made of their product (which has pumice as an aggre- gate.) In the first test, the inner face of the wall was brought to 2000 F. in four hours under a load of 80 psi at all times. In another test, the entire wall was placed in a gas furnace and heated to 1700°F. in one hour. A fire hose was then sprayed on the wall immediately. fihen the well was cool, it was loaded to 160 psi. These tests were performed successfully with no failure resulting. numerous other tests have proved that pumice concrete will meet all the standard requirements of heat resistance. Pumice has other characteristics which add to its desirability. It can be sawed, nailed, and drilled with little more difficulty than wood. Pumice concrete is also vermin proof, which is an important property in states like California, where termites can be a menace.51 Pumice concrete has greater acoustic qualities than regular con- H erete. In addition, concrete made of pumice has a greater ability to take a change of shape, or resist stress without cracking, than regular concrete; its modulus of elasticity is between 750,000 and 1,500,000 as compared to between 3,000,000 and 4,500,000 for conventional concrete.51 This is especially important in parts of the country subject to earth quakes, such as California. Actual cost comparisons of pumice aggregate and regu- lar aggregate are rather difficult to make and are subject to local conditions and price trends. There is, however, some available data that will serve as an approximate com- parison. The average cost of pumice aggregate at the quarry in California in 1946 was $2.70 per yard as compared to $3.65 per yard in 1926.22 The price of pumice aggregate delivered at the Job site in Los Angeles from California mines in 1947 ranged from $3.75 to $4.50 per yard,1 Idepending upon the kind of haulage and the presence or lack of terminal facili- ties. This was opposed to a cost of $2.40 for regular sand and gravel aggregates. The Pumice Aggregate Sales Corporation quotes a price of $2.00 to $2.80 (depending on quantity) plus freight, with a 10% discount for payment within ten days of the invoice. ‘ It would appear, at first, that the additional cost of pumice aggregate would render it a luxury. Actually, l2 however, the savings in steel and dead weight and the in- sulation and other properties that are afforded, make its use desirable in a great many cases. In small buildings, especially in the precast panel construction type, the lighter weight cuts down the labor by providing greater ease of handling. This is also true of lightweight block units. Insulation is also saved, or a saving in fuel and comfort can be realized. Pumice aggregate has been used on many large and small housing projects in the California and Raw fiexico areas. The Federal Government has built large housing facilities of pumice concrete at Imyoken, California (Havel Ordinance Test Station), and st Albuquerque, s.s.1 A loo-sore subdivision 16 miles east of Lee Angeles, known as Hugheston meadows, is being built employing gunited pumice concrete. However, it will be seen that these projects are con- fined to areas in the almost immediate vicinity of large pumice deposits, where the freight charges have no appre- ciable affect on the cost of the aggregate. For housing projects, the use of pumice will probably be confined to local or semi-local projects. Competition from other lightweight aggregates in other areas of the country be- comes too strong as the freight charges increase. The ad‘. vantages of little processing, ease in mining, and probably a little better quality, that pumice has over other aggregates, becomes overbalanced by freight rates as a certain distance from the quarry is reached. The advantages of using a lightweight aggregate in- crease with the height of a building, for, in addition to the advantages already mentioned for a small building, there are the added advantages of saving in steel, saving in form work (lighter forms) and greater earthquake resis— tanoe (increased strength to weight ratio) where this is important. A great many large buildings are being built, or have been built in the last 3 or d years with proven cost savings in addition to other advantages. The $397,000 Jackson County Memorial Hospital at altus, Oklahoma was designed using pumice aggregate because it would afford an anticipated: (1) 50% reduction of frame dead load; (2) 45% reduction of reinforcing with the same live load capacity; (3) greater heat insulation value: (4) and the sound absorption qualities necessary in a hospital design.1 The 31,600,000 Telephone Company building in Los an- gelee resulted in a net saving of $18,000 through the use of pumice concrete. This was in addition to advantages already mentioned for lightweight aggregate structures.1 The General Petroleum‘Building and the Prudential Life Insurance Building which are being constructed in Los Ln- Eelee at about $7,000,000 apiece, expect to save between 10 and 12% of the cost by using pumice concrete, vermiculite 1r..\~ n . .. ..-.v. f . .u I .An ....‘ Inn" agsregatee, becomes overbalanced by freight rates as a certain distance from the quarry is reached. The advantages or using a lightweight aggregate in- crease with the height of a building, for, in addition to the advantages already mentioned for a small building, there are the added advantages of saving in steel, saving in form work (lighter forms) and greater earthquake resis- tance (increased strength to weight ratio) where this is important. A great many large buildings are being built, or have been built in the last 3 or d years with proven cost savings in addition to other advantages. The $397,000 Jackson County Memorial Hospital at Altus, Oklahoma was designed using pumice aggregate because it would afford an anticipated: (1) 50% reduction of frame dead load; (2) 45% reduction of reinforcing with the same live load capacitY: (3) greater heat insulation value: (4) and the sound absorption qualities necessary in a hospital design.1 The 31,600,000 Telephone Company building in Los An- geles resulted in a net saving or $18,000 through the use of pumice concrete. This was in addition to advantages already mentioned for lightweight aggregate structures.1 The General Petroleum Building and the Prudential Life Insurance Building which are being constructed in Los Ln- geles at about $7,000,000 apiece, expect to save between 10 and 12% of the cost by using pumice concrete, vermiculite i4- aggregates, becomes overbalanced by freight rates as a certain distance from the quarry is reached. The advantages of using a lightweight aggregate in- crease with the height of a building, for, in addition to the advantages already mentioned for a small building, there are the added advantages of saving in steel, saving in form work (lighter forms) and greater earthquake resis- tance (increased strength to weight ratio) where this is important. A great many large buildings are being built, or have been built in the last 3 or d years with proven cost savings in addition to other advantages. The $307,000 Jackson County hemorial Hospital at altus, Oklahoma was designed using pumice aggregate because it would afford an anticipated: (1) 50% reduction of frame dead load; (2) 45% reduction of reinforcing with the same live load capacity; (5) greater heat insulation value: (4) and the sound absorption qualities necessary in a hospital design.1 The 31,600,000 Telephone Company building in Los an- geles resulted in a net saving of $18,000 through the use of pumice concrete. This was in addition to advantages already mentioned for lightweight aggregate structures.1 The General Petroleum‘nuilding and the Prudential Life Insurance Building which are being constructed in Lee in- gelee at about $7,000,000 apiece, expect to save between 10 and 12% of the cost by using pumice concrete, vermiculite )4- plaster, and general lightweight construction.31 The 36,000,000 Eichelson Research Laboratory at In- yoken, California was built with pumice concrete with a great saving being realized.1 However, it is my Opinion, that, although pumice is being shipped by the Aggregate Sales Company alone to over twenty atatea,°° its use will eventually be confined to the West and Southwest almost entirely, as the new local aggre- gates now coming onto the market in larger quantities, be- gin to take over in their con local. In the Southwest, pumice appears destined for greater usage, and cities such as Los Angeles may resort to the use of pumice almost entirely, with the exception of foundations and roads, which account for about 20% of the concrete used. 51 Pumicite Fumicite is chemically similar to pumice, but is different physically. It is also known as "volcanic ash" or ”tuff.“51 It is a very fine sand, made of minute par- ticles of glass which have been deposited either by wind or’sater. The particles have been defined as ”atomized" by volcanic explosion. Particles are small and angular in shape and have an abrasive looking contour. Due to the lightness of the fine particles, they are transported great distances from their volcanic origin. There are states, such as Kansas and Nebraska, where con- siderable pumicite is found and little if any pumice.51 Fumicite has for many years been used as an abrasive in the manufacture of abrasive soaps, household cleansers, and securing powders.51 (It is rather soft and frail and has little use as an aggregate, except as a plaster eggre~ gate, or in other uses where insulation and not strength goverhi12 l6 Pumicite Pumicite is chemically similar to pumice, but is different physically. It is also known as "volcanic ash" or "tuff."51 It is a very fine sand, made of minute par. ticles of glass which have been deposited either by wind or water. The particles have been defined as ”atomized" by volcanic explosion. Particles are small and angular in shape and have an abrasive looking contour. Due to the lightness of the fine particles, they are transported great distances from their volcanic origin. There are states, such as Kansas and Nebraska, where con- siderable pumicite is found and little if any pumice.51 Fumicite has for many years been used as an abrasive in the manufacture of abrasive soaps, household cleansers, and scouring powders.51 (It is rather soft and frail and has little use as an aggregate, except as a plaster aggre- gate, or in other uses share insulation and not strength goverhlla I6 Pumicite Pumicite is chemically similar to pumice, but is different physically. It is also known as "volcanic ash" or ”turf.“51 It is a very fine sand, made of minute par- ticles of glass which have been deposited either by wind or water. The particles have been defined as "atomized" by volcanic explosion. Particles are small and angular in shape and have an abrasive looking contour. Due to the lightness of the fine particles, they are transported great distances from their volcanic origin. There are states, such as Kansas and hebrasks, where con- siderable pumicite is found and little if any pumice.51 Pumicite has for many years been used as an abrasive in the manufacture of abrasive soaps, household cleansers, and scouring powders.51 .It is rather soft and frail and has little use as an aggregate, except as a plaster aggro- gate, or in other uses where insulation and not strength govern;12 l6 rerlite Perlite is a natural hard volcanic rock containing some internal water.81 It is found near the volcanic core, is inert and has a specific gravity of 2.4. ahen crushed and heated to a high temperature, it exfoliates to about ten times its normal size and will weigh from 8 to 16 pcf. It has been found advantageous to preheat the crude perlite, for too sudden a heating explodes the material and produces too many f1nes.12 By preregulating the temp- erature in the preheater, an almost sized final product can be obtained.8 The expanding heat range is from 1400- 2600 F. Perlite has been expanded in horizontal, vertical, and inclined stationary and rotary type furnaces.22 Expanded perlite is light and rather frail; however, 1 it has excellent insulation properties.51 Table 5 5 gives the thermal conductivity factors of various perlite mixes. Volume mix Density Thermal perlite-cement _ip9f) Cgpduotivigl 8 - 1 25.4 .643 7 "' 1 250‘ 9657 6 " 1 27s]. 0693 5 - 1 29.2 .726 expanded . perlite 9:; 0.39 - 0.49 aggregate ‘ loose earth f ---. . Table 5.18 Density and thermal conductivity of various perlite mixes. \7 Perlite is used in precast slabs, blocks, floor fill, fireproofing, and plaster. It makes a good insulation plaster with more plasticity than sand plaster. Farlite concrete has a strength as given in Table 6.18 Volume mix Compressive strength .Qperlite-cement ). 3 - l 1?30 5 - l 918 7 - l 560 Table 6.18 Compressive strengths of various perlite mixes (typical) rerlite concrete will weigh between 53-55 pef. First attempts at expanding perlite in the United States date back to about 1940, although it was expanded and used in Germany prior to 1926.22 There are nos some thirty com- panies involved in developing perlite aggregate in Cali- fornia alone. Two of the largest perlite producers are the Continental Basic Eateriale Company of Chuls Vista, California, and the Perlite Corporation of America.9 The Builders Supply Company of Phoenix has mixed red-black volcanic oinders with perlite resulting in s concrete block that is cheaper and stronger (not to mention - heavier).a ' It is much cheaper to ship perlite in its original state to kilns located in the vicinity where it is to be used, since the freight rates will be reduced. a good grade of crude perlite could be purchased at about 89.00 per ton at Los Angeles in 1947 (cost of expanding not in- eluded).22 The cost of expanded perlite at this time ranged from about $4.00 to e15.50 per cubic yard.22 It sill be noted that, due to the processing necessary, and the fact that perlite deposits, so far, have been found in remote areas, that perlite is priced considerable higher than pumiceoll I9 grade of crude perlite could he purchased at about $9.00 per ton at Los Angeles in 1947 (cost of expanding not in- cluded).22 The coat of expanded perlite at this time ranged from about $4.00 to e13.50 per cubic yard.22 It sill be noted that, due to the processing necessary, and the fact that perlite deposits, so far, have been found in remote areas, that perlite is priced considerable higher than pumice.11 I9 Obsidian Obsidian is a rock of volcanic origin which has as- sentially the same chemical analysis as other volcanic ores (see Pumice, table 1). Obsidian is very similar to perlite in many ways.28 when heated, a product seighing about 20 pcf is pro- duced which is strong and poeesses a thermal conductivity shich is comparable to the best insulating materials on the market today. The aggregate has been given the trade name of Con- tinental Basic Material, or ”GEM" as a trade mark. It is being produced by the Continental Basic hateriele Corpora- tion of Chule Vista, California, from two deposits both located at Beatty, Hevada.2‘ ‘Up to 194?, these were the only the deposits of this rock known to exist. Concrete made with obsidian is claimed to have equal strength with that of conventional concrete and still weigh less than one half as much. It is further claimed, that it sill give without cracking when subjected to overloads.2‘ The use of this material is still in the embryo stage as yet. It has proved very successful in its initial appli- cations, and it does appear to have definite possibilities for future usage.2E3 Scorie Scoria, or natural cindere, are dark colored, volcanic clinkers, a little tougher and somewhat harder than pumice. However, they are considerably heavier than most lightweight aggregates. According to F. Sominsr Schmidt, Consulting mining En- gineer or California, who has done considerable research on the subject, ”they do not have a field in which they excel, and they make no contribution to the science of lightweight aggregates."51 They are being used at present in the manufacture or cored floor slabs and blocks by Edgar D. Otto and Son, of Albuquerque, Haw Hexioo. 2| Vermiculits Vermiculite is a nicacecue material ehich expands upon application or heat to as much as 30 times its ori- ginal volume. The dried ground ore is subjected to about 1800‘ F. for 4 to 8 seconds, after which it weighs between 6 and 12 pet. The minute mica layers expand like the pages of a book. Verniculite was first marketed from a Colorado deposit in 1915.12 It is also mined in north Carolina. However, the principal and actually the only large scale production of vermiculite is near Libby, hostess.12 The trade name of expanded vermiculite is zonslite. Until 1940, the chief use of this material was as a loose fill insulation. However, today it is being used in large quantities as an aggregate in concrete for fire- proofing steel, and as an aggregate in concretes and plasters for insulative and acoustic purposes.5 Verniculite concrete and plaster were used in the con- struction of the Mercantile national Bank Building of Belles, Texas for fireproofing steel framework and ceilings, and as s 1111 for cellular steel rioors.13 Dead load was reduced by 15,634 tons, resulting in a saving of 1,880 tons of steel according to talter a. Ashecchlager, the architect. The Alexite Engineering Division of the Alexander Film 00., Colorado Springs, Colorado, sells expanded vermiculite 22 in bags u price of The ton] of verci: 1000 met cede rec The Iouroe g total on Africa, This co! and in . 1/20 01' Th reach a been 1; about 1 Ian 75: rifiure: in bags under the trade name Per Alex, at an equivalent 93100 Or about $9800 per yard F. 0. B. Colorado Springs. This company also manufactures nailable lightweight bricks of vermiculite and perlite which sell locally for 350 per 1000 made sith a 6-1 mix and meeting all local building code requisites. There is also the threat of a foreign vermiculite source giving competition to the local product.25 The total output of s vermiculite mine in northern Transvaal, Africa, has been contracted for by an American company. This company stated that the ore was of a much higher grade, and in addition, labor costs in African mines are about 1/20 of the American labor costs. The 1947 output of this African mine was expected to reach about 25,000 tons: and after American machinery had been installed, the production was expected to Jump to about 180,000 tons. The total American production in 1946 see 75,000 tons. It is not known exactly hos closely these figures were fulfilled. 2.5 Bayditc Haydite is a lightweight, burned shale or clay aggre- gate.56 It is ground to a maximum size or about 1; inches, and heated slowly reaching a temperature of about 2000 F., at which the carbon content oxidizes forming gases, which result in the aggregate taking a light cellular structure. It is then crushed and screened to size. Haydite concrete will develop strengths of 4000 to 5000 psi, and weighs between 100 and 110 per.61 Due to its cellular nature, it should be presaturated before use. Haydite has been used rather extensively for about 26 years with proven advantages.66 Tests on haydite have been conducted by practically every engineering society and university in the country. It is one or the oldest lightweight aggregates on the market today. Haydite was used extensively during‘Sorld War II in the building or concrete ships.56 In 1930, there were two licensed manufacturers of Haydite aggregate: today there are eightjlg located in: Kansas City, Kissouri; St. Louis, Missouri; South Park, Ohio; Daneville, Illinois; Buffalo, has York; San Rafael, California; Toronto, Canada; and Bothell, Washington. The Carter-Waters Corporation of Kansas City, hissouri, has set up a new plant on a cs-acre tract, and are mining and processing a 75-100 foot seam of shale.19 Operations 24- include: stripping the overburden, blasting, loading, crushing, storage, burning, cooling, crushing and screen grading. Burning is done in oil-fired rotary kilns e x 60 feet, with a dO-minute travel time for the shale through the kiln. The material emerges as a clinker at 2,150 F. and cools for 10 days before being crushed and graded. An 6 x 8 x 16 block of Haydite weighs 25%, and has a minimum compressive strength or 1000 psi with good sound ab- sorption, and heat insulating properties. The Carter-Waters Corporation is now experimenting with Baydite in precast units. Other companies are already pro- ducing these units successfully. 2.5 Rocklite Rocklite is a product manufactured at Venture, Cali- fornia28 from a shale having a water content both chemically and physically combined. When heated to 2500:F., the ex- pansion of the water puffs the material and control of temp- erature gives a more or less continuous surface coating to the particles. Rocklite is crushed before heating, and the different sizes heated separately, thus preserving the skin costing. This is a particular advantage and the result is an aggre- gate that will require 1ess cement and provide greater strength than an aggregate which is crushed afterfexpansion. Rocklite is capable of developing a concrete of over 6000 psi and has low absorption qualitiuuw3 It is somewhat heavier than pumice and is more eXpansive due to the heat treatment and increased crushing expense over that of pumice. It is a very desirable lightweight aggregate where high 51 strength is required and insulation and cost are secondary. .26 Sinterlitc The Stearne Manufacturing Company, Incorporated, of Adrian, Eichigan, have developed a lightweight aggregate from fly-ash.20 Fly-ash is a coal ash still containing some unburned coal, which, when mixed with clay, shale, earth, or slag, can be burned to produce a very satisfac- tory lightweight aggregate, which they have called Sister- lite. The burning takes place in a specially designed ma- chine. The basic unit of this Sinterlite machine consists of an automatic continuously rotating pan.27 The raw ma- terials, mixed with a small amount of fuel, are fed to this pan and sintered. Airox Airox is made of diatomsceous earth which is sub- Jected to two heat treatments to provide a silica coating on spongy structural fragments with a hard interior. Good strength is obtained up to 6000 psi with a weight of 113 pot.81 The process, however, has not been able to com~ pets in the general building program because of its high production coat.‘51 It was first prepared for and spon- sored by the Raritime Commission for ship building pur- poses during World flar II.51 The Air-Ox Company, of Los Angeles, producers of airox have now developed a cheaper product using an oil impregnated diatomacsoue earth.20 The material is cal- cinated, expanded, and is atomized with an exterior clay- I like coating. It is again burned giving a strong, synthe- tic coated aggregate weighing 86 pcf, with strengths up to 4000 psi in a standard mix. Lite Rock The Empire Building Material Company, of Portland, Oregon, is manufacturing a lightweight aggregate block under the trade name Lita Rock.21 Lite-Rock is an expanded shale product. The shale is blasted from a shale mine near iortland, crushed to 2} inch maximum size, expanded, and pulverized. Expansion takes place in an oil-fired rotary kiln 6 x 60 feet. Lite-Rock aggregate weighs 9 pcf after expansion, and an 8‘1 8 x 16 block made of this material weighs 3‘. Empire claims that their product is of greater strength than pumice block, and still retains all of the advantages of insulation, nailsbility, etc., present in a pumice block . The price of Lite-Rock block is slightly above that of pumice block. 29 Celocrete Celocrete is a lightweight aggregate produced by the Celotex Corporation of Chicago.54 Celocrete was marketed under the name Pottseo for a number of years by the Celotex Corporation. Celocrete is an expanded blast furnace slag. By a patented process, molten slag is converted into a hard, tough, cellular, annealed mass, which, when crushed and graded, can be mixed with cement and water, and will form a chemically inert concrete. Celocrete is sold to various manufacturers of building units throughout the country. Celocrete blocks, 8 x 8 x 16, weigh between as; and 295 and have the usual advantages of lightweight units. Celocrete blocks are sold very extensively and have a pleasing, attractive surface appearance. However, the availability of celocrete aggregate is now limited by the fact that its production is far behind demand. Concrete Flank The Concrete Plank Company, Incorporated, of Jersey City, fies Jersey, has, for several years, turned out a concrete plank consisting of hard coal cinders, and crushed blast furnace slag, as an aggregate, and portland cement as the cementing ingredient.52 The planks weigh the equivalent or about 75 pot, and come in 2-inch and 2 3/4-inch thicknesses of varying lengths and widths. They are reinforced both top and bottom.with a mesh of welded steel rods. The actual compressive strength or the material is 850 psi with an increase due to the reinforcing rods present. The planks are not considered as fireproof, but can come under the fireproof codes in many cities, it used in conjunction with vermiculite plaster. The planks have several advantages including: good insulation and sound properties, rot-proof, form work can be saved, planks can be nailed,out and sawed, and a reduc- tion in dead load can be realized. 3| Vegetable Fibers The University of Michigan has made over 8,000 tests on 225 different lightweight materials that may be suitable for building purposes, when mixed with portland cement and small quantities of certain inexpensive chemicals.51 The light, strong fibers bind the concrete and also contribute lightness, bulk, and insulative properties. The chemicals are added to lessen the amount of cement, prevent shrinking, and increase strength. For fiber materials, peanut hulls, cotton stalks, rice and wheat straw, corn- stalks, flax chives, and sawdust can be used.52 Among the best fibers are materials obtained from northern Jack 32 Processing these pine and winter-cut papple or aspin. woods consists of a single grinding operation. The tests have shown that these fibrous concretes are exceedingly practical for farm structures, where the raw materials are readily available. One of the disadvantages is that many fibers require special preparation to remove harmful Juices.32 The Juices in ordinary farm.eaates, such as straw, and cornstalks, usually contain substances that are harmful to the set of the cement. It is not difficult to remove these substances, but the special treatment requires a certain amount of time. The mixers on the market at the present time are not en- tirely satisfactory either, for mixing these fibrous sub- stances. IV Slabs made of fibrous concrete weighed from 1/3 to 1/2 that of regular gravel-sand concrete.32 Two inch boards of the new material showed, in the tests, almost as great an insulation value as two layers of Cclotex between plywood facings, and having a thickness of slightly over two inches. Slabs of insulative concrete will not burn, but will 52 In use, the new ma- char when exposed to intense heat. terial sill probably be cast into slabs, and fastened over the building frame. It is claimed that these slabs, pro- perly made, will be non-rotting, and termite proof. Eurisol Durieol is a lightweight, precast slab employing a mineralized organic aggregate. Chemically mineralized sood shavings are combined with portland cement, and moulded into modular slabs, blocks, and tiles, to meet a variety of uses in building construction.53 Durisol units weigh about 50 pct, are fire resistant, insulating, sound absorbing, and inert. These units are not subject to attack by mould, fungi, rats, or termites, and are unaffected by moisture. Durisol, Incorporated, is a very new company and is completing the first of nine proposed plants at Beakon, has York, at a cost of $500,000.33 Durieol originated in this country a short time ago in a small plant at Aberdeen, Maryland.35 However, Durisol has been used successfully for.msny years in Switzerland and other European countries ”for all types of construction.” Durisol units sell for from $.30 ~ $.40 per square ft. for the plain type, and from 3.80 - $.90 fm' reinforced units, coated with f inch of white cement. These rates are F.0.B. Beakon, new York, or Aberdeen, Maryland.53 34- Coral Concrete Good quality concrete was successfully made during World War II with coral and sea water.34 This was done on Bermuda, where fresh water was not available, and where there is none of the ordinary rock usually employed in concrete making. _ The National Bureau of Standards and the cement in- dustry had conducted research on the use of sea water for mixing concrete. It had been found, that sodium and other chlorides would not induce corrosion, that sulfides might, but that these were present in very small quantities only. The engineers in Bermuda obtained a considerable re- duction in eater-cement ratio by using a pozzolanic (vol- canic ash) compound in the mixture. Chemically, the comp pound used was calcium lignosulfate. Its use reduced water requirements by about 17% and resulted in a concrete that tested over 4,000 filing. 35 Wood-Wool Blocks in Norway The use of concrete blocks mmde with lightweight aggregate seems to be gaining in favor in Rorway.w A recent develoPment is the use of "wood~wool" with a ce- ment binder for wall construction, placed within rein- forced concrete frames. Sweden's Ytong Sweden is now producing a celular lightweight concrete called Ytong.an a finely ground mixture of burnt lime and burnt shale and aluminum powder constitute the raw materials. The processed materials are then cured in an autoclave. Concrete having a unit weight of 44 per will develop over 800 psi with a X factor of 1.06. At a density of 28 pcf Ytong has a compressive strength of 300 psi with a K factor of .68. German By~rro¢uct Aggregate Germany has been using a lightweight aggregate con- sisting of a molten blast furnace slag treated with steam 12 This aggregate and highly controlled, for many years. is used for precast blocks, oast—in-place walls of houses and for panel filling of steel frame buildings. 0‘ fiodulised Fuller's Earth A process was recently developed in Florida whereby Fuller's earth is nodulizsd with water and processed in rotary kilns.28 The principle objective is to produce a lightweight aggregate that sill require no crushing after manufacture. Bodulized Diatomaceous Shale a recent California development, based on the pre- sizing of aggregate, is the nodulizing of an oil impreg- nated diatomaceous sheila"?8 A fine powder of high fusion is used to coat the particles and prevent their sticking together. hul-Kra "dander Block" The marketing Association of Saginaw, Michigan has produced a building block made of wood fiber, special ”Tn mastice, and cement. e blocks are said to have ten times the insulation value of common concrete blocks and are claimed to be sawabls and naileble. Blocks subjected to a 900 I. degree flame for two hours did not burn. Forste Concrete Units The Portte Manufacturing,Company of North Arlington, $7 New Jersey manufactures a number of lightweight precast units for floors and roofs.‘55 They have employed mineral- iaed wood fibers and air in different proportions to obtain unite for various purposes. 56» PRESTRESSED CONCRETE Introduction to Prestressed Concrete Prestressed concrete sill some day be commonplace in this country because of the many advantages that it affords. It was mentioned not long ago at an A. C. I. Convention that preetressed concrete was the ”big future” of the reinforced concrete design field?8 To date, little has been done with prestreesed concrete in this country, with the exception of its use in the construction of prestressed pipes and tanks. This has been mainly due to the fact that prestressing re- quires a multitude of small manual Operations involving great attention and close supervision.78 31th labor costs as they are in this country today, many engineers have been frightened away from the use of prestressing in their de- signs. However, the United States has on no previous oo- casion refused to recognize an improvement merely because of an apparent obstacle. Prestressed concrete is destined for great things in this country, as engineers begin to successfully devise labor saving devices for its economical employmefit. What is prestressed concrete? Briefly, it consists of subjecting high strength rods or wires to initial stresses before the concrete has been poured about them. when the concrete has been poured, and has set, the stressing de~ vices are released, and the concrete is subjected to a precelculated compressive stress by the tension in the pre- stressing rode or wires. fihen a load is applied to the prestressed concrete, the compressive forces in the concrete are merely reduced. The design is usually such that, for any design loading, the concrete will never be taken out of compression. The design principle is based on the following facts: that smell rods and particularly steel wires and cables can be designed for very high tensile strengths: that in normal reinforced concrete design, a large part of the compressive strength of the concrete is never utilized. The advantages of prestressed concrete are, therefore, rather obvious, and can be outlined as below: (1) Iran normal reinforced concrete design, the thickness of a slab is determined by the shear and bending moment for which it is designed. In a preetressed slab design, the bending moment and shear are resisted by the initial tension in the preetressed steel, and the initial compression in the concrete; and the slab thickness has little part in the design at all. Thus, a slab must only. be designed thick enough to withstand the initial come pressive stress imposed by the prestressing steel, provide a suitable bond for the prestressing wires, and provide an impervious waterproof thickness. Concrete is therefore reduced in quantity, with a subsequent reduction in useless dead load. (2) Since the steel wires or cables used can be made With very high tensile strengths, and since no steel is required to withstand tension, as no tension exists, a reduction in steel is therefore realized. (5) Since the concrete is always in compression, cracks due to shrinkage, temperature changes, etc., cannot develop, and a waterproof slab can be insured. (4) Since slabs can be made thinner with the same live load capacity, more headroom will be available in a prestressed design. (5) with no fear of cracks developing, and less dead weight present, longer spans can be designed safely. (6) The factor of safety can be reduced in a slab design, for even if an unpredictable overload should be sufficient to induce tension in the concrete of a slab and cause cracks to develop, with the removal of the load, the cracks will close tightly and an impregnable surface will again be present. . From these tremendous advantages that preetressing offers, so may well say that prestressed concrete is the ultimate in reinforced concrete design (if it can be classi- fied as such). Therefore, hos can it fail to become an integral part of this country's future in construction design. 44 Historical Sketch Freetreesed concrete originated in Europe and its develOpment has practically been confined to Europe up to the present time."’8 The Germans employed prestreseed tie rods in arches as early as 1928. In 1936, a river separation structure of 220 feet was built by German engineers, a radical step in the right direction. During the war, the Germans de- signed and built many structures employing prestressing principles including the covering of their submarine pens. Two other countries have been instrumental in the I prestressed concrete field, namely: France, under the guidance of Eugene Freyssinet, and Belguim, under the direc- tion of George Magnel. In France, the famous Plougastil Bridge, with three spans of 660 feet, a combined highway and railway bridge of prestressed concrete, was handed over to traffic in 1931. The success of this and other projects were inspira- tion enough for Freyssinet, and he has since designed many such bridges and structures. In France, about three years ago, Freyssinet completed a highway girder bridge with a span of 180 feet, and the phenomenally shallow depth of 4' 2' at the center. It spans the Marne River in the neighborhood of Chateau Thierry. Five other such bridges on the same system are in the process of erection or Just recently completed. Professor George fiagnel has designed numerous pre- stressed railway and highway bridges with opens up to 66 feet in the vicinity of Brussels. In 1944, magnel de- signed several structures for carrying pipelines over long spans. The Swiss have employed prestreseed concrete for a number of short-span highway and railway bridges, and for galleries as a protection from avalanches. many airport hangars with spans of 150 feet or more were built shortly before, and during the war in several EurOpean countries, as well as in India. Prestreesed concrete has been used in this country for about ten years in the construction of large pipes and tanks. Also, in the early 30's, the 230 foot arches of the Rogue River Bridge in Oregon were built employing one phase of prestressing. Jacks were used at the crown to induce compression in the ribs. Frestressed beams have been tested in our labs, but their actual use has never come about, with the exception of a warehouse recently built in Cicero, Illinois, which will be discussed later. Philadelphia is planning to build a prestressed con~ crete girder bridge employing high tension wires and using modern prestressing methods,82 which have been employed in Europe for some time. It will be the first of its kind in this country and could provide the necessary force for ”1.3:. 5.... ,1. .. , . .lwid. as“ the construction of similar projects in the near future. At the September, 1948, meeting of the Congress of the International Association of‘Bridge and Structural Engineers held at Liege, Belgium, more than 600 delegates, representing 28 countries attended.8‘ It was the first such meeting since the Berlin meeting of 1936. A prefabricated, prestressed concrete factory building, covering 350,000 square feet, was one of several remarkable developments reviewed and discussed.8‘ The building, lo. cated in Ghent, has 70 foot spans of prefabricated, prestreesed concrete, and only half a dozen forms were used in the entire building. About 80 engineers and contractors representing 10 countries of this group, laid the groundwork for the forma- tion of an International Association for Prestreesed Con- crete.83 4u4 Preetreesed Concrete Pipe -.The Largest Preetressed Concrete Tips on Record-- Preetressed concrete pipe has been manufactured in the United States in fairly large numbers for the last decade by several companies. This pipe has ranged in sizes from 20 inches up to as large as 50 inches, usually accompanied by an inner steel liner. However, recently Montreal, Canada, let bids on the manufacture of concrete pressure pipe for an intended new and larger water supply intake from the St. Lawrence River.71 0n the strength of reports of the successful use of prestreased pipe in Europe and Australia, notably those built by Ereyssinet in France and Rode patents in Australia, the Montreal Water Board tendered alternate designs-~the conventional type, and the prestressed type.70 Bids on the conventional design were 50% higher than the one accepted employing the prestressed design. The contract was awarded Jointly to the Preload Company of Canada, Ltd., and the Atlas Construction Company, Ltd., both of Montreal. It consisted of the construction (not installation) of approximately 9500 feet of 84 inch pipe. Using the preetrese design, a saving of 800 tons of steel and 10% of the cement was realized over the conventional design. Each pipe section weighs about 16 tone, is 18 feet long and 64 inches inside diameter, with walls 5% inches thick. The plant for making the pipe was completed in May, 1946, and the first pipe length use made in December, 1946. Difficulty in obtaining materials and equipment delayed operations until April 1947, when the scheduled production of 8 pipes per day got underway. The pipes are stressed with longitudinal and circump ferential steel. Longitudinal steel consists of 12 pairs of sires each .44 inches in diameter equally spaced around the parameter and located in the center of the core well. These sires were given an initial stress of 70,000 psi, which induced 188 psi in the concrete. This would leave a calculated residual stress of 69,700 psi in the steel and 103 psi in the concrete after loss due to elastic deforma- tion, plastic flow, shrinkage, and bending induced when supported by a sling at the mid-girth. Circumferential reinforcing consisted offs continuous spiral of #8 gags sire having an ultimate strength of 220,000 psi and wound on the concrete core. It was spaced at .31 inches on the flanges and .63 inches on the barrel, and see applied under an initial stress of 725 psi in the concrete. This*eould leave a calculated 108 psi in the concrete, and 114,120 psi in the steel under full 60 psi hydrostatic pressure, and after the losses of elastic de- fornsticn, plastic flow, and shrinkage had been subtracted. The actual plant layout and the pouring methods em- ployed are too lengthy to describe at this time. The longi- tudinal sires sere threaded at the top and the prestresaing Ate was accomplished by elongating the sires to e precalculated length (about } inch) with a pneumatic wrench. The concrete used averaged sell over 4500 psi, had practically a zero slump, and was vibrated into place. After steam curing, the core passed to a turntable where the circumferential wire was applied. The turntable was geared to the prestreesing mechanism, which ran on tracks parallel to the length of the core. As the table revolved, the prestreseing mechanism fed the sire through c tension die, and at the same time moved up the vertical tracks in sycronism with the rotation of the turntable. A second gear was employed for winding the flange. The unit stress in the wire was checked by a calibrated torque wrench connected to the tension die, and also by micrometer reading of the wire diameter. After the wire had been wound, it was gunited with 3/4 inches of concrete with a mix preportion of 4 parts send, one part cement, and 0% by weight of hydrated lime. The gunite cost was then cured and the pipe removed from plant by crane to a storage yard, or the testing bed. One pipe of every twenty was subjected to a hydrosta- tio test of 60 psi for 15 minutes. Not a single pipe showed any sign of leakage or failure. The first pipe produced was subjected to various tests designed to approximate field and handling conditions. After the pipe had withstood all normal tests without 4"? measurable deflection, it was allowed to drop on a knife edge at its midlength from various heights up to 24 inches. The only damage noted was a local scoring of the surface of the covercoat. The wire was not cut, and there was no sign of failure of bond between the gunite and the con- crete core. This is quite remarkable as the pipe weighed 16 tons. A 4p-foot section of the same pipe was then cut out and subjected to the A.8.T.¥. bearing crushing strength tests with excellent results. Failure occured at a load of 10,600 pounds/foot by clean breaks at the four quarter points. The bond of the gunite cover coat remained ex. cellent, there was no spelling, and no flying of wire. All of these tests had been performed on a pipe section employing only 800 pounds of steel as compared with about 3800 pounds in a conventional design; truly, an impressive material economy. its Prestressed Tanks The Preload Corporation, the Canadian branch of’which has already been mentioned in connection with the Montreal prestressed pipe project, has also designed some 060 tanks for water, sewage, oils, chemicals, and other liquids withp ,in approximately the last eight years.90 To my knowledge, it is the only company to date in North America, which has 1the equipment and facilities to undertake this task (other companies have done such work using Prelosd methods and e- quipment) and I am sure that it is the largest such company if others exist. The Prelosd Company has offices in about fifteen major cities in the United States and Canada.90 The average size of these tanks have been those with a 7‘ Prestressed wire is wound around capacity of 80-100 feet. the circumference of the tank with a patented wire winding mmchine, which is suspended from a vehicle which travels on tracks located on the top of the tank walls. The mechanism travels at about 5 miles per hour and the wire is stressed (by being drawn through a die) to 140,000 psi. The largest of these tanks is located in Rockford, Illinois and several large tanks are now being built for the city of Los hngeles. These projects will be discussed individually in some detail. 1&9 The World's Largest Covered Prestressed Tank Recently completed at Rockford, Illinois, by the Pre- load Corporation was the world's largest prestressed covered tanks,3 The tank measures 167 feet outside diameter, and has a capacity of 6,000,000 gallons. subcontractor on the job was the Jack Construction Company of Kansas City, a slipform specialist. Employing 8 foot high steel elipfcrme, the entire wall was poured continuously in 75 hours. The slipform principle consists of jacking special forms gradually up the wall as soon as the concrete below has set up. One inch jack rods spaced 20 feet apart were employed for this purpose. The wall was prestreseed with both vertical and air. cumferential steel. The vertical prestressing was accomp- lished by placing .31 inch rode in slots left in the poured wwell at two toot centers and applying the required stress using special turn buckles. The horizontal prestressing'was accomplished by applying 180 miles of #8 piano wire using the Preload prestressing mechanism.a1ready mentioned. The wire had an initial dis- meter of .162 inches and after being drawn through the pre- Ietressing die, the wire was reduced to a diameter of .1e2 inches. One layer of wire was applied to the entire 30 foot height of wall, a second layer covered the bottom two thirds of the wall and a final layer was placed on the 50 lower third of the wall. A gunite cost was applied after each layer. The initial concrete wall has a thickness of 15 inches which was increased to 18 inches after guniting. The top two feet of the well was wound with five layers of prestressing wire. It is interesting to note that this prestreesing was sufficient to raise this 5 acre, d inch concrete dose cover 2 inches off of the dome forms. The foundation for the wall had been trowel finished and coated with emulsified asphalt to permit free lateral movement of the well after the prestressing wire had been applied. The joint was then caulked and filled with a permanently pliable mastic. The cost of the project, excluding excavation and bachfill amounted to $2.75 per gallon of storage capacity. 5| Prestressed Digestion Tanks for Los Angeles The Pacific Bridge Company is presently engaged in perhaps its largest contract employing the Preload.method. The contract calls for the construction of 18 prestressed concrete digestion tanks having a capacity of 2,000,000 gallons each.76 The tanks are part of an activated sludge plant being built for the city of Los Angeles, and located near Segundo, California. The tanks are 110 feet, 11 inches inside diameter and have a wall thickness of 20} inches and a height of 34 feet. Each tank is equiped with a concrete roof dome of 5 inches thickness. The prestreseing is carried out in the same manner as that already described for the Rockford project. 'Work was started on these tanks April 12, 1948, and is expected to be completed in.harch, 1949. 52. England‘s First Frestressed Cast-in-Place Highway Bridge hark was recently completed on England's first pre- stressed cast~in-plece highway bridge over Hob Hole drain at Fishtoft, near Boston, Lincolnshire.80 The bridge has a span of 74 feet with an 8 inch roadway slab incorporated on d3 inch concrete deck girder beams. Five girders spaced at d} feet carry the prestressing cables. The cables consisted of a one inch diameter bobbined core and twelve .2 inch high tensile steel wires. A total prestress of 26 tone was induced in each cable imparting 138,000 psi to the prestreseing wires. The prestressing was sufficient to induce an estimated 2000 psi compression in the bottom of the girders, and 100 psi in the top flange of the girders. This will be sufficient to just counteract the full design moving and stationary live load. The prestressing produced a 0/8 inch camber in the bridge besides the 4 inch dead load camber which had been allowed. The work followed the Freyssinet methods and employed Treyssinet prestreseing equipment as well. England has con- structed structures of minor importance of prestreased con» crete for a number of years; however, like the United States, they have not kept pace with the radical designs of France or other European nations. Orly Field Runway hear Paris Prestreesed Concrete-designed by Freysainet One of Eugene Freyssinet's most recent projects was the construction of an airstrip at Orly Field near Paris.81 The runway is 1400 feet by 200 feet and is incorporated alongside of regular conventional strips where a comparison can be made. The runway is d 3/8" thick and can stand a load 10 times greater than a conventional reinforced con- crete strip of the same thickness or is equivalent to the strength of a conventional strip at least two feet thick. The entire runway is made up of one meter square pre- cast blocke using a l:2.2:2.6 concrete mix with a water cement ratio of 3} gallons per bag of cement. The slabs are laid on a 14 inch deep consolidated foundation with a maximum bearing of 100 psi. The 14 inch foundation is covered with 2 inches of fine sand and is tapped with asphalt paper. The interesting part of the design, is that the entire strip is laid out with diagonal joints, in order to give prestressing in two directions using uni-directional pre- stressing cables. The diagonal Joints are separated with roller bearings to insure as nearly full stress transfer as possible. The transverse cables were laid between the one meter blocks. They consist of thirty parallel-i inch diameter stee1.wiree with an average ultimate tensile strength of 54- 220,000 psi. The cables were dipped in asphalt and wrapped with heavy building paper. at the edge of the strip, the 30~wire cables were separated into three strands and anchored by pinching them between Freyasinet patented interlocking cones. The cables were tightened in steps up to 128,000 psi imparting a stress of 4,700 psi to the concrete. In order to withstand the pressure in the longitudinal direction which would be imparted when the cables were re- leased, end butresses e feet wide running the full width of the runway were constructed. Freyseinet claims that his 6 3/8 inch runway will carry several times the weight of the largest plane yet built. Because of its thinness, temperature stresses are reduced to a minimum. Under very heavy loads, cracks may develop, and, in fact, are desirable, since the cracks will increase the flexibility of the concrete, enabling full use of the foundation support, without large bending moments. The tension in the cables automatically close the cracks completely when the load is removed. America's First Preetressed Floor. About two years ago in Cicero, Illinois, America‘s first prestressed project was completed.79 It was in the form of a floor for a warehouse owned by J. A. Roebling none. After 18 months of service, the floor has shown no signs of cracking, when under microscopic examination, even though subjected to loads estimated at 1000 psi (seven times the contact load of the largest airplane.) The load is in the form of large rolls of cable resting on wooden rollers. The floor is 96 x 144 feet in size, and is built without joints. It consists of a 3minch prestressed slab placed on a 0-inch reinforced concrete base. The base is tapped with a patented surface material to obtain a smooth finish. In addition, a l/SZoinch film of paraffin was applied and a layer of copper coated building paper was placed face down on this paraffin surface. This was de- signed to keep the coefficient of friction between .30 and .38 and allow free movement of the prestressed slab over the base. The slab is prestresaed in two directions. The breadth of the slab is prestressed with seven wire strands of gale vanised wire, having an ultimate strength of 45,000g each or 181,000 psi. These strands are placed midway in the slab and wrapped with paraffin paper tubes to prevent bonding with the concrete. The length of the slab is 56 . .11! ’1‘ prestressed with two layers of No. 6 bridge wire placed 4% inches on centers horizontally, also wrapped to prevent bond. After the concrete had been poured and had set suf- ficiently, the stranded wires across the breadth of the slab, which had been fabricated in two pieces, were pulled together by special jacks at openings which had been left at the center of the slab. The outer ends of these wires were bonded in the concrete. When the concrete had been stressed to about 050 psi, the wires were clamped together and the jacks removed. The wires running the length of the slab were anchored in the concrete at one end and jacked against steel plates at the other end. when the concrete had been stressed to about 700 psi, the nuts were placed on the threaded ends of the wires and drawn up against bearing plates. The jacks were then removed. After 1} years of service, the longitudinal wires were tested and were found to have lost 9%% of their ini- tial stress, the transverse wires had lost 95%. Tests were made by placing concentrated loads up to 36,000? on an area of 63 square inches directly over a construction joint of the base slab. A deflection of .05 inches was noted. When the load was removed, no permanent deformation had taken place. The cost of this initial prestressing project was more 57 than that of a conventional design. However, the greater durability and low maintainance cost sere held to justify the extra first cost. It was built as a trial adaption of prestressed concrete to highways and airplane runways. -I!l .rC- . all f «1 . a . . alsi‘ Frestress Bond It might be eondered as to the capability of the bond between the stretched steel wires and the concrete being sufficient to maintain the initial stress in the sire. This is probably one of the things that would give the most concern to the novelist in the preetressing field. It has been proved conclusively in hundreds and thous- ands of tests that sufficient bond can be obtained without a great deal of trouble. Sweden has found in its ten years of rather extensive use of "piano wire concrete” that the quality of the bond is dependent upon the following factors:75 (1) quality of the concrete (2) working of the concrete in the form (3) strength of concrete at release of wire (4) type of curing before and after release (a) prestress of the concrete (6) diameter and surface properties of the wires (7) distribution of the wires in the concrete The breaking of a wire of e prestressed tank, for ex- ample, is said to only affect a few inches in the immediate area of the break. It may be better explained by realizing that a break in the wire will release its tension at that point, and the length will begin to decrease with a corres- pending increase in diameter. It is this increase in die- meter of the wire that, it is felt, is responsible for plugging the hole and preventing further slip of the broken strand.7‘ It is apparent that this phenomenon is a very fortunate one indeed. 60 PRECAST CONCRETE Precast Concrete Precast concrete units have been manufactured for many years in this country and have found a rather sizable market. The wartime construction program.eas a big selling point for these units, for they provide a much quicker means of building erection than actual on-thenjob mono- lithic concrete structures. The postwar boom in the building industry also has provided a ready market for precast units again principally on the strength of their time saving advantage. There were many companies producing precast units before the war and the number has been many times multi- plied in recent years. It would be more than a big job in itself to attempt to give a thoroughly comprehensive picture of the precast industry today. I shall therefore not even attempt to mention the many types of units now being produced nor the companies producing these products. I have rather chosen to give a fee illustrative examples of a few of these precast unit developments, perhaps cover two or three of the more recent and more formidable con- tributions, and make some general statements concerning these contributions, which in most cases will be purely my own opinions to be taken merely as speculative comments by a very green speculator. I have already mentioned that precast units are time savers. This is generally true. To say that precast structures are generally more or less expensive than mono- lithic structures would be impossible. In some cases, pre- cast units have proved to be many times cheaper and in other cases, the opposite is true. The economy factor is controlled by such things as: type of unit, type of struc- ture, time value of erection, availability of suitable monolithic aggregates, height of structure, labor costs and efficiency, number of structures to be built, etc. It will be seen that economy is controlled in general by local, and specific conditions, and that on no two pro- jecte will this factor be the same, or very often nearly the same. The Large Structural Units of the Cementstone Corporation of Pittsburgh Perhaps the greatest contribution to the precast type of construction has been made by the Cementstone Corporation of Pittsburgh. This company manufactures precast units for the complete framing of buildings up to four stories in height.108 These units include columns, girders, beams, roof, floors, and walls. The number of shapes have been standardized and simp- lified to cut down on cost and increase the design simplicity. However, these standard shapes are being made over a large range of sizes to cover a multitude of uses. Special de- sign tables have been devised to further simplify the de- signers problems. The precast units are cast in adjustable steel forms to fulfill the size requirements. The reinforcement is welded into a rigid cage before the form is poured, and all steel ends which may appear at the surface of the con- crete ere coated.sith Monel metal to prevent rust. The concrete used is very richvoeé sacks of cement per cubic yard-oand is placed with a slump of 2 inches and vibrated both internally and externally. The units are steam cured for three days and develop a strength of 6000 psi during this time. The 28-day strength of these units is 7000 psi. The units are hauled to the job site by truck and erected by crane. Connections are made by patented dowel and pipe sleeve connections, or with bolts. Precast con- crete brackets are bolted to the columns for supporting the girders; and precast "U” shaped brackets are bolted to the girders for supporting the floor Joints.”O All units are designed for handling as sell as for their structural function.101 Precast girders, Joints, and slabs are designed as simply supported beams using a sorting stress of 2250 psi for concrete and 20,000 psi for steel. In addition to standard buildings, Cementstcne shapes have been applied to standard precast grandstands, small bridges, airport hangers, and other projects.99 It is claimed that Csmentstone buildings can be erected as cheaply as structural steel unprotected, and for at least 20% less than steel fireproofed, or poured~in~place concrete. The sister time saving is even greater. The company esti- mates the practical economic distance from the factory for Cementstone structures at 200 miles, although Cementstone units have been shipped by rail for considerably longer distances on a competitive cost basis. The erection time of Cementstone units is very short. The frame of a tee story building in Pittsburgh with a floor size of 110 x 120 feet was erected by a cres of six men and e crasler crane in 13 working days. fifltetttttt Venturing a little commentary at this time---it does seem that these units could be an up and coming design feature, that could be expanded to other municipalities. It is apparent to anyone who has had occasion to ob- serve labor in the field in the last few years, that the tradesmen is not doing the efficient and productive Job that has been expected of him in the past. This existing condition is the result of ten facts: first, that the building trades have not kept their training or apprentice systems in stride with the increased construction programs, fearing that, by expanding their trades, their can posi- tions would be weakened, especially in the event of an economic collapse: second, that plentiful Jobs have made the tradesmen less concerned about the security of his Job, since the fear of his being ”fired” for inefficiency has been very greatly reduced. Therefore, by cutting down our labor to the very minimum, eliminating all the elaborate fora work ehich a monolithic structure entails, we are subsequently increasing our efficiency and also accuracy. It is also true that concrete poured in the field is affected by many variable conditions such as: weather, poor form work (resulting from poor lumber, awkward loca- tion, or labor inefficiencies and inaccuracies), over or under mixing, variable slump, improper vibration, hap- hazard reinforcement location, and often improper curing conditions. By confining the pouring operation to the ideal settings of a presenting plant, it seems reasonable to empect that the resulting concrete units are much more 65 liable to be up to design specifications. Realizing this, the safety factor could be reduced by assuming larger working stresses, with the units still remaining on the safe side. It does seem in the light of these arguments, that the precast system does have definite economic and structural advantages. ‘ It might also be quite practical to incorporate a lightweight aggregate into certain of the precast units, such as the floor, wall, and roof panels, with a saving in transportation and design dead loading with increased insulation value. Prestreseing might also be made appli- cable to these precast units, with a saving in steel, dead load, and handling costs, if the extra labor can ever be Justified. I definitely feel that the precast unit has a pro- mising future, although I am sure there are those who are of Just the cppoeite cpinion. It is true that the time saving element may not continue to be as large a selling point as it has been shen things settle down; but, the economy factor seems to be gaining, and this is always a sure sales promoting item. _6€5 Large Precast Slabs Kormac Incorporated, a Los Angeles building concern, is constructing a large number of buildings employing large precast slabs.95 These slabs, which are often large enough to form one side of a room, are cast with aluminum window and door casings embedded in the concrete. The slabs consist of a lightweight perlite concrete poured between layers of standard concrete reinforced with wire mesh. The perlite is obtained from a plant operated by the Great Lakes Carbon Company and located at Terrence, California. The Norman plant is located at Pusnte, and had a cape- city of 4 complete houses per day in 1947 with each house requiring about 36 slabs. This included all interior and exterior‘ealls and roof. Houses were available in a variety of different designs. In 1947 each house, having a floor area from 600 to 1140 square feet, was erected complete with all plumbing, lights, etc., and a two car garage for from.35200 to $9200. This price applied for medium to large housing projects. 67 Lightweight Precast Panels A east coast firm, Buttress and medlellan Incorporated of Los hngeles has developed a process in which sell panels and other precast units, such as roof slabs, beams and rigid frames are poured horizontally using low curb-like forms.97 These units are poured at the Job site, often using pumice as an aggregate, and erected with a crane. Isnels are troweled or broomed for the desired finish. Steel plates are incorporated on the edge of the sell slabs for welding to steel columns or to each other, and dowels are left protruding from the edges of the panels if concrete columns are to be used. All Joints are grouted after erection. Using this precast method for standard buildings, sell costs are estimated at $.75/sq. ft. as compared to $1.10/sq. ft. for brick or £1.35 - 31.50 for poured concrete. On a standard warehouse building of about 10,000 sq. ft. and of truck height with average lighting, plumbing, painting and a wood roof, the quotation is $3.?5/sq. ft., which can be reduced to $2.80 sq. ft. on Jobs of 40,000 to 60,000 feet; eith a concrete roof, quotations are $4.00 to $3.00. Concrete - Gypsum Precast Units In the construction of s new nylon plant at Chattanooga, Tennessee, the du Pont Company used a precast - gypsum con- crete unit for the sell construction at a cost comparable with that of brick.96 The call consisted of a 4" core of gypsum block between concrete fecings, and strengthened with a light perimeter bar mesh. The inside walls ears poured on Kraftapaper laid on concrete. The concrete was poured with zero slump and the steel mesh vibrated into place. The pro-setted gypsum tile was next laid on this slab and the outside of the slab poured. A finish coat of grout % inch thick was hard steel troweled in place, the edges tooled, and the surface tex- tured sith a hair puahbroom. The panels were then cured for 7 days under net blankets. The finished panels weighed on psf and averaged 80 square feet in area. Under ideal conditions, one crew placed 2700 square feet in one day. The finished building has a very pleasing appearance with very good insulating qualities. 69 WHOLE HOUSE CASTING “I... ‘A.’.‘ 0. he: Pouring Concrete Houses in A Big Way The need for large scale housing units in the war and post-war eras started a lot of wheels turning in the heads of a lot of engineers; the outcome-~a lot of ideas, some good, some not so good. What was actually needed was a quick, cheap, efficient method of furnishing substantial, adequate housing facili- ties: and fulfilling these requisites on a competitive basis. or course, for some time there were almost enough of these Jobs to go around, so the competition wasn't too keen. However, a smart contractor is always looking toward the next Job, and usually from a competitive angle. Besides, there is always present the incentive to cut down on costs of a Job already under contract, that is, insofar as speci- fications will allow; ls lumber began to get coarser and poorer, many sections of the country turned to the use of masonry units for cheaper and faster house erection. Concrete blocks came into use rather extensively until the block plants got be- hind, and bricklayers became scarser. Monolithic house pouring then appeared, employing the use of various sized panel forms that could be moved from house to house. How- ever, the erecting and stripping of these forms still re- quired considerable time and labor. Precast units were the next phase of economy, although considerable labor was still involved in their production, transportation, and '70 e rection. The engineers of R. 0. Le Tourneau Inc., a large coup treating firm of large construction equipment, came up re- cently with a rather large idea for the erection of housing units on a large scale. A similar idea was introduced by the Callas Builders, Inc., a contracting tirm.or Port Washington, Long Island. These two ideas appear to be the ultimate in the large scale mass production or housing units. A discussion or each or these methods follows. 7| The Le Tourneau House The Le Tourneau method of house building has been employed for several years. The method consists of pouring a housing unit into large steel forms located at the batch- ing plant directly under a concrete shuts, and transporting the entire finished unit in one piece to the proposed building site. A specially designed vehicle has been built to carry these units, and is called the Tournalayer. To the inner form are attached all of the necessary fixtures that are to become an integral part of the sells: this includes door and window frames as sell as plumbing, and electrical appurtenances. Steel reinforcing mats are next fixed in place, and the Tournalayer then deposits the outer form over that of the inner form. The units are poured in about one hour, depending on the size. After about 16 hours, the Tournalayer picks the completed struc- ture and the outside form up over the inside form, and carries it to the building site. Here the building is properly positioned, and the outside form picked up over the structure and returned to be placed over the inner form again for another pour. The batching plant is usually centrally located on the project, and the inner forms re- main directly under the batching bin until the last house is completed, without ever being moved. Le Tournesu forms come in various sizes for both single and double family dwellings. a typical double 72 family dwelling consists of a 32 I 24 foot unit and an 18 x 24 foot unit, which are poured separately and con- nected sith a corridor. Pumice aggregate is generally used for weight saving and insulation purposes. The La Tourneau equipment for these projects is leased by the company on a lease-royalty basis.110 The economic advantages are said to cover projects of 50 or more units. The Tournalayer has been used on many projects in the Southeast including the Murdoc Air Force Bass,111 Lake Murdoc, California; Los hngeles; and Corpus Christi, TOXaBe 75 The Csllan House On a loo-house project at Port hashington, Long Is- land, Eew York, the Cullen Builders Incorporated of Ken- haaset, has York are employing large size elaborate forms for pouring complete housing units. a total of 23 forms is required to form all exterior and interior rooms, end roof gables, and chimney for a 900 square foot dwelling with a 220 square foot garage attached. The sells consist of three inch layers of concrete on either side of a one inch thickness of insulation board. The novel feature is that all windows and door frames, trim, and mouldings are actually poured of concrete in one initial monolithic unit. The forms are given a high polish and thoroughly oiled between each pouring, so that the walls can be painted or papered directly without any plaster coat re- quired. The inner forms are first placed on a six inch insu— . lated, and radiantly heated floor, and anchored together. A 6 x 6 inch mesh of #6 welded wire is placed on either side of the insulation board in the wall forms. Door and window frames are additionally reinforced with §¢inch rode. Finally, the outside forms are erected and bolted to the cores through.sindol and door openings. The forms are then poured with ready mix concrete of a l~2~3 mix, 5 gallons per sack, and with i-inch maximum size aggregate. The cores are collapsible and are easily 74- removed. Of course, the size of the units makes the use of a crane in the placing and removal of the forms impera- tive. I A concrete shell is built in two 8-hour days by ten men.112 It takes four men another seek to complete a home ready for occupancy. Like the Le Tourneau system, this type of house can only be built economically in large nuns bars. However, it was undoubtedly designed to more than pay for itself in a single project. The cost on the Port Washington project was claimed to be 30% less than for 3 comparable houses built in the conventional manner.11 75 AIR I‘JR’I‘RJ‘.II-fli?£}h'1‘ AND Oil-CENT DISPERSION 19.5: Air Entrainment Air entrainment of concrete has been recognized and accepted for the past eight or nine years. However, the principle of air entrainment has actually been employed for about twenty years unknowingly, through the use of Portland-natural cement b1ends.137 It was discovered that a blending of a natural cement sith.Portland cement pro- duced a more durable pavement surface, and the.mixture was adopted by the highway departments of several states. It is not known exactly what causes this greater durability in these mixtures, although it is now generally accepted that air entrainment is one of the principle factors. It has also been proposed that the surface characteristics of a natural cement are such as to favor a greater water retentivity, and hence increase the fattiness of the mix. Other.materials were subsequently found to produce air entrainment including resin, beef tallos, Orvus (sodium lauryl sulphate), stearates and other soaps, grasses, and foam forming materials. As investigations became more numerous and thorough, many of these air entraining agents were dropped for the use of better and more economical substitutes. Yinsol resin, a by-product in the naval stores in- dustry, sas probably the greatest asakener of interest in air entrainment.137 It was discovered that small quantities added to the cement clinker to facilitate grinding caused 76 ‘the cement to entrain a considerable amount of air, and to be more cohesive and fatty. Vinsol resin is still used extensively today together with such other accepted air entraining agents as Orvus, and Darex (a triethano- lamina salt of sulphonated hydro-carbon). There are actually three methods of introducing air into concrete.137 One method is the use of such substances as aluminum or hydrogen peroxide, shich form gases due to a reaction with the constituents of the cement. This ne- thod has been used very little because it has not proved as effective, or economical as some other methods. A second method, is the use of a dispersing agent. Actually, a dispersing agent is capable of absorbing a comparatively small amount of air, its principle function being to die- parse the cement particles. The dispersing agent sill be discussed later. The third method is the use of those substances already mentioned--rosin, beef tallcs, stearates, Vinscl resin, Orvus, and Darex. These substances, in gen- eral, are wetting agents or foaming agents. They absorb air by decreasing the surface tension of water, and form stable foams. It is these substances that are generally referred to shes the term sir entraining agent is employed, and it is these substances which will be non discussed. for many years the advantages of air entraining agents were confined to their use in preventing scaling and de- terioration of highway pavements. It is Just within the past four or five years that they have become generally 77 accepted as invaluable for use in any concrete structure. The use of air entrained concrete is probably in its most rapid stages of increase at the present time. Much pro- grese is also being made in the further development of air entraining agents and their applications. It is generally recognized that the durability of a concrete road surface is governed by its ability to re- eist not only the load and the friction of traffic, but in particular the stresses introduced by changes in temp- erature, with freezing and thawing being of special imp portanoe. All conventional concrete has a tendency to segregate and bleed to varying degrees depending on several variable factors, chiefly: consistency, water~cement aggregates, the degree of mixing, and.method and care in placing. It is this segregation, and bleeding that is indirectly reaponsible for the failure of a pavement sur- face to withstand freezing and thawing cycles and traffic frictional sear. ‘When bleeding occurs in a plastic con- crete, minute channels are left in the interior of the hardened concrete, and provide an entrance for water at the surface. 'Upon freezing, the water exerts a detri- mental stress on the surface of the concrete that can be further enlarged by traffic friction. The result is a deteriorated pavement. The action of an air entraining agent on a concrete .nix is to cause the mix to absorb air which becomes a part of the mass in the foam of millions of tiny, even micro- 7E5 scopic air cells distributed throughout the mix. These tiny air cells, because of their greater surface area, immobilize the free water in the plastic concrete thereby greatly decreasing bleeding and the resulting channels. The combination of fewer channels and the disconnected air cells in the hardened concrete, minimizes the Opportunity for water to move into the surface. Furthermore, if some eater does get into the air cells, there is space enough for ice crystals to expand, which greatly decreases the dangers from temperature change.181 Air entrained concrete also has greater resistance to attack by chemicals. This is again principally due to the fact that bleeding is reduced, for if the resistance of e pavement to water absorption is increased, the harmful chemicals cannot be carried by the water into the concrete pores. An air entrained concrete has considerably greater workability and plasticity. It is thought that the air particles act somewhat like water in making the mix mObile. A reduction in the amount of water required of from f to 1 3/4 gallons per each can be realized.123 In its application to other than its use for highway pavements, the advantages of its greater increased worka- bility make it highly desirable. In addition, it gives a very pleasing appearance free from the streakedness and surface irregularities often inherent in a conventional 79 non-air entrained mix. Vibration can also be cut down to a minimum. The amount of air which is desirable to be entrained in a concrete is generally specified as from 3 to 5 percent by volume. A concrete with an air content less than this amount, begins to lose its effective properties, while a concrete containing over the specified percentage of air will begin to lose its strength with little advantageous gain in w orkab ility . It has been found that the air entraining ability is governed by many factors other than the amount of air entraining agent present. Commenting on air entrained concrete, John Chambers, a Chicago city engineer recently stated,126 ”The advantages of air entrained concrete for scale prevention on steel paving subject to dc~ioingzchemi- sale has been proved conclusively on city streets. he with other street and highway departments, however, Chicago’s department of streets has experienced difficulty in con- trolling the air content in concrete ----- ." For this rea- son, with the air entraining agents on the market to date, it is generally considered better to add the agent at the mixer rather than purchase the cement which has had the agent already added, where the size of the Job warrants the extra empenoe. This has been accented by the fact that different brands of air entrained cement often give different percentages of entrained air. Chicago has successfully used Darex purchased in 65 gallon drums ready to use, for air entraining purposes.126 It has been found that the grading of the fine aggre- gate hss a considerable effect upon the amount of entrained air. In general, fine aggregate entrains more air than cearse aggregate.131 However, the finer sands, particularly those passing a #loo.mesh sieve, tend to serve as air en- training depressants.126 The amount of sand in the $30 and 150 mesh class seems to have the greatest control over the actual amount of air entrained.“2 There is some con- flict as to the actual effect of the grading of the aggre- gate on the amount of air entrained. The majority agree however, that this effect is slight if not negligible. Temperature has a very definite effect on the ability of concrete to absorb air. A high temperature will cause a decrease in the air absorbed by as much as B or afi'over a range of 38 to 50 degrees F. In the use of air entrained concrete on the building of a bridge over the Chesapeake Ship Canal, built with PCA assistance, it was discovered that the percentage of air entrained was directly affected by the temperature of the mix, type of mixer and time of mixing, porosity of the constituents, and the consistency of the mix.128 Factors such as time of mixing in transit trucks, and type of transitotruek had no effect on the entrained air within normal time limits. It was also discovered that, using air entrained cement, in which the air entraining agent 6| had been interground with the cement at the factory. that the control or air content was most easily accomplished by careful control or the mix consistency. For clumps of l} to 8 inches, the air content could be kept within allowable limits. For a 3-inch slump, the air entrainment ran as high as 8 percent over the maximum allowable. A .1} to 2 inch slump was found to be still quite workable. Authorities of this project concluded that addition or the air entraining agent at the batching plant would have been more advisable. The air entrained in a concrete mix causes bulking and an increased volume. This volume change makes it necessary to compensate the mix to maintain the desired eenmnt content. Because the entrained air greatly improves the workability and increases slump, the mix is usually adjusted by reducing the sand and water contents. With the mix so adjusted, the concrete made with air .entraining cement generally has a higher strength in lean concrete where a considerable reduction in sand and water can be made, and slightly lower strength in rich concrete. At a recent ACI convention, it was stated that the approved air entraining agents reduce the strength or an average design mix by about 200 psi for each one percent or air content. A new agent was also diecussed which had been tested and required only half ae much water in the mix as with approved agents, with no loss in strength re- «‘52 sulting. It was reported to be or an expansive type and being considered for approval. It was also mentioned that Vinsol resin and Darex would not corrode steel, and that these agents cannot be premixed with calcium chloride or hard waters, even though such combinations can be success- fully carried out in the mixer.1 The decrease in the strength of an air entrained con- crete is accompanied by a decrease in bond and flexursl strength of the mix. These decreases are, within a res- aonsble degree or accuracy, about of the same percentage as the loss in compressive strength.127 About three years ago, an air.meter was devised by e. K. Klein, a former cement company official, and Stanton halter, director of engineering of the National heady Mixed 132 This meter has been a great aid Concrete Association. in the determination of the percent of air entrained in a mix. It is a great improvement over the fommsr method of computing the air content from.the specific gravity of the mix ingredients and the quantity of ingredients in the mix; and a later method known as the Hook method which consisted of determining the amount of water required to displace the air in the mix. The KleinéWslker method utilizes Boyle's Law which states that the pressure at a constant temperature varies as the volume occupied by the gas. In a concrete mix, the aggregate, cement. and water are relatively incompressible; however. the air entrapped in the concrete will be compressed 55 according to Boyle's Law. A container or fixed volume is filled with concrete in three layers with 25 roddinge or each layer. The surface is then struck off. A re- servoir is clamped to the top or the bucket and filled sith water to a certain height. Air is pumped into the portion or the reservoir above the water until a fixed pressure is established. The change in height or the water column indicates the compression or the air in the concrete and is read directly in percent or air meters now being produced similar to the Kleineflalker type. It is felt that the air entrainment principle will eventually be used almost universally. to some greater or lesser degree. The air entraining agent that will finally become recognized as having the better qualities is possibly still undiscovered. <54- Cement Dispersion In a mixture of Portland cement and water, the indivi- dual particles tend to group together and form floss. This is due to a certain amount of adhesive quality possessed by the particles of which there is present no counteractive repellent force. However, if a suitable dispersing agent is introduced into the mix, the floss will acquire like negative charges and will be repelled from each other, re- sulting in a sell dispersed medium. This action is essen- tially what takes place when a dispersing agent is added to concrete.132 In addition, a certain amount of air is absorbed at the surface of the mix; although this amount of air is generally below 3% by volume, or below the range of what are generally considered as acceptable air en- training agents.157 The action of dispersing agents has been known and used in other industries for many years.132 In the tire industry for example, the dispersion of carbon black in the rubber is a very valuable action indeed, increasing the searability of a tire many times. The dispersion principle has also been used in ceramics, dyes, paints, and other products. It was about 19 years ago when a suitable diapersing 2 agent for concrete was discovered.13 This material is calcium lignosulphate, a derivative of lignin, the sub- 55 stance found in the cells of wood. About 500 pounds of lignin are found in every ten of wood waste. The principle dispersing agent now being produced and used extensively throughout this and other countries, is Pozzolith, a product of the Master Builders Company of Cleveland (also Buffalo and Toronto). Pozzolith has been manufactured since 1933 and has calcium lignosulphate as a base. Dispersion of a cement increases the effectiveness of the cement by increasing its surface area, and releases the water that is normally trapped in the colloidal group8.137 The workability is also increased by this action, in addition to the action of the air which is en- trained in the process. A reduction in the mixing water can therefore be realized. also, due to the greater ef— fectiveness of the cement, the strength of the mix is in- creased, as compared to a decrease with an air entrained concrete. It is claimed that the percentage of entrained air in a Pozzolith mix remains fairly constant regardless of the variable conditions which normally effect an air an- trained concrete.132 Of course, a change would be less noticeable with the smaller amount of entrained air present. It is difficult if not impossible to compare the merits of an air entraining agent, and s dispersing agent. Both are to be desired in controlled amounts, and an agent which 56 which would act in a dual capacity would seem to be the most desirable. The manufacturers of Pozzolith claim that their product acts in such a capacity. There are possibly other materials which are more effective, or will be when they become recognized. ‘ Pczzolith has been mentioned in connection with its use in pumice concrete to improve the workability, and de- crease bleeding in connection with the Prudential Insurance Company building in Los Angeles. Pczzolith has been used on thousands of structures137 such as: the Matiliia Dam in OJai, California (40,000 cubic yards of concrete); the Foley Bros. Building, Houston, Texas (50,000 cubic yards of con- crete); the concrete used in constructin the largest bull ring in Latin America at Sports City, Mexico; the General Motors Office, Havana, Cuba; Sears Roebuck Store, Washing- ton, D. 0.; Shamrock Hotel, Houston, Texas; etc. Pozzolith sells for about 3.16 per pound (.6 pounds being normally used to a bag of cement) or contributes a- bout six percent to the cost of a concrete mix. 67 GU RITE Gunite Gunite is the material which is applied with the cement gun. It consists of cement and a fine aggregate (usually sand) intimately mixed with.water under pressure, and ap- plied from a nozzle under pressure. The cement gun is a machine manufactured by the Cement Gun Company of Allentoen, Pa. It consists of a hopper-like machine into which the dry mixed aggregate and cement raw materials are fed, a rubber hose through which the mixed material is forced under pneumatic pressure, and a mixing and application nozzle, where the hydration of the material takes place. The hydration is accomplished by water being forced by high pressure Jets to the center of the nozzle, 149 and the dry material passing through these streams of water. The amount of mixing ester is controlled at the nozzle, and can be determined by the appearance of the surface to which the gunite has been applied.150 The cement gun was manufactured by Carl Ackely, the African explorer, as a means of filling the inside of the framework over which his animal skins had been stretched.151 The cement gun was first used commercially by a fee railroads in 1911 and has been employed in increasing quan- tities since this date. It has lately found several new uses to which it can be adapted. A sand-cement gunite mix is usually specified in the Gib li...bn‘ 3. 4 a .. . its" HQ 3:1 to dizl preportional mix class. When applied by a skillful operator, within a normal pressure range, and with the proper consistency, a 28-day strength of 6000 psi can be obtained. Gunite is generally applied in con- junction sith a wire reinforcing mesh. 1940 Joint Com- mittee Specifications have recommended practice relative to prcportioning, consistency, and reinforcement design for pneumatically applied mortar mixes. One of the principle advantages of the cement gun process is that coatings can be applied to surfaces without the necessity of form work. This advantage becomes greatly accented when the surface has an irregular shape such that a very elaborate system of form.work would be otherwise re- quired. Being applied under pressure, gunite can have a much dryer consistency, and a greater penetration ability than a conventional concrete mix. The pressure application has a tendency to produce a more dense and quite waterproof .mortar, with a greater fireproofing quality than concrete cf the same thickness. The chief drawback to a gunite application is that there is a considerable loss of the material due to rebound *shich introduces an extra cost factor. Gunite has been used extensively in the repair, re- clemation and renovation of old concrete and masonry build- ings, stacks, tanks, canals, tunnels, etc. It has also found usage in the fireproofing, insulating and waterproofing cf 69 'various structures. The application of gunite directly to the soil for canals, irrigation ditches and swimming pools has proved adequate and economical. Among the new uses to which gunite has been applied, is its use in connection with prestressed wire for con- cretc tanks and pipes,90 which has already been discussed. A discussion of gunite in connection.with steel panel house construction, and in dry block masonry walls will follow. The economy of using gunite cannot be discussed in general terms. For many applications it is the only practical answer, especially in its use in connection with the repair of deteriorated stacks, dams, tunnels and other structures; in the encasement of steel; and as a coating over prestreesing sires for tanks and pipes. The use of lightweight aggregate instead of sand mixed with cement may give gunite a new field of usefulness. There are at present approximately a dozen companies which specialize in gunite work exclusively and on a large scale.151 Two of the larger of these firms are the Na- tional Cunite Contracting Company, and the Gunite Concrete and Construction Company. Both of these companies have several branch offices throughout the country. 90 Steel Panel Gunited Houses The Steel Building Unite Corporation of California has developed a hydraulic loom.which weaves pencil steel into structural panels for use in house erection.1‘z The panels consist of two layers of steel in the form of mate consisting of 3/8-inch rods running vertically st 16-inch centers, and é-inch rods running horizontally at the same spacing. Each mat is further stiffened with diagonals from every other Joint and the two mats are welded apart with S/e-inch spreadera at each joint. The hydraulic loom provides initial tension in the steel so that all connec- tions are tight. An 8 x 20 foot unit can be produced every thirty minutes.141 The entire house is assembled using these panels, in- cluding the interior walls and the roof. The exterior wall panels are supported by pouring a l4~inch foundation wall around them, and the remaining panels are tied to these wall panels. Hext, the door and window openings are cut out and the frames and the conduits are layed in place. Plywood forms are buttoned to the inside of the wall panels for a portion of the house and gunite is sprayed against these panels in three or four coats to a thickness of 8 inches. Meanwhile, the forms can be moved to another sec- tion of the house. A lightweight aggregate is used in the gunite mixture on these California projects. The use of this type of structure has been so far limi- 9| ted to a fee California projects, including a loo-acre subdivision east of Les Angeles known as Hugheaton Meadows. However, the Steel Building Units Corporation is planning to expand their idea to other parts of the country. This type of construction is said to cut the building time in half over conventional methods. 92. Gunited Dry Block Hall A recent experiment at Dallas, Texas, may prove of a national interest.‘m‘o The eXperiment was conducted by the Pittsburgh Testing Laboratories and the Southwestern Labo- ratories. A well of block was laid up dry and coated with a .Sl~inch layer of gunite on one side and .92 inches on the other. One side of the wall was reinforced with steel .mesh. Another wall was laid up with mortared joints in the conventional manner. These walls were subjected to various test loadings. With each well resting on two supports 42 inches apart, they were loaded with concentric loads at the tap center. The plastered dry-block Wall failed at ll,500#; the con- ventional well at 4,400#. Each wall was also subjected to a loading in the flat position. The conventional wall failed at 2,080é; the dry laid gunite wall at 6,770f. The tests were so successful that the city of Dallas indicated that it would approve the method, and the local F.H.A. Agency made application to its Washington office for approval. There was no economy factor mentioned, al- though it is assumed that the gunite method would provide a substantial decrease in cost where the size of the Job warranted the use of the equipment required. The method would certainly reduce the work of the bricklayer, if not eliminate his need altogether. This could be considered an important factor considering the great shortage of bricklayers in the country today. 935 MI 8- C ELLAN EOU S Building Economics Arthur J. Boase, manager or the structural and rail- says bureau of the PSA, Chicago, has recently presented several recommendations that will tend to yield a better 181 His recommendations are concrete at a lower cost. these: (1) the use or air entrained concrete (8) the use of a controlled high strength concrete (3) proper vibration (4) the use of mechanical floats (5) the use of cranes (6) the employing of skeleton framing for‘buildings over two stories (rather than bearing walls) (7) the use of precast units The world's Longest Reinforced Concrete Arch Spans Further indicating that this country is still a £01- lower when it comes to concrete design, is the interesting fact that there are is reinforced concrete arch spans in the sorld that are longer than the longest which the United States can exhibit.182 The longest of these spans is the Sandoe Bridge located in Sweden. This bridge has a span of 866 test. The longest such span in the United States is the George Westinghouse Bridge located in Pittsburgh and having a span of only 418 feet or less than one half that of Sweden's giant. new Jobeite Concrete Testing Method The city of Fort fisyne, Indiana uses a rather novel means of testing concrete sampled at the jobsite.183 A sample of 500 to 3000 grams is obtained from each pour on the Job and is sealed and taken to the city laboratory. The sample is tested for moisture content, and then broken down and subjected to a screen analysis. The city claims that they can obtain the 28 day strength of the concrete within 200 psi, and the water content within } gal/cu. yd. The city performs these tests for all of its projects and at a fixed fee for private individuals desiring the information. Comfort Concrete A new concrete mix has been introduced recently to improve the softness or resiliency of concrete floors.184 The concrete consists of an ordinary mix with some asphaltic emulsion added, and is called "comfort concrete." Along this line, the American Bitumuls Company of San Francisco has recently introduced a colloidal asphalt con- crete admix product which they have named hydropel.185 Hy- dropel is added to regular concrete in the quantity of 1} gallons per sack. The company claims that their product has these advan- tages: ‘35 ”'1 (1) (2) ‘3) (4) improved cement dispersion reduced aster absorption increased shock ability or resiliency complete protection from alkaline, salt or destructive gas attack The company claims HydrOpel can be used advantageously for pavements, sewage plant structures subject to sulfide or gas corrosion, and floors of all kinds. a steel ball is said to bounce 2% times as high on plain concrete as on Bydropel concrete, indicating its resiliency or softness. 96 Concrete Floors Youred in Reverse Order A Kexican civil engineer has succeeded in developing a system for pouring concrete floors from the top down. Manuel Gonzales Flores of‘mexico City came up with the idea and in a practical application of his principle, a consider- able degree of success was achieved. The system was devised for pouring concrete floors for a steel frame building. The steel framework is first e- rested in the usual manner. Assuming a flat concrete roof, the roof forms are suspended from vertical rods which are connected in some adjustable manner to the steel framework above. After the concrete has been poured and has suffi- ciently set, the vertical rods are loosened and the build- ing is lowered by enough of the rods to keep the form to- gether. Since the rods must pass through the floor which has already been poured, wooden spools are set in the for- eround the rods. These spools are later removed and the holes grouted. After the form has been lowered to the po- sition of the top floor, the rods are again secured in place, and the floor poured. The remaining floors are poured in the same manner from the top down. The advantages of such a system are rather obvious. The same forms can be used for every floor without the necessity of tearing them down and reasaembling them-a; gain. This not only saves time but it also saves on material, for the continual stripping and reassembling of €37 forms is hard on them. another advantage is that after the first pouring the building has been provided with a roof protecting the workmen from inclement weather. T is is e particularly advantageous feature for localities that have a great deal of rain certain times of the year. The economic adrantages would, of course, be limited to multi-etory buildings having certain types of framing. 98 Reinforcing Steel in Bundles In most ordinary reinforced concrete beam or girder designs. there is ample room in the beam to space the re- inforeing steel. at the specificational separating distances required for prOper bonding with the concrete. without the necessity of enlarging the size of the bean to carry this spaced steel. However, it is quite often the case, that s bean.ie loaded in such a manner that this enlargement be- comes apparently necessary. It is in these instances that it may often be economical to locate the bare in bundles and thereby reduce the size of the bean in width and depth.177 It is. of course. necessary to anchor each bar of these bundles firmly to compensate for the loss in bond. This extra anchorage is not always practically possible but in many cases it can be done without difficulty. a small bridge in Rhatcom.County, Nashington, employed bundle reinforcing and made possible the use of beams 9% inches thick, where 11% inches would have been required with normal spacing; a similar but smaller saving was also rea- lized in the depth of the beam. The beam span was so feet. The large scale use of bundle bare was employed in the design of the Quitandinha hotel in Petropolis, Brazil. Reinforcing bundles were used in rigid frames of 100 foot span. over an ice skating rink incorporated with the hotel. sith a considerable saving. 99 Heat Control of Large Concrete Masses using Ice In 1959, in the building of seven dams for a hydro- electric plant in the Harz Hountains of Germany, it was decided to use crushed ice to counteract the heat generated during the early stages of setting. This was believed to be the first use made of ice for such a purpose.178 The success of this project is not known. Since the time of this early esperiment, it has been definitely established that, except in an exceptionally large mass of concrete, precooling the.mix with ice will keep the concrete within safe temperature limits during the setting period, and prevent shrinkage cracks.172 Ice is now being employed in the construction of the Davis Dam, on the Colorado Riven”o and the Fort Gibson flood control and hydroelectric dam on the Grand River near Huskogee, Oklahoma. ’ The Fort Gibson Dam is a $32,800,000 project and will require about 500,000 cubic yards of iced concrete. An ice making plant has been set up and consists of three ms- chinea each with a 48~inch diameter freezing unit. These units have a total daily capacity of 180 tons and furnish 135 tons of ice (2" x }” cylindrical pieces) and the re- maining tonnage of cold water for use in mixing concrete for the dam. It has been found that 162§# of ice added to each cubic yard of concrete will lower the temperatwe of the mix from so or. to as T371 \cma The refrigeration plant at the Davis Dam consists of three machines each with a 54~inch diameter freezer unit. supplying 60 tons of crushed ice per day. The ice is con- veyed on belts to the adjacent batching plant and weighed for proPer preportioning. As much as 400# of ice is added to each four yard batch to keep the temperature of the concrete within limits---- 80°F when placemmo With the air often reaching 110°! in this part of the country, the concrete often reaches 170°F. It might be pointed out, that the ice has, of course, melted by the end of the mixing period, so that no actual ice goes into the dam as such (the effects that this would have are apparent). These iced mixes eliminate the use of cooling pipes running through the dam, and prove cheaper and more effective. \OI Expanding Concrete a French engineer, B. Bossier, claims that he has developed a cement capable of producing a controlled ex- pansion.”6 He has published a series of articles ex- plaining his cement in the French Journal, "Genie Civil.” The expanding cement consists of a portland cement base, sulfoosluminate cement, and a powdered blast furnace slag. The sulfa-aluminate cement is the expanding agent, and the blast furnace slag is the stabilizing or controlling agent. Expansion takes fifteen days and requires moist curing for this period. The effect of the expanding agent on the reinforced concrete is to place the reinforcement in tension and the concrete in compression, or sort of a self induced pre- streasing effect. This action decreases the diagonal ten- sion considerably and increases the strength of the slot to as much as 1000 psi in 60 days in actual tests made. The expansion is caused by the grosth of the sulfa- aluminate crystals, which are usually needle shaped. It remains to be proved that this reaction can be adequately controlled to prevent continued expansion on extensive weathering, which would have disastrous effects on the strength of the concrete. However, it is definitely a thought worth mentioning. ‘02 l. 3. d. 7. 8. 10. 11. 13. 18. 14. 15. 16. 17. BIBLIOGRAPHY The Story of Pumice (6 parts) Rock Products Ag, 8, o, N, D '47 How Strong is Concrete Rock Products D '4? Factory Roofed with Pumice Concrete‘Units Engineering News Record D9 '48 PumaliteoeA Lightweight Block Book Products Is '47 Concrete Products Output Summarized for 1946 Rock Products Ag '47 Available Washington State Pumice Deposits Rock Products Pumice Plaster Rock Products My '47 Steam Plus Hot Air for "Preshrinking' Rock Products Ag 'i? Floating Concrete Rock Products My '47 Light-eight Aggregate Rock Products 3 'e7 Manufacture Perlite Concrete Block Book Products 0 'e7 Lightweight Aggregates‘flin New Attention architectural Record 11 '48 New Trends in Concrete Rock Products Concrete Lumber Rock Products Mr '47 Lightweight Aggregate Plant For Sale Rock Products Mr"47 Sell Light-eight Aggregate Plant Rock Products My '4” Engineering News Record Reports Engineering News Record D 30, '48 18. 19. 21. 22. 23. £3. 86. 87. 88. as. 31. 33. Fron.thc Movies to Lightweight Aggregates Rock Products 0 'ev Modern Plant Makes Lightweight Aggregates Engineering News Record S 16, ‘48 Invite Machinery Manufacturers to Tell about new products Rock Products My 'd? Meeting Big Demand for Lightweight Units Rock Products 0 '47 Don-Metallics Rock Products D '47 Scoria for Concrete Block Book Products :1 '47 Msking Concrete That Floats Rock Products My '47 Verniculite from Africa Rock Products H '47 Sawable Block Rock Products N '4? New Lightweight Aggregate Rock Products B '47 Lightweight Aggregates for Concrete Rock Products Ap ’d? Lightweight Root Slabs Rock Products 8 '47 Ytong-A Swedish Lightweight Building Unit Rock Products Ag '49 Prudential Insurance and General Petroleus.Buildings in Lcs Angeles new under Construction Architectural Record 0 '48 Lightweight Concrete is Termite Proof, Cheap Science B. L. Is 23, '45 Wood Concrete Rock Products 0 ’47 Concrete tron Coral Science H. L. r 9, '46 35. 50. 31. 32. 53. 55. 36. 5?. 58. 39. 60. 70. 71. 78. New Products Engineering News Record D 16, '48 Material furnished by the Zonalite Company of Chicago, Illinois Pumice as a Lightweight Aggregate, by F. Sommer Schmidt, published by American Institute of Mining and Metallurgical Engineers Pub. Oct. at, 1947 Material furnished by the Concrete Plank Company of Jersey City, New Jersey Material furnished by the Durisol Company of new York City Material furnished by the Celotex Company of Chicago. Illinois Material furnished by the Porite Manufacturing Company of North Arlington, New Jersey Material furnished by the Carter-Waters Corporation of Knnsas City, Missouri Material furnished by the Pumice Aggregate Sales Company of Albuquerque, New Mexico Material furnished by the Kraftile Company of Niles. California Material furnished by the Sante r. Pumice Company of Sante Fe, New Mexico Materiel furnished by the Pumice Producers Association of Albuquerque, New Mexico #**###**##***¢* Reinforced Concrete Pressure Pipe Manufactured on Two Levels Rock Products F '48 Prestrsssed Pipe Without Steel Cylinders Engineering News Record Is 24. ‘48 i 60 miles of Prestressed Pipe L" ng Engineering News Record My 13, '48 73. 74. 75. 73. 77. 78. 79. 80. 81. 82. 83. 83. 86. 90. 93. World's Largest Covered Prestressed Tank American City S '48 High Stressed Wire in Concrete Tanks Engineering News Record D 30 '43 What will be Prestress Loss Due to Creep? A.C.I. Journal D '48 Prestressed Concrete Digestors Contractors and Engineers Monthly la '49 Merry-Co-Round Machine Applies High Tensile Steel Wire to Prestressed Concrete Tanks Construction Methods la '44 Prestressed Concrete American City S '47 Jointless Prestressed Floor Resists Heavy Loads in Warehouse .Engineering News Record Is 6 '49 Prestressed Cast-In-Place Concrete Bridge Engineering Rows Record H ll '48 Prestressed Concrete for Runways Engineering News Records S 16 '48 Editorial Engineering Hews Record D 30 '48 Structural Engineering Engineering News Record D 16 '48 Structural Engineering Engineering News Record R 4 '48 Notes on Prestressed Reinforced Concrete Pipe American City B '45 New Runway Laid A.C.I. Journal D '48 Material furnished by the Preload Corporation of New York City sxrsesssessemeseeese Building Houses Using Large Precast Slabs Rock Products Ag '47 93. 97. 98. 99. 100. 101. 102. 108. 110. 111. 112. 113. 120. 121. Insulated Precast Concrete Wall Panels Prove Economical Substitute for Brick A.C.I. Journal.D '48 Precast Method Eliminates Vertical Forms Architectural Record E '48 Precast Frame for Two-Story Plant Erected Like Structural Steel Architectural Record Ag '47 Precast Concrete Building The Constructor Jl '47 Speeding'Up Construction with Large Structural Units Rock Products N '47 Cementstons Precast Construction A.C.I. Journal B '48 Cementstone‘Units Architectural Record Is '48 Material furnished by the Camentstone Corporation of Pittsburgh, Pennsylvania essesssaassweasseaee This is the House the Tournalayer Builds American City My '4? 0n the Job with Tournalayer Architectural Record Ag '48 Concrete Houses Cast in.Box Forms Construction Methods 0 '48 Whole House Cast Like Toy Popular Science B '48 meaasssssasseasaassss Highsay Research Engineers are Urged to Translate Findings into Practice Engineering fiews Record D 25 '48 Air Entrained Portland Cement Architectural Record 0 '46 122. 123. 12‘. 183. 183. 127. 128. 129. 130. 131. 132. 133. 137. 140. Sand Grading Influence on Air Intrsinment in Concrete AeCeIe Janrnal N .‘8 Influence of Size Grading of Sand on Air Entrainment A.G.I. Journal H '48 Effect of Entrained Air on Concrete Made with So-called "Sand-Gravel" Aggregates AsCeIe Journal 0e .‘8 Air Bubbles Improve Quality of Concrete Science N. L. O 26 '46 Air Entrainment Control Test Project Completed in Chicago Effect of Entrained Air on Bond Strength of Concrete Concrete Is '49 Innovations In Bridge Pier Concrete Engineering News Record Feb 6, '48 Concrete Problems and Progress Discussed at A.C.I. Convention . Engineering News Record Mr 4 '48 Protection of Concrete from Attack by Alkali Soil or See Water Engineering News Record N ll '48 Controlling Quantity of Entrained Air in Concrete Concrete Ap '47 Cement Dispersion and Air Entrainment are Important in Good Concrete Southwest Builder and Contractor Is 13 '47 Portland Cement Dispersion by Absorption of Calcium Lignosulphate Industrial and Engineering Chemistry e Material furnished by the Master Builders Company of Cleveland, Ohio **¥**¥**$*$**#***##** Dry Rock Panel Shot With Jet-crete Promises New High Strength‘Wall 141. 142. 143. 144. 143. 146. 147. 170. 171. 172. 173. 177. 179. 181. Hydraulic Loom.Weaves Reinforcing Mats Construction Methods D '48 Now They're Weaving Houses Papular Mechanics D '48 Clever Design and Erection Speed Texas Fair Structure Engineering News Record S 9 '48 Low Cost Thickener Engineering and Mining Journal 3 '47 Cement Lining Large Maine in Place Using Pneumatic Pressure Water Parks Engineering Ap SO '47 Low Cost Irrigation Flume Cover Engineering News Record My 13 '48 Nintertime Guniting at the Soo Engineering News Record Je lo '48 mstfimswcfiasxatrwetfi Admixtures Combat Alkali Reaction in Davis Dam Concrete Engineering News Record Ja 20 '49 Review of "Iced Concrete" A.C.I. Journal D '48 Ice in Mix Precools Concrete for Dams Compressed Air Magazine Mr. '48 Expanding Cement Rock Products My '4? Bundle Reinforcement Saves Materials Engineering News Record Ap l '48 Pouring a Building from the Tap Down Pepular Mechanics J1 '48 Stretching the Concrete Building Dollar Engineering News Record 0 28, '48 182. 183. 184. 185. Contractor'Meets Close Desiganolerances in Building Long-Span.Concrete Arch Bridge Civil Engineering In '49 Dissect Your Fresh Concrete American City D '46 Floors of Concrete Better Homes and Gardens N '48 Make Improved Concrete with this Admixture American City J1 '48 , h " a a- i _ .Lvr‘...,:.-1*u . 13.3.7; .VJ... . . . .9.‘ DJ 4-. . . , .. WED)...“ [I'll‘lt I 0’s-e'tw7§\.e (7:14.173... ‘1‘"?!(ii. .13‘i’i‘lilgi’e vitr-tl. 9'). 5 l . I” l