73311.4“. .l A STUDY OF TREMIE CONCRETE 1 v I-.- The.“ ‘0' the DWCO 0‘ Bo 3. L'PFX U”),- 7 ’7 155,0? M‘vlb ‘1'7'tg1177 . MICHIGAN STATE COLLEGE Robert Knowlton F022 Dtvid Richard Mou-lton .“k.\ .ODv 5~Uf1 (5.75WN’73‘U1515171417..PDLE...p9¢\1’1r1...QrI... .. . nfiiafl »¢PL.ru1\Pb€I'F P7115...- Vfrhrvv. #71. . .kut-rL-srvru 4.71.17.57.75 . “Pclftw n4. . 5.1.1.095- biv. «iv..- 11.11.. :F’DJ_D_1.&1 I942 .. 1. 1'.- ...-....111‘1Hu17r._l.nhx‘ 71.7 ’r rl‘... \‘1111.7!.! .....1. . . -- 11... 1.110... :1.‘ .11.». 1:10.... 11.6 *9§v!\( 0*.IISI: It" . .. 1-. .1 1 .. .1. J.........1.7.1. . 11.1.117117751117i1l41‘5w '. .5 on ..J 1.1-. 0.: 71 1 1. ...11 ‘V1 17“}41.’ if \VNUC‘JIv,O1!_1‘V.~ 11.. 11! ”to: -..-r.‘ V.- 1,111.! 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Moulton Candidates for the degree of Bachelor of Science Jun. 1942 THE5§T§ C. 24 I. II. III; 7. VI. CONTENTS Acknowledgment Discussion of Subject lodel Studies Method of Placing Tremie Concrete Drawings Bibliography ACKNOWLEDGHENT The authors of this paper take this opportunity to thank Mr. K. H. Talbot, an engineer of broad experience in the field of concrete, and members of the Civil Engineering staff at Michigan State College for their cooperation in the writing of this thesis. Habert Xe F068 David R. moulton Discussion of Subject Use of the Tremie Depositing concrete through water is not recommended if it can be avoided, as there is always uncertainty as to the results. However, there arises certain occasions when it is advisable to place the concrete underwater. Such occasions arise when the bottom is soft and it is difficult to keep the water out by means of cofferdams or when the water is too deep for a cofferdam. There are three methods generally used of depositing concrete under water. They are the tremie, or pipe, through which the concrete is conveyed through the water; the drop bottom bucket, and by means of bags. The tremie is perhaps the best method as it permits of the greatest control over the pour and makes for a homogeneous mass with no laitance seams and very little washing of the mix. Drop bottom buckets are used to advantage at great ' depths where it is impractical to lower a tremie pipe. They have the disadvantage, however, of causing washing of the concrete and the possibility of laitance between buckets of concrete. Bags are used in places where a homogeneous mix is not necessary. The general characteristics of the sacks of concrete lend themselves to the formation of laitance along with the inclusion of the bags themselves in the mass of concrete. The following are extracts from the Portland Cement Association's specifications number 420-3, Depositing Concrete Under Water. (a) when it is necessary to deposit concrete under water the methods, equipment, materials and proportions of the mixture to be used shall be submitted to and be approved by the engineer before the work is started. (b) Concrete shall not be placed in water having a temper- ature below 35 deg. F. The temperature of the concrete, when deposited, shall be not less than 60 deg. F. nor more than 120 deg. F. (c) The concrete shall contain not less than 7 sacks or 658 pounds of cement per cubic yard. The volume or weight of the coarse aggregate shall not be less than one and one- half, nor more than twice that of the fine aggregate. The concrete shall be mixed with sufficient water to produce a concrete having a slump of not less than 4 inches and not more than 7 inches. (d) Cofferdams or forms shall be sufficiently tight to reduce the flow or current of water through the space into which concrete is to be deposited so as not to exceed 10 ft. per minute. Cofferdams or forms in still water shall be sufficiently tight to prevent loss of mortar through the walls. Pumping will not be permitted while concrete is being placed, nor sonner than 24 hours after the placing of concrete has been stopped. (e) Concrete shall be deposited continuously until it is brought to the required height. While depositing, the top surface shall be kept as nearly level as possible and the formation of seams avoided. The methods to be used for depositing concrete under water shall be one of the following: (1) TREHIE: The tremie shall be watertight and large enough to allow a free flow of concrete. It shall be kept filled with concrete at all times while depositing. The concrete shall be discharged and spread by so moving the tremie to maintain as nearly as practicable a uniform flow and avoid dropping the concrete through water. If the charge is lost, while depositing, the tremie shall be withdrawn and refilled. The slump of concrete shall be maintained between 5 and 7 inches. (2) DEC? BOTTCH BUCKETS: The top of the bucket shall be open. The bottom doors shall open freely downward and out- ward when tripped. The bucket shall be completely filled and slowly lowered to avoid backwash. It shall not be dumped until it rests on the surface upon which the concrete is to be deposited and when discharged shall be withdrawn slowly until well above the concrete. The slump of concrete shall be maintained between 4 and 6 inches. (3) BAGS: Bags of at least one cubic foot capacity of Jute or other coarse cloth shall be filled about twoothirds full of concrete and securely tied. They shall be carefully placed in header-and-stretcher courses so that the whole mass is interlocked. Bags used for this purpose shall be free from deleterious materials. (f) To minimize the formation of laitance, great care shall be taken to disturb the concrete as little as possible while it is being deposited. Upon completion of a section of concrete, all laitance shall be entirely removed before work is resumed. Model Studies Hodel Studies Before using a tremie it is best discover the behavior of the concrete under varying conditions of size of tremie and the texture of the concrete. As a preliminary to the actual pouring of concrete, studies were made consisting of passing dry sand through a pipe held vertically at a distance of about one inch from the bottom. The flow was controlled by the distance that the bottom of the pipe was held above the bottom surface. With the tremie pipe above the sand, the sand flowed from the pipe until it reached the point where the resisting pressure of the pile of sand is equal to the downward pressure of the sand in the tremie. It is evident that when the material in the pipe stopped flowing, that a cone formed around the end of the pipe. The height of the sand measured from the bottom of the pipe to the top of the frustrum of the cone was affected by the head of sand in the pipe. As soon as the material reached its normal angle of repose under this surcharge, it became necessary to raise the pipe and to allow the flow to continue over the top of the already placed sand and down the sides of the cone. It is quite evident that if real concrete were allowed to flow down the sides of the pile in this manner it would wash out a great deal of the cement, and segregate before coming to rest. If, however, the pipe full of sand is dropped, the slopes and lines of force are readjusted and more is released by the head pressure. In this case, the whole cone moved outward and flattened, but there was no noticeable flow over the top, except by particle movement from the extruding force. The pile of sand is built up from the inside which is the principle upon which concrete is placed under water by means of the tremie. The action of the sand in this case is similar to the action of real concrete in the tremie. The sand is made quick by the sudden application of pressure and flows like a plastic material until released.from the pressure or vibration. To determine the behavior of the tremie with conditions as near as possible to those using actual concrete, a cement mortar in the ratio of three parts of sand to one part of cement was used. This gave a concrete with a rather high slump but was sufficiently homogeneous so that there was a very little separation while being placed. A tremie six feet high and 2% inches in diameter was used. This was connected to the bottom of a hopper which held approximately one cubic foot of material. The concrete was poured onto a concrete floor plate two feet square with wooden sides as shown in drawing number one.- Concreting was first carried on in air. Observations showed that concrete, extruded from the end of the tremie travelled outward along the bottom of the plate until the friction on the plate, combined with the internal friction of the concrete, caused the concrete to raise near the pipe and to form a dome with a crater around the pipe. Continued pouring of the concrete showed a series of mass movements outward and downward. As the concreting continued, the dome continued to rise around the pipe and spread outward over the floor plate. As the dome spread outward, periphery cracks developed showing that the dome was being built up from the inside. These cracks were gradually absorbed as the mass expanded. When the tremie was raised, new lines of pressure and new flow lines developed. The continuous flow of the concrete through the tremie maintained somewhat uniform slopes, whereas, delays allowed the hardening of the surface of the concrete, changed the direction of flow and the characteristics of flow under the surface. Deep tremies caused the flatter surface slopes; shallow tremies steep slopes. Drawing number 2(a) shows the profile of the dome as each batch of concrete was added. As long as the concrete below the surface has not hardened, the dome rises at a somewhat uniform rate. The pressures at the bottom of the slope, being more nearly horizontal than those nearer the pipe, cause outward flows until these pressures are resisted by the side walls or internal friction of the concrete. Outlines of ties lines and pressure lines were obtained by the addition of a mineral color to the sand. These lines are shown in drawing No. 2(b). The first batch to be poured was in natural color and is shown by the grey color. Its original position is shown by done (1) in figure 2(a). As the second batch, which was colored red, was poured it forced the natural batch outward from the tremie and up against the form walls. The third batch was a natural color. This flowed upward along the tremie until it began to overcome the opposing pressure from the previously poured concrete. as more concrete was added the sphere of pPeSSer began to increase and force the red back. This action is shown by the natural colored ball around the tremie. The dome of the mass rises all the time, but there is very little surface action of the concrete. It is this feature which suits the tremie for pouring concrete under water as there is no washing out of the cement content. A batch of concrete of the same proportions as that poured in the dry was placed under a head of two feet of water. The concrete was poured into the same form so that comparisons could be made. There was very little difference between the concrete placed under water and that placed in the dry. If anything, the under—water concrete was a little more dense then the other. This is probably due to the added pressure of the head of water on the concrete. The internal characteristics of flow were similar to the results previously obtained. An interesting variation was a ring of washed concrete which was in a position as shown in figure 3. The concrete was the first to be extruded from the tremie and the cement was washed out before the end of the tremie became sealed in the rising dome of concrete. This washed material was then forced outward by the pressure of the extruding concrete. It will be noted that the tremie pipe in this pour was located six inches from one side of the form. In a pour involving a considerable depth of concrete it would be impractical to keep the tremie at its full depth. To overcome the head of concrete on the bottom of the tremie pipe and allow the concrete to flow, the pipe would have to be kept filled with concrete to a considerable height. Also, the depth of the tremie would allow a shell to form on the dome and increase the back pressure in the tremie. A model batch was poured using two colors, natural and red. The first batch of natural was poured with the bottom of the tremie about two inches above the concrete plate. The tremie was then raised about six inches and the red batch poured. It is necessary to keep the end of the tremie below the surface of the concrete or it will lose its seal and washing of the concrete Will result. Figure 4 shows the results of this pour. The second batch forced the first batch out toward the sides and then began to flow down over the surface of the first batch. In this method the slopes of the done are somewhat steeper, but the concreting may be carried on a little faster due to the de- creased pressure head against the bottom of the tremie pipe. Method of Placing Tremie Concrete Vethod of Placing Tremie Concrete Taking a simple underwater foundation such as might be found in a bridge pier as an example, we shall briefly run through the steps of construction. Figure number 5 gives an elevation View of the set-up. The first step in the construction is the preparation of the sub-base. The mud, clay or rock, whichever it may be, is finished off to the desired elevation and slope. Care should be taken to keep the area as free as possible from heavy silt and mud. Next comes a layer of gravel or crushed rock. The purpose of this is to hold the mud and clay in place to '0 *1 a) vent it from mixing with the fresh concrete. The thickness of this layer will depend mainly upon the consistency of the soil upon which it is placed and the thickness of concrete on top or it. The gravel is then dragged so that it will present a fairly level and clean eurface to the concrete. As it would be difficult to smooth the gravel with pile butts sticking up, they are driven and cut off to_the proper elevation after tee gravel has been placed. The forms are usually one of two general types. One type is made with corrugated steel sides with the reinforcing bare built in as part of the form structurally. This form is then sunk into place and filled with concrete. mhe other type is a form built of wood with eteel braces on the inside. This is then weighted and sunk into place. The wooden form should be removed after the concrete has set. Any interior bracing should be of steel, as wooden bracing will rot and weaken the concrete unless extreme care is taken to prevent it. The next step in the process of constructing our foundation is the design of our concrete mix and choosing the size of tremie pipe that is best suited for our needs. The requirements for mix design for tremie concrete are more exacting than for concrete not placed under water. Cnly by an appreciation of the difference between the requirements for mass concrete, placed in large batches and solidified by vibration, and concrete that has within itself all of the dharacteristics of a plastic material that can be extruded into the place under pressure, can a successful design of the concrete be developed. Tremie concrete requires more than a well graded aggregate with minimum particle interference. It requires a cement content and a water-cement ratio which when sub- Jected to sufficient time and sufficient thoroughness of mixing, combined with the grinding and rubbing action of the aggregates in the mixer drum, will form a paste which will uniformly coat all surfaces of the aggregate with a cohesive smooth lubricant, thereby giving to the concrete the desired flowability and re-moldability. Slump is not a true measure of flowability, but as a rough measure it may be adopted for preliminary study. In general it may be said that there is a relationship between slump and flow provided the difference in slump reflects a change in the same characteristics of the concrete. Harsh, low slump concrete cannot be distributed by tremie as can plastic, remoldable concrete. The coarser particles will segrerate from the finer and the concrete will move for shorter distances. Segregation causes internal friction requiring the tremies to be raised to deliver the concrete. This in turn results in steeper slopes and may 91166 the tremie to be carried so high that the only distribution can be over the top of concrete already plaCGd. "aehing of the surface may result. The slump, according to the Portland Cement Association's specifications, should be kept between five and seven inches. It as been found that a tremie equipped with a foot :30 valve and baffle such as in figure 6 will effectively change the direction of flow of a column of concrete from vertical to horizontal, and will deliver controlled concrete where where required to a maximum horiZOntal distance with a minimum vertical movement; or in other words, to distribute concrete through the greatest possible horizontal circle with a minimum depth of t -mie. H O The size of tremie will depend upon several things, mainly the flowubility of the concrete and the rate at which it Peflsefi through thfi tremie. a flowable concrete is best handled with a smaller tremie than is a harsh mix. The size tt\WL \ ‘.. of the tremie will usually vary from 3 to 15 inches. The depth at which the end of he tremie is kept below the exrface of the concrete will depend upon the- cheracterietice of the concrete, the size of tremie and t toe head of water on the concrete. The best depth will have to be determinei by trial after these other factors have been detarmined. Tremies equippeé only with foot Valves are best kept between three and five feet below the surface of the concrete. As yet, no definite standards have been developed for tr mie placed concrete. The engineer contemplating such work will have to combine the work and investigations of ‘0 others to lit the particular Job at hand. Drawings Photograph showing arrangement of model tremie. HOPPER I TEEN/E P/Pf Fame: 47/ FOE/‘7 5364‘ El / I ,1/ E 'o‘ k A j TEEN/E ”0051 No. 1 / Eleuaf/an 01C Dome a/Ehd or“ 5465 547165 M/ _.J J‘c 1‘70” 0)" C 5/04»? 0“ 7‘ 775m Ce» K” A we 07’ flew/e A” M/ No. 2 M4 .1470? Co/(czens' 0N0 £9 14/4756 P003 fl. No.3 j) 5 I z 7 9 v , ~‘NW'WK “\d’x W\\,\——’_\«»\"’-‘\..“~”‘-‘\‘-’%—-' Photograph corresponding to Fig. 4 q I :xg/ HM". Fbw 7/0” M 5337 10057770/1/ 1‘50: Mao: W/ 779 725M/é' 14 7' TWO D/Ffieeexvr L 51451.! 0. For” 24 72:45 (W 610’?! 5:; Li—_ /1///’ I £4274! [ 1” flop/45¢ 7217/15 M PI)! . .3726; ' Warm/w A ’777777777/ PM.” “a; /// Wu 44/007 Fae PL fltl/VG coA/aeirf (/Nflfe A49 7-52 Mai TEE/W! w/ m 5,9 pa E ”W .1110 ”V6 fiat/E Foo: V]; V! J55 T/O/V 19-14 BIBLIQGRATHY Tlein Concrete, 3.3. Bauer; Pages Engineering Ieneeflecord g2, 144 Engineering flows-Record‘gg, 251 Engineering Rews—Reeord 112, 17 Engineering Howe-Record 120, 492 Depositing Concrete Under water 163-164 {July 27, 1922) (Feb. 10,'1927) (Jan. 4, 1924) (April 7, 1933) Portland Cenent Association Concrete Information Sheet 3r—12 Doc 15 104. ‘RGOM USE ONLY o O U ‘0 ... . i . 1 y o e .p. M. Aal “HZ ..IGOCOWIAN. t .103 t . 1“.. I . A P-U-l.- ~~-’ W S 0 .w E R 1“ n A . R. 1 l . _ Bug " HIM. ‘3 Y 1:. Sill R. ‘ El V JO le3 U|"0 Elrl‘ . I; 3 . Ml‘i 9 . l S l \' 2 I‘ ‘l‘lflli‘1 . o. WH‘: 3 G 1‘ ml} m . . ... Fl. :I. r... - ...u .. . . -, .- . . . . . .7..