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A Research Study of Concrete

Set Under Pressure

A Thesis Submitted to
The Faculty of
MICHIGAN’STATE COLLEGE
of
AGRICULTURE AND APPLIED SCIENCE

by

e x
fix?) 6))
S. D..Lgng
Candidate for the Degree of
Bachelor of Science

June 1932

11-1551:

,1 \s‘
V (£33933

In the building industry of to-day there is one
material which presents a vast field for researchive
study. It is concrete. Although Portland cement was
patented in 1824, it is still baffling the world's best
engineers when it comes to designing a mix that will in
every way surpass the advantages of steel.

Research.work in this field has been carried on by"“
all cement manufacturers in a vain attempt to produce a
product that would meet the utmost of demands. A great
deal of work was done on the fineness modulus. which ce-i
ment companies tell us is no longer the accepted method
giving way to a mix determined entirely by weight. thh _
time and energy was spent be for the water-cement-ratio V
theory was advanced. But in spite of all the previous
study given this subject, the ultimate strength of con-
crete is much the same to-day as it was a quarter of a
century ago. Attention has been paid almost entirely to
the designing of the mix rather that to increasing its
ultimate strength. In these designs a 4,000 lb. concrete
was considered of extremely high strength. The purpose
of these experiments was to determine if it was possible
to raise the ultimate compressive strength of concrete,
to determine the reason for any increase in strength.
and lastly to what extent it is applicable to the build-
ing industry of to-day and future days. If one of these
statements is determined to our benefit something of

real value will have been accompolished.

(1)

The methods used in this work, through the best
knowledge available, are entirely new in this country.
There has been some talk that a French concrete was de-
signed for an ultimate strength above 10,000 lbs. per.
sq. in. The method of setting under pressure is believed
to have been used. However, for the American engineer it
is something entirely new and worthy of a great deal more
study in the future.

The idea behind the experiment is in itself very
Simple. There are two known ways of increasing the comp-
ressive strength of concrete; namely, by designing a very
dense mix or by decreasing the water-cement-ratio. By
allowing concrete to take the initial set under pressure
it might be able to accompolish both of the above items.

To make this possible a steel cylinder was designed
which would allow a concrete cylinder to be cast inside
ithaving a finished size of 5' by 2%" dia. It was neces-
sary to use a 2%" diameter in view of the fact that the
compression machine had available a maximum pressure of
200,000 lbs., or would give a unit pressure of 41,000
lbs. on the concrete cylinder. The complete design was
carried out as follows:

A butt Joint cylinder of #14 gauge sheet iron was
rolled to a size of 7' by 2%” inside diameter. A steel
cylinder, 7' long, 5' 0.D.. 2%” core. was cast in grey
machine iron having an ultimate tensile strength of 40000

lbs. per. sq. in. The core hole was then reamed out to

(2)

take the sheet iron cylinder in a good tight fit. A piece
of cold rolled steel shafting. 2%" in diameter and 3"
long was used as a piston to apply the pressure from the
press to the concrete.

The assembly was used in the following way. The in-
side of the steel cylinder was greased with a heavy gra-
phite grease and the sheet iron cylinder forced in until
one end was flush with the steel cylinder. The inside of
sheet iron cylinder was greased with the same grease and
the concrete placed in resulting mould. The height of
the concrete in the mould was about 6' leaving 1' of the
cylinder above the concrete. This left a convenient,rest
for the piston. The assembly was placed in the compres-
sion machine and any desired pressure applied.

The walls of the steel cylinder were designed as
though under absolute hydraulic pressure and were made
1” thick. This proved erroneous by more than 50%.

Out side of the fact that the concrete cylinder
and the sheet iron sleeve had to be forced out of the
steel cylinder by pressure, the assembly served admié
rably. withstanding pressures of 200.000 lbs. on the
piston.

The plan of the experiment was to make four cyl-
inders at a time, allowing three of them to set as
standard 4” by 8' cylinders and one as a pressure set
Cylinder. This would allow a comparative test of each

set of cylinders. The pressure was raised from 0 to

(3)

200.000 lbs. on the piston. The equivalent unit pressure
is 0 to 41,000 lbs. per sq. in. Since a 28 day compres-
sive test was desired, only a limited number of cylinders
could be made and tested during the alloted time. These,
with a number of 7 day compressive tests, should give
comparative results.

The mixing of the concrete was carried on in a un-
iform manner. The temperature was constant, the mixing
of the aggregate was methodical each time. After remain-
ing in the cylinders for twenty-four hours, the concrete
was placed in water and allowed to cure for 28 days. At
the end of the curing period all four cylinders were
tested at the same time. Those having set under pressure
were capped with plaster of paris and allowed to harden
be fore testing. All data pretaining to the tests was
kept on abstract cards.

As time was of great importance it was necessary to
confine the tests to one standard mix. From.a collaborap
tion of data, namely. fineness modulus of the aggregate,
type of aggregate. size of standard and pressure cylinders
it was decided that a l::l.5::2.6 mix would be the best
suited for the tests. This mix was used in all the tests.

The coarse aggregate used was crushed stone. During
the first part of the tests the coarse aggregate was a
combination of crushed and uncrushed stone screened to a

size of i" to %'. This gave a very dense mix. The last

(4)

part of the experiment was run using an aaregate of pure
crushed stone already screened to a size of f" to %”. This

mix was not quite as dense as the previous one.

A Study of the Results

A study of the results of this experiment are very
interesting. being somewhat opposite of those expected.
In this type of work a comparison study is best suited
to bring about the desired ends. To do this three curves
'have been plotted showing the functions of two variables.
A fourth plate shows the three curves plotted on a common
axis.

‘The first plate shows the variation in compressive
strength of the standard cylinders. The abscissa is in
cylinder sets and the ordinate is in lbs. per. sq. in.

It must be rembmbered that cylinder sets correspond to
applied pressure. since for each cylinder set made there
is a corresponding applied-pressure. It will be noticed
that the first part of this curve is stable at an aver-
age of 4,500 lbs. per sq. in. It is then seen to drop
suddenly to an average of 3,500 lbs. per. sq. in. This
is in all probability due to the change in the coarse
aggregate that was mentioned before. The first aggregate
gave a very dense mix, being of crushed and uncrushed
stone, sise }' to %". The second aggregate of pure crush-
ed stone didn't give as dense a mix as the first one.

Taking the curve as a unit it shows that a good average

(5}

 

   

 

 

    

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concrete was uaed throughout.

Plate #2 shows the unit compressive strength of the
pressure set cylinders. The abscissa is in lbs. per. sq.
in. of setting_pressure, while the ordinate is the ultimate
unit compressive trength in lbs. per. sq. in. This curve
follows the general characteristics of the curve shown in
plate #1. This shows that there is a definite relation be-
tween the respective strengths of the two types of cylinders.
Under ordinary conditions this would be expected. The point
of interest is that the unit compressive strength of the
pressure set cylinders is at all times above that of the
sorespOnding standard cylinders. The maximum.point on this
curve is reached at 9,500 lbs. per. sq. in. while the min-
1mum is reached at 4,000 lbs. per. sq. in.

To study this curve further it is necessary to find
Just what effect the pressure applied during the setting
period has on the ultimate strength of the concrete. To do
this it is necessary to obtain a curve which will have
only the characteristics due to the application of the
pressure during the initial setting period. To accompolish
this a third curve, called the index curve, is plotted. The
coordinates of this curve are obtained by dividing the ord-
inates of the second curve by those of the first curve.
This index curve represents the ratio of the unit compres-
sive strength of the pressure set cylinders to that of the
Standard cylinders. Since it is a ratio, all of the strength

(6)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

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characteristics of the two curves which are variations

in the concrete, will be identical and will cancell out

of the equation of curve characteristics when the first
curve is divided into the second curve. The third curve,
Or the index curve, will have its characteristics determp
ined byithe application of pressure to the setting concrete.
It is this curve which is desired and is bést suited for
study. It shows two distinct maximum points, which in
themselves indicate that there must be two reasons for an
increase in strength. Further, it shows that these two in-
creases do not come at the same time. This is unfortunate.

In studying this curve it will be seen to rise very
rapidly. This is a strong indbation that the increase is
do to a partial decrease in the water-cement-ratio. When
the low pressures were applied to the setting concrete,
it was noticed that clear water was forced out of the mould.
This decrease in the water-cement-ratio would account for
the sudden rise in the curve.

After reaching the maximum point the curve drops
slowly down. This can be readily understood. As the pres-
sure increases it forces out along with the water a little
cement. As the pressure increases it forces out more and
more cement. This would have a decided effewt in lowering
the compressive strength of the mix.

Up until this time no decided settling of the piston
was noticed. This was an indication that the mix was not
being compressed to any considerable extent. That is, the

mix was not made much denser by the application of the

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pressure up to this point. As the pressure was increased
above 12,000 lbs. per. sq. in. a settle was noticed. As
the pressure went on up to 42,000 lbs per. sq. in. the
settling was in some cases as high as 1”. This showed a
much denser mix was being effected. This second maximum
point is due, then, to the effecting of a denser mix.

As the pressure was raised above 20,000 lbs. per.
3Q. in. the settling was rather uniform. This is to be
expected, for some place along the curve a point must be
reached where any further increase in pressure would not
Produce a further increase in strength, but would serve
to fracture the aggregate. When it is seen that some of
aSgregate was under a unit pressure of 42,000 lbs. and
further that this pressure was not purely hydraulic, it
will be easy to realize that some of the larger pieces of
the aggregate were under considerable pressure. If a few
0f the larger pieces carried the brunt of the pressure
and did fracture, they would certainly serve to bring
the index curve down very suddenly as it is seen to do.

In the complete study of this curve it is quite
Probable that the following are true: The strength of
Concrete can be increased by the application of pres-
sure during the setting period34that this increase is
due to two things, namely, decrease of the water-cement-
ratio and effecting a denser mix; and lastly that these

two increases do not come at the same setting pressures.

(8)

So far it has been shown that high ultimate strength
concrete can be obtained, a reason has been forwarded to
explain this increase, and now the use of such a concrete
in the future will be taken up.

It is hard to conceive of a concrete structure in
which the concrete is set in forms under pressure. The
cost of such a set-up would be prohibitive in modern con-
struction. With the exception of concrete cast in the form
of blocks it is unlikely that pressure set concrete will
ever find its way into the building industry. However, con-
crete in this form could be used in the construction of
arch bridges and the like. But in the ordinary structure
the advantages of pressure set concrete must be used in an-
other manner. Some way must be deve10ped to decrease the
water-cement- ratio after the water has been placed into
the mix to make it workable. Whether this is to be done by
mechanical or chemical means remains to be worked out. In
this study the method of pressure was used because it pre-
sented the easiest method of reducing the water. In a fur-
ther study of this subject it should be carried on at low
pressures and with a machine that is capable of effecting
and recording these low pressures. Pressure applied from
a lever would be ideal for these low pressures. Also with
low pressures the size of the cylinder could be increased
which would be a decided advantage. A close tabulation on
the amount of water pressed out would be valuable. This

was done on several of the cylinders and the new water-

(9)

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cement-ratio computed. When referred to the strength curves
it gave a strength fairly close to that observed. Another
interesting thing was noted on some of the 7 day tests: It
was discovered that at seven days some of the tests gave
the same compressive strength as they did at twenty-eight‘
days. Since only a few seven day tests were made it is
difficult to make any conclusions from the results. How-
ever, in the future use of pressure set concrete this mat-
ter should be investigated.

In conclusion it will be seen that in the all t00'
short time alloted for such a study several rather inter-
esting things have been discovered. It has shown the way
for a further study along the general lines of high ultim-
ate strength concrete. It has shown too, that the water-
cement-ratio theory has sound reasoning behind it and can
be further studied. To be short, it has shown that there
is a method yet unknown that will make concrete as desir-

able as steel in the construction industry of the world.

(10)

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Mix #1.

Mix #2.

Set#la.

Set #lb.

Set #2a.

Set #2b.

Data

l::l.5::2.6

.8 water from strength curve,'Concrete Practice“.

Aetna Cement

Coarse aggregate of crushed and uncrushed stone
size after screening f'-%”.

Fine aggregate as found in the bin.

l::l.5::2.6

.8 water as above.

Aetna cement

Coarse aggregate of crushed stone already screened
to a size of f'- 3'.

Fine aggregate as found in bin.

Date: 3-30-32
Mix: #1.
Setting pressurfi: 500 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
5000 lbs 3,800 lbs.

4,200

4,000

Date: 3931.32
Mix: #1.
Setting pressure: 500 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
4,800 lbs 3,600 lbs.
5.800 lbs.
4,300 lbs.

Date: 3-31-32
Mix: #1.
Setting pressure: 1,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
8,200 lbs. 3,400 lbs.

3,200

3,800

Date: 4-4-32
Mix: #1.
Setting pressure: 1,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
89000 1138. 5.500 lbs.
3,200.
3,500

(11)

'1

Set #3a. Date: 4-5-32

Mix: #1. .
Setting pressure: 2,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
9,500 lbs. 4,000 lbs.
3,800
4.000
Set #3b. Date: 4-7-32
Mix: #1.

Setting pressure: 2,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
9,200 lbs. 3,800 lbs.
3,900 lbs.
4,000 1‘8.
Set #4a. Date: 4-8-32
Mix: #1.

Setting pressure: 4,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
5,100 lbs. 4,000 lbs.
3,700
4,100
Set #4b. Date: 4-10-32
Mix: #1.

Setting pressure: 4,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
5.000 lbs. 3,600 lbs.
3,900
3,800
Set #Sa. Date: 4-11-32
Mix: #1.

Setting pressure: 6,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
5,500 lbs. 3,700 lbs.
3,900 lbs.
4.000 lbs.

(12)

Set #5b.

Set #6a

Set #6b.

Set #Va.

Set #7b.

Date: 4-12-32

‘Mix: #1. .
Setting pressure: 6,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St‘d-set
5,200 lbs. 3,600 lbs.
3,800 lbs.
3,700 lbs.

Date: 4-13-32

Mix: #1.
Setting pressure: 8,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
6:100 lbs. 3,000 lbs.
3,800 lbs.
4,800 lbs.

Date: 4-14-32

Mix: #1. .
Setting pressure: 8,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
6,200 lbs. 3,900 lbs.
5,600 lbs.
3:800 lbs.

Date: 4-15-32

Mix: #1.
Setting pressure: 10,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'dset
6,300 lbs. 4,400 lbs.
3,600 lbs.
4,000 lbs.

Date: 4-16-32

Mix: #1.
Setting pressure: 10,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
6,200 lbs. 4,500 lbs.
5,500 lbs.
3,600 lbs.

(13)

Set #8a.

Set #8b.

Set #9a.

Set #9b.

Set #IOa.

Date: 4-19-32

Mix: #1.
Setting pressure: 12, 000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
6,500 lbs. 4,000 lbs.
5,000 lbs.
3:800 lbs.

Date: 4-20-32

Mix: #1.
Setting pressure: 12,000 lbs. per. sq. in.
Ultimate unit compressive strength.

Pressure-set St'd-set
6.500 lbs. 3,900 lbs.
3,800 lbs.
39800 lbs.

Date: 4-21-32

Mix: #1.
Setting pressure: 14,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
7.500 lbs. 4,400 lbs.
4.000 lbs.
49500 lbs.

Date : 4922-32

Mix: #1.
Setting pressure: 14,000 lbs. per. sq. in.
Ultimate unit compressive strength.

Pressure-set St'd-set
7,750 lbs. 4,100 lbs.
4,300 lbs.
4,250 lbs.

Date: 4-23932

Mix: #1.
Setting pressure: 17,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
2,400 lbs. 4,900 lbs.
5,300 lbs.
5,300 lbs.

(14)

_ Set #lOb. Date: 4-24-32

Mix:#l
Setting pressure: 17,000 lbs. per. sq. in.
Ultimate unit compressive strength.

Pressure-set St'd-set
75300 lbs. 5,500 lbs.
4,600 lbs.
4,800 lbs.
Set #lla. - Date: 4-25-32
Mix: #2.

Setting pressure: 21,000 lbs. per. sq. in.
Ultimate unit compressive strength.

Pressure-set St'd-set
7,500 lbs. 4,200 lbs.
3.800 lbs.
3:600 lbs.
Set #1lb. Date: 4-26-32
‘Mix: #2

Setting pressure: 21,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
7400 lbs. 4,100 lbs.
- 3,400 lbs.
3:800 lbs.
Set #l2a. Date: 4-27-32

Mix: #2
Setting pressure: 26,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set'
4,900 lbs. 3,200 lbs.
3,600 lbs.
29900 lbl.
Set #l2b. Date: 28-4-32
Mix: #2.

Setting pressure: 26,000 lbs. per. sq. in.
Ultimate unit compressive strength

Pressure-set St'd-set
4,700 lbs. 3,600 lbs.
3,300 lbs.
3,200 lbs.

(15)

Set #l3a.

Set #13b.

Set #l4a.

Set #14b.

Set #15a.

Date: 4-29-32

Mix: #2
Setting pressure: 31,000 lbs. per. sq,

Ultimate unit compressive strength.

Pressure-set St'd-set
49300 lbs. 3,200 lbs.
3,600 lbs.
4,000 lbs.
Date: 4-30-32
Mix:#2

Setting pressure: 31,000 lbs. per. sq.
Ultimate unit compressive strength

Pressure-set St'd-set
49100 lbs. 3,400 lbs.
3,800 lbs.
3,700 lbs.
Date: 5-1-32
Mix: #2.

Setting pressure: 36,000 lbs. per. sq.
Ultimate unit compressive strength

Pressure-set St'd-set
4,100 lbs. 3,800 lbs.
4,000 lbs.
39600 lbs.
Date: 5-2-32
Mix: #2.

Setting pressure: 36,000 lbs. per. sq.
Ultimate unit compressive strength

Pressure-set St'd-set
4,000 lbs. 3,900 lbs.
3,500 lbs.
3.300 lbs.

Date: 5-3-32

Mix: #2.
Setting pressure: 42,000 lbs. per. sq.
Ultimate unit compressive strength

Pressure-set St'd-set
4,000 lbs, 3,30041bs.
3,600 lbs.
3,400 lbs.

(16)

in.

in.

in.

in.

in.

Set # 15b. Date: 5-4-32

‘Mix: #2.
Setting pressure: 42,000 lbs.per. sq. in.
Ultimate unit compressive strength

Pressure-set St‘d-set
4,000 lbs. 3,400 lbs.
3,500 lbs.
3:500 lbs.

(17)

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