Compression test

Expt No.
Date:
COMPRESSION TEST ON CONCRETE
AIM:
a) To prepare the test specimen.
b) To conduct a compression test on concrete cubes to find the ultimate crushing
strength.
APPARATUS:
Cubical mould of length 15 cm and height 15 cm, compacting rod, Universal
Testing Machine.
MATERIALS:
2 kg cement, 4 kg sand, 8 kg coarse aggregate.
1) PREPARATION OF TEST SPECIMEN
PRINCIPLE:
Concrete is a homogeneous mixture of cement, sand and coarse aggregate with
adequate quantity of water. The voids in coarse aggregate, fine aggregate and cement
with adequate quantity of water. The voids in coarse aggregate will be filled up by fine
aggregate and those in fine aggregate by cement paste. The cement when mixed with
water behaves as an adhesive material and binds the aggregate together to form a solid
block of concrete after a specific period of curing. This is the concept of a no-void
concrete. For nominal mixes, the ingredients are mixed in a specific proportion
(1:2:4,1:1.5:3 etc.) according to their volume or weight in volume batching or weight
batching respectively. The quantity of ingredients is determined based on the total
volume of concrete required. The freshly mixed concrete is placed in moulds of proper
size and shape to prepare the specimen for testing.
PROCEDURE:
1. Calculate total density of concrete required from the volume of each test
specimen and the number of such specimen required for testing.
2. Adopting the nominal mix of 1:2:4 with W/c ratio of 0.65 calculate the volume of
coarse aggregate, fine aggregate and cement. Calculate the required quantity of
water for mixing.
3. Mix dry sand and cement well.

OBSERVATIONS AND CALCULATIONS:
Size of the cube =
Area of the specimen, A = cm2
.
Mix ratio =
Water cement ratio =
S.No
Size of cube
(cm)
Area
(cm2
)
Mix ratio
Load at failure
(kg)
Ultimate crushing
load
(kg/cm2
)
Ultimate crushing strength = kg/cm2

4. Keep the coarse aggregate slightly spread and place the sand cement mixer over
it. Add water in stages and mix the aggregate well by means of shovel to get a
homogenous uniform mixture.
5. Apply grease to the inside surface of mould.
6. Place the fresh concrete in the mould in three layers, each layer being tamped 25
times by a 16 mm diameter rod.
7. Finish the surface clean and write the date of preparation of specimen on the top
surface by a scribe. This also helps to identify top surface of the specimen later.
8. After one day, remove the specimen from the mould and keep them in water for
curing. The test is conducted after curing for the required number of days.
Concrete mix can be used in case the quantity of concrete to be prepared is large.
9. Consolidation may be done using vibration table.
B) COMPRESSION TEST
PRINCIPLE:
Concrete is a homogeneous mixture of cement, sand and coarse aggregate with
adequate quantity of water. Since all the physical properties of concrete are directly or
indirectly related to the crushing strength, this is the important of all the properties of
concrete. The following are the factors, which influence the compressive strength of
concrete.
i) Water-Cement ratio.
ii) Aggregate-Cement ratio.
iii) Aggregate grading and maximum size of aggregates.
iv) Compaction.
v) Curing.
vi) Age of concrete.
Concrete obtains the maximum strength where complete hydration of cement
takes place. Any excess of water introduces porosity in concrete due to evaporation of
the excess water, and in turn reduces the strength of concrete. In other words, the
strength of concrete is adversely affected when the water-cement ratio increases beyond
what is necessary for the complete hydration of cement.
For fixed water-cement ratio and workability, the increase of aggregates-cement
increases the strength of concrete. The grading of aggregate is important since a properly
graded aggregate will produce a mix with maximum voids. The strength of concrete

increases with the increase in the density of concrete. It is also increases with the
increase in the density of concrete. It is also clear that the density improves with better
compaction, which results in higher strength.
Curing is done during the early stages of hardening in order to keep concrete
saturated until the originally water-filled space in fresh concrete has been filled by the
products of hydration. The maximum strength of concrete is reached only after 28 days
of curing.
TEST SET UP:
The compression test is carried out in a standard cylindrical specimen, using the
compression-testing machine. It is placed in the machine with its axis vertical. To reduce
the effect of restraint and lateral instability the size of the specimen is standardized.
Uneven surface of the test specimen induces local stress-concentration influencing the
test results. This is rectified by providing either capping or packing with a holding
material. The load is applied gradually till structure takes place.
The maximum load at failure divided by the cross-sectional area by the specimen
gives the ultimate compressive strength. It can be seen that the ultimate compressive
strength will be roughly equal to 3 times the compressive strength.
The compressometer is attached to the specimen such that the gauge points are
symmetrically about the center of the specimen and in no case are nearer to either end of
the specimen. While testing, the compressometer reading are noted at different load
levels in order to calculate the stress and the corresponding strain.
The cubes are tested on the sides since the sides provide a uniform surface
capping need not be provide. Cube test is conducted for determining the ultimate
compressive strength of concrete (cube strength).
PROCEDURE:
1. Prepare the standard concrete cube (3 nos.) 15 cm sides and cylindrical specimen
(3 nos.) of 15 cm diameter and 30 cm length, using 1:2:4 concrete with a water-
cement ratio equal to 0.65 (IS 516-1959).
2. Study the operation of the compression-testing machine.
3. Select the range of the machine by compression strength of concrete (cured for
28 days) to be equal to 200 kg/cm2
.

4. Continue the loading until the specimen falls by crushing, then note down the
ultimate crushing load.
5. For testing cubes, the specimen is placed on its sides and the load is applied as
explained above until failure occurs. The ultimate crushing load s noted.
RESULT:
1) The test specimens were prepared.
2) The ultimate crushing strength of concrete at the end of 28 days at a mix
ratio 1:1.5:3 with the water-cement ratio 0.65 = N/mm2

Compression test

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