4.2. COMPRESSIVE STRENGTH TESTING OF CEMENT MORTAR
The compressive strength test of the cement mortar is done for the purpose of testing the quality of the recycled fine aggregates (less than 1.18mm size) which is used in place of the natural sand. Indirectly our purpose is to test the quality if recycled fine aggregates. As per IS: 4031 (Part 6) and IS: 4031 (Part 7).
APPARATUS: - Compression testing machine, cube mould of size 7.06cmx7.06cm x7.06cm, temping rod, vibrator, others
PREPARTAION OF THE CUBE SPECECIMEN: - The preparation of the cube specimens have been done as per IS code.
SPECIMEN: - 10 cubes of 7.06cm x 7.06cm x 7.06cm in which cube 01-05 made of mix ratio 1:3 and cube 06-10 made of mix ratio 1:6
HAND MIXING
a) Mix the cement and fine aggregate on a water tight none-absorbent platform until the mixture is thoroughly blended and is of uniform color.
b) The quantity of water shall be (p/4+3) % of combined weight of cement and fine aggregates where, p is the % of water required to produce a paste of standard consistency determined earlier. Add water and mix it until the cement mortar appears to be homogeneous and of the desired consistency.
SAMPLING
a) Clean the mounds and apply oil
b) Fill the cement mortar mix in three layers
c) Compact each layer with not less than 20 strokes per layer using a tamping rod
d) Level the top surface and smoothen it with a trowel.
CURING
The test specimens are stored in moist air for 24hours and after this period the specimens are marked and removed from the molds and kept submerged in clear fresh water until taken out prior to test.
PROCEDURE
a) Remove the specimen from water after specified curing time and wipe out excess water from the surface.
b) The dimension of the cube should be checked.
c) Clean the bearing surface of the testing machine.
d) Place the specimen in the machine in such a manner that the load shall be applied to the opposite sides of the cube cast.
e) Align the specimen centrally on the base plate of the machine.
f) Rotate the movable portion gently by hand so that it touches the top surface of the specimen.
g) Apply the load gradually without shock and continuously at the rate of 350kg/cm2/minute till the specimen fails.
h) Record the maximum load for the further calculation of the compressive strength.
CALCULATIONS
Size of the cube =7.06cm x 7.06cm x 7.06cm
Weight of the Specimen (Kg) = W Kg Area of the specimen = approx. 50cm2 Compressive strength (fck) at 7 days or 28 days = Load/Cross Section Area of cube (N/mm2)
RESULT
Compressive strength at 7 days = 6.0 N/mm2 (average) Compressive strength at 28 days = 9.0 N/mm2 (average)
Note: - For ordinary Portland cement 43 grade, the compressive strength at 3 days, 7 days and 28 days curing shall not be less than 23 MPa, 33 MPa and 43 MPa respectively.
CONCLUSION OF THE TEST
The ordinary Portland cement stands on their strength, but the recycled fine aggregates used in place of the natural sand could not stand on their strength. The binding between the recycled fine aggregates was very weak and hence it could not carry appropriate load during testing in the compression machine. Hence, the result were not satisfactory. The recycled fine aggregates cannot be used in cement mortar and plaster.
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