Theory:

This test is carried out to indirectly find out the compressive strength of cement paste as shirking cracks are formed indirect cement paste test can’t be properly carried out on the block of mortar or made of cement sand and water cured for 7 to 28 days cement sand is structure in the form of mortar or concrete. The most important property of cement is its compressive strength. The compressive strength of cube is 7.07 mm tested after 3 to 7 days. It should not be less than 60 N/mm2 or 22 N/mm2. Many other property of cement concrete or mortar durability porosity, shear or tensile strength are related to its compressive strength and so knowledge of its strength is essential. This test is thus indicate the quantity of cement.

Items Required:

1.     Standard mould of sand is 7.07.Vibrating machine.
2.     Main balance with weight box.
3.     Trawel.
4.     Compressive testing machine.
5.     Standard sand 5kg and water.

     Diagram:


                                 Compressive Testing Machine

        

Procedure:

1.     1.5 kg of cement sample was taken and weight correctly. Standard sand 3 times weight of cement mixed thoroughly with cement and sand.
2.    ( Pn / 4 +3 ) % by total weight of cement and sand together quantity of water was added (where Pn = Percentage of water consistency) mixed about 3 to 4 min.
3.     Care was taken to oil the inner surface of the mould before placing mortar.
4.     The cube was vibrated by using standard vibrating machine for 2 min.
5.  Remove the moulds and placed in atmosphere at 270c to 20c for 24 hours and at humidity 9
6.     Remove the cubes from mould and sub-merged in clean water for crushing.
7.     The cubes was tested in compressive testing machine immediate after age of 3 days and 7 days.
8.     The load of failure of cube was noted and calculated the compressive strength.

Precaution:

1.     Cement, sand and water should be correctly weighted.
2.     Mix should be homogenous.
3.     Water should be portable.
4.      Mortar should be compacted carefully.
5.     Reading on compressive testing machine should be noted accurately.

Observation:

1.     Mix proportion of cement sand 4:8:16
2.     Weight of cement = 4 kg
3.     Weight of standard sand = 8 kg
4.     Total weight of sand and cement = 12 kg
5.     Area of cube = 150 X 150 = 22500 mm2

Observation 1:

1.     Mix Proportion = 4:8:16 (By work)
2.     W/C ratio           = 0.6
3.     Date of casting
4.     Size of cube       = 15 cm X 15 cm X 15 cm
5.     Area of cube     = 150 X 150 = 22500 mm2

Observation Table:

Sr. No.
Identification of testing
Date of testing
Age days
Main Load N (W)
Type of failure
Compressive strength in N/mm2  (w/A)
Average compressive strength N/mm2
1
Sp1
-
7
320000
Crack
14.22 N/mm2  
13.33 N/mm2  
2
Sp2
-
7
280000
Crack
12.42 N/mm2  
3
Sp3
-
28
499000
Crack
22.00 N/mm2  
21.86 N/mm2  
4
Sp4
-
28
480000
Crack
21.30 N/mm2  



Result:

Compressive strength of concrete at

7 days = 13.33 N / mm2

28 days = 21.86 N / mm2