The following important test are carried out for ordinary Portland cement:
1) fineness test- This test is carried to check the proper grinding of cement. It may be noted that the finest cement has quiker action with water and gain early strength. The fineness of cement is tested either by seive method or air permeability method.
In the seive method, the fineness of cement is measured in terms of percentage weight retained on IS seive number 9( i.e 90 micron IS seive). According to Indian standards the percentage of residue left after sieving a good Portland cement through a sieve number 9 should not exceed 10%.
In air permeability method, the fineness of cement is measured in terms of surface area in cm square per gram of cement. A good Portland cement should not have specific surface less than 2250cm2/g of cement.
2) consistency test:-this test is conducted to determine the percentage of water required for preparing cement paste of standard consistency for others tests (i.e setting time, soundness and compressive strength test). This test is performed with the help of vicat’s apparatus which consists of a plunger having 10 mm diameter and 40 to 50 mm length. The vicats apparatus determines the initial and final setting time and normal consistency of cement.
a) to make a cement paste of normal consistency the percentage of water varies from 25 to 35%.
b) to perform the initial setting time test the water is added to the cement at the rate of 0.85P by weight of cement, where p is the percentage of water required for normal consistency paste.
c) to perform the compressive test the cement paste is prepared by adding water at the rate of (p+3 %of water).
d) to perform the soundness test the cement paste is prepared by adding water to the cement at the rate of 0.72P by weight of cement.
e) initial setting time of ordinary and rapid hardening cement should not be less than 30 minutes.
f) the final setting time of ordinary and rapid hardening cement should not be less than 10 hours.
3) soundness test:-this test is carried out to detect the presence of uncombined lime and magnesia in cement which cause the expansion of cement. The soundness of cement is tested with Le-chatelier apparatus. According to Indian standard the expansion should not exceed a 10mm for any type of Portland cement.
4) tensile strength test:-this test is carried out on standard briquettes made of good Portland cement and standard sand mortar in the ratio of 1:3 to determine the tensile strength of cement. The average tensile strength after 3 and 7 days of curing should not be less than 2N/mm2 and 2.5N/mm2 respectively.
5) compressive strength test:-this test is carried out on standard cubes made of good oral and cement and standard sand mortar in the ratio of 1:3 to determine the compressive strength of cement. The size of cube mould should be70.6mm. The average compressive strength for three cubes should not be less than 11.5N/mm2 and 17.5N/mm2 after 3 and 7 days of curing respectively.
During field test the cement is said to be pure and of good quality when
a) the colour of cement is uniformly greenish grey.
b) a handful of cement, thrown into a bucket of water, floats.
c) hand is thrusted into a bag of cement, it feels cool.
d) rubbed in between fingers, it feels smooth.