When it comes to testing and verifying the strength of cement here in INDIA, as per Indian standard code IS 269, we do check all Ordinary Portland cement grades does meet the requirement for compressive strength specified in it.
To check the compressive strength of the cement, we do follow the method specified in IS 4031 Part 6 which state how to do compressive strength test for cement.
I will explain the process in very brief;
Standanrd consistency of the cement is calculated first which is nothing but a water demand by cement (this normally between 25 to 36 % depending on verious factors such as atmospheric condition, freshness of cement etc)
For doing compressive strength test proportion is used as cement 1 part and 3 parts of standard sand and 85% of water required for standard consistency test of cement.
When we say standard sand to be used for testing, again there are specifications given for it in IS 650.
This sand is generally need to be taken from 3 specified sizes and equal proportions of each.
Sand passing through 2mm size and retaining on 1mm size = 33.33%
Sand Passing through 1mm size and retaining on 500 Micron = 33.33%
Sand Passing through 500 micron and retaining on 90 micron = 33.33%
Those above 3 sizes, all together makes standard sand for testing of cement.
Once the standard consistency is calculated the next things are very is to done for determination of compressive strength of cement.
Take an example you have cement OPC 53 grade or OPC 73 grade (here in India grades directly denotes its compressive strength in MPa)
So it means if you test the cement as per standard procedure and maintaining atmospheric conditions as mention in IS code those cement at age of 28 days will give minimum compressive strength of 53 MPa or 73 MPa (N/mm2)
So it does not matter how strong cement you have, you always need to test its strength by casting a mortar cube which surely yield to that strength if casted correctly.
I am considering you are using 53 grade or 43 grade portland cement
Now consider, you have violated many parameters which are considered in method statement of testing cement compressive strength.
What is going to happen
It will directly impact on the strength of mortar which is prepared.
At the end of day, it is important to know what strength i am desiring and at what age (requirements are lesser, lesser quality control on mix can be OK and it increases with each increased demand in your final product).
I hope now you would have understood the concept of how strength gain occurs, what sand can do and importance of water cement ratio in it.
