How to determine the strength grade of cement?

Cement strength is an important index to evaluate cement quality, and it is also the basis to classify cement strength grade. The strength of cement refers to the ability of hardened cement mortar specimens to withstand external damage, expressed in MPa. Stir with standard method and standard mortar mixer: stir the pot-add water-add cement-put the pot in place-start the machine-stir slowly for 30 s-add sand automatically for 30 s-stir quickly for 30 s-stop stirring for 90 s-stir quickly for 60s Put the mixed mortar into a triple mold of 40× 40×160 mm. After curing at 20±2C for 24h, remove the mold; Cured in water for 28 days, and carried out compression and bending tests. Determine the strength grade of cement according to the compressive strength and flexural strength.