Example: For 55 grade cement, 55 N/sq.mm is the 28th day compressive strength of a cement mortar cube of standard size made in the ratio 1 cement : 3 standard sand. Why cant the value of strength of a cement cube be used instead?
Because cement is only an ingredient of mortar. What they put between bricks is mortar, not cement. It would be like assessing the value of chocolate milk by only assessing the value of the chocolate.
Actually, cement alone is just only used for finishing smooth surfaces and doesnt have any aload bearing capacity at all. Cement mortars of different proportions is what we used as filling material for blockworks, floor screeding, plastering and other civil/masonry works.
