Every bag of cement in Kenya carries a strength class such as 32.5N or 42.5R. The number is the minimum compressive strength in megapascals that standard mortar made with the cement reaches after 28 days. The letter tells you how fast it gets there: N for normal early strength, R for rapid early strength.
Use 32.5 for masonry mortar, plaster, floor screeds, concrete blocks and general repairs. It is more forgiving to work by hand and is usually the economical choice for non-structural work.
Use 42.5 for structural concrete: columns, beams, suspended slabs, water tanks and precast elements, wherever the engineer or the design mix calls for it. The R versions earn their keep when you need to strike formwork early or keep a precast yard cycling fast.
The class does not replace the mix design. A 42.5 cement in a weak mix still gives weak concrete. Match the cement class to the job, batch the mix properly, and cure it. If you are unsure which class your drawings call for, ask your engineer or send us the Bill of Quantities with your quote request.