Different grades of cement and where to use them

You have probably seen different bags of cement labelled 32.5(33), 42.5(43) and 52.5(53) Grade cement. What does this number mean?

This is the strength that the cement used has the ability to achieve when used. The strength is measured by crushing 150mm by 150 mm by 150 mm concrete cubes that have been continuously cured over a period of 28 days. 28 days is used as a standard measure since concrete usually achieves about 99% of its strength by then and no big gains are expected after that.

This means that for grade 32.5 the maximum strength that it can achieve after 28 days is 32.5N/mm2, 42.5 is 42.5N/mm2, and 52.5 is 42.5N/mm2.

Therefore, suppose you want to cast concrete with a strength of 25N/mm2, your cement of choice should be 32.5. However, if you need to achieve a concrete strength of 35N/mm2 you should use grade 42.5 cement.

You can use 42.5 to achieve 25 N/mm2 cement too. Most people do this, however, note that the cost of cement increases with grade and therefore if you have no particular need for strong grade cement, you can make savings during construction.

Also noteworthy is the fact that higher grade cement releases high heat of hydration in comparison to the lower grade cements. This means that they heat up quicker when the cement is setting especially in the initial days.

This reaction should be well monitored and concrete well cured. Especially for mass construction where a mechanism for cooling the concrete elements should be provided since if it is not, there may be formation of micro cracks inside the concrete that actually weaken and cause the final strength of concrete to become lower than expected.

High grades of cement are typically used in areas where high strength is required in a short time and methods of cooling the concrete are available. It also has the benefit of being weather resistant since it hardens quickly.

Next time you see a grade on cement, 32.5, 42.5 and 52.5, you will know what it means.

I hope this read has been useful.
Build Wisely!