OPC = Ordinary Portland Cement
PPC : Pozzolonic Portland cement
(FYI : PPC is environment friendly as it consists fly ash in some specific percentages by parts, which is a waste product of burnt coal, usually collected from thermal power plants)
OPC (m53) attains strength in a shorter time, while PPC (m43) takes longer.
OPC therefore dries more quickly, but produces more heat during chemical reaction during which it gains strength, as compared to PPC
Faster is the drying process, more is the risk of cracking of cement, and therefore it need more care and more amount of water for curing in a lesser time.
PPC on the other hand can attain strength equal to OPC, but takes a longer time.
For a building slab, PPC is more widely used since it requires less care.
The strength depends on design mix (the water cement and aggregate ratio) more than type of cement.
so essentially, If you need construction to take place faster and have means for good curing, you may use OPC.
But if you need better quality and strength in less effort, use PPC.
It still depends on the structure’s design requirements and a structural designer’s advice is to be followed.
Hope this helps, but do consult an engineer before using any type of cement.
Building construction is a responsible job and needs to be done safely and one must adhere to engineer’s specifications.
But you can always ask questions for necessity of specified materials and design.
Both the OPC and PPC for RCC slabs of varying sizes and thicknesses.
My views are :
PPC is economically better than OPC.
Strengthwise , PPC is always grade 33 ( although this is never mentioned on the bag ) whereas OPC is availabie in grades 43 & 53.
The setting process of PPC is slower than OPC and hence the striking off period for the form work gets extended by about 50%.
PPC has a relatively low heat emission process as compared to OPC and hence the finer shrinkage cracks which are normally seen on fresh RCC slab cast with higher grade cement are not seen with PPC.
In case , a nominal mix is used for the concrete ( say 1:1.5: 3 ), which assumes grade 33 cement is used , PPC matches the strength requirements.
If design mix is opted , the laboratory does consider the exact strength available from the specific brand/ grade of cement being deployed .
Thus use of OPC or PPC cement shall be properly weighed in the design mix.
In the backdrop of this , my preferred use shall be PPC at site since :
It’s environment friendly.
Its economically attractive.
Its low heat ( cracks free surface ).
The extra time spent in deshuttering can be certainly compensated in subsequent activities.