[Readers' Q&A]: What is the difference between OPC and PPC (cements)?

Question posted by one of B-n-M's readers, Muthiah in the comments section of one of our earlier posts [Readers' Q&A]: Difference between types of cement":
titled: "
Hi!
Want to know the difference of OPC and PPC cements
-Muthiah
Team B-n-M answers...

Dear Muthiah,
This is a very common question people ask. As a quick reference, you can also go through the above-mentioned earlier post and its comments section to get the answer in brief.  Further, let us explain again for easy understanding of yours and all our other interested readers...

OPC (Ordinary Portland Cement) is the basic form of cement with 95% of it being the clinker and 5% being gypsum which is added as an additive to enhance the setting time of the cement to a workable 30 minutes odd or so.  This cement is the standard norm being manufactured and sold by cement manufacturers around the world. As the Understanding-Cement website puts it: "In particular, 'Ordinary Portland Cement' is the normal, grey, cement with which most people are familiar".

However, with changing times and with enhanced energy requirements and associated environmental implications that came along with, the thermal (coal based) power plants the world over started producing multitude of coal ash (commonly known as 'Flyash or Fly Ash'), which is a waste product otherwise, in the form of finely divided residue resulting from the combustion of ground or powdered bituminous coal or sub bituminous coal (lignite) and transported by the flue gases of boilers fired by pulverized coal or lignite.

Then, with the bitter fact the world faced about the disposal of fly ash becoming a serious problem in itself, and on the other hand this fly ash being found to have certain useful cementetious properties, the worldwide statutory and academic bodies allowed addition of up to 35% of fly ash in making the type of cement, commonly known as the Pozzolanic Portland Cement (PPC). This way, the waste product which could have become a serious environmental hazard, has now become a sought-after raw material for manufacture of modern day large-scale produced cement known as the Pozzolanic Portland Cement (PPC).

One common question relating to use of OPC / PPC that people usually ask us is:
Is PPC good to use for the construction of my house/ factory/ repair works/ heavy engineering works?
Some people have presumption that since PPC uses a waste product as an ingredient, it makes it less good than the good old OPC. However, on the other hand PPC has certain distinct advantages over OPC, as listed below:
  • Low heat of hydration reducing chances of surface cracks
  • Longer setting time making it more workable than OPC
  • Ultimate strength higher than OPC
  • Lower porosity imparting the concrete more water tightness
  • Lower manufacturing cost compared to OPC
  • Waste utilization making it more environmental friendly
Thus, it can be safely inferred that PPC (Pozzolanic Portland Cement) can be used invariably for all common uses that OPC (Ordinary Portland Cement) can be used including one's construction works, concrete works, repair works, finishing works (plastering, flooring, etc.), and the likes.

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