PPC is special blended cement useful in general construction work and is especially suitable for applications in aggressive environmental conditions. It can be confidently employed in construction of hydraulic structures, marine works, mass concreting such as dams, dykes, retaining walls foundations and sewage pipes. It is also suitable for use in common applications such as masonry mortars and plastering.PPC utilizes two types of Pozzolanas:
|Fly ash||Covered under IS:1489 (Part I)||Calcined clay||Covered under IS:1489 (Part II)|
PPC with fly ash as Pozzolana is more popular in the country owing to the easy availability of quality fly ash from modern coal-based thermal power plant. With the advent of fly ash based PPC, the availability and use of calcined clay based PPC has more or less been decimated.
PPC provides improved workability, has less segregation and bleeding, increased water-tightness and reduced tendency of lime to leach out. It produces less heat of hydration and offers greater resistance to the attack of aggressive water containing sulphates and chlorides. It improves the durability of structures and also the strength of concrete over a period of time by making it more corrosion resistant and impermeable. It protects concrete against alkali-aggregate reaction.
The minimum compressive strength of PPC after 28 days, as prescribed by BIS is 33 MPa or 330 kg / Cm2. However, the ultimate, long-term strength of PPC is better compared to OPC 53. Since the pozzolanic material reacts with calcium hydroxide liberated by the hydrating Portland cement and forms cementatious compounds, PPC makes the concrete more impermeable and denser as compared to OPC and it is this property coupled with its cost effectiveness that has helped in its emerging more popular in the construction industry.
PPC is manufactured either by inter-grinding Portland cement clinker, gypsum and fly ash obtained from thermal power plants or by intimately blending OPC and fly ash. The percentage of fly ash in PPC permitted by IS:1489 varies from 15% (in minimum) to 35% (maximum). The fly ash to be used for manufacturing of PPC should conform to IS:3812 (Part I) – 2003.
The colour of PPC containing fly ash as pozzolana will invariably be of slightly different colour than that of OPC, depending on the colour of the pozzolonic fly ash that is used in the manufacture. However, the colour of cement, whether it is PPC or be any other grade, has no relationship with the quality of cement. The colour of the cement is gauged by its C4AF content and the pozzolonic material used. The higher the C4AF the darker the cement will be. Similarly, the lighter the colour of the pozzolonic material, the lighter the shade of the cement will be. As such, there is no governing specification for the colour of cement. One can not gauge the quality of cement by looking at its colour. The quality of cement can be assessed only by testing its physical and chemical properties.