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Materials

Cement

  • Cement is the binder that holds concrete and mortars together. Which is why it plays the most critical role in giving strength and durability to your home. It is used to make concrete for slabs, foundations, beams, columns, lintels, chhajja (sunshades), and mortar for brickwork, plastering, flooring and other such work.

    Cements used for domestic building such as your home are basically of three types:

  • Portland Slag Cement (PSC) conforming to IS:455
    A combination of good quality blast furnace slag (from the iron and steel industry) with clinker (which makes OPC) and gypsum

  • Portland Pozzolana Cement (PPC) conforming to IS:1489 A combination of fly-ash (from thermal power plants) with clinker and gypsum

  • Ordinary Portland Cement (OPC) 33 Grade conforming to IS: 269, 43 Grade conforming to IS: 8112 and 53 Grade conforming to IS:12269 A combination of clinker and gypsum has high 28 day strength gains, even though it has slower initial setting characteristics. PSC also has a lighter colour, which makes it very desirable for many architectural applications such as mosaic flooring and plastering. This will result in better reflection of natural and artificial lighting and more effective paint coverage. However, the colour of cement has no relation to the strength characteristics.

PSC is preferred over OPC for the following reasons:

  • Reduced water requirement.
  • Improved workability.
  • Less permeable to moisture.
  • Improved resistance to acids and chlorides.
  • Reduced heat of hydration.
  • Easier to finish.
  • Reduced shrinkage.
  • Reduced leaching problems because it is low on free lime.

The right Cement and its application

  • It is very important that you use only a reputed brand of cement. Good brands of cement may cost 2 to 5% more but offer quality, consistency and reliability as well as 10 to 20% greater strength characteristics. Cement accounts for a mere 12 to 18% of the total expenditure on your home. So, using cheaper cement gives you little overall savings.
  • Cement must be added to the concrete and mortar in a precise, consistent manner. Too little or too much cement in concrete can cause lower strengths, shorter design life and lower durability.
  • Ask your engineer/architect whether you can alter the ratios of the mix. Never try to save on cement use by diluting the concrete mix. Remember, that by using 30 to 40 bags less of cement, you would save no more than Rs 3000 to Rs 4000. But it could permanently weaken a building that costs Rs 5,00,000 to Rs 7,00,000 to build!
  • Please note that good quality blended cements like PSC and PPC will take more time to set and gain early strength in lower temperatures during winter than OPC, but final strengths at 28 days will be high.
  • Cement must be kept dry, say by covering with tarpaulin, until final mixing.

 

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