A low water-cement ratio is necessary for strength but a high water-cement ratio is necessary for wo

Water to cement ratio (W/C ratio) is the single most important factor governing the strength and durability of concrete. Strength of concrete depends upon W/C ratio rather than the cement content.

Abram’s law states that higher the water/cement ratio, lower is the strength of concrete. As a thumb rule very1% increase in quantity of water added, reduces the strength of concrete by5%.

A water/cement ratio of only 0.38 is required for complete hydration of cement. (Although this is the theoretical limit, water cement ratio lower than 0.38 will also increase the strength, since all the cement that is added, does not hydrate) Water added for workability over and above this water/cement ratio of 0.38, evaporates leaving cavities in the concrete. These cavities are in the form of thin capillaries. They reduce the strength and durability of concrete. Hence, it is very important to control the water/cement ratio on site. Every extra liter of water will approx. reduce the strength of concrete by 2 to3 N/mm2 and increase the workability by 25 mm.

As stated earlier, the water/cement ratio strongly influences the permeability of concrete and durability of concrete. Revised IS456-2000 has restricted the maximum water/cement ratios for durability considerations by clause8.2.4.1, table5.

There is nothing like optimum w/c rati