WATER-CEMENT RATIO

Water-cement ratio (w/c)  is one of the major factor, but not the only one influencing the strength of concrete. It is the responsible mainly for the porosity of the hardened cement paste.

Water-cement ratio, defined as the mass of free water (i.e, excluding that the absorbed by the aggregate) to that of cement in mix, is the major factor that controls that the strength the many other properties of concrete.

In practice, this ratio lies generally in the range of 0.35 to 0.65, although the purely chemical requirement (for the purpose of complete hydration of cement) is only about 0.25

Abram law states that compressive strength of hardened concrete is inversely proportional to the water-cement ratio, provided the mix is of workable consistency.

It is also observed that water-cement ratio of 0.4, 0.5, and 0.6 are expected to produce respectively 28-day concrete strengths that are about 0.95, 0.72 and 0.55 times that the 28-day strength of the cement used.

Water-Cement Ratio

When W/C is decreased to less than 0.4 there is improper consistency and workability of cement and honeycombed structure.

But concrete compacted by vibrator displays higher strength even up to w/c = 0.3. ratio more than 0.6, the increase in volume of hydrated products will not be able to occupy the space already filled with water. Therefore porosity increase and strength decreases.