Water Cement Ratio

The water-cement ratio (w/c) is one of the major factors but not the only one influencing the strength of concrete. It is responsible mainly for the porosity of the hardered cement paste. Water-cement ratio is the water used to the quantum of cement in the mixture by weight. For proper workability the w/c ratio varies from 0.4-0.5. However, maximum strength is derived at w/c 0.4 at which minimum capillary cavities are expected to form. It may be noted. that for complete hydration of cement under controlled conditions the water requirement is about 38 per cent. When it is decreased to less than 0.4 there is improper consistency and workability of cement and honeycombed structure However, concrete compacted by vibrator displays higher strength even up to w/c=0.3 as shown by dotted line in Fig. 10.13 At w/c ratio more than 0.6. the increase in volume of hydrated. products will not be able to occupy the space already filled with water. Hence, porosity increases and strength decreases. In arriving at the w/c ratio values it is assumed that aggregates are saturated with the surfaces in dry condition. Suitable adjustments should be made for dry aggregates. Sometimes cement-water ratio versus strength is plotted. Being a straight line it is supposed to be a better mean to interpret the results.