The effect of paste volume and of water content on the strength and water absorption of concrete

The W/C ratio is generally considered to be the governing parameter, which affects the strength and durability of concrete. In this paper, the effect of paste volume and of water content on capillary absorption and strength is investigated on concrete mixes having the same Wef/C ratio. Four Wef/C ratios (0.3, 0.4, 0.5, 0.6) were used and for each Wef/C ratio four mixes were prepared with effective water contents 140, 180, 220 and 260 l/m3. It is found that although the Wef/C ratio is kept constant, strength increases and capillary absorption decreases when the volume of the water or the volume of the paste decreases. The effect of the paste or water content by volume on strength is stronger for lower W/C ratios and for water contents at the lower or upper values (140 l/m3, 260 l/m3) used in the investigation. Similarly capillary absorption is higher the higher is the value of Wef/C ratio and, with constant Wef/C ratio, increases approximately linearly as the paste content increases. The rate of increase is lower for lower values of Wef/C ratios.