Just after casting, a cement paste had a porosity of 60%. After 3 months, the porositywas reduced to 48%. Compute: a) the degree of hydration at 3 months, b) the originalwater to cement ratio.

The cement hydrates in the presence of water. On hydrating the cement begins to harden. It uses up the water present in the cement paste. Therefore, curing is done to maintain the required amount of water in the cement mixture. The amount of voids also changes with the change in the amount of water present in the cement paste.The cement paste just after casting has not used up any water. Assume a saturation of 100%. This means all the voids are filled up with the water. Assuming a volume of V. Since the cement is fully saturated the volume of voids will be equal to the volume of water. Just after casting, Porosity is given by: n = VVVVv1 = 0.6V After 3 months porosity is reduced to 48%. Therefore, volume of voids now: 0.48 = VvV Vv2 = 0.48V Therefore the degree of hydration will be: D = Vv1-Vv2Vv1D = 0.6V-0.48V0.6VD = 0.2 or 20% Therefore, the degree of hydration will be 20%.Now we have to calculate the water cement ratio originally. The amount of cement in the cement paste will be the amount left after deducting the amount of voids. Therefore, the volume of cement in the cement paste will be: C = V-VvC = V-0.6VC = 0.4V Therefore, the water cement ratio will be: W/C = 0.6V0.4VW/C = 1.5 Therefore the water cement ratio will be 1.5.