The objective of this study was to determine the changes in the hydration process of cement paste as increasing amounts of silica fume are incorporated at high and low w/(c+sf) ratios. The hydration process of cement/silica fume paste was followed from the estimation of heat of hydration, Ca(OH)2 content, and nonevaporable water.
These quantities were estimated at w/c+sf ratios of 0.48 and 0.28 for silica fume content increasing from 0 to 25%. The hydration study indicated that the hydration reaction of the cement is altered due to the presence of silica fume. At both w/c+sf ratios the initial maximum rate of heat of hydration is reduced due to the presence of silica fume. At the higher w/c+sf ratio, silica fume appears to accelerate the hydration of cement, this effect is not significant at the lower w/c+sf ratio.
A higher dosage of silica fume was required to consume all the Ca(OH)9 at the higher w/c+sf ratio, since the amount of Ca(OH)2 produced at the higher w/c+sf ratio is greater.
A large proportion of the pozzolanic reaction takes place as early as 3 days. Although the pozzolanic reaction was found to continue up to 180 days, the amount taking place after 28 days is relatively small.