Short-term performance of cement paste with high-volume fly ash: Effect of silica fume addition

Abstract

Improvement of early-age properties of materials incorporating high-volume industrial by-products has recently attracted many researchers worldwide. This work was employed to study the effect of silica fume (SF) addition on the short-term performance of paste with 30% Portland cement (PC) and 70% type F fly ash (FA). The aim was to enhance the short-term performance of the cement paste with high-volume FA and to utilize the abundant by-products including SF and FA for replacing PC which significantly contributes to the huge amount of carbon dioxide emission and global warming. The influence of SF addition on the flowability and setting time (ST) of fresh pastes as well as on compressive strength (CS), water absorption (WA), and drying shrinkage (DS) up to 28 days of the hardened cement pastes were examined. The powder mixture consisting of PC and FA was replaced with SF in 3, 6, 9, 12, and 15% by mass while a ratio of FA-to-powder was kept constant to be 70% by mass. For all mixture proportions, the ratio of water/powder was kept at 30% (by mass). This investigation found that the SF addition reduced flowability and significantly affected the ST of the cement pastes with 70% FA replacement. The SF addition in a range of 3–15% increased the CS of the samples, with an increase of 4.6–51.3% when compared with the reference paste sample with 0% SF. Adding 3–15% SF to the paste mixtures decreased WA of the samples, with a decrease of 7.5–47.7% when compared with the reference sample. Moreover, the SF addition reduced the DS of the paste samples corresponding to each age. This study found that the optimum SF addition of 15% by mass was effective in enhancing the short-term performance of the paste with 30% PC and 70% FA.