Effect of silica fume and nano-silica on hydration behavior and mechanism of high sulfate resistance Portland cement

Abstract The main focus of this study was to investigate the effect of silica fume (SF) and nano-silica (NS) on hydration behavior and mechanism of high sulfate resistance Portland cement (HSRPC), and were analyzed in terms of chemical shrinkage, setting time, compressive strength, rheology, pore structure, hydration heat, and hydration products. Experimental results showed that 5 wt% SF deepened the secondary hydration reaction of HSRPC, because calcium hydroxide (CH) produced by HSRPC hydrating effectively stimulated the pozzolanic activity of SF at later ages. Compared with HSRPC, the 28 d total porosity and CH content of HSRPC with 5 wt% SF respectively reduced by 6.1% and 4.4%. The corresponding compressive strength increased by 14.4%. 0.1–0.3 wt% NS moved up the acceleration period of the hydration and reduced setting time. Meanwhile, NS with high pozzolanic activity evidently increased chemical shrinkage and compressive strength at early ages. Compared with HSRPC, the 28 d total porosity of HSRPC with 5 wt% SF and 0.3 wt% NS reduced by 16.3%. The CH content in TG-DTG curve was reduced by 24.7%, which was consistent with the reduction of CH characteristic peak value. Therefore, in the later hydrating process, the synergistic effect of SF and NS significantly promoted the second hydration reaction.