Potential Effect of Surface Modified Nano-SiO2 with PDDA on the Cement Paste Early Hydration

The potential application of surface modified nano-SiO2 (NS) particles with poly (dimethyl diallyl ammonium chloride) (PDDA) has been reported in other fields, but not in civil construction. This paper aims to assess the influence of surface modified NS with PDDA on the early-age hydration of cement paste, where cement is replaced by 0.3%, 1% and 3% of NS particle. PDDA can be introduced onto the surface of NS via long-distance charge pairs. Calorimetric measurements of cement pastes with 0.35 w/b (water/binder) ratio show that NS particles accelerate the cement hydration, while PDDA retards it. Moreover, the cement hydration is controlled by PDDA at lower dosage of NS/PDDA particle, which delays the exothermic peaks of cement hydration, while the cement hydration is controlled by NS particle aggregates at higher dosage of NS/PDDA particle. Based on the results above, the mechanism of the adsorption of NS/PDDA particle on cement particle surfaces is proposed.