Effect of nano C–A–S–H seeds on the early-stage hydration and pore structure of Portland cement pastes

Abstract

Most previous studies have focused on the addition of nanoparticles of silicon dioxide, calcium carbonate, aluminium oxide, tin(IV) oxide or calcium silicate hydrate to speed up cement hydration. In this research, nano seeds of calcium aluminium silicate hydrate (C–A–S–H) were added to Portland cement systems. It was found that, with the addition of 1%, 3% and 5% C–A–S–H seeds, the hydration process was brought forward by about 2 h, 3 h and 7 h, the initial setting time was reduced by 16.4%, 25.5% and 34.5%, and the final setting time was reduced by 16.8%, 35.1% and 41.1%, respectively. However, the paste fluidity was reduced by 11.6%, 21.6% and 28.9%, respectively, resulting in decreased workability. X-ray diffraction analysis showed that adding C–A–S–H seeds accelerated the formation of calcium monosulfoaluminate hydrate (AFm). Compared with a control sample, the compressive strength of the mortar doped with 1% C–A–S–H seeds was increased by 4.6%, 3.4% and 5.2% at 3, 7 and 28 days, respectively. However, an increase in the content of C–A–S–H seeds to 3% and 5% led to decreases in compressive strength. The total porosity declined with the addition of 1% C–A–S–H seeds, whereas the total porosity with 3% and 5% C–A–S–H seeds was higher than that of the control sample.