Comparison on early hydration of Portland cement and sulphoaluminate cement in the presence of nano ettringite

Abstract

This paper proposed adopting ettringite-based nucleation seeds to induce ettringite to precipitate in the pore solution, and thus facilitated early hydration reaction. In present work, sulphoaluminate cement (SAC) and Portland cement (PC) paste were considered, and 0 ∼ 5 % nano-ettringite prepared by hydration-wet grinding method was extra incorporated. The hydration kinetic of the blends was studied by hydration heat, chemical shrinkage and setting time. The effects of nano-ettringite on the dissolution behavior were also examined by dynamic conductivity of cement slurry, ion concentration and conductivity of pore solution. Meanwhile, the hydrate assemblage was determined by XRD, TGA, FTIR and 27Al NMR, and the compressive strength was also tested. On this basis, the hydration mechanism was discussed. Results indicated that nano-ettringite significantly hastened ions dissolution and ettringite precipitation, whether it was SAC or PC paste. The initial hydration heat release and chemical shrinkage were obviously promoted, and even cracks were generated in SAC paste; besides, the setting time was also shortened dramatically. In the presence of 1 ∼ 5 % nano-ettringite, the compressive strength of PC pastes at 8 h was increased by 54 ∼ 180 %. However, the strength of SAC paste at all ages was degraded by adding nano-ettringite, due to the appearance of cracks and reduced amount of AH3.