Potential application of Portland cement-sulfoaluminate cement system in precast concrete cured under ambient temperature

Abstract

In precast concrete, high early strength was achieved by steam curing, while the heat damage was inevitable and harmful to the durability of concrete. In this research, calcium sulfoaluminate cement (CSA) was added into Portland cement (PC), with the intention to obtain high early strength under ambient temperature curing. Binders composed of PC and CSA (0–15%) were designed, and meanwhile different water/binder ratio (w/c) was also considered. Compressive strength, drying shrinkage, and chloride permeability of PC-CSA system was investigated. Moreover, the hydration process, hydrates, and microstructure evolution of this system were also characterized by hydration heat, XRD, TG, MIP, and SEM. Results showed that under w/c of 0.3, more than three times increase on 12 h age strength of PC mortar was obtained by the addition of 5% CSA; the drying shrinkage and chloride permeability of PC-CSA mortars was significantly lower than that of PC. The initial formed ettringite was acted as crystal nuclei to promote the hydration of PC-CSA system, and the fast consumption of free water and the centralization of releasing heat was also good for the early strength development. However, due to the covering effect of initially accumulated ettringite on the cement particles and the fast consumption of free water at the early period, the further hydration of PC in PC-CSA system was delayed, leading to the limited strength at the later age. Moreover, the enhanced efficiency of CSA on the early strength of PC mortars seemed decreased with the growth of w/c, because the higher w/c resulted in the looser microstructure. Research could provide help for the design of precast concrete under ambient temperature curing.