Effect of carboxylated styrene–butadiene copolymer on the hydration of tricalcium aluminate in the presence of gypsum and calcium hydroxide

Abstract

The clinker mineral tricalcium aluminate (C3A) determines largely the early hydration characteristics of Portland cement. Therefore, understanding the influence of the polymer on the hydration of C3A is contributed to clarify the mechanism of polymer on the early hydration of cement-based material. The hydration environment of C3A in Portland cement was simulated by using C3A mineral, gypsum ( $${\rm C}\bar{S} \cdot {\text{H}}_{2}$$ ) and calcium hydroxide (CH). The specimens, whose water cement ratio (mw/mc) was 0.4 and carboxylated styrene–butadiene (SB) copolymer cement ratio (mp/mc) was 0, 5, 10, 15 and 20%, were cured at 20 ℃/RH90% for 6 h, 12 h, 1 day, 3 days, 7 days and 28 days, respectively. The effect of SB copolymer on the system of C3A– $${\rm C}\bar{S}\cdot{\text{H}}_{2}$$ –CH was investigated by the combination of isothermal calorimetry, X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM). It was found that the SB copolymer retards C3A hydration and reduces the heat of hydration. The XRD results revealed that addition of SB copolymer inhibits the consumption of C3A, delays the conversion of ettringite (AFt) to calcium monosulfate aluminate hydrate (AFm), promotes the formation of hydrated calcium aluminate (C4AH13), and reduces the crystallinity of AFm.