Influence of carboxylated styrene–butadiene copolymer on tetracalcium aluminoferrite hydration in the presence of gypsum

In mixes with gypsum and hydrated lime, the influence of carboxylated styrene–butadiene (SB) copolymer at dosages of 0 to 20% on the hydration of tetracalcium aluminoferrite (C₄AF) curing from 12 h to 28 d was investigated through X-ray diffraction (XRD) analysis coupled with environmental scanning electron microscopy (ESEM). The XRD results revealed that the addition of SB copolymer accelerated C₄AF hydration, favouring the formation of AFt and AFm at the early hydration stage, but leading to a decrease in crystallised AFm content at the late hydration stage. With an increase in SB copolymer dosage, the content of unhydrated C₄AF showed an inflection point after 12 h of hydration and tended to decrease after 1 to 7 d of curing. A dormant period was found to exist between 12 and 24 h for SB copolymer dosages of less than 10%. The ESEM observations complemented the XRD findings and also revealed a morphological change in the hydrates with the addition of SB copolymer.