Regulation and inhibition of early whitening of calcium aluminate cement/hemihydrate gypsum decorative mortar by polymer emulsion

Abstract

Whitening of decorative mortar is an important factor hindering its application, which is difficult to mitigate. This paper studied the effect of different polymer emulsions on the early whitening of decorative mortar using calcium aluminate cement (CAC) and hemihydrate gypsum (HH) as cementitious material. The whitening phenomenon and white deposits of CAC/HH decorative mortars were investigated through digital processing of images, optical microscopy (OM), scanning electron microscopy (SEM) and Raman spectroscopy analysis. The results show that the white deposits were mainly ettringite (AFt) and CaCO3, whose quantity and size determined the severity of whitening. The addition of vinyl acetate-ethylene copolymer emulsion (VAE) and poly acrylic ester emulsion (PAE) could inhibit the generation of AFt and reduce the crystal size and amount of CaCO3, thus inhibiting the whitening. In order to reveal the inhibition mechanism of polymer emulsions on the whitening, the effect of polymer emulsions on the cement hydration was studied by hydration heat and X-ray diffraction (XRD), the porosity and capillary water absorption were also tested. It shows that the inhibition of whitening of CAC/HH decorative mortar by polymer emulsions was mainly achieved by reducing the open porosity and capillarity water adsorption, which directly decreased the pathway of the ion transport from the interior to the exterior of the mortar, thereby reducing the generation of the white deposits on the mortar surface and improving the anti-whitening property of CAC/HH decorative mortar.