Effect of Al2O3/SiO2 ratio on the chroma and phase compositions of white sulfoaluminate cement clinker

Abstract

Fe element is the main factor affecting the whiteness of white sulfoaluminate cement (W·SAC). With the reduction of high-quality raw materials, the Fe content of the raw materials used to produce W·SAC has been increasing. In this study, increasing the Al2O3/SiO2 ratio (N) was found to increase the whiteness of W·SAC, which can help to alleviate the scarcity of resources for manufacturing W·SAC. The effect of N on the phase compositions, chroma and hydration of clinker was studied by the Rietveld method, scanning electron microscopy–energy dispersive spectrometry (SEM–EDS), spectrophotometry and calorimetry. The whitening mechanism for W·SAC by increasing N was elucidated. With increasing N, Fe was more dispersed into ye’elimite, and for N above 1.5, 0.5% Fe2O3 completely dissolved into other phases without forming C4AF, which increased the brightness (L*) and greenness (a*) and reduced the yellowness (b*) of the clinker, thereby significantly improving the whiteness. With increasing N, the ye’elimite content increased, the C2S and unquantifiable crystalline phase (ACn) content decreased, and the content of gehlenite (which does not have hydraulic activity) decreased, which increased the overall early hydraulic activity of W·SAC and the accumulated heat of W·SAC hydration.