Effect of ZnO on the whiteness of white Portland cement clinker

The addition of ZnO to significantly improve the Hunter whiteness of white Portland cement (WPC) clinkers is introduced in this paper. The effects of ZnO on the whiteness of WPC were studied by chroma analysis, X-ray diffraction (XRD), the Rietveld method, hydration heat measurements and SEM-EDS. The results showed that adding ZnO increased the visible light reflectance, increased the brightness (L*), and reduced the yellowness (b*) of WPC clinker with high Fe2O3. Therefore, ZnO can increase the whiteness of WPC clinker. Zn was mainly distributed in the amorphous phase and unquantifiable crystalline phase (ACn), and then dissolved in the silicate phase. ZnO stabilized R-C3S, reduced the crystallization of C(3)A, and increased the ACn content. ZnO increased the amount of Fe in the ACn and minerals, thereby reducing the formation of C(4)AF and improving whiteness. ZnO increased the accumulated heat of hydration but prolonged the induction period. This method provides a new approach for the WPC industry to broaden sources of raw materials and improve product quality.