Oxide zinc addition in cement paste aiming electric arc furnace dust (EAFD) recycling

Large amounts of electric arc furnace dust (EAFD) are generated in steel production, highlighting the need for recycling alternatives like the use of EAFD in production of building materials. However, EAFD delays hydration reactions of concrete. This study presents a model of cement hydration using ZnO as admixture and analyzes phenomena associated with zinc oxide compounds in cement pastes. Cement samples were analyzed by X-ray diffraction (XRD) with Rietveld refined, scanning electron microscopy (SEM), and characteristic X-ray mapping 1, 2, 4, 7, and 14 days into setting. Zn was present as ZnO on day 1. A new phase formed containing CaZn2(OH)6·2H2O on day 4, suggesting the transition of ZnO to Zn hydroxide, especially on day 7, when hydration reactions were visually detected and Zn was found only as hydroxide. CaZn2(OH)6·2H2O enables the hydration of cement with ZnO. A model to explain hydration reactions of cement admixed with ZnO was proposed.