Influence of lead, zinc, iron (III) and chromium (III) oxides on the setting time and strength development of Portland cement

A fractional factorial design (2(4-1)) of experiments was cat-tied out to study the influence of metal oxides on cement properties: unconfined compressive strength (UCS), setting time (ST), bulk density (BD) and noncombined water (NCW). Four metal oxides, usually contained in inorganic wastes from thermal processes, were studied: ZnO, Cr2O3, PbO, and Fe2O3. The amount of these metal oxides in the formulations was selected according to the composition of inorganic wastes from thermal processes: 0-30% dry wt. for Fe2O3, 0-15% dry wt. for ZnO, and 0 -2.5% dry wt. for PbO and Cr2O3. The analysis of the experimental results shows that ZnO retards strongly the ST with respect to that of the cement; it also decreases the UCS of the final product at short ages, but its effect decreases with the sample age. Fe2O3 does not affect the ST and UCS at short sample ages; however, at long sample ages, it decreases the UCS of the product. (C) 2001 Elsevier Science Ltd. All rights reserved.