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 s tudy the influence of metal oxides on cement properties: unconfined compres sive strength (UCS), setting time (ST), bulk density (BD) and noncombined w ater (NCW). Four metal oxides, usually contained in inorganic wastes from t hermal processes, were studied: ZnO, Cr2O3, PbO, and Fe2O3. The amount of t hese metal oxides in the formulations was selected according to the composi tion 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 o f the experimental results shows that ZnO retards strongly the ST with resp ect to that of the cement; it also decreases the UCS of the final product a t 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, i t decreases the UCS of the product. (C) 2001 Elsevier Science Ltd. All righ ts reserved.