Chemistry of cement hydration in polymer-modified pastes containing lead compounds

The role of polymeric additives on the hydration process of cement pastes admixed with a lead compound (Pb3O4) was investigated. Three series of pastes were prepared: the reference series, mixing water with Ordinary Portland Cement (OPC), and two series in which whether a styrene-butadiene rubber latex or a superplasticiser based on acrylic-modified polymer was added to the pastes. For each series, 5 and 10 wt% of Pb were mixed with the pastes. Phase analysis and microstructural characterisation were carried out by means of X-ray powder diffraction and SEM-EDX. Thermogravimetric analysis was performed to monitor the hydration degree of the three pastes; indeed, quantitative determination of portlandite and calcite was performed. Dynamic leach tests were performed on solidified monoliths to evaluate the effective immobilisation of Pb3O4. After 384 h leaching., excellent results were obtained by pastes mixed with superplasticiser that showed a cumulative release of Ph equal to 0.62 mg/l for samples containing 5 wt% of Pb, and equal to 0.84 mg/l for samples bearing 10 wt% of Pb.