Pb-induced retardation of early hydration of Portland cement: Insights from in-situ XRD and implications for substitution with industrial by-products

Using industrial by-products as substitutes for Ordinary Portland Cement (OPC) is a promising strategy to reduce its environmental impact. However, heavy metals like Pb strongly interfere with initial kinetics. The dynamic physicochemical environment makes it challenging to identify the key factors. Here, we employed in-situ XRD as a time-dependent method, alongside conventional characterization techniques and geochemical modeling, to investigate the Pb-induced retardation in CEMI 42.5R and 52.5R. The results show that Pb-hydroxides and Pb-O-Si clusters are expected to be the primary mechanisms for this inhibition. Among clinker phases, C3A dissolution is less affected and serves as the primary source of alkalinity in early hydration, promoting hydration products precipitation and gypsum dissolution. Geochemical modeling suggests that Pb species concentration in the solution regulates the precipitation of hydration products, especially portlandite. The comparison of hydration kinetics of 2 types of OPC highlights optimizing particle size as a solution to mitigate retardation impact.