Physicochemical properties of cement waste-derived portlandite-substituted limestone calcined clay cement (LC3) binders

This study explores the use of cement kiln dust (CKD)-derived portlandite (CDP) as a sustainable substitute for limestone powder (LSP) and clinker in limestone calcined clay cement (LC3) mixtures. Motivated by the environmental cost of clinker production and the underutilization of CKD, CDP was incorporated up to 15% as LSP and 30% as clinker replacement. Characterization included XRF, XRD, TG/DSC, isothermal calorimetry, and SEM-EDS, alongside tests for fresh properties, compressive strength, and shrinkage. The reference LC3 mix showed only a 27% strength drop at 28 days despite a 50% clinker reduction, highlighting good clinker efficiency. Substituting LSP with CDP had minimal effects on strength and reactivity, while clinker replacement led to significant early strength losses of up to 75%. Higher CDP content reduced hydration heat, increased porosity, and lowered Ca/Si ratios. Overall, CDP is suitable as a partial LSP substitute but limited as a clinker replacement due to reduced performance.