Performance enhancement of cementitious composite using polyethylene glycol functionalized C–S–H based sustainable accelerator derived from calcium carbide slag and rice husk ash

Calcium silicate hydrate (C–S–H) seeding is an effective approach to accelerate cement hydration and early-age performance, yet its application is often constrained by particle agglomeration, loss of workability, and uncontrolled pore development. This study examines the synthesis and performance of polyethylene glycol (PEG)–functionalized C–S–H seeds prepared via a co-precipitation route using calcium carbide slag and rice husk ash as alternative calcium and silica sources. Normal C–S–H (CSH_N) and PEG-modified C–S–H (1.0 and 1.5 wt.% PEG) were characterized using X-ray diffraction, scanning electron microscopy, and nitrogen adsorption–desorption analyses to elucidate phase composition, morphology, and pore structure. Their effects on cementitious systems were assessed through setting time, workability, compressive strength and drying shrinkage, supported by cubic spline interpolation, functional ANOVA, and sensitivity analysis. PEG functionalization refined the C–S–H pore network, transforming a broad meso–macroporous structure into well-dispersed hierarchical micro–mesoporous. In cement pastes, PEG-modified C–S–H significantly accelerated hydration, reducing initial setting time by up to ~ 67%, compared with ~ 38% for unmodified C–S–H. Early-age strength was markedly improved, with CSH_PEG1.5 delivering the highest 1- and 3-day strengths and gains exceeding 4 MPa per 1% C–S–H addition. Overall, PEG-functionalized, waste-derived C–S–H seeds provide a promising approach to enhance fresh-state performance in high-performance cementitious systems. This study also contributes to sustainability by developing a resource-efficient supplementary material derived from industrial and agricultural by-products.