Application of Phosphogypsum in Ultra-High-Performance Concrete (UHPC) Matrix for Strength Enhancement and Shrinkage Reduction.

Ultra-high-performance concrete is a high-strength and durable material widely used in infrastructure, but its high cement content raises environmental concerns, particularly in terms of CO₂ emissions and resource consumption. Phosphogypsum, an industrial by-product of phosphoric acid production, presents a sustainable alternative by partially replacing cement, thereby reducing cement demand and addressing solid waste disposal issues. This study investigates the effects of PG incorporation (0-40%) on hydration kinetics, mechanical properties, and volume stability in UHPC. The results indicate that increasing PG content delays hydration, affecting the induction period and peak hydration time. XRD and TG analysis confirm that PG modifies hydration product formation, influencing the development of key hydration phases. Strength tests reveal that moderate PG replacement (10-20%) maintains or improves long-term mechanical performance, while excessive PG replacement negatively impacts strength development. Additionally, PG effectively reduces autogenous shrinkage, improving the volume stability of UHPC. These findings highlight that PG can serve as a viable supplementary cementitious material in UHPC, contributing to both environmental sustainability and enhanced material performance.