Enhanced waterproofing of phosphogypsum-based foamed concrete via long-chain alkyl-modified poly(methylhydrosiloxane): Synthesis, characterization, and performance evaluation

Phosphogypsum (PG), a major industrial by-product of phosphoric acid production, presents significant environmental challenges due to its low utilization rate and poor water resistance when used in construction materials. In this study, a novel long-chain alkyl-modified poly(methylhydrosiloxane) (L-PMHS) was synthesized via hydrosilylation to enhance the waterproof performance of PG-based foamed concrete. Under the optimal conditions (80 °C, 10 mg/L catalyst, 1:1.4 molar ratio, and 4 h), the modified L-PMHS exhibited significantly improved hydrophobicity and viscosity balance. Comprehensive characterization using FTIR, ¹H NMR, XRD, and XPS confirmed the successful grafting of long-chain alkyl groups onto the siloxane backbone and the formation of a hydrophobic barrier on PG surfaces. Compared to unmodified PMHS, L-PMHS achieved a greater reduction in water absorption (down to 5.03 %) at a much lower dosage (10 %), without significantly compromising compressive strength. Surface chemical analysis revealed enhanced C–H and C–C bonding, reduced surface hydroxyl content, and inhibited hydration reactions—indicating that the waterproofing mechanism was dominated by effective surface shielding and molecular-level hydrophobic enrichment. This work provides a cost-efficient and scalable strategy for improving the durability and performance of PG-based construction materials. The use of structurally tailored organosilicon hydrophobes offers new insights into the design of high-performance, water-resistant building composites derived from industrial solid wastes.