Mechanical Performance and Environmental Benefits of Ternary Blends of Phosphogypsum, Calcium Carbide Residue, and Rock Demolition Waste for Use in Road Subgrade

Global collection of rock demolition waste (DW) is a significant environmental concern due to their high volumes, limited disposal options, and risk of contaminant leaching. An integrated approach of sustainable valorization of this industrial waste is use of phosphogypsum (PG), and calcium carbide residue (CCR) as alternative binder systems during non-structural building applications. A series of investigations were conducted to evaluate the optimum PG–CCR–DW combination based on their best performance of mechanical, environment safety, and evolution of their microstructure. Analytical tests like X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed formation of calcium silicate hydrate (C–S–H) and ettringite due to their pozzolan nature of CCR and their sulfate addition of PG. The 5% CCR and 10% PG combination had a significant increase of compressive strength, stiffness modulus, and shear strength parameters (cohesion, internal friction angle), whereas effectively reduced their leached concentration of zinc, arsenic, and nickel at U.S. EPA-compliant levels. UCS increased from 543–749 kPa (DW) to 1005–1705 kPa (10% PG) and peaked at 2,201 kPa (5% CCR) after 48 days, indicating a significant strength enhancement of CCR, with an MDD of 1.95 g/cm 3 attained by adding 5% CCR. E 50 increased sharply to 169.26 MPa with 5% CCR, which is 158% higher than plain DW and 32% stiffer than 10% PG. The 10% PG–CCR combination also achieved a peak strength of 2306 kPa. The maximum pH was 8.91 at 20% PG, however 5% CCR showed improved mechanical performance at pH 10–10.5, indicating its higher chemical and structural stability. Besides, a life cycle assessment (LCA) was conducted in comparison with their environment impacts and economic feasibility of established mixes. The PG–CCR mixture had a record of lowest carbon emissions and material cost of all variants evaluated, confirming its suitability of a circular economy incorporation. By disposing of hazardous industrial by-products at a landfill with reduction on virgin raw material reliance and hazard on ecologically delicate environments, this investigation indicates a scalable, efficient form of waste disposal. The findings contribute towards improved broader sustainable material reuse agenda and a feasible avenue of material recoveries within this construction and demolition sector. • Valorization of phosophogypsum (PG), calcium carbide (CCR), and rock demolition waste (DW) into alternative construction binders. • Improved strength, stiffness, and shear parameters in optimized waste-based mixes. • DW-PG-CCR blend indicates formation of C–S–H and ettringite confirmed by XRD and SEM microstructural analysis. • Heavy metal leaching reduced to EPA-compliant levels in PG-CCR hybrid binder systems. • Life cycle assessment shows lower carbon footprint and cost of PG–CCR blends.