Mechanical properties and environmental implications of excess-sulfate cement concrete with phosphogypsum-based cold-bonded fine aggregates

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Recycling waste phosphogypsum (PG) into phosphogypsum-based cold-bonded aggregates (PCBAs) for eco-concrete production has received extensive attention due to its sustainability for construction industry development. Currently, PCBAs mainly replace the coarse aggregates in concrete while the fine aggregates remain natural sand (NS). This study substitutes NS with phosphogypsum-based cold-bonded fine aggregates (PCBFAs) for the preparation of excess-sulfate cement concrete (ESCC), and the compressive strength, tensile splitting strength, flexural strength, and stress-strain curve were studied by considering replacement rations (0%, 25%, 50%, 75%, 100%). The results indicate that when the replacement ratio is 100%, the compressive strength, splitting tensile strength, and flexural strength of ESCC were reduced by 17.2%, 26.9%, and 29.2% respectively. The addition of PCBFAs will make the ascending segment of the stress-strain curve flatter and make the descending segment steeper. Based on the tested results, the prediction formulas of the mechanical properties and the uniaxial compressive stress-strain model of the concrete under different replacement ratios are proposed. Microstructure analysis indicates that the PCBFAs gradually integrate with the cement matrix, reducing the defects in the interface transition zone. Furthermore, ESCC effectively immobilizes impurities contained in PG. The research findings demonstrate the feasibility of using PCBFAs as a substitute for NS.