Reuse of phosphogypsum as a sustainable retarder in PCB40 cement production

Vietnam faces a significant challenge due to its limited natural gypsum resources, which have been imported to meet the demand of cement production. Besides, the country is grappling with the environmental issue of thousands of tons of phosphogypsum waste discharged annually from Diammonium Phosphate (DAP) fertilizer production. This industrial byproduct poses substantial environmental concerns, highlighting an urgent need for sustainable waste management solutions. This study addresses these critical issues by reusing phosphogypsum as a sustainable alternative to natural gypsum in the manufacturing of PCB 40 cement. This work investigates the effect of varying phosphogypsum content, ranging from 1.5% to 5%, on cement properties, including standard water content, soundness, setting time, and compressive strength. To establish a comparative analysis, the experimental results were compared against a reference cement that incorporates 4% natural gypsum. The findings demonstrate that phosphogypsum can effectively substitute natural gypsum without compromising the quality or performance of the cement. Furthermore, the study confirms that cement produced with phosphogypsum consistently meets all established Vietnamese national standards for the examined properties. In an innovative step, the study also leveraged a 4th-degree polynomial regression model to predict the optimal phosphogypsum content. The model identified an optimal dosage of 3.5% phosphogypsum for maximizing compressive strength. The optimized 3.5% phosphogypsum formulation achieved a compressive strength of 58.3 MPa, which is 3% higher than that of the natural gypsum control. This prediction illustrated remarkable alignment with the experimental data, underscoring the potential of predictive modeling in cement production. This study paves a promising way in the reuse of phosphogypsum in construction materials, aiming at reducing impact on environment and sustainable development.