Effect of curing temperature and particle size distribution on unconfined compressive strength of raw and treated fly ash-lime modified phosphogypsum waste

The Voluminous quantity of phosphogypsum waste is generated by phosphoric acid manufacturing industry and end up being landfilled, resulting into environmental pollution. This study was done to determine applications for raw and treated waste phosphogypsum in building and construction, to determine the best conditions to produce the final product. Two readily available wastes namely phosphogypsum and fly ash were used and blended with hydrated lime. Best strengths was obtained from a mixture of phosphogypsum-lime-fly ash specimens were at elevated temperatures. The strengths obtained at the temperature of 80C were above the 3.5 MPa permissible strength for building masonry with unconfined compressive strength up to 4.8 MPa. At lower temperature of 40C the optimum strength obtained was at the minimal phosphogypsum content of 30%. The optimum strength was achieved at the PG content of 50% for raw PG and 60% for treated phosphogypsum. The strengths obtained for the treated phosphogypsum were lower than the minimum permissible load bearing strength due to the non-uniform particles distribution and the presence of impurities and forces of adhesion between citric acid and phosphogypsum. Increasing the curing temperature also reduced the radionuclides initially present in the raw PG without any prior treatment.