Phosphogypsum valorization in cement: Experimental study of the PG effect and the water-to-cement ratio on the flexural strength of cement paste

This study focuses on an environmentally friendly valuation of Phosphogypsum (PG) in the manufacture of building materials. This work aims to recover phosphogypsum waste from the large phosphate industry in El Jadida Jorf Lasfar Morocco in the cement industry. The PG recovered after sieving is treated with concentrated sulfuric acid. The weight ratio PG/H2SO4 used is 1/2 at 60 degrees C during 2 h The preparation of cement (Ce) test pieces involves the use of 95% clinker (C) and 5% PG (raw, washed with water, purified with sulfuric acid (PG.P)). A comparative study was conducted to demonstrate the influence of gypsum type on the mechanical resistance to flexural. Previous resistances were compared with those prepared from commercial gypsum (CG). Another comparison was made to demonstrate the influence of the water-to-cement ratio (W/Ce) and the day on the evolution of cement paste mechanical properties. The flexural strength and deformation characteristics of cement specimens were obtained by performing mechanical tests on the cement paste after different days of hydration. For different curing days, the maximum flexural strength of cement paste is as follows: sigma(f 90d) > sigma(f 28d) > sigma(f 14d) > sigma(f 7d). The PG.P has the most significant effect on increasing strength. Indeed, after a duration of 28 and 90 days of hydration, the best resistance to flexural is obtained with a W/Ce ratio equal to 0.35. The specimens are analysed by flexural strength simple three-point and X-ray diffraction. These analyses were applied to observe chemical and structure modifications in the specimen, whereas the MEB measurements and ATD-ATG were performed to evaluate the progressive evolution changes in the structure of the C-S-H in several specimen. These analyses and measurements demonstrate the strength evolution of cement specimens on different days.