Investigation of Mechanical Properties and Mechanisms of Sand-Calcined Phosphogypsum (CPG) Biomineralization

Calcined phosphogypsum (CPG), a solid waste material, can be used as a raw material for subgrade. However, the engineering properties of soil with CPG should be improved to meet construction requirements. In this study, the enzyme induced carbonate precipitation (EICP) method was used to treat the sand-CPG, as EICP technology can effectively improve soil properties. To investigate the effect of CPG on the biomineralization process, a series of laboratory tests at macro and micro levels were conducted, including mineralization reaction rate tests by static multiple light scattering (SMLS) techniques, unconfined compression (UC) tests, water immersion tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The results indicate that CPG has an effect on biomineralization process. A small amount of CPG can accelerate the mineralization reaction process and increase the deposition rate of precipitates. However, the biomineralization rate decreases with the increase of CPG content. Similarly, larger amount of CPG can also cause smaller unconfined compressive strength, with the highest strength at 3% content.