The evolution characteristics of water absorption, hydration products and microstructure of supersulfated cement containing phosphogypsum by microbial induced carbonate precipitation

Abstract

In this paper, microbial induced calcite precipitation (MICP) was adopted as a modifying technology for surface property enhancement of supersulfated cement (SSC) containing phosphogypsum (PG). A series of tests including waster absorption test, mercury intrusion porosimetry (MIP), X-ray diffractometry (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were conducted to investigate the modification mechanism of SSC containing PG. The results indicate that the enhancement of surface properties is highly dependent on the modification methods and conditions. The effect of surface treatments on the reduction of water absorption and the refine of pore structure is superior to that of the direct-addition method (DM). After surface treatment, the content of ettringite slightly drops, while the calcite content rises significantly. TM with the volume ratio of bacterial solution to cementation solution of 1:1 leads to the formation of more bio calcite with spherical or square particles, which can fill the inner pores and surface holes of the surface layer. The increase of treatment cycle has a limited effect on the increase of calcite content, while can refine the pore structure and reduce the absorption coefficient when the treatment cycle was 9. DM has a great influence on the alkalinity of SSC mortar, which can significantly reduce the content of ettringite and slightly increase the calcite content and it also changes the morphology of ettringite in matrix.