Desert sand cemented by bio-magnesium ammonium phosphate cement and its microscopic properties

Abstract

Loose desert sand grains can be cemented through the microbially-induced magnesium ammonium phosphate sediment into sandstone. Ammonia and ammonium were produced by Sporosarcina-Pasteurii hydrolyzing urea and effectively became environmentally friendly magnesium ammonium phosphate in the presence of HPO42− ions (hydrogen phosphate). This a new kind of the bio-cement based on Sporosarcina-Pasteurii, and the bio-phosphate mineral has cementation. The chemical components of the bio-sandstone were mainly MgNH4PO4(H2O)6 (struvite) and quartz, as discovered through X-ray diffraction (XRD) analysis. The internal micro-structure of the desert sand was observed by scanning electron microscopy (SEM), and its morphology was of irregular spheres with a size in the range of 100–300 µm. SEM images of the bio-sandstones showed the morphology of the cementation products as irregular flakes. The average hardness of two bio-sandstones cemented by spraying 1 and 3 times with cementation solution was 4.4 and 12.3, respectively. The evolution law of the micro-structure for the bio-sandstone cemented by spraying 3 times with cementation solution was revealed by the X-ray computed tomography (XRCT) technique. Maximum defect volume and average porosity of the bio-sandstone was 134 mm3 and 18.39%, respectively. Interface binding forces between the bio-cement and smooth sheet glass (SiO2) were determined with WS-2005 coating adhesion scratch tester, which was 3.69 ± 1.02 N.