Smart soil grouting using innovative urease-producing bacteria and low cost materials

Grouting Mechanism of Polyurethane Composite Materials in Asphalt Pavement Subsidence

The mechanical properties of polyurethane grouting materials were significantly improved when cement, sodium meta-silicate, red mud, slag, and fly ash were added. However, the grouting mechanisms of polyurethane composite materials are not clear. The grouting mechanisms of polyurethane composite materials in asphalt pavement subsidence were investigated. The results of computed tomography analysis show that polyurethane foam is filled with geopolymer hydration products. The results from ground penetrating radar after grouting show that mapping has no significant fluctuation or dislocation effect, which indicates that the grouting effect is strong. The high-density electrometer can also test the pavement subsidence place and distribution. The grouting mechanisms indicate that polyurethane foam acts as the consolidation structure, and the geopolymer filled with the foam pores of polyurethane and geopolymer forms a stable consolidated body. The seriflux includes under-layer seriflux (red mud, slag, water, and polyurethane composite materials) and upper-layer seriflux (polyurethane seriflux), and there exists a weak phase separation phenomenon, in which the separation phase is mainly polyurethane with little red mud-based geopolymer.

Heavy metals remediation through bio-solidification: Potential application in environmental geotechnics

Heavy metals are pervasive pollutants found in water, soil, and solid wastes. Bio-solidification offers an environmentally friendly approach to immobilize heavy metal ions using two types of bacteria: urease-producing bacteria (UPB) and phosphatase-producing bacteria (PPB). UPB, exemplified by Sporosarcina pasteurii, secretes urease to hydrolyze urea and generate CO32- ions, while PPB, like Bacillus subtilis, produces alkaline phosphatase to hydrolyze organophosphate monoester (ROP) and produce PO43- ions. These ions react with heavy metal ions, effectively reducing their concentration by forming insoluble carbonate or phosphate precipitates. The success of bio-solidification is influenced by various factors, including substrate concentration, temperature, pH, and bacterial density. Optimal operational conditions can significantly enhance the remediation performance of heavy metals. UPB and PPB hold great potential for remediating heavy metal pollution in diverse contaminated areas such as tailings ponds, electroplating sewage, and garbage incineration plants. In conclusion, harnessing the power of these microbial methods can provide effective solutions for remediating heavy metal-induced pollution across a range of environmental conditions.

Influencing factors on ureolytic microbiologically induced calcium carbonate precipitation for biocementation

Microbiologically induced calcium carbonate precipitation (MICP) is a technique that has received a lot of attention in the field of geotechnology in the last decade. It has the potential to provide a sustainable and ecological alternative to conventional consolidation of minerals, for example by the use of cement. From a variety of microbiological metabolic pathways that can induce calcium carbonate (CaCO₃) precipitation, ureolysis has been established as the most commonly used method. To better understand the mechanisms of MICP and to develop new processes and optimize existing ones based on this understanding, ureolytic MICP is the subject of intensive research. The interplay of biological and civil engineering aspects shows how interdisciplinary research needs to be to advance the potential of this technology. This paper describes and critically discusses, based on current literature, the key influencing factors involved in the cementation of sand by ureolytic MICP. Due to the complexity of MICP, these factors often influence each other, making it essential for researchers from all disciplines to be aware of these factors and its interactions. Furthermore, this paper discusses the opportunities and challenges for future research in this area to provide impetus for studies that can further advance the understanding of MICP.