No abstract

Microbially induced carbonate precipitation (MICP) is a process that has emerged as an attractive alternative ground improvement technique in Geotechnical and Civil Engineering using ureolytic bacteria for soil strengthening and stabilisation. Locally isolated Sporosarcina pasteurii from limestone cave samples of Sarawak were found to have high urease-producing abilities. Optimisation of various cultural conditions (incubation temperature, initial pH medium, incubation period and urea concentration) were performed using conductivity and optical density measurements to determine the maximum specific urease activity. In addition, an in vitro biocement test was done to define the prospect of using these bacterial isolates in civil engineering work for the improvement of soils with inferior properties. The experimental results showed that urease activities were optimum at 25 to 30°C, pH 6.5 to 8.0, 24 hr incubation and 6 to 8% (w/v) urea concentration. It was also demonstrated that biocementation using the local ureolytic bacteria can improve the strength of poorly graded soils. However, the efficiency of the MICP process in improving the soil's strength varied among samples treated with different bacterial cultures.

Low-cost cultivation of Sporosarcina pasteurii strain in food-grade yeast extract medium for microbially induced carbonate precipitation (MICP) application, Biocatalysis and Agricultural Biotechnology,

In this study, fly ash was added to residual soil to produce soil-fly ash geopolymer bricks. This study investigated the effects of fly ash/soil, alkali activator/ash, Na2SiO3/KOH (or NaOH), additional water content, curing condition and curing temperature on the compressive strength of soil-fly ash geopolymer. The results showed that the optimum compressive strength was obtained when the ratios of alkali activator/ash, Na2SiO3/KOH (or NaOH) and additional water were 0.6, 0.5 and 10 % respectively. Higher amount of alkali activators was required for strength development in soil-fly ash geopolymer than conventional fly ash-based geopolymers. The formation of the rigid structure at low ratios of alkali activator/ash and Na 2SiO3/KOH (or NaOH) was unlikely. Compressive strength decreased when additional water was increased. High curing temperature and long curing duration showed negative effect on strength development. The compressive strength of soil-fly ash geopolymer varied as different mixing sequences of raw materials were used, indicating the importance of the formation of geopolymer gel in the structure. Compressive strength results obtained in this study demonstrate that soil-fly ash geopolymer can be a potential alternative to traditional clay fired brick.