No abstract

Microbial induced calcite precipitation method MICP is a sustainable and eco-friendly technique for soil stabilization. To show the optimum effectiveness of the bioremediation within the silty sand matrix, a model of plastic boxes and PVC molds was made with an air pump placed in an isolated room at a temperature range of 25–27°C. The molds were perforated from sides and bottoms and opened from the top with a transparent film of filter paper (placed on the inner surface). The major feature of this treatment system is allowing the cementation solution to penetrate easily into soil samples. The results showed a positive effect of Bacillus subtilis in enhancing the strength properties of lead contaminated soil. Unconfined compressive strength increased from 65 kPa to 539, 527, and 525 kPa. Cohesion increased from 4.5 to 40, 41.9, and 42 kPa at concentrations of 15, 20, and 25% respectively. Angle of internal friction increased from 18.94° to 38.2°, 40°, and 40.74° respectively after 14 days. Thereafter, it become 40.92° and 41.5° at concentrations of 15 and 20%, respectively and decreased to 36.75° of 25% at 28 days. Microstructural characteristics represent the formation of calcium carbonate and lead compounds, which were the reasons for the improvement in the strength and the alteration in lead from a soluble to insoluble form, a hence less toxic element.

The type of stabilizer, heavy metal and soil can typically affect the strength and compressibility development in the treatment of contaminated soils. This is due to the difference in chemical reactions and interferences occurring among the stabilizers, metals, and clay minerals. A standard consolidation test using an oedometer was carried out to investigate the cement–lime induced changes in the compressibility of clay soils contaminated with either copper or zinc. In this study, laterite clay soil obtained from the hilly area at Universiti Teknologi Malaysia was used. Control samples of cement-and lime-stabilized soils without heavy metals were compared with the treated contaminated stabilized soil at various contaminants contents. Such percentage of contaminants means that the soil falls under industrially contaminated soil. To highlight the effect of the two heavy metals on the consolidation behavior of clay samples treated with cement and lime, a comparison has been made at a curing period of 7, 28, 100, and 200 days respectively. It was found that the interference of heavy metals during the process of hydration (cement and lime) contributed directly to the inhibition of the compression development of the tested soil samples. Therefore, it is crucial to identify the type of stabilizer, heavy metal, and soil involved to ensure successfully and remediate treatment.

No abstract

It is known that the stabilization of normal soils with chemical substances will gradually affect their properties like shape, size and soil particles arrangement. The current study concerns with artificially contaminated clayey soils immobilized by fly ash waste materials and quicklime (CaO). In this research, the time-dependent factor changes the morphology of stabilized – contaminated soil. Energy Dispersive X-ray Spectrometry is performed to further examine components on the clay particles’ surface. The results showed that with an increase in hardening time, morphology analyses by FESEM shows a transformation of soil fabric due to the effect of chemical treatment, and due to the production of cementitious pozzolanic compounds (CSH and CASH). However, with the presence of contamination, it can notice a transformation in the fabric of clay particles towards a more flaky nature at the early curing time due to precipitation of heavy metals as hydroxide or sulphates on the surface of particles. Regarding the EDAX analysis, the Al:Si ratio for cement - fly ash treated clayey soil decreases over time. This is attributed to the increased release of alumina from the mineral of clay structure. However, an increasing Ca:Si ratio is observed, especially after 100 days related to the formation of the portlandite compound from cement hydration over time. While, it is detected variation in these ratios with respect to contaminated soil with time.