In addition, CaO/SiO2 and CaO/SiO2+Al2O3 ratios were found to be good indicators of pozzolanic activities at longer curing periods, and higher strengths were obtained when the ratios were between 2 and 2.5. It was deemed that 10% to 12% calcium oxide (CaO) in stabilizers was optimum for stabilizing expansive soils. Test results indicated that cement was preferable for higher strength at shorter curing times (7 days), while lime produced the maximum strength at longer curing periods (90 days). Specimens were subjected to Atterberg limits (LL/PI), pH, unconfined compressive strength, and volumetric swell tests. Three different soils with variable sulfate contents were treated with Type I/II portland cement, lime, Class C fly ash (FA), and Class C FA-cement and Class F FA-cement blends. In this paper, the effectiveness of different chemical stabilizers in improving the engineering properties of expansive soils is investigated. However, presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones.

Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction. The degree of stabilization is controlled by several factors such as additive type, additive content, soil type, soil mineralogy, curing period, curing temperature, delay in compaction, pH of soil matrix, and molding water content, including presence of nano-silica, organic matter and sulfate compounds. It is observed that the stabilization process primarily involves hydration, cation exchange, flocculation and pozzolanic reactions. In this paper, suitability of such additives under various conditions and their mechanisms are reviewed in detail. This can be achieved through chemical stabilization using additives such as lime, cement and fly ash. It is, therefore, necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements. Volume instability of expansive soils due to moisture fluctuations is often disastrous, causing severe damages and distortions in the supported structures. This investigation has revealed that the BEICP method provided a similar capacity in F–T resistance of soil as using the traditional Portland cement stabilizer, whereas the class F fly ash did not improve F–T durability of medium dense soil.

It was found that although bio-stabilizer was able to increase a frost duration of soil, the F–T cycling significantly impacted on the compressive strength of bio-treated soil, due to a formation of microcracks.

Engineering properties of bio-cemented soil including unconfined compressive strength, calcium carbonate contents, moisture contents, porosity, permeability, and microstructure were examined before and after the F–T durations. The bio-treated soil columns were subjected to freeze and thaw (F–T) cycling for a durability evaluation. pasteurii was used as a biological source along with calcium chloride and urea to solidify sandy soil and silty sand soil. This paper addresses a soil bio-stabilization technique using bacterial enzyme-induced calcium carbonate precipitation (BEICP) as an alternative to previous conventional methods including microbial-induced carbonate precipitation and plant-derived enzyme-induced carbonate precipitation.

Air doc belle fourche