Abstract
Microbially induced calcium carbonate precipitation (MICP) results in the formation of biocement (BC). This process, also known as biocementation, is recently widely used to improve the strength and durability of building materials including soils. In the present study, effectiveness of biocement as admixture with fly ash (FA) was investigated as first few studies to improve geotechnical properties of expansive soils. Biocement precipitated by Bacillus megaterium was blend with four formulations of fly ash at concentrations of 0, 10, 25 and 50%, namely 0% FABC, 10% FABC, 25% FABC, and 50% FABC, respectively. These formulations were separately added to expansive soils. Specimens with 25% FABC resulted in significant improvement in unconfined compressive strength of expansive soil that was more than two-times higher than control. Further, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses characterized microstructures of soil specimens, and depicted the process of MICP in improving strength of expansive soils. This research indicates that incorporation of biocement in fly ash is an effective means of increasing the strength of expansive soils.
Highlights
Expansive soils are present throughout the world that have tendency to swell upon increase in moisture content
The liquid limit values of the expansive soil decreased with an increasing amount of fly ash till 25% concentration and similar trends of plasticity index and plastic limit were observed (Fig. 1a)
The activities of expansive soil were reduced greatly at 25% fly ash in the presence of biocement (25% FABC)
Summary
Expansive soils are present throughout the world that have tendency to swell upon increase in moisture content. Carrier material to enhance the metabolic activity of calcite-precipitating bacteria that supports survivality of bacteria for effective calcite production[8] Due to this mechanism, fly ash together with bacterial calcium carbonate could enhance the strength of expansive soils. In the present study a fixed amount of biocement precipitated from Bacillus megaterium added from lower to high concentrations of fly ash at 10, 25 and 50% was used as stabilizer to improve the engineering properties of expansive soils. All such soils were tested to obtain Atterberg limits, swelling potential, and unconfined compressive strength (UCS). This is few of such detail studies carried out to improve the strength of expansive soils
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