Hybrid bacteria mediated cemented sand: Microcharacterization, permeability, strength, shear wave velocity, stress-strain, and durability

Abstract

Microbially induced calcite precipitation (MICP), a sustainable approach for sand biocementation, was investigated in previous studies based on metabolic activity of individual microorganisms. The individual bacteria, specifically Sporosarcina pasteurii (SP), Bacillus subtilis (BS), and Lysinibacillus sphaericus (LS), were found capable enough for sand biocementation. However, present study investigates synergistic effects of using bacterial-hybrids on cementation and consequent improvement in sand properties. The SP, BS, and LS strains were used in different combinations to create bacterial-hybrids and applied under simulated non-sterile field conditions. Initially, sand biotreatment was carried out in plastic tubes up to 14 days, using bacterial mixtures and 0.5 M cementation solution. Biocemented specimens were tested for calcite precipitation, XRD, FTIR, and SEM. The SP and LS combination (SPLS hybrid) showed maximum calcite precipitation, which is further used for biotreatment to create cylindrical sand samples for testing improved engineering properties. These samples were prepared using 0.5 M cementation solution in three pore volumes (1, 0.75, and 0.5 PV) and treatment cycles (12, 24, and 48 hrs TC) up to 18 days. Biocemented samples were tested for permeability (6th, 12th, and 18th days of biotreatment), unconfined compressive strength (UCS), split tensile strength (STS), ultrasonic pulse velocity (UPV), and consolidated undrained stress-strain response. Durability of biocementation was also investigated by determining reduction in strength and UPV subjected to freeze-thaw (FT) cycles (5, 10, 15, and 20). The results showed maximum UCS of 1902 kPa, STS of 356 kPa, UPV of 2408 m/s, and coefficient of permeability reduction up to 91%. The higher results were achieved with 11.11% calcite content in 1PV-12TC treated samples. The 1PV-12TC treated samples resulted in 4.2%, 8.3%, 17%, and 35% reduction of strength after 5, 10, 15, and 20 FT cycles, respectively. Overall, biocementation using hybrid bacteria is shown significant to improve sand's engineering properties, including potential to mitigate liquefaction.

Rock‐like strength enhancement of Indian desert sand using commercially available polysaccharide biopolymers

“…Ultrasonic pulse velocity (UPV) tests were performed to analyse the rock behaviour of biotreated sand samples, with Figure A2b showing a test performed on UCS biotreated desert sample. According to the literature, the shear wave velocity of poorly graded sand ranges from 149 to 303 m/s (Sharma et al, 2021c). Figure 5 shows the UPV values for biotreated desert sand samples for different treatment conditions and was found that the maximum values for AG, SA and P were 1579, 1490 and 1400 m/s, respectively.…”

Experimental Study on Optimization of Cementation Solution for Wind-Erosion Resistance Using the MICP Method

“…The coefficient of variation was less than 19 for all layers and combinations, which was acceptable as calcite-content formation depends on many factors, such as type of bacteria, bacterial density, crystal formation, temperature, and pH value. Various studies [6] have found that the coefficient of variation of more than 21 was within the acceptable limits. Figure 9 shows the percentage of calcite content for different treatment combinations for all three layers.…”

“…The reaction between carbonate ions and calcium ions started, and precipitation of calcite crystals occurred. Sharma et al (2021) [6] suggested that the stopped-flow pouring method was more effective for enhancing uniformity in calcite formation from top to bottom than the continuous-flow pouring method. After every 24 h, the cementation solution was drained out using a discharge nozzle (a bottle flap cap), and a freshly prepared cementation solution was provided after closing all flaps of the bottles.…”

“…In recent years, the MICP method has gained popularity for its potential to reinforce soil particles [5][6][7] in comparison with other ground-improvement practices, which use industrial waste, ashes, agricultural waste, and fibers [8][9][10][11][12]. It is one of the environmentally friendly methods for soil improvement [13].…”

Simplified biogeochemical numerical model to predict pore fluid chemistry and calcite precipitation during biocementation of soil

“…The specimens treated with this combination resulted in 12-13.6% calcite precipitation, irrespective of the bacteria augmentation. Sharma et al (2021a) demonstrated that the samples treated with 0.50 M concentration using 12 h treatment cycle up to 18 days resulted in 2333 kPa unconfined compressive strength and 437 kPa split tensile strength with 96.6% hydraulic conductivity reduction. The similar biocemented specimen with 12% calcite content also showed rock-like (similar to sandstone) behavior and resulted in ultrasonic pulse wave velocity 2670 m/s.…”