Microstructural and Geomechanical Study on Biocemented Sand for Optimization of MICP Process

Abstract

9Limited research has been reported on strength improvement of bio-cemented soils in relation 10 to crystal patterns of microbial induced calcite precipitation. In this study, sand samples were 11 treated under the co-effect of different bacterial culture (BC) and cementation solution (CS) 12 concentrations, to evaluate the optimum BC and CS combination that yields the highest soil 13 strength. It was found that for lower CS condition (0.25 M), higher BC produced stronger 14 samples, whereas for higher CS condition (0.5 M or 1 M), lower BC was more dominant in 15 improving the soil strength. This can be attributed to the effectively precipitated CaCO3 16 crystals, which were in rhombohedral shape and large size, and were concentrated at the soil 17 pore throat rather than deposited on the individual sand grain surface. This finding was 18 confirmed with the scanning electron microscopy (SEM) analysis. The strength and 19 permeability of the optimized bio-cemented samples were also compared with sand samples 20 treated with ordinary Portland cement (OPC). The optimized bio-cemented sand provided 21 higher strength and permeability than those obtained from the samples treated with similar 22 content of OPC at curing period of 28 days. 23 24 29cementing agent, binding soil particles together inside the soil matrix (Cheng, et al., 2013). 30 Another potential of microbial grouting is through the concept of bio-clogging, as a result of 31 the agglomeration of the CaCO3 crystals in the soil pore throats, thus, controlling the water 32 flow in the porous media to reduce the hydraulic conductivity of the bio-clogged soils 33 (Ivanov and Chu, 2008). 34 35 The mechanical performance of MICP stabilized soils largely depends on the microstructure 36 of the precipitated CaCO3 crystals, which are affected by various chemical, environmental 37 and physical parameters. Studies by Chu, et al. (2013), Al Qabany, et al. (2012), Mortensen, 38 et al. (2011) and Martinez, et al. (2013) discussed the treatment conditions to achieve an 39overall MICP treatment process efficiency in terms of the uniformity of CaCO3 precipitation. 40It was suggested that the use of lower concentrations of cementation solution (CS) and 41 bacterial culture (BC) would result in better distribution of CaCO3 precipitation, particularly 42 at lower cementation levels. Cheng, et al. (2013) demonstrated that the bio-cemented soils 43 treated at partially saturated conditions resulted in higher strengths than those achieved under 44 full saturation conditions, due to the more CaCO3 crystals precipitated at the contact points 45 between the sand grains. In other words, alteration of the CaCO3 crystals precipitation 46 patterns can have significant effect on the mechanical response of bio-cemented soils. 47 48 3 Earlier studies found in the literature concluded that the alteration of the cementation solution 49 concentrations (in terms of different combinations or the equimolar amount of urea and 50 calcium) would result in uniformly distributed CaCO3 crys...

Bioremediation of Coal Contaminated Soil as the Road Foundations Layer

“…MICP could be carried out after the cultivation of high urease activity bacteria by inducing high concentrations and put in the soil before the cementation solution was inserted. With the addition of nutrients to the soil, the loss of ureolytic activity during the bio-cementation process can also be reversed so that further cementation is possible [13].…”

Effect of Binder Coatings on the Fracture Behavior of Polymer–Crystal Composite Particles Using the Discrete Element Method

“…Polymer-crystal composite particles formed by crystals coated with binders are widely used in the fields of medicine [1], energy [2,3], the chemical industry [4,5], and civil engineering [6,7]. Coatings can effectively improve the physical properties of materials, including their corrosion resistance [8][9][10], thermal conductivity [11], stiffness, and strength [12,13].…”

“…The interfacial fracture mechanism of composite materials is a topical issue, and many mechanical test methods have been proposed to evaluate the adhesion of coatings, including the Brazil split test [14], the indentation test [15], the double cantilever beam test [16], and the four-point bend test [17]. For cemented sand particles, the uniaxial compression test [7] and triaxial compression test have been more widely used [12,13,18]. However, as the polymer-crystal composite particles are much smaller than the sample sizes in traditional mechanical tests, the above methods are not suitable.…”

Compatibility of Landfill Leachate with Compacted Biocemented Lateritic Soil Through Microbial Induced Calcite Precipitation Technique

“…The product responsible for the soil improvement in MICP is the calcite or the by-product of the reaction between a urease producing micro-organism in the presence of calcium source (Keykha et al, 2017). MICP has been reported in literature as an alternative and sustainable soil improvement method in terms of strength and stiffness, remediation of chemical species in soil, soil liquefaction resistance and erosion control (Whiffin et al, 2007;DeJong et al, 2013;Osinubi et al 2017b;2018a;2019a;Mujah et al 2019). Several biological procedures that can lead to calcite precipitate have also been reported; however, urea hydrolysis has been more widely used because the mechanism is straight forward and can produce up to 90% chemical conversion efficiency of precipitated amount of calcite in less than 24 hours (Cheng et al, 2016;Mujah et al, 2017).…”