A comparison of mechanical responses for microbial- and enzyme-induced cemented sand

Abstract

The overall effectiveness of bio-cementation techniques such as microbial-induced carbonate precipitation (MICP) or enzyme-induced carbonate precipitation (EICP) can be different due to different sources of urease enzyme and treatment approach used. This paper compares the behaviour of oven-dried MICP and EICP-treated sand from macro- and micro-mechanical point of view with the number of treatment cycles and average calcium carbonate (CaCO3) content used as a comparison basis. The results indicate that in both processes, the calcium carbonate content increased with the number of treatment cycles and led to an improvement in strength (unconfined compressive and splitting tensile strength) and stiffness. For similar average calcium carbonate content, EICP-treated samples showed significantly higher splitting tensile strength (compared to MICP) even though a slightly smaller amount of precipitates were observed at particle contacts through scanning electron microscopy. This indicates, besides the average calcium carbonate content, its distribution along the height of the sample is likely to have a significant contribution towards the strength. X-ray powder diffraction and energy-dispersive X-ray spectroscopy analyses confirmed that precipitated calcium carbonate in both types of treatments were mainly calcite crystals with minor traces of aragonite.

State-of-the-Art Review of Microbial-Induced Calcite Precipitation and Its Sustainability in Engineering Applications

“…The calcite precipitation modifies or enhances the strength of the sample and different studies have investigated this influence through various laboratory tests namely, UCS tests [43,[76][77][78][79][80][81], STS tests [54,79,80,[82][83][84][85], direct simple shear tests [30], triaxial tests [28,79,[86][87][88][89][90][91], cyclic triaxial tests [92] and cone penetration tests [62]. Some of the observations are summarised below.…”

“…Other studies have also investigated the UCS of different types of soil and also analysed the CaCO 3 content [38,41,76,78,81,84,93,[95][96][97][98][99][100][101][102][103][104]. In some studies, the influence of CaCO 3 precipitation via MICP treatment on soil permeability has been assessed [38,78,80,84,95,97,100,101].…”

“…Similar to UCS, a series of STS tests on MICP-treated soils have been reported in recent literature [54,79,80,[82][83][84][85]. In these studies, STS values have been assessed and compared with other parameters such as the CaCO 3 content [79,80,82], different soil types [54,82], and reinforced fibre content [83][84][85]. A summary of the studies can be found in Table 3.…”

“…Figure 11a shows a plot of UCS versus RC for different soil types (specifically D10). It is worth noting that RC shows an exponential relationship with UCS for a few datasets especially data from the authors [80], who proposed the RC parameter. However, for other sets of data from different authors, RC did not have a good correlation with UCS.…”

A Review of Enzyme Induced Carbonate Precipitation (EICP): The Role of Enzyme Kinetics

“…Enzyme induced carbonate precipitation (EICP) is an innovative ground improvement technique that involves calcium carbonate (CaCO 3 ) precipitation via the hydrolysis of urea (CO(NH 2 ) 2 ) into ammonium (NH + 4 ) and carbonate (CO 2− 3 ) ions catalysed by the urease enzyme. The EICP process has the potential to be applied as bio-cementation and bio-remediation solutions in many environmental, construction, geotechnical and civil engineering problems, such as improving soil strength, reducing soil liquefaction potential, surface erosion control, reducing permeability, heavy metal contaminant remediation and so forth [1][2][3][4][5]. One advantage of EICP is the smaller size of the urease enzyme crystals (typically 12 nm or 120 Å), rendering the process effective for a wider range of soils, including fine-grained soils [6].…”