Impact of New Combined Treatment Method on the Mechanical Properties and Microstructure of MICP-Improved Sand

Abstract

Microbially induced calcite precipitation (MICP) is a green bio-inspired soil solidification technique that depends on the ability of urease-producing bacteria to form calcium carbonate that bonds soil grains and, consequently, improves soil mechanical properties. Meanwhile, different treatment methods have been adopted to tackle the key challenges in achieving effective MICP treatment. This paper proposes the combined method as a new MICP treatment approach, aiming to develop the efficiency of MICP treatment methods and simulate naturally cemented soil. This method combines the premixing, percolation, and submerging MICP methods. The strength outcomes of Portland-cemented and MICP-cemented sand using the percolation and combined methods were compared. For Portland-cemented sand, the UCS values varied from 0.6 MPa to 17.2 MPa, corresponding to cementation levels ranging from 5% to 30%. For MICP-cemented sand, the percolation method yielded UCS values ranging from 0.5 to 0.9 MPa, while the combined method achieved 3.7 MPa. The strength obtained by the combined method is around 3.7 times higher than that of the percolation method. The stiffness of bio-cemented samples varied between 20 and 470 MPa, while for Portland-cemented sand, it ranged from 130 to 1200 MPa. In terms of calcium carbonate distribution, the percolation method exhibited higher concentration at the top of the sample, while the combined method exhibited more precipitation at the top and perimeter, with less concentration in the central bottom region, equivalent to 10% of a half section’s area.

Non‐ureolytic microbially induced carbonate precipitation: Investigating a cleaner biogeotechnical engineering pathway for soil mechanical improvement

“…This can be attributed to the rupture of the calcium carbonate‐induced bonds between the grains, which is progressively spread through the samples. Such fluctuating trend has also been observed in the previous studies [45, 46]. It seems that the calcium carbonate crystals on the surface of the samples along with the sand particles lead to an uneven surface [46].…”

“…Tangent Young's Modulus (𝐸 𝑓 ) was determined by taking the ratio between the peak strength (q 𝑢 ) and the corresponding strain at failure (𝜀 𝑓 ). The same procedure has been followed by previous studies [45].…”

Effect of Cementation Ratio and Molarity on Mechanical Properties of MICP-Treated Sand Subjected to Freeze-Thaw Cycles

“…Secondly, it fills the pore space between the sand grains, increasing the sediment density. Finally, the precipitation occurs at the contact points between the sand grains, which confirms the findings of Zeitouny et al (2023) and Lai et al (2021). Figure 9c corresponds to the SEM image of the treated sample with a molarity of 0.5 mol/L.…”

Assessment of the Composition Effect of a Bio-Cementation Solution on the Efficiency of Microbially Induced Calcite Precipitation Processes in Loose Sandy Soil

“…Additionally, to reduce the usage of urea and the emission of ammonium ions, calcium lactate (CaL) was selected as a source of calcium and organic carbon. The individual chemicals used to prepare the cementation solutions have molar concentrations in the range from 0.1 M to 0.5 M, which, according to [47], may be considered as low and high concentrations, respectively. The compositions and concentrations of the various components of the bio-cementation solutions were chosen to allow deductions to be made about the influence of (1) B. subtilis cell concentration (expressed as OD), (2) calcium lactate concentration, (3) urea concentration, and (4) Mg/Ca molar ratio on the efficiency of sand cementation.…”