Abstract:Microbial-induced calcium carbonate precipitation (MICP) is a new soil remediation technology, which can improve the physical and mechanical properties of soil by transporting bacterial solution and cementation solution to loose soil and precipitating calcium carbonate precipitation between soil particles through microbial mineralization. Based on this technique, the effects of different fine particle content and pore ratio on the physical and chemical properties of silt after reinforcement were studied. The c… Show more
“…The results of this study along with previous ones indicate that the CaCO 3 bonds formed as vaterite polymorph can also provide reasonable mechanical strength; our results indicated an improvement in surface resistance up to 350 kPa as well as an increase in the threshold detachment velocity from 4.32 to more than 25 m/s. The results agree with the findings of previous studies, where precipitated CaCO 3 substrate induced by MICP was vaterite, in which reasonable mechanical strength and wind erosion resistance was achieved 13 , 40 and reasonable wind erosion resistance was maintained even after 180 days exposed to field environmental conditions 13 . Figure 14 SEM micrograph of ( a , b ) untreated soil, ( c ) control ureolytic MICP, ( d - f ) AA-composition treated sample, ( g – i ) AS-composition treated sample, ( j – l ) FA-composition treated sample, ( m – o ) FS-composition treated sample, at application rate of 3 L/m 2 at different magnifications.…”
The detrimental effects of sand storms on agriculture, human health, transportation network, and infrastructures pose serious threats in many countries worldwide. Hence, wind erosion is considered a global challenge. An environmental-friendly method to suppress wind erosion is to employ microbially induced carbonate precipitation (MICP). However, the by-products of ureolysis-based MICP, such as ammonia, are not favorable when produced in large volumes. This study introduces two calcium formate-bacteria compositions for non-ureolytic MICP and comprehensively compares their performance with two calcium acetate-bacteria compositions, all of which do not produce ammonia. The considered bacteria are Bacillus subtilis and Bacillus amyloliquefaciens. First, the optimized values of factors controlling CaCO3 production were determined. Then, wind tunnel tests were performed on sand dune samples treated with the optimized compositions, where wind erosion resistance, threshold detachment velocity, and sand bombardment resistance were measured. An optical microscope, scanning electron microscope (SEM), and X-ray diffraction analysis were employed to evaluate the CaCO3 polymorph. Calcium formate-based compositions performed much better than the acetate-based compositions in producing CaCO3. Moreover, B. subtilis produced more CaCO3 than B. amyloliquefaciens. SEM micrographs clearly illustrated precipitation-induced active and inactive bounds and imprints of bacteria on CaCO3. All compositions considerably reduced wind erosion.
“…The results of this study along with previous ones indicate that the CaCO 3 bonds formed as vaterite polymorph can also provide reasonable mechanical strength; our results indicated an improvement in surface resistance up to 350 kPa as well as an increase in the threshold detachment velocity from 4.32 to more than 25 m/s. The results agree with the findings of previous studies, where precipitated CaCO 3 substrate induced by MICP was vaterite, in which reasonable mechanical strength and wind erosion resistance was achieved 13 , 40 and reasonable wind erosion resistance was maintained even after 180 days exposed to field environmental conditions 13 . Figure 14 SEM micrograph of ( a , b ) untreated soil, ( c ) control ureolytic MICP, ( d - f ) AA-composition treated sample, ( g – i ) AS-composition treated sample, ( j – l ) FA-composition treated sample, ( m – o ) FS-composition treated sample, at application rate of 3 L/m 2 at different magnifications.…”
The detrimental effects of sand storms on agriculture, human health, transportation network, and infrastructures pose serious threats in many countries worldwide. Hence, wind erosion is considered a global challenge. An environmental-friendly method to suppress wind erosion is to employ microbially induced carbonate precipitation (MICP). However, the by-products of ureolysis-based MICP, such as ammonia, are not favorable when produced in large volumes. This study introduces two calcium formate-bacteria compositions for non-ureolytic MICP and comprehensively compares their performance with two calcium acetate-bacteria compositions, all of which do not produce ammonia. The considered bacteria are Bacillus subtilis and Bacillus amyloliquefaciens. First, the optimized values of factors controlling CaCO3 production were determined. Then, wind tunnel tests were performed on sand dune samples treated with the optimized compositions, where wind erosion resistance, threshold detachment velocity, and sand bombardment resistance were measured. An optical microscope, scanning electron microscope (SEM), and X-ray diffraction analysis were employed to evaluate the CaCO3 polymorph. Calcium formate-based compositions performed much better than the acetate-based compositions in producing CaCO3. Moreover, B. subtilis produced more CaCO3 than B. amyloliquefaciens. SEM micrographs clearly illustrated precipitation-induced active and inactive bounds and imprints of bacteria on CaCO3. All compositions considerably reduced wind erosion.
“…The MICP process occurs naturally in various situations and can be induced artificially under appropriate environmental and nutritional conditions in order to benefit from the good cementing qualities produced throughout the process [2]. MICP technology has been developed for various types of soil, such as sand [3], expansive soils [4], loess [5], and silt [6], and has been successfully applied in many engineering areas related to stability and erosion prevention, such as wind erosion resistance [7], mitigation of beach erosion [8], and rainfall erosion resistance [9]. The MICP technique is classified into six types depending on the pathway used, such as ureolysis, photosynthesis, denitrification, ammonification, sulfate reduction, and organic compound oxidation by bacterial metabolism [10], among which only denitrification and sulfate reduction occur under anaerobic conditions and are difficult to apply under unsaturated conditions in soil.…”
Soil properties are the most important factors determining the safety of civil engineering structures. One of the soil improvement methods studied, mainly under laboratory conditions, is the use of microbially induced calcite precipitation (MICP). Many factors influencing the successful application of the MICP method can be distinguished; however, one of the most important factors is the composition of the bio-cementation solution. This study aimed to propose an optimal combination of a bio-cementation solution based on carbonate precipitation, crystal types, and the comprehensive strength of fine sand after treatment. A series of laboratory tests were conducted with the urease-producing environmental strain of bacteria B. subtilis, using various combinations of cementation solutions containing precipitation precursors (H2NCONH2, C6H10CaO6, CaCl2, MgCl2). To decrease the environmental impact and increase the efficiency of MICP processed, the addition of calcium lactate (CaL) and Mg ions was evaluated. This study was conducted in Petri dishes, assuming a 14-day soil treatment period. The content of water-soluble carbonate precipitates and their mineralogical characterization, as well as their mechanical properties, were determined using a pocket penetrometer test. The studies revealed that a higher concentration of CaL and Mg in the cementation solution led to the formation of a higher amount of precipitates during the cementation process. However, the crystal forms were not limited to stable forms, such as calcite, aragonite, (Ca, Mg)-calcite, and dolomite, but also included water-soluble components such as nitrocalcite, chloro-magnesite, and nitromagnesite. The presence of bacteria allowed for the increasing of the carbonate content by values ranging from 15% to 42%. The highest comprehensive strength was achieved for the bio-cementation solution containing urea (0.25 M), CaL (0.1 M), and an Mg/Ca molar ratio of 0.4. In the end, this research helped to achieve higher amounts of precipitates with the optimum combination of bio-cementation solutions for the soil improvement process. However, the numerical analysis of the precipitation processes and the methods reducing the environmental impact of the technology should be further investigated.
“…As evident from Figure 7, the surface of unmodified GCC has crystal cleavage planes with different widths, it presents irregular open Frontiers in Materials frontiersin.org layered structure with a large specific surface area and stable skeleton structure. However, after modification by the modifying agent, the angular surface and crystal cleavage surface of the GCC powder basically disappear, and the unfavorable morphological characteristics are improved (Habte et al, 2019;Shan et al, 2022;Zhao et al, 2022). As can be seen in Figures 7B,C,D, the surface of the modified GCC is coated with a layer of oily bright substance, which indicates that the modifying agent is bonded with the matrix particles.…”
The study investigated the modification mechanism of modified ground calcium carbonate (GCC) mineral powder using in asphalt concrete. Two types of Titanate coupling agents, namely, K38S (TCA-K38S) and 201 (TCA-201), as well as sodium stearate coupling agent, were adopted to prepare modified GCC. The optimized preparation process was obtained through the orthogonal test. Two kinds of modified GCC were preferably selected to prepare asphalt concrete according to modification mechanism characterization, their performance was analyzed and evaluated at macro and micro levels. The study results show that, the optimal scheme of sodium stearate modified GCC is modification temperature of 80°C, modification time of 50 min, modifying agent dosage of 2.0%. The crystal structure of GCC remains unchanged after modification, with the original lattice structure being maintained. TCA-201 and sodium stearate exhibit better coating properties than that of TCA-K38S. The contact angles of TCA-201 and sodium stearate modified GCC are larger than that of TCA-K38S modified GCC. The in-service performance of AC-13C asphalt concrete modified with sodium stearate is found to be superior to that of TCA-201 modified AC-13C asphalt concrete. Compared with the unmodified AC-13C asphalt concrete, the Marshall modulus, residual stability, freeze-thaw splitting strength ratio, and maximum flexural tensile strain of sodium stearate modified AC-13C asphalt concrete are increased by 54.55%, 2.73%, 10.47%, and 26.41% respectively. This paper provides theoretical guidance for the application of GCC mineral powder in asphalt concrete.
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