Перегляд за Автор "Chu, Jian"

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Biocement: green building-and energy-saving material
(2012) Chu, Jian; Ivanov, Volodymyr M.; Stabnikov, Victor; He, Jia; Li, Bing; Naemi, Maryam
Cement and chemical grouts have often been used for soil strengthening. However, high cost, energy consumption, and harm to environment restrict their applications. Biocement could be a new green building- material and energy-saving material. Biocement is a mixture of enzymes or microbial biomass with inorganic chemicals, which can be produced from cheap raw materials. Supply of biocementing solution to the porous soil or mixing of dry biocement with clayey soil initiate biocementation of soil due to specific enzymatic activity. Different microorganisms and enzymes can be used for production of biocement.
Development of microbial geotechnology in Singapore
(2011) Chu, Jian; Ivanov, Volodymyr M.; He, Jia; Li, Bing; Naemi, Maryam; Stabnikov, Victor
Both nature processes and laboratory studies have shown that microorganisms can be used to improve the engineering properties of soil. As such, it is possible to develop methods that utilize the microbial process to treat soil in a way similar to that of cement. When more knowledge is accumulated through research findings and technology development, a new branch of geotechnical engineering – the Microbial Geotechnology can be established. The Microbial Geotechnology can have the following three applications: (a) biocementation to increase the strength of soil, (b) bioclogging to reduce the permeability of soil, and (c) biogas to increase the liquefaction resistance of sandy soil. Some types of microorganisms or bioprocesses that may contribute to the biocementation, bioclogging or biogas effects are identified and discussed. Some experimental data are presented to show that the permeability of sand can be reduced by four orders of magnitude and the strength of sand can be increased to a substantial value after the soil has been treated using bacteria. However, the whole study still stays at the laboratory stage and much more efforts are required to turn this scientific idea into viable technologies
Formation of water-impermeable crust on sand surface using biocement
(2011) Stabnikov, Victor; Naemi, Maryam; Ivanov, Volodymyr M.; Chu, Jian
This paper examines the feasibility of using calcium-based biocement to form an impermeable crust on top of a sand layer. The biocement used was a mixture of calcium salt, urea, and bacterial suspension, which hydrolyzed urea with production of carbonate and an increase of the pH level. Applying 0.6 g of Ca per cm2 of sand surface, the permeability of the biocemented sand can be reduced from 10−4 m/s to 1.6•10−7 m/s (or 14 mm/day) due to formation of the crust on sand surface. The rupture modulus (maximum bending stress) of the crust was 35.9 MPa, which is comparable with that of limestone. The formation of a water-impermeable and high strength crust layer on sand surface could be useful for the construction of aquaculture ponds in sand, stabilization of the sand dunes, dust fixation in the desert areas, and sealing of the channels and reservoirs in sandy soil.
Iron-and calcium-based biogrouts for porous soils
(2012) Ivanov, Volodymyr M.; Chu, Jian; Stabnikov, Victor
Chemical grouts are often used to reduce the hydraulic conductivity of soil for seepage control purposes. However, chemical grouts can be expensive and environmentally unfriendly. Therefore, two new biogrouts or microbial-based grouting materials were developed.
Microbial method for construction of aquaculture pond in sand
(2013) Chu, Jian; Ivanov, Volodymyr M.; Stabnikov, Victor; Li, Bing
A method to construct an aquaculture pond in sand using microbial biocementation is presented in this paper. The microbially induced calcium carbonate precipitation process was used to form a low-permeability layer in sand for the construction of a water pond model in the laboratory. The test results indicated that the permeability of sand was reduced from the order of 10−4 m/s to 10−7 m/s when an average 2.1 kg of calcium (Ca) per m2 of sand surface was precipitated. The bending strengths of the walls and the base of the model pond were in the range of 90–256 kPa. The unconfined compressive strengths for the samples taken from the walls and the base of the pond were in the range of 215–932 kPa.
Microbially induced calcium carbonate precipitation on surface or in the bulk of soil
(2012) Chu, Jian; Stabnikov, Victor; Ivanov, Volodymyr M.
Microbial precipitation of calcium carbonate takes place in nature by different mechanisms. One of them is microbially induced carbonate precipitation (MICP), which is performed due to bacterial hydrolysis of urea in soil in the presence of calcium ions. The MICP process can be adopted to reduce the permeability and/or increase the shear strength of soil. In this paper, a study on the use of Bacillus sp., which was isolated from tropical beach sand, to perform MICP either on the surface or in the bulk of sand is presented. If the level of calcium salt solution was below the sand surface, MICP took place in the bulk of sand. On the other hand, if the level of calcium salt solution was above the sand surface, MICP was performed on the sand surface and formed a thin layer of crust of calcium carbonate. After six sequential batch treatments with suspension of urease-producing bacteria and solutions of urea and calcium salt, the permeability of sand was reduced to 14 mm/day (or 1.6×10−7 m/s) in both cases of bulk and surface MICP. Quantitiesof precipitated calcium after six treatments were 0.15 and 0.60 g of Ca per cm2 of treated sand surface for the cases of bulk or surface MICP, respectively. The stiffness of the MICP treated sand also increased considerably. The modulus of rupture of the thin layer of crust was 35.9 MPa which is comparable with limestone.