Study On Microscopic Mechanical Properties Of Mineralized Materials Induced By Sand-based Microorganisms

A good ecological environment is an important precondition for sustainable development.However,a series of environmental problems have resulted from the rapid development of society and the economy,one of which concerned the soil problem.Thus,microbial-induced mineralization is proposed serving as an environmentally friend soil improvement technology.And systematically deep material mechanical characteristic research on microbial-induced mineralized soil seems of significant meaning.This study is extensively conducted in following fields,including the control and optimization of microbial induced calcium carbonate mineralization process,the microscopic mechanism on the formation of mechanical strength for soil materials based on microbial induced calcium carbonate mineralization,and the reliability analysis of cemented sand materials based on microbial induced mineralization technology.The main research contents and results are summarized as follows:1 ? The experiment condition is optimized based on the effective control on biochemical reaction with sporosarcina pasteurii being culture;The sensitivities of contributing factors were analyzed,with the effective production rate of induced calcium carbonate being targets to design orthogonal experiments;Exploring the material characters of induced mineral under the temperature of 10 degrees to 60.The results indicate:(1)Low concentration of nutrient and low inoculation quantity of bacterial fluid equipped higher calcium carbonate reaction rate could propel the process of calcium carbonate deposition more quickly compared to higher ones.(2)Environment temperature has great influence on morphology,phase,crystal texture,crystal particle size and surface energy.(3)The results from range analysis and variance analysis suggest that the importance order of effect factors is bacterial fluid inoculation quantity > mineralization time >nutrient concentration.The optimal combined scheme is determined as: the environment temperature of 20 degrees to 30,bacterial fluid inoculation quantity 1%,nutrient concentration 50%,mineralization time 24 hours.2?Nano-hardness of 1 to 6 days and abrasion characteristics of microbial-induced mineralization materials are measured on the condition of 30 degree Celsius.The results indicate:(1)The valid data points from Nanoindentation test increased with time.However,the maximum modulus obtained are different from them,which would fluctuate within a range of 35 to 65 GPa.(2)A calcium carbonate was induced producted,whose friction coefficients after 5minutes reciprocating grinding under 20 N load maintain stable.And the friction coefficient is 0.3.3 ? The effect of physical parameter and mineralization time on unconfined compressive strength of microbial-induced mineralize sand column,correlation mechanism,and formation mechanism of strength are analyzed by test the compressive strength of microbial-induced mineralize sand column prepared.The results indicate:(1)At the initial stage of reaction,the strength increased rapidly,and then was tended towards stable when the unconfined compressive strength reched 2.38 MPa.(2)The generation rate of maximum calcium carbonate could reached 24.07%,when the mass of induced generated calcium carbonate increased gradually with mineralization reaction time.(3)The porosity of microorganism cemented sand material decreased significantly,and the minimum porosity of sample filled could reached 14.11%.(4)The unconfined compressive strength has a linear relationship with porosity and generated ratio of calcium carbonate,respectively.(5)There are matrix soil are microbially mineralized in three partical sizes.The calcium carbonate located at the contact of coarse sand particles could reinforce bite force.The calcium carbonate located at the surface deposition of medium sand particles could reinforce surface roughness.The calcium carbonate staying in fined sand could fill porosities to make material denser,which improves the strength of microorganism cemented sand materials.4?The PFC three-dimension numeric model of microbial-induced mineralized sand column was constructed to simulate its destruction process under real triaxial compressive load by assignment from experiment results,with matrix soil particle morphology grain composition,particle morphology,content ratio of calcium carbonate,distribution character of porosity,contact among particles being considered.The numeric simulation results coincided with in-door experiment ones well.5 ? For the uncertainties existing during the microbial-induced mineralized cementation sand,a uncertainty analysis of sand column example under triaxial compression is performed.Through above examples,a PCE surrogate model is constructed on the basis of PFC numeric simulation results to perform reliability of obtained sand column,with particle size and sand column porosity being effective impact factors.