Experimental Studies And Microstructure Analysis Of Perlite Thermal Insulation Mortar Prepared By Microbial Mineralization

In this paper,the mineralization ability of microorganism KJ01 is combined with perlite material,and the cementitious calcium carbonate induced by microorganism is used to instead of the traditional cementing material which is used to consolidate perlite to produce "microbial thermal insulation mortar".In this paper,the effects of bacteria and nutrient liquid,additives and curing conditions on the properties of microbial thermal insulation mortar is studied by experiment.The microcosmic mechanism of calcium carbonate crystals and microbial thermal insulation mortar were analyzed by SEM and XRD.The main work of this paper is as follows:(1)As the cementitious material of microbial thermal insulation mortar is provided by microorganism,the bacteria and nutrients solution were studied first.Mainly through single factor experiment to investigate the bacteria solution concentration,the ratio of bacteria and nutrients solution,the urea concentration in the nutrient solution,the type of calcium source,calcium ion concentration,kinds of magnesium and magnesium ion concentration affect the performance of microbial thermal insulation mortar,and urea,calcium,magnesium in the nutrient solution was analyzed through orthogonal experiment.The results of single factor test showed that: The optimum urea concentration was 0.3mol/L.The optimal ratio of bacterial liquid to nutrient liquid is 1:1.Among the three calcium sources,calcium nitrate,calcium chloride and calcium acetate,calcium nitrate is the best calcium source.Magnesium chloride is the best additive among magnesium chloride,magnesium nitrate and magnesium acetate.The optimum concentration of magnesium chloride is 0.01mol/L.The results of orthogonal test of nutrient solution showed that,the influence degree of dry density and compressive strength was calcium nitrate > urea > magnesium chloride.In terms of thermal conductivity,the influence degree is urea >calcium nitrate > magnesium chloride.(2)On the basis of the bacterial concentration and mixture ratio of nutrient solution in preparation of microbial mortar,the expanded perlite,admixture and curing conditions were studied,and main investigation factors are:the expanded perlite aggregate,HPMC,emulsion powder,polypropylene fiber,liquid-solid ratio(bacteria and nutrient solution content),curing age,curing temperature,water repellent.The conclusion is as follows:The optimum content of expanded perlite insulation aggregate is 25%;The optimum dosage of HPMC is 0.4%.The optimum content of emulsion powder is 2%.The optimum liquid-solid ratio(mixing amount of bacterial liquid and nutrient liquid)is 2.0.The optimal curing age is 14d;The optimum curing temperature is 30℃;The optimum dosage of hydrophobic agent A is 2% and that of hydrophobic agent B is 30%(3)SEM and XRD were used to analyze the crystals of calcium carbonate and internal materials in the microbial thermal insulation mortar.SEM analysis is mainly to analyze the micro-structure of microbial insulation mortar internal material and calcium carbonate crystals at different urea concentrations,kinds of calcium sources,concentration of calcium ions and kinds of magnesium ions.The results showed that the concentration of urea would affect the degree of crystal condensation and surface morphology.The calcium source can affect the crystal shape,particle size and condensation state.The concentration of calcium ions can affect the crystal size and surface morphology.The lattice structure of expanded perlite is attached with calcium carbonate crystals which cement the fragments of perlite;At the same time,microbial spores in different positions of thermal mortar can be observed.Microorganisms in different positions of thermal mortar will mineralize different types of calcium carbonate crystals,which are pellet aragonite and calcite respectively.The calcium carbonate crystals attached to the perlite fragments are layered,suggesting that the microbe induced calcium carbonate production is a gradual deposition process.XRD analysis is mainly about the calcium carbonate crystals induced by microorganism and the internal materials of microbial thermal insulation mortar.The results show that the mineralization product of microorganisms is mainly calcite calcium carbonate.The wave peak of the whole material of microbial thermal insulation mortar is more,the reason is the composition such as expanded perlite and admixture,and the crystallization degree of calcium carbonate is lower.