Study On Mechanism And Multi-scale Performance Of Biomineralization For Repairing Fire Damage Of Concrete

With the rapid development of social economy and modernization construction,high-rise buildings are constantly emergingand the density of buildings is increasing,coupled with the application of flammable materials and the popularity of electrical products and gas utensils,so the building fireis getting more and more common.Concrete material is the most common used structures in the modern architecture.When exposed to high temperature suddenly due to fire accidents,the physical and mechanical properties of concrete material is probably to be weakened in a short period,and the concrete member or structure can be wholly cracked,deformed with its bearing capacity decreasing,which further affect the security and durability of the concrete construction.Therefore,a scientifically reasonable post-fire fix planis the key to ensuring the safe use of concrete structure.Macromolecule organic matter and cement-based materials in the traditional restore materialare not environment friendly due to the irpoor adhesion and durability,weak anti-aging properties,and contained objectionable constituents.Through the regulation of bio-organic macromolecules,biological mineralization repairing techniques generates inorganic minerals with the cementitious property that could consolidate materials,fill cracks and fix defects.At the same time,such inorganic mineralshas advantages of less environment pollution and project costand good compatibility with cement-based materials.It is innovative to use biological mineralization to improve concrete material damage repair technology.The study mainly does research on the fire damage mechanism and multi-scale performance of biological mineralization repairing concrete on the basis of fire damage repair of concrete,and explores the intersection between engineering materials and life science.The thesis could be summarized as follows:(1)The study of biological urease activityThe activity of urease catalytic hydrolysis of urea determines the efficiency of biological mineralization.In order to explore the Sporosarcina pasteurii(DSM33)and diversities of the soybean urease,and to promote the engineering application of soybean urease,the research,adopting the contrast test in the same condition and using urease activity of electrical conductivity characterization,focuses on main factors including urease concentration,nickel ions,pH,substrate concentration,concentration of cementing fluid and external environment conditionsand does the modified test on the conservation and thermal stability of urease activity.Experimental results prove that:The activity of urease can be increased by 4 times with the addition of 10μmol/L nickel ion.Urea or ammonia are necessary inducers for biourease synthesis of DNA chain,and the maximum concentration should not exceed 1.5 mol/L.When the pH value is 12,the microorganism can grow and maintain a certain activity,indicating that the microorganism has alkali resistance.In non-aseptic environment,the retention rate of urease activity was above 77%,showing strong engineering applicability.The soybean urease,with its easy extraction and good activity,can be as useful in the field of concrete material repair as DSM33 does.The characteristics of precipitation,flocculation and dispersion of soybean urease in pH 5～13 solution indicate that it has typical negative charge characteristics.(2)The study on properties and synthesis mechanism of biological mineralization calcium carbonateThe study of different factors on the crystal phase,particle size,mechanical properties of calcium carbonate and its regulation mechanism is the key problem of calcium carbonate as biomeralization repair material.he effects of 9 pH indicators、5 cementing fluid concentration gradient and 2 calcium salt addition sequence on the regulation of biological organic matter on calcium carbonate were studyed.The results show that: The yield of calcium carbonate is more than80% when the pH value is 7～9 and the concentration of cementing fluid is not higher than 1.5 mol/L.Add calcium first,pH value is not 7～9 physical and chemical conditions,priority mineralization calcite,content is more than 80% of the total mineral,the more adverse conditions for urease activity,calcite purity is higher,crystal morphology is different,crystal structure stacking and assembly degree is high,particle size distribution range is wide,good adhesion properties;On the contrary,the product is spheraragonite with single morphology,uniform particle size and low adhesion.The experimental results are consistent with those of phase transition theory and crystal system theory,revealing that low ion activity product is the mechanism of calcite precipitation.The results of SEM,EDS and Gram staining showed that both the microbe cell wall and soybean urease had negative charge,which was the key for the nucleation site to participate in the mineralization reaction.(3)The study on the mechanism of biological mineralization to repair concrete damage by high temperaturesAppropriate physical and chemical conditions are the key to improve the effect of bioremediation on concrete fire damage.Through the study of the physical and chemical conditions of biological mineralization and the characteristics of concrete fire damage,the adaptation mechanism between the two was discussed.The results show that: Temperature at 300℃ and above,concrete surface crack width is greater than 60μm,the most pore size is greater than 3.6μm,average pore size is more than 10μm,micropore(> 1μm)accounted for more than 25.4%,pore connectivity is strong,apparent crack in the form of V-shaped extension and concrete internal damage connected as a whole,and the internal pH value is lower than 13.This particular damage pattern provides a pathway for oxygen and repair fluids needed for biological mineralization;The size of fracture and pore damage meets the minimum space required by biological mineralization and is consistent with the size distribution of calcium carbonate.The reduction of pH value of concrete at high temperature ensured urease activity and delayed the adverse effects on biological survival.(4)The study on multi-scale performance and internal relationship of biomineralization in repairingconcrete damage by high temperatureThe study of multi-scale performance of biomineralized concrete for fire damage repair is the key to reveal the biomineralized repair mechanism and establish the theory and evaluation method.Through C60 concrete fire simulation test and bioremediation effect evaluation,the results show that:Concrete is affected by 300℃～700℃ fire action,strength and durability index decreased,microscopic pore structure deterioration,material conductivity enhancement,500 ℃ is the starting point of concrete damage serious temperature.After the bioremediation,the apparent cracks are covered effectively.The water absorption of the damaged specimen at 300℃～600℃ can be repaired to the state at room temperature.The chloride ion migration coefficient decreased by 60.6%,and the chloride ion penetration resistance of specimens under 500 ℃ recovered to grade ⅲ or above.The strength of concrete is up to 42% higher than the reference temperature.Biomineralization is more suitable for repairing moderate and mild damage of concrete at 300℃～500℃.The results show that the porosity of concrete is reduced by more than12.9% and the multi-damage pore is reduced by more than 40%,and the pore structure characteristics are effectively repaired and optimized.The decrease of the concentration of conductive ions in concrete pore solution and the reduction of the mass transfer conductivity of the material indicate that the conductive path and connectivity of the pores in concrete are reduced.Multi-scale performance parameter tests reveals that the mechanismof biological mineralization repairto high temperature concrete damage works on cementation of deposits into acontinuous-densewhole,seals the damaged location and enhance the compactness of damaged concrete specimens.