Experimental Study And Mechanism Analysis Of Microbial Mineralization In Repairing High-Temperature Concrete Damage

High-temperature damage of concrete manifests as defects such as looseness,peeling,and cracks macroscopically,and most of them are visible.This allows microorganisms,oxygen and repair fluids to enter the interior of concrete through the surface cracks.Utilizing the mineralization of microorganisms to mineralize and deposit in the surface and internal cracks of concrete,thereby achieving the repair effects.However,there are still some problems while applying microbial mineralization in repairing high-temperature concrete damage.The environment of high-temperature damaged concrete is alkaline,it is necessary to select a type of alkaline-resistant microorganism.It is necessary to optimize and regulate the mineralized products to match the cracks of high-temperature damaged concrete.It is also necessary to select a suitable type of admixtures to immobilize microorganism.Another problem that urgently needs to be solved is how to fill the mineralized products deeply and extensively in the concrete cracks.In addition,the multi-scale characteristics are also hot issues in the research of high-temperature concrete damage repair.The study and resolution of these problems have important theoretical and practical significance for the use of microbial mineralization in repairing high-temperature concrete damage.Each important aspect of microbial mineralization was gradually studied in this dissertation,including urease-producing bacteria,calcium source,admixture,repair technique,and multi-scale characteristics.Through the cultivation optimization and breeding of Sporosarcina Pasteurii,the selection of calcium sources and the optimization and regulation of mineralization conditions,the selection of admixtures and the optimization and regulation of repair system compatibility ratio,the optimization of repair techniques,and the multi-scale characteristics research and mechanism analysis of high-temperature concrete damage repair,the system of theories and techniques to repair high-temperature concrete damage can be established The main research contents of this dissertation are as follows:（1）Cultivation optimization and breeding of Sporosarcina PasteuriiBased on the characteristics of high-temperature concrete damage,Sporosarcina Pasteurii was selected as the urease producing bacteria.By changing the physicochemical conditions in the cultivation process,the influence of nutrient substances,cultivation conditions and inoculation conditions on the growth and urease activity of Sporosarcina Pasteurii were studied,the high-urease-activity and alkali-resistant strain of Sporosarcina Pasteurii that match the environment of high-temperature concrete damage was breed.The results showed that,OD₆₀₀and urease activity increased rapidly and then decreased slowly over time.The appropriate physicochemical conditions for Sporosarcina Pasteurii were:the Merck 105458+20g/L urea culture medium,temperature of 30℃,initial p H value of 8.0～8.5,rotational speed of 150r/min,inoculation amount of 2%and inoculation age of 24h.Temperature and rotational speed were the primary influencing factors of OD₆₀₀ and urease activity.The high-urease-avtivity and alkali-resistant strain of Sporosarcina Pasteurii could tolerate an initial p H value of 12.0,the OD₆₀₀ increased by 1.36%and the urease activity increased by 61.62%compared to the seed bacteria.（2）The selection of calcium source and the optimization and regulation of mineralization conditionsBased on the theories of phase transformation and crystal system,by changing the mineralization conditions,the influence of calcium source types,calcium source addition methods and mineralization conditions on mineralized products and mineralization efficiency were studied to determine the appropriate calcium source,calcium source addition method and mineralization condition.The crystals that matched the cracks of high-temperature concrete damage were obtained.The results showed that the mineralized products were calcium carbonate,mixed crystals of aragonite and calcite,and most of them were spheres.Under all calcium source types and calcium source addition methods,the mineralized products were calcium carbonate.The mineralized products of calcium nitrate and calcium chloride tended to be calcite.The mineralized products of the post-calcium source group were calcite,while that of the pre-calcium source group tended to be aragonite.The shapes of calcite varied,while aragonite often presented as spherical aggregates.Calcium acetate was the appropriate calcium source,and pre-calcium source was the appropriate calcium source addition method.The appropriate conditions of calcium carbonate mineralization were:mineralization temperature of 30℃,initial p H value of 10.0,bacterial concentration OD₆₀₀ of 1.0 and repair fluid concentration of 0.5mol/L.Repair fluid concentration and mineralization temperature were the primary influencing factors of calcium carbonate mineralization efficiency.Mineralized products could enter various widths of the surface and interior concrete cracks.（3）The selection of admixture and the optimization and regulation of repair system compatibility ratioBased on the volcanic ash effect and micro aggregate effect of minerals,fly ash,mineral powder,silica fume,zeolite powder and metakaolin were selected as admixtures.The interaction law between admixture,Sporosarcina Pasteurii,repair fluid and concrete high-temperature damage system were studied to determine the appropriate admixture and compatibility ratio of repair system.The results showed that all admixtures could enter the surface cracks of concrete,metakaolin and silica fume could enter the interior concrete cracks of various widths.The suitable compatibility ratio of repair system were:initial bacterial load OD₆₀₀ of 0.5 and solid-liquid ratio of 0.6.The initial bacterial load was the primary influencing factor of the repair system’s mineralization efficiency,and the solid-liquid ratio was the primary influencing factor of the compressive strength of the cured specimen.（4）Optimization of repair techniqueBased on the two perspectives of surface repair and internal repair,by measuring the compressive strength,water absorption rate and chloride ion permeability of concrete,combined with material analysis,phase analysis and morphology analysis,the repair effects of different repair techniques were evaluated.The appropriate repair techniques were determined.The results showed that both surface repair techniques could effectively reduce the water absorption rate and chloride ion migration coefficient of concrete.Spraying method was slightly better than brushing method,the higher the damage temperature,the more obvious the repair effect.The white sediments on the upper surface of the repaired specimen had obvious stratification phenomenon.Both layers of the sediments were calcium carbonate,the upper layer were aragonite crystals while the bottom layer were calcite crystals.Both internal repair techniques could restore the compressive strength of the concrete specimens,negative pressure method was better than immersion method,the higher the damage temperature,the more obvious the repair effect.（5）Multi-scale characteristics study and mechanism analysis of microbial mineralization in repairing high-temperature concrete damageThrough macro,meso and micro multi-scale parameters,the repair effect was evaluated,and the mechanism of microbial mineralization in repairing the high-temperature concrete damage was analyzed.The results showed that the film thickness increased with the repair time,the film thickness increased rapidly before 48h and then slowed down after 48h.Surface repair had a certain effect on the rise of mechanical properties when the damage temperature was high,internal repair had a certain effect on the reduction of water absorption rate and the rise of chloride ion penetration resistance,the higher the damage temperature,the more obvious the repair effect.The crystals on the surface of the specimen were mainly spheres with small spacing,which adhere evenly to the cement stone.At each damage temperature,the number and porosity of pores in the repaired concrete specimen decreased,most of the pores were compacted.After exposure to high-temperatures,the number of pores in various widths increased,and after repair,most of the pores were compacted.The synergetic repair effect of microbial mineralization,admixture pozzolanic effect and micro aggregate effect had obvious repair effect on the more distributed pores in concrete caused by high-temperature.After repair,the area of pores in various widths decreased,the repaired pores showed a trend of dwindlement.The decrease of indentation hardness and modulus of concrete mainly occurred in the interfacial transition zone.After repair,the average indentation hardness of the interfacial transition zone recovered by 229.5%,and the average indentation modulus recovered by 210.25%.