| Concrete fire damage repair is the key to ensuring the safety and durability of concrete structures.The use of microbial induced carbonate deposition(MICP)technology,that is,the research on the restoration of cement substrates by microbial mineralization deposition,has become a research hotspot in repairing and improving the safety and durability of civil infrastructure in recent years.However,the culture process of bacteria is more complicated,and its activity is greatly affected by environmental factors.On this basis,the plant enzyme-induced deposition of carbonate(EICP)technology has been further developed.Compared with bacteria,plant enzymes are more economical,green and environmentally friendly,and at the same time the extraction is more convenient.Therefore,in-depth study of the influencing factors and repair effects of plant urease-induced deposition of calcium carbonate to repair concrete fire damage has important engineering application value and socio-economic significance for the development of EICP technology and concrete fire damage repair.Based on the key research and development project of Shanxi Province(201903D321113),this article takes soybean urease and high-temperature damaged concrete as the research object.By changing the solid-to-liquid ratio,temperature and p H value of the soybean powder solution,the activity of soybean urease extracted from the soybean solution is affected by the environment.Changes in the influence of factors;by changing the ratio of urea to calcium acetate in the cementing solution,the ratio of enzyme solution to cementing solution,the temperature and p H of the soybean urease-urea-calcium acetate mixed solution,to study the influencing factors of soybean urease calcium production rate;At the same time,ultrasonic detection technology,infrared thermal imaging technology,XRD and scanning electron microscope are used to conduct multi-scale evaluation of the repair effect of high temperature damaged concrete under different repair conditions,to explore the most suitable repair conditions,and to repair high temperature damage of concrete by soybean urease-induced deposition of calcium carbonate Provide test and theoretical reference.The main research contents are as follows:1.Experimental study on soybean urease extraction and its activity influencing factors.Configure 1:5,1:10,1:15,1:20,1:25,1:30,1:40,1:50,1:100 soy flour solutions with different solid-to-liquid ratios,after standing to room temperature The activity of soybean urease extracted from the soy flour solution was measured by the conductivity method;the temperature and p H value of the solution were controlled by a constant temperature water bath and Na OH and HCI solutions respectively,and the urease activity was obtained by measuring the change in conductivity of the solution.The results show that as the concentration of the soybean powder solution increases,the soybean urease activity and the ability to hydrolyze urea extracted from the soybean powder solution also increase and strengthen,and the unit mass concentration of soybean urease activity is less than 67g/L in the soybean powder solution.Soybean urease activity decreased gradually after 67g/L;the soybean urease activity extracted from the soybean powder solution basically showed a linear growth pattern with the increase of the temperature of the solution;when the p H value of the soybean powder solution was 7,the soybean urease activity was extracted from it.Soybean urease activity is the largest.2.Experimental study on the factors affecting the calcium production rate of soybean urease.Design 1:0.75,1:1,1:1.25,1:1.5,the ratio of urea to calcium acetate in the four cementing liquids,0.025,0.05,0.1,0.15,0.2,0.25,0.3,0.5 eight enzyme solutions are mixed Proportion,the temperature of the six mixed solutions at 15℃,25℃,35℃,45℃,55℃,and65℃ and the p H values of the six mixed solutions 6.0,7.0,7.5,8.0,8.5,9.0,by measuring the soybean urease-In the urea-calcium acetate mixed solution,the change in conductivity,the concentration of ammonium ion,the concentration of calcium ion and the actual production of calcium carbonate were studied to study the influence of different environmental conditions on the calcium production rate of soybean urease.The results show that: when the concentration of calcium acetate in the cementing liquid is constant,increasing the concentration of urea will increase the actual amount of calcium carbonate produced.At the same time,when the concentration of calcium acetate in the cementing liquid is 1mol/L,the actual amount of calcium carbonate produced is the largest;With the increase of the volume of soybean urease enzyme solution,the actual amount of calcium carbonate produced shows an upward trend.When the volume ratio of enzyme solution to cementing solution is 1:1,the actual amount of calcium carbonate produced is the largest.The utilization rate of soybean urease decreases as the utilization rate of calcium ions in the solution increases.When the enzyme-to-gel ratio is1:1,the utilization rate of soybean urease reaches the limit;when the temperature of the soybean urease-urea-calcium acetate mixed solution increases,the calcium carbonate The actual production of calcium carbonate also increases,and the actual production of calcium carbonate is relatively large at 45-65℃;the mixed solution of soybean urease-urea-calcium acetate is more conducive to the deposition of calcium carbonate in an alkaline environment.3.Experimental study on soybean urease repairing concrete high temperature damage.Prepare concrete test blocks with two sizes of 100mm×100mm×100mm and50mm×50mm×50mm and place them in the curing room for 28 days and then take them out;set five temperatures of 200℃,300℃,400℃,500℃ and 600℃ for high temperature Test;repair methods are immersion method repair and vacuum method repair,by measuring the thickness of the surface coating,water absorption,ultrasonic velocity,infrared temperature rise and compressive strength of the specimen after repair.The effect of repairing high-temperature damaged concrete with soybean urease was carried out experimentally.The results show that the thickness of the coating on the surface of the specimen after the high temperature damaged concrete is repaired by soybean urease is less affected by the repair method,and the thickness of the coating is the largest when the repair time is 48 h and the cement concentration is 1mol/L;the negative pressure is 0.095 After 48 hours of repairing by MPa vacuum method,the water absorption rate of the concrete specimens damaged by high temperature is the lowest,and the ultrasonic speed of the specimens is restored the most compared with that before repairing,and the repairing effect is better;through infrared thermal image analysis,it can be known that after soybean urease repair,The average infrared temperature rise on the surface of the concrete damaged by high temperature is greatly reduced compared with that before the repair,but different repair methods and cement concentration have little effect on the average infrared temperature rise of the surface of the specimen after the repair;soybean urease deposits calcium carbonate to repair the high temperature damage of the concrete The effect of restoring the compressive strength of concrete specimens is very limited,and it is only slightly improved when the fire temperature is after 400℃ compared with before repairing.4.Microscopic study of soybean urease repairing high temperature damage of concrete.Microscopic tests such as XRD and SEM were performed on the chemical composition of the white precipitate generated by the soy urease repairing the concrete damaged by high temperature and the bonding between the product and the damaged concrete under the immersion method and the vacuum method.The results show that the use of soybean urease to repair the high temperature damage of the concrete The large amount of white precipitate generated is calcium carbonate,and its crystal type is calcite;scanning electron microscope observation of the samples under different repair methods shows that the calcium carbonate generated after the vacuum repair method can continuously cover the high temperature damage defects of the specimen,and the concentration of the cementing liquid When it is 1mol/L,calcium carbonate crystal particles are more closely connected and have better continuity. |
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