Research On Concrete Crack Healing And Performance Compensation Under Microorganism Action

Due to its high strength,good durability,cheap and easy to use,cement concrete has become the most used building material at present.However,because of its own material properties and poor construction technology,it produces a large number of cracks during service.This paper based on Sporosarcina pasteurii and the mechanism of calcium carbonate deposition by bacteria mineralization repair the cracked concrete specimens,evaluate the repair effect and improve the durability of the specimens.In this paper,two kinds of repairing methods,injection method and bacterial liquid soaking,are used to repair the cracks of concrete.The healing degree of the cracks on the repaired concrete specimens after repair is observed.Then the repaired cracks in different depth ranges of the concrete is observed by industrial CT in order to evaluate its repairing effect.The fractured specimens were tested for flexural strength to evaluate the cementation ability of microbial deposited calcium carbonate crystals.In view of durability,the tests of anti-penetration of chlorine ion,single surface water absorption of cracks,evaluation of frost resistance and ultrasonic detection are carried out respectively to reflect the durability of the repaired specimens.Research results show that mixing the bacteria liquid and urea solution,let stand for 2 h after then inject its mixture and calcium nitrate solution into concrete cracks,after then concrete specimen which were maintained under standard curing conditions has the best repair effects,12 times liquid injection can be completely closed fracture surface,and its electric flux is 38.5% lower than the fracture specimen which repair rate is 87.5%,the repair effect is remarkable.the CT scan shows that the repair depth is about 15 mm,and the microbiological repair can improve the frost resistance of the fractured specimen,which can bear 40 more times of freeze-thaw cycle before the freeze-thaw damage.After microorganism repair specimen of the recovery of flexural strength to a certain extent,but the effect is not stable with large discreteness,effect is one of the most obvious for CU90 which the maximum flexural strength is 1.84 Mpa,about 23.6% of the whole specimen.The quality water absorption rate of the unrepaired crack specimens was 1.17%,and that of the BU90 group with the best repair effect was reduced to 0.99%.The repairing effect of predoped substrate was slightly better than that of BU90 in terms of quality water absorption.The repairing effect of predoped substrates is almost the same as that of injection group,and some indexes are even better,which proves that bacteria can absorb preembedded substrates in concrete and have good mineralization ability.The study proves that the microorganism repair concrete crack has a certain effect,can better closed fracture surface,and the flexural strength and durability of the specimen fracture has good effect.