| Microbially induced calcium carbonate deposition（MICP）technology gives cementitious materials the function of ’self-diagnosis+self-healing’ of cracks,making it a hot topic of research in the field of cementitious materials,which has great potential for ensuring the durability of cementitious materials.At present,research on the effectiveness of microbial self-repair of cracks in cementitious materials has focused on crack width,area repair rate and percolation characteristics in static water environments,while little research has been reported on the effectiveness of crack repair in dynamic water environments.However,water often appears in a flowing state when concrete cracks appear in underground structures and hydraulic structures.Based on this,and considering the actual service environment of concrete,this paper investigates the effect of fiber type and admixture amount and different water flow rates on the self-healing effect of fiber-reinforced cement mortar cracks,using chloride ion permeability,crack healing rate,average repair width,compressive strength loss rate,flexural strength loss rate and capillary water absorption as indicators,and combining SEM and XRD microscopic testing methods.The main research contents and findings include the following aspects:（1）Study of the effect of fiber type and fiber content on the effectiveness of crack repair.The study showed that basalt fibers were superior to glass,polypropylene and polyvinyl alcohol fibers,with 100%crack repair at 7d for mortar specimens doped with basalt fibers at 0.71mm.The mineralization adhesion rate was increased by 17.2%,9.6%and 9.3%respectively compared to the other three fibers.At a fiber content（volume fraction）of 0.1%,mortar specimens with a healing time of 28d had a 1mm increase in penetration depth and a 0.0103 decrease in chloride binding value compared to specimens before cracking,which was better than specimens with fiber contents of 0,0.05%,0.15%and 0.2%.The initial and secondary capillary water absorption rates of uncracked specimens were 1.2133 ×10-5 and 4.69517 ×10-6,respectively,at 0.1%fiber dosage,while the initial and secondary capillary water absorption rates of specimens repaired for 28 d after cracking were 2.02514 ×10-5 and 6.02901 ×10-6,respectively,an increase of 0.67 times and 0.28 times respectively.（2）Study on the effect of different repair water environments on the effectiveness of crack repair.Based on the above study,the crack healing effect under static and dynamic water environment was further investigated.The healing effect of cracks in static water environment is related to the liquid level,when the liquid level is 1cm,the repair rate of cracks with a crack width below 0.8mm is 100%,and the maximum repair width of cracks at a liquid level of 9cm is 0.68mm.In a dynamic water environment,the maximum width of crack repair was 0.63mm,0.31mm and 0.32mm when the water flow was 0ml/h,10ml/h and 20ml/h respectively,and all cracks could not be repaired when the water flow was ≥30ml/h.Water flow is an important factor preventing sedimentation from occurring（3）Study of the mechanical properties of microbial self-healing cement mortars.The rate of recovery of strength properties increases over time for specimens containing bacteria,and the rate of recovery of compressive strength can increase to 100%after 28 days of repair,which is better than that of specimens without bacteria.This indicates that not only can cracks be repaired using mineralization,but their compressive properties can also be restored to their initial values up to 28 days after repair in cases where internal damage is produced,and that the use of the MICP technique to repair internal damage is an effective means of doing so. |
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