微生物矿化沉积碳酸钙技术修复混凝土既有微裂缝研究进展

Research Progress of Microbial Mineralization and Deposition of Calcium Carbonate Technology for Repairing Existing Micro-cracks in Concrete:a Review

混凝土由于具有容易成型、价格低廉、抗压强度高等特点而被广泛应用。但由于混凝土具有各向异性特性,其在服役期间往往不可避免出现裂缝,导致混凝土结构出现渗水,严重时导致结构失效。为延长既有混凝土在实际工程应用中的服役寿命,近年来,研究人员探索利用一种微生物诱导碳酸钙沉积(Microbial-induced carbonate precipitation,MICP)技术进行既有混凝土微裂缝的修复。该技术绿色环保,生物碳酸钙与混凝土基体相容性好,而且修复液粘性低,易进入裂缝空间,修复物质在裂缝内分布更均匀,成为当下的研究热点。MICP技术在混凝土中的应用与碳酸钙矿化沉积机制和修复工艺存在密切关系。本文拟从微生物矿化诱导碳酸钙沉积机制、修复工艺两个方面总结微生物矿化沉积碳酸钙技术在混凝土既有微裂缝修复的研究进展。微生物矿化机制中脲酶催化作用沉积碳酸钙机制由于时间短、碳酸钙产量高,在许多领域中被广泛研究,但是副产物氨不容忽视,对此提出多种矿化机制相结合的方法。修复剂各组分的添加建议采取一步法或两步法中的“细菌、尿素+钙源”组合。而添加工艺方面,相比于浸泡法和喷洒法,注射法对混凝土既有裂缝修复适用性更强,在使用注射法时建议添加滞留剂或保湿剂延长修复剂在裂缝内的滞留时间。本文为进一步推动MICP技术在混凝土既有微裂缝修复中的实际应用进程提供参考。

Concrete is the most widely used construction material because of its easy-cast,low price and high compressive strength.However,due to its intrinsic heterogeneity and non-ideal working environment,concrete could not tolerate too much tension forces and hence is prone to crack during service,which is the start of concrete deterioration(such as water seepage)and concrete failure.In order to prolong the service life of existing concrete structures,global researchers have acquired positive progress in recent years in exploratively utilizing a new technology to repair micro-cracks in existing concrete,i.e.microbial-induced carbonate precipitation(MICP)technology.This technology is environmentally friendly and compatible with concrete matrix.The repairing agents used are of low viscosity and hence easy to penetrate into the deep part of the crack,which can result in a homogeneous healing inside crack space.The repairing efficiency is closely related to the bio-CaCO_(3) deposition mechanism and repair procedure.This review intends to summarize the research progress of MICP technology in the repair of existing concrete micro-cracks from the aspects of microbial-induced calcium carbonate deposition mechanism and repair procedure,both of which are of great significance in that applicative research topic.The biogenic CaCO_(3) precipitation based on bacterial urease catalyzed urea hydrolysis is one of the mostly studied processes owing to its high CaCO_(3) production and ease of control.But that process has an unignorable flaw-generation of ammonia as a by-pro-duct.So we suggest in the paper the combinational use of two or three mineralization mechanisms maybe a solution for that problem.With respect to the repair procedure,either a one-step or a two-step procedure can be used for MICP-based crack repair and the addition of healing components can be realized by the methods of immersion,spraying and injection.Among the three methods,the injection is most applicable in practice,and the use of a retention aid or a moisturizing agent can help to prolong the retention of the repairing agents inside cracks and consequently to obtain effective CaCO_(3) precipitation.This paper is expected to provide a prospect and reference for further promoting the practical application of MICP technology in the repair of existing micro-cracks in concrete under service.