脲酶诱导碳酸钙沉积原位修复再生骨料缺陷及其机理研究

The recycling of construction and demolition waste is an important strategy to solve the current serious problems of natural resource shortage and environmental pollution in the field of civil engineering. One of the most often used applications is used as recycled aggregate (RA) for new concrete casting. However, due to the fact that the recycled aggregate contains a large number of harmful pores and micro-cracks (>100nm), the performance of the recycled aggregate concrete (RAC) is extremely deteriorated, which greatly limits the reuse of the recycled aggregate. The current defects repairing techniques of recycled aggregate have limitations in the repair of the nano-micro flaws (100nm<d<1000nm) in the attached mortar and the original stones. Based on the size characteristics of the pores and micro-cracks in the recycled aggregate, the proposal applies a nano-scale urease enzyme to penetrate deeply into the flaws of different sizes, and to induce the precipitation of biogenic CaCO3 to repair the flaws in-situ, aiming at strengthening the whole matrix of the recycled aggregate. The research will be firstly focused on the relationship among urease activity, CaCO3 deposition kinetics and mechanical properties of CaCO3, to obtain the strongest CaCO3 under an optimized urease activity. Furthermore, the influence of precipitation rate, polymorph, and morphology of CaCO3 on the mechanical properties (hardness and adhesion) will be investigated in detail. Meanwhile, the interaction between enzyme molecules and CaCO3 particles will be disclosed. And therefore, the reason why bio-genic CaCO3 has adjustable strength and adhesion force can be interpreted. The interaction between urease and the defect surface will be illuminated based on the adsorption characteristics of urease on the defect surface and some testing results. By the consideration of the generation mechanism of biogenic CaCO3 adhesion force, the adsorption mechanism of urease on the flaw surface, and the transportation behavior of the substrate and calcium source under different urease activities, the mechanism of urease enzyme induced CaCO3 precipitation (EICP) for defects in-situ repair in recycled aggregate will be clarified. The efficiency of applying EICP technique for strengthening recycled aggregate will be demonstrated in this research, which provides both theoretical and practical foundation for the sustainable development of civil engineering.

废弃混凝土资源化是解决土建行业资源短缺和环境污染双重难题的重要途径。因再生骨料含大量有害裂隙（>100nm），导致再生骨料混凝土性能劣化，限制了再生骨料的再利用。现有的强化技术对再生骨料附着砂浆和石子的纳微裂隙（100nm<d<1000nm）的修复存在局限性。本项目从裂隙尺度特征出发，提出利用纳米尺度脲酶渗入深层裂隙并原位诱导碳酸钙沉积修复裂隙，主要研究脲酶活性-碳酸钙沉积动力学-碳酸钙力学性能的关联，分析碳酸钙沉积速率、晶型、颗粒尺寸等对其粘结性能的影响，明晰酶分子与碳酸钙颗粒的相互作用以及生物碳酸钙产生强度和粘结力的机理；采用测试手段并结合脲酶在裂隙内吸附特征，探明脲酶与裂隙面之间的相互作用；结合生物碳酸钙具有粘结力的机理、脲酶于裂隙内的吸附机理以及底物和钙源在不同脲酶活性下的传输特征，厘定脲酶诱导生物碳酸钙原位修复裂隙的机制，强化再生骨料，为推进废弃混凝土资源化奠定理论和实践基础。

项目主要针对目前废弃混凝土骨料资源化过程中，现有强化技术对再生骨料所含纳微裂隙修复存在的局限性问题，研究利用脲酶诱导生物碳酸钙沉积技术（Enzyme Induced Carbonate Precipitation，简称EICP）原位修复再生骨料缺陷的新方法，通过纳米尺度的游离脲酶分子渗入深层裂隙并诱导碳酸钙原位沉积，既而实现纳微缺陷的修复，提高再生骨料的性能。本项目从资源化实际需求出发，首先遴选来源广泛兼具经济性的产脲酶细菌作为脲酶来源，优化脲酶制备工艺，明晰制备工艺参数及环境因素对脲酶活性的影响规律，制备出性能稳定、活性可调控的脲酶制剂；通过研究单一溶液环境下脲酶诱导碳酸钙沉积过程基本特性及动力学，探明了脲酶活性以及其他影响因子对酶促反应速率的影响规律；研究对应于不同酶活和酶促反应速率下的生物碳酸钙的沉积速率以及物理力学性能，建立了脲酶活性-沉积动力学-生物碳酸钙性能的定性和定量关联，确定了溶液环境中脲酶诱导碳酸钙沉积动力学及其生物碳酸钙形成的最优条件。基于骨料裂隙环境对脲酶活性的抑制，提出相应的脲酶活性稳定技术；创新研发了海藻酸钠固载协同生物碳酸钙强化机制，解决了生物碳酸钙在骨料表面沉积不均的难题；从加入添加剂和优化处理工艺两种途径对传统浸泡法强化再生骨料基础上进行优化，揭示了不同处理工艺强化再生骨料的机制，探索了生物碳酸钙强化再生骨料沉积的稳定性，并利用生物强化后的再生骨料制备出力学和耐久性能均显著提升的再生混凝土。研究成果将为建筑固废强化处理提供一种新的技术途径，并有利于进一步促进其资源化利用。