捕捉侵蚀性介质的自修复水泥基材料制备技术及作用机理

Cracks reduce the durability of reinforced concrete structures. Self-healing of cracks is an intelligent method that can make cracks inaccessible for man-made repair healed automatically. However, it is still difficult for self-healing methods available now to heal cracks completely with a width larger than 300 µm. In this case, aggressive agents can still penetrate into the matrix and reach reinforcement steel bars through the void spaces between self-healing reaction products. This restricts significantly the effect of self-healing on the improvement of concrete durability. In this proposed project, a novel self-healing cementitious material with functions of capturing aggressive agents will be developed. Once the aggressive agents penetrate into cracks, they will be captured and chemically bound in reaction products of self-healing. As a result, the durability of concrete will be improved significantly. To develop this novel self-healing material, self-healing agents will be design based on the expected minerals that can chemically bind aggressive agents. Then the self-healing agents will be coated as “self-healing aggregates” for mixing into concrete. The kinetics of chemical reactions of self-healing agents and capture of aggressive agents will be investigated. Transmission of reaction products during the capture of aggressive agents will be studied. A coupled transport-reaction model will be developed for simulating the process of self-healing and the capture of aggressive agents. Based on these investigations, the key theory and technology will be proposed for producing the novel self-healing cementitious materials with functions of capturing aggressive agents.

裂缝是导致混凝土结构耐久性下降的重要因素。与传统人工修补技术相比，自修复技术具有智能化的优点，使难以触及的裂缝得以修复。但目前的自修复技术仍难以使宽300微米以上的裂缝完全闭合，侵蚀性介质仍能通过自修复产物间的缝隙到达钢筋表面并入侵基体内部，严重制约了自修复提高材料耐久性的作用。本项目提出具有捕捉侵蚀性介质能力的自修复体系，使其在智能修复裂缝的同时捕捉和固化侵蚀性介质，构建针对侵蚀性介质的双重防御体系，有效提高材料耐久性。课题从预期形成的对侵蚀性介质具固化作用的难溶沉淀物出发，根据化学反应热力学原理逆向设计自修复用活性组分，对其封装以制备成与水泥基材料相容的“自修复骨料”；通过研究侵蚀性介质的传输及其与自修复体系的相互作用、自修复沉淀物的矿相演变，揭示自修复体系捕捉侵蚀性介质和修复裂缝的机理，建立“离子传输-化学反应与沉积”耦合模型以预测该自修复过程，提出新型自修复体系制备关键技术与理论。

针对海洋侵蚀性离子在水泥基材料开裂后可迅速进入裂缝内部，严重制约裂缝自修复对材料耐久性的提高作用，本项目深入研究了在海洋离子和干湿循环作用下水泥基材料裂缝自愈合产物的矿物组成及演变，定量分析自愈合率的经时特点，从而探明了海洋环境下水泥基材料裂缝自愈合机理，揭示了海洋离子和干湿循环对水泥基材料裂缝自愈合的影响规律；在此基础上，首次提出了具有捕捉海洋侵蚀性离子并催化自修复反应作用的自修复复合组分，实现了裂缝快速自修复从而阻隔侵蚀性离子的进一步入侵，并捕捉固化已入侵的海洋离子从而消除其对材料的腐蚀作用，以此实现了对外部侵蚀性离子的双重防御作用。具体研究成果和突破如下：.（1）针对海洋多离子和干湿循环对水泥基材料裂缝自愈合的影响，发现了海水中的Mg2+对裂缝自愈合有明显的促进作用，从裂缝口向内形成大量以Mg(OH)2为主的自愈合产物。在干湿循环条件下，裂缝吸收海水及海水从裂缝中蒸发的过程与Mg2+共同促进了自愈合产物的沉积与生长，促使裂缝愈合率进一步提高。.（2）发现内掺于水泥基材料的三乙醇胺可迅速提高裂缝溶液碱度，OH-离子增多，与海水中高浓度Mg2+离子共同作用，从而使得Mg(OH)2在裂缝口局部位置首先达到饱和状态并快速析出沉淀。在含1.5%（水泥质量比）三乙醇胺的水泥净浆中初始宽度为400 μm的裂缝在海水下浸泡2天即可完全修复。在同等条件下，文献中的自修复技术使初始宽度为400 μm的裂缝完全修复一般需要28天以上。.（3）首次提出了具有捕捉海洋侵蚀性离子并催化自修复反应作用的自修复复合组分，为裂缝溶液迅速提供大量Ca2+、OH-和Al3+，有效地将进入裂缝的侵蚀性离子Cl-、SO42-和Mg2+化学固化于Friedel盐、Kuzel盐、水滑石、水镁石等自修复产物中，并使初始宽度为400 μm的裂缝在海水浸泡3天后愈合率可达90%、7天后愈合率可达100%，从而消除已入侵离子对材料侵蚀的同时快速阻隔有害离子的进一步入侵。通过此研究，阐明了自修复复合组分固化海洋侵蚀性离子与离子在裂缝中扩散的交互作用机理。