Dual-functional graphene-modified fibre reinforced cementitious matrix (FRCM) for simultaneous corrosion protection and structural strengthening

钢筋混凝土（RC）结构是每个国家基础设施的支柱，其预埋钢筋的腐蚀是一个主要问题。据估计，与钢筋混凝土结构腐蚀有关的干预措施约占全球建筑部门所有工作总量的35%。钢筋腐蚀是由海洋环境、冬季除冰盐、混凝土搅拌中的氯化物含量、海砂的使用等多种原因引起的，主要是由钢筋混凝土内部的流动氯离子或其他结构有害污染物引起的。钢筋腐蚀降低了钢筋混凝土结构的承载能力，存在严重的安全隐患和巨大的经济损失。最近提出了一种新的干预方法ICCP-SS（外加电流阴极保护和结构强化）。ICCP-SS结合了外加电流阴极保护（ICCP）和结构强化（SS）技术的优点，但使用了一种双功能材料——碳纤维增强胶凝基质（C-FRCM）。在这种双功能材料中，碳纤维（CF）网既是ICCP的阳极，也是SS的增强材料，而胶凝基质既是ICCP的导体，又是SS的粘结材料。以往的研究已经证明了ICCP-SS技术在RC构件中的有效性。然而，研究发现，长时间的ICCP会导致胶凝基质在阳极界面处的钙浸出，导致胶凝基质与CF网之间的键结的力学性能急剧下降，电阻显著增加。通过增加胶凝基质的致密性和导电性，从而在阳极界面中获得更均匀的电阻场，可以将钙浸出降低到不会对结构电阻产生不利影响的水平；在胶凝基质中加入少量石墨烯就有可能做到这一点。解决问题的关键是在相同的ICCP电流密度和持续时间下，防止（或显著减缓）C-S-H凝胶在阳极界面的击穿（即钙的损失）。石墨烯的显著特性使其成为解决这一问题的潜在理想方案，它可以产生更均匀的电场和更紧凑的胶凝基质微观结构。该项目旨在解决两个问题：量化浸出导致的粘结力学行为（对于SS）和CF/胶凝基质界面（对于ICCP）的电阻，并研究减少浸出的方法。综上所述，ICCP-SS干预方法在延长RC结构寿命方面具有巨大的潜力，在双功能胶凝基质中引入少量石墨烯片具有许多有益的协同效应，有助于充分发挥ICCP-SS的潜力。

The corrosion of embedded steel rebar in reinforced concrete (RC) structures, which are the backbone of every nation's infrastructure, is a major issue. Interventions relating to the corrosion of RC structures are estimated to amount to about 35% of the total volume of all work in the global building sector. Reinforcement corrosion is induced via mobile chloride ions or other structurally harmful contaminates within the reinforced concrete, which happens due to a variety of reasons such as marine environment, de-icing salt in winter seasons, chloride content in concrete mixing and the use of sea sand, etc. With reinforcement corrosion, the load-bearing resistances of RC structures are reduced, with severe potential safety issues and also immense economic loss.A new intervention method, ICCP-SS (impressed current cathodic protection and structural strengthening), has recently been proposed. ICCP-SS combines the merits of impressed current cathodic protection (ICCP) and structural strengthening (SS) technologies, but uses one dual-functional material - carbon fibre reinforced cementitious matrix (C-FRCM). In this dual functional material, the carbon fibre (CF) mesh serves as the anode for ICCP and also the strengthening material for SS, while the cementitious matrix is the conductor for ICCP and the bonding material for SS. Previous studies have demonstrated effectiveness of the ICCP-SS technology for RC members. However, it has been found that prolonged ICCP would cause calcium leaching in the cementitious matrix at the anode interface, leading to drastic loss of mechanical properties and significant increase of electrical resistance of the bond between the cementitious matrix and CF mesh. Reducing calcium leaching to a level that does not adversely affect structural resistance is possible by increasing the compactness and the electrical conductivity of the cementitious matrix to achieve a more uniform electrical resistive field in the anode interface; introducing a tiny amount of graphene into the cementitious matrix has the potential to do so. The key to solving the problem is to prevent (or significantly slow down) the breakdown of C-S-H gel (i.e. loss of calcium) at anode interface under the same ICCP current density and duration. The remarkable properties of graphene make it a potentially ideal solution to this problem by producing a more uniform electrical field and more compact microstructures of the cementitious matrix. This project aims to solve two issues: to quantify the bond mechanical behaviour (for SS) and the electrical resistance at the CF/cementitious matrix interface (for ICCP) due to leaching, and to investigate means of reducing leaching. In summary, the ICCP-SS intervention method has vast potential in prolonging life of RC structures and introducing a small amount of graphene flakes in the dual-functional cementitious matrix has a number of beneficial synergistic effects to help realise the full potential of ICCP-SS.