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

钢筋混凝土(RC)结构是各国基础设施的支柱，钢筋的锈蚀是一个主要问题。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业所有工作量的35%。钢筋锈蚀是由于海洋环境、冬季除冰盐、混凝土拌和中的氯离子含量以及海砂的使用等多种原因引起钢筋混凝土内部的流动氯离子或其他有害结构污染物引起的。钢筋锈蚀会降低钢筋混凝土结构的抗力，带来严重的安全隐患和巨大的经济损失。最近，人们提出了一种新的干预方法--外加电流阴极保护与结构加固。ICCP-SS结合了外加电流阴极保护(ICCP)和结构加固(SS)技术的优点，但使用了一种双功能材料-碳纤维增强水泥基(C-FRCM)。在这种双功能材料中，碳纤维网既是ICCP的阳极，又是SS的增强材料，而胶凝基质则是ICCP的导体和SS的粘结材料。以前的研究已经证明了ICCP-SS技术对RC成员的有效性。然而，研究发现，延长ICCP时间会导致阳极界面处胶凝材料中钙的浸出，导致力学性能急剧下降，胶结材料与碳纤维网孔之间的结合电阻显著增加。通过增加胶结基质的致密性和导电性，在阳极界面上获得更均匀的电阻场，可以将钙浸出减少到不对结构电阻产生不利影响的水平；在胶结基质中引入微量石墨烯是有可能做到这一点的。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凝胶在阳极界面的破裂(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，因为它可以产生更均匀的电场和更紧密的胶凝基质微观结构。本项目旨在解决两个问题：量化粘结力学行为(对于SS)和由于浸出而在CF/水泥基界面处的电阻(对于ICCP)，以及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潜力，在双功能水泥基质中引入少量石墨烯鳞片具有许多有益的协同效应，有助于实现ICCP-SS的全部潜力。

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.