Development of a Novel Self-Healing Composite for Sustainable and Resilient Concrete Infrastructure

混凝土是世界上应用最广泛的建筑材料。建筑业每年使用43亿吨普通波特兰水泥(OPC)作为混凝土粘结剂，约占全球二氧化碳排放量的7%。为了减少英国混凝土工业对环境的影响，工业副产品，如磨细的燃料灰(PFA)和磨细的高炉矿渣(GGBS)，通常被用来部分取代OPC。虽然OPC的部分替代率可达50%，但如果不添加碱性激发剂，完全取代OPC在混凝土中是不可能的。土聚合物也被称为碱激发材料，是通过低钙PFA和GGBS等铝硅酸盐原料在常温或高温下碱激发合成的无水泥生态友好材料，作为一种有前途的OPC替代品而受到人们的极大关注。与OPC混凝土(OPCC)相比，GPC具有重量轻、耐火性好、碱集料膨胀率低、耐腐蚀、耐酸蚀和抗冻融循环等优点。在混凝土中使用地聚合物作为粘结剂可以帮助减少高达80%的体现能量和碳足迹。然而，GPC的脆性与OPCC相似，容易产生裂缝，导致钢筋锈蚀，损害钢筋混凝土结构的耐久性，从而阻碍其广泛应用。此外，与RC结构的可用性相关的混凝土基础设施的弹性是一个主要问题。GPC必须具有在屈服时恢复永久变形的能力(即重新定心)或在循环荷载作用下减小残余裂纹尺寸(即裂纹闭合)的能力，以便在结构的使用寿命内保持其功能性和适用性。因此，发展应变硬化纤维增强GPC，也被称为工程地质聚合物复合材料(EGC)，通过控制裂缝宽度的多重裂缝扩展来抑制GPC的脆性，提高其耐久性是至关重要的。在本项目中，将首次开发一种新型的自愈式EGC，它集成了GPC的绿色潜力和形状记忆合金(SMA)纤维的能量吸收能力，而不会发生永久变形。该项目涉及开发一种新的混合设计方法，该方法集成了微观机械建模、实验设计和生命周期分析。一系列先进的实验技术(如原位X射线计算机层析成像、图像体积相关和扫描电子显微镜)和建模方法(如多尺度格子Boltzmann有限元方法和多尺度断裂模型)将分别用于表征EGC的微观结构和模拟工程特性，这将有助于深入了解EGC的整体性能及其自愈效率。本研究将使开发具有优异力学性能和期望的裂纹愈合能力的新型EGC成为可能。这将加快GPC和SMA纤维在民用基础设施应用中的使用，特别是在承受动态载荷和侵蚀性环境的混凝土结构中，这将有助于大大提高混凝土基础设施的弹性、可持续性和耐久性。预计这一项目的成果将通过延长钢筋混凝土结构的使用寿命、减少对环境的影响以及维修和维护成本而产生直接的社会效益。

Concrete is the most widely used construction material in the world. The construction industry annually uses 4.3 billion tons of ordinary Portland cement (OPC) as binder for concrete, accounting for around 7% of global CO2 emissions. To reduce the environmental impact of concrete industry in the UK, industrial by-products, such as pulverised fuel ash (PFA) and ground granulated blast-furnace slag (GGBS), are usually used for partial replacement of OPC. Although partial replacement of OPC can reach up to 50%, the total replacement of OPC in concrete with these wastes is not feasible without the addition of alkaline activating agents.Geopolymers, also called "alkali-activated materials", that are cement-free eco-friendly materials synthesized at ambient or elevated temperature by alkali activation of aluminosilicate source materials such as low-calcium PFA and GGBS, have been drawing a lot of attention as a promising alternative to OPC. GPC has many advantages over OPC concrete (OPCC), such as light weight, good fire resistance, low alkali-aggregate expansion, and good resistance to corrosion, acid attack and freeze-thaw cycles. Using geopolymer as the binder in concrete can help reduce embodied energy and carbon footprint by up to 80%. However, GPC is inherently brittle similar to OPCC and susceptible to cracking that would facilitate corrosion of reinforcing steel and impair durability of reinforced concrete (RC) structures, and thus hinder its widespread application. In addition, the resilience of concrete infrastructure that associates with the usability of RC structures is a major concern. It is essential for GPC to possess the capability to recover permanent deformation upon yielding (i.e., re-centring) or the ability to reduce residual crack sizes (i.e., crack closure) when subjected to cyclic loads in order to maintain the functionality and serviceability of a structure over its service life. As such, it is vital to develop strain hardening fibre reinforced GPC, also known as engineered geopolymer composite (EGC) to suppress the brittleness of GPC and improve its durability through multiple crack propagation with controlled crack widths. In this project, for the first time, a novel self-healing EGC that integrates the greenness potential of GPC and the energy absorption capacity of shape memory alloy (SMA) fibres without permanent deformation will be developed. The project involves the development of a novel mix design methodology that integrates micromechanical modelling, design of experiment and life cycle analysis. A range of advanced experimental techniques (e.g., in-situ X-ray computed tomography imaging, image volume correlation, and scanning electron microscope) and modelling approaches (e.g., multiscale lattice Boltzmann-finite element method, and multiscale fracture model) will be used to characterise microstructure and simulate engineering properties of EGC respectively, which will provide insight into the overall performance of EGC and its self-healing efficiency.This research will make it possible to develop a novel EGC with eminent mechanical properties and desired crack-healing capacity. It would expedite the use of GPC and SMA fibres in civil infrastructure applications, particularly for concrete structures subjected to dynamic loads and aggressive environments, which will help greatly enhance resilience, sustainability and durability of concrete infrastructure. The outcomes of this project are expected to result in direct benefits to society by extending the lifetime and by reducing the environmental impact, and repair and maintenance costs of RC structures.