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

混凝土是世界上使用最广泛的建筑材料。建筑行业每年使用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，如粉煤灰（PFA）和颗粒状高炉矿渣（GGBS），通常用于部分替代OPC。虽然OPC的部分替代率可达50%，但如果不添加碱性活化剂，用这些废物完全替代混凝土中的OPC是不可行的。地聚合物，也称为“碱活化材料”，是在环境温度或高温下通过碱活化铝硅酸盐源材料（如低钙PFA和GGBS）合成的不含水泥的生态友好材料，作为OPC的一种有前途的替代方案，已经引起了很多关注。GPC混凝土与OPC混凝土相比，具有重量轻、耐火性好、碱-集料膨胀小、耐腐蚀、耐酸腐蚀、抗冻融等优点。使用地质聚合物作为混凝土中的粘合剂可以帮助减少高达80%的隐含能源和碳足迹。然而，GPC具有与OPCC相似的固有脆性，并且容易开裂，这将促进钢筋的腐蚀并损害钢筋混凝土（RC）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）或减小残余裂纹尺寸的能力（即，裂纹闭合），以便在其使用寿命期间保持结构的功能性和可使用性。因此，开发应变硬化纤维增强GPC（也称为工程地质聚合物复合材料（EGC））以抑制GPC的脆性并通过具有受控裂缝宽度的多裂缝扩展来提高其耐久性至关重要。在该项目中，将首次开发一种新型的自修复EGC，该EGC将GPC的绿色潜力和形状记忆合金（SMA）纤维的能量吸收能力整合在一起，而不会产生永久变形。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（例如，原位X射线计算机断层摄影成像、图像体积相关和扫描电子显微镜）和建模方法（例如，本文采用多尺度格子Boltzmann有限元法和多尺度断裂模型分别对EGC的微观结构和工程性能进行了模拟，为研究EGC的整体性能和自修复效率提供了理论依据，为开发具有优异力学性能和裂纹愈合能力的新型EGC提供了可能。这将加快GPC和SMA纤维在民用基础设施应用中的使用，特别是用于承受动态载荷和恶劣环境的混凝土结构，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。该项目的成果预计将通过延长钢筋混凝土结构的使用寿命和减少对环境的影响以及维修和维护成本，为社会带来直接利益。

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.