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.
|