Applications of Geopolymer in Civil Engineering: Feasibility Study of Loess Stabilization and Waste Concrete Recycling

Abstract

The fast growing population and economic development have resulted in an increasing demand for residential and commercial buildings and infrastructures. However, there are problems identified to fulfill this demand, including that (1) problematic soils need to be treated/improved before the construction of building and infrastructures; (2) the Portland cement industry, which is used for concrete production and as the conventional soil stabilizer, is not environment friendly; (3) qualified natural aggregates for concrete production are being depleted; and (4) great amount of construction & demolition waste (C&D waste) is being produced every year. This means that green materials and recycling the C&D waste are of great significance to the civil engineers for the sustainable development. Geopolymer, which is an inorganic material formed by alkaline activation of aluminia- and silica-containing material through a polycondensation process, could be synthesized from various industrial by-products, such as fly ash and furnace slag, with high compressive strength, low shrinkage, and other engineering properties. This renders geopolymer a prospective future in civil engineering applications. This dissertation was therefore conducted to investigate the feasibility of applying the fly ash based geopolymer in the loess stabilization and waste concrete recycling. With the integration of composition and microstructure, a four-tier conceptual microstructure model is proposed to elucidate the origin of loess collapsibility. Based on the understanding of the origin of the collapsibility, the feasibility study of loess stabilization with geopolymer is then conducted. Results indicate that improved compressive strength, together with a compact and stable microstructure, has been rendered by the binding effect of geopolymer gel. Meanwhile, numerical analysis on recycled concrete shows that the new interfacial transition zone (NITZ) plays a detrimental role to the performance of recycled aggregate concrete (RAC), and could even contribute more to the mechanical failure of RAC at the microscale than the old interfacial transition zone (OITZ). With this observation, how to produce the RAC more effectively was then investigated in the feasibility study of waste concrete recycling with geopolymer.