Designing printing parameters for geopolymer concrete prepared from construction and demolition waste and industrial side streams

Abstract

The high demand for construction and infrastructure materials, the reduction of global warming potential (GWP) and the European union (EU) environmental protection policy have led to the use of environmentally friendly materials for domestic and industrial applications. The use of sustainable geopolymer concrete (GPC) and 3D printing are considered two environmentally friendly innovations in the construction sector. The utilization of industrial by-products and waste from construction, mining and the timber industry is considered a potential source to produce GPC. Researchers are already focusing on the use of new sustainable geopolymer (GP) materials prepared from different industrial side streams through advanced manufacturing techniques to promote the digital transformation and increase sustainability in the construction industry. The composition of the GPC mixture depends on the source, quality, size and type of filler and binder materials. Depending on the source of the raw materials and the number of impurities, various parameters need to be addressed to enable side streams to become a potential source of GPC. The pre-treatment processes, cost analysis, design mix formulation, mixing process, concrete curing conditions and environmental burdens are essential parameters to consider for newly developed GPC.

This dissertation investigates the key parameters required for the various stages of GPC formulation prepared from locally available industrial side streams and the printable properties of the GPC mix design. The pre-treatment techniques in a single and combined line, as well as the printable properties of the formulated GPC in fresh and cured states, a cost analysis, and the environmental impact of the different production stages of GPC were investigated. A number of separation techniques and the energy required to activate by-products and waste for concrete formulation were investigated. The effects of each raw material on the strength and printable properties of the formulated mix were studied experimentally. The economics of each primary stage, from raw material procurement to 3D printing of GPC in factories and on site, were investigated. Finally, the environmental impact of GPC compared to Portland cement-based concrete (PC) was investigated.

The results show that the pre-treatment techniques allow industrial by-products and waste to be used for 3D printable GPC. The removal of various unwanted materials and impurities from the waste composition through separation processes provided sustainable raw materials for concrete formulation. The printable properties of the newly developed GPC in fresh and cured states depend on the heat treatment, particle size and the ratio of different binders, fillers, and alkaline solution. The economic evaluation shows that the use of 3D printing technology using the newly developed GPC reduces production costs by 32% and energy and labour costs by almost 50% compared to conventional methods. The use of a higher proportion of recycled materials helps to reduce the environmental impact associated with concrete production. In addition, challenges were observed in defining suitable mixes for higher strength concrete applications and in controlling the alkaline solution. These challenges can be addressed through the environmentally friendly, cost-effective replacement and controlled use of alkaline solution to achieve structural and non-structural applications of GPC on a larger scale that could promote sustainable materials for construction and infrastructure purposes.