Innovative utilization of various industrial byproducts in clinker-free high performance cementitious composites

Abstract

With CO2 emissions being a major global environmental concern, many researchers are focusing on reducing emissions by recycling industrial byproducts to replace cement and other traditional natural resources. However, challenges remain in achieving the required performance and validation to fully replace ordinary cement and conventional natural resources, both in technological advancements and practical construction applications. Therefore, in this thesis, new approaches are proposed to develop high performance composites by upcycling in a way that has not been utilized in existing studies, leading to improvement of performances of cementless composites. First, the experimental study focuses on the development of cementless ultra-high performance concrete (UHPC) with enhanced electrical properties. Alkali-activated slag (AAS) binder was employed as a substitute for ordinary Portland cement (OPC) binder, while rapid-cooling electric arc furnace oxidizing slag (REOS) was utilized as a filler due to its advantageous electrical properties. The cementless UHPC demonstrated mechanical properties comparable to those of cement-based UHPC. In addition, incorporating REOS into cementless UHPC resulted in superior self-sensing performances compared to the UHPC with silica sands. Therefore, REOS can be used not only as a fine aggregate replacement but also as a conductive material to improve the electrical properties of cementless UHPC. Secondly, the main objective of this research is to utilize coal bottom ash (CBA) as an activator and filler on strain-hardening alkali-activated composites (SH-AAC). Many previous studies have focused on the utilization of CBA as an industrial byproduct, replacing conventional fillers. In order to maximize the consumption of CBA, this study simultaneously utilizes CBA for the synthesis of activators as well as filler substitutes. Silicon (Si) ion was extracted by CBA could be used as a silica source to fabricate alkaline solution. In addition, the residual after treatment of CBA were used as filler, and it is found that the residuals significantly improved the mechanical performance of SH-AAC, which is possibly attributed to the surface modification of the treated CBA. Therefore, utilizing CBA with novel treatments can improve the mechanical properties of SH-AAC, broadening the utilization potential of the industrial by-product. Thirdly, the main objective of this research is to develop strain-hardening CaO-activated GGBFS cementless composites (SH-CASC) using a CaO-activated GGBFS binder, incorporating calcium formate (Ca(HCOO)₂) as an accelerator to enhance the early strength of the binder. The study evaluates the effect of calcium formate on the mechanical properties of SH-CASC, with the aim of achieving performance comparable to AAS-based strain-hardening cementitious composites (SHCC) and cement- based SHCC. It was found that calcium formate is an effective accelerator in SH-CASC because it enhanced the microstructure of matrix and the bond strength between matrix and fibers. In addition, SH-CASC with calcium formate has a lower environmental impact than cement-based SHCC and AAS- based SHCC, resulting in a composite with both performance and environmental benefits. Finally, a novel utilization method of synthesizing alkaline solution with waste liquid crystal display (LCD) powder was proposed. Waste LCD glass has abundance of Si ion, and almost every phase shows amorphous. Therefore, By extracting silica ions from LCD powder into a NaOH solution at 80°C for 72h, alkaline solution was successfully synthesized. To demonstrate the effectiveness of the solution synthesized by LCD, compressive test and several chemical analyses were performed. The results showed higher compressive strength than the alkali solution made from conventional silica fume, suggesting a new sustainable method of the utilization of waste LCD powder.