PSI - Issue 70

Muhibur Rahman S. et al. / Procedia Structural Integrity 70 (2025) 627–634

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poses major sustainability concerns, as noted by Tahri et al. (2015). In recent decades, its widespread use has led to numerous environmental drawbacks, as highlighted by Kandasamy et al. (2024). Cement, a key component of concrete, significantly contribut es to global CO₂ emissions nearly 8% according to Andrew (2019), Gao et al. (2015), and Worrell et al. (2001). Moreover, the large-scale extraction of aggregates to support construction has caused issues such as habitat degradation and soil erosion. These challenges underline the urgent need for sustainable alternatives and renewable materials to mitigate the environmental impact of concrete, as emphasized by Silva et al. (2017) and Spence & Mulligan (1995). The extraction and use of coarse aggregates an essential ingredient in concrete have reached unsustainable levels, as noted by Collivignarelli et al. (2020). The escalating rate of CCA (conventional coarse aggregate) mining raises serious concerns about future resource scarcity. This practice not only exhausts limited natural reserves but also disturbs ecosystems, threatens biodiversity, and increases energy usage, as reported by Aïtcin & Mehta (1990) and Beshr et al. (2003). Tackling these environmental challenges necessitates a shift toward more sustainable material options. In response, recent research and industrial efforts have increasingly focused on artificial aggregates. These include recycled aggregates and industrial by-products, as explored by Chinnu et al. (2021), Alqarni et al. (2022), and Sekar et al. (2011), as well as synthetic aggregates produced through advanced technologies, according to Mohammed et al. (2021), Rehman et al. (2020), Shanmugan (2020), and Sahoo & Selvaraju (2020). Artificial aggregates have demonstrated promising benefits for concrete performance, such as improved workability due to uniform grading, increased strength from superior particle bonding, and enhanced durability in challenging environments, as highlighted by Ren et al. (2021), Zhang et al. (2022), Almadani et al. (2022)). Coal ash, a residual material from coal combustion in thermal power plants, is a largely underexploited resource. Global production of coal ash surpasses 100 billion tonnes annually, yet only a small portion is effectively utilized, as noted by Ahmaruzzaman (2010). In contrast, bottom ash being coarser and heavier remains largely unused, with the majority ending up in landfills or storage facilities. Geopolymer technology, which utilizes alumino-silicate-rich materials and alkaline activators, presents a novel method for converting fly ash into coarse aggregates. Aggregates formed through geopolymerization are known for their superior compressive and tensile strength, lower porosity, and greater resistance to sodium chloride exposure and freeze-thaw conditions, as observed by Bijen (1986). Furthermore, fresh concrete incorporating geopolymer aggregates demonstrates improved workability and minimized shrinkage, positioning it as a strong alternative to conventional aggregates, according to Jayasinghe (2009). While major advances have been made in coal ash and other industrial waste by-products use, the application of the bottom ash (BA) for coarse aggregate manufacturing has attracted limited research. Perhaps most of the existing research has concentrated upon BA for the replacement of fine aggregates or cement, leaving a glaring lack of knowledge on BA’s potential as a coarse aggregate (Chaisakulkiet et al., 2022). That gap has been addressed by this research, which develops Bottom Ash Coarse Aggregates (BACA) utilizing Geopolymer technology and the evaluation of their viability in concrete. This research explores the mechanical behavior of concrete reinforced with BACA and compared with a concrete reinforced with conventional aggregates (CCA). 2. Production of Bottom Ash Coarse Aggregate (BACA) Geopolymer techniques were used to synthesize the coarse aggregate using Bottom ash (BA) at 8M to 16M molarity levels with L/B proportions of 0.3, 0.35 and 0.4. The NaOH/Na₂SiO₃ ratio of 0.5 used for this investigation indicates the mass ratio between the sodium hydroxide solution and the sodium silicate solution (Muhammed, & Thangaraju, (2019). Finally Bottom Ash was thoroughly mixed with alkaline solution. After mixing, the mixture was casted in the moulds, cooled and pulverized to get 20 mm BACA. Table 1 shows the specific mix proportions of BACA.

2.1 CCA and BACA properties

CCA and BACA properties were assessed through various tests and results were shown in Table 2. The Fig.1 compares the IV, CV, and AV of CCA with BACA.