Abstract
This study investigates the utilization of rice husk ash (RHA) as a sustainable alternative activator for low carbon geopolymer concrete (GPC) production. The study employed qualitative X-ray diffraction (XRD) analysis to assess the influence of incineration duration and temperature on the silica phase in RHA. It was determined that burning durations exceeding 4 hours resulted in the formation of crystalline structures, while temperatures above 600 °C and below 700 °C yielded the highest silica content in the ash without compromising its amorphous structure. The implementation of pre-treatment using 0.1M HCl was found to enhance burning efficiency by reducing the duration required to produce high amorphous ash. Dissolving high amorphous silica ash in 10M sodium hydroxide at increased temperatures led to proper dissolution. The project identified that dissolving 160 g of ash in 1000 mL of 10M sodium hydroxide at 80 °C for 1 hour facilitated successful synthesis. To prevent gel formation, the extraction temperature and duration must be controlled in accordance with the methodology outlined. The study also revealed that increasing the sodium silicate-to-sodium hydroxide (SS/SH) ratio using rice husk ash-derived sodium silicate (SSR) resulted in higher compressive strength in GPC mortars. The optimal SS/SH ratio of 2.1 achieved a compressive strength of 9.52 MPa after 7 days, projected to increase by 60% to 19 MPa after 28 days. Further investigation on the substitution of commercial sodium silicate (SSC) with SSR in GPC demonstrated that a 10% substitution proportion yielded compressive strengths appropriate for commercial use. However, exceeding this substitution level led to a decrease in compressive strength. The decreasing compressive strengths trends after exceeding the 10% proportion indicates the excessive amount of silica added to the GPC mixture from the high silica containing SSR created. The addition of disproportionate sodium silicate in the alternative activators created a large gel network leading to reduced strengths of mortar. Moreover, the use of SSR in GPC demonstrated a significant reduction in carbon emissions compared to ordinary Portland cement (OPC). Pre-leaching rice husk in 0.1M HCl resulted in lower burning durations and reduced energy requirements compared to un-leached rice husk. A 10% substitution of preleached SSR in the alternative activator achieved a 51% reduction in emissions compared to OPC. The use of rice husk ash to produce sodium silicate for the alternative activator offered lower carbon emissions and environmental impact, contributing to a more sustainable and circular economy. While this research provided valuable insights, further investigations are recommended, these include exploring the addition of recycled aggregates in the binder to lower emissions, investigating the use of Indonesian Class C fly ash, investigating acid treatment after rice husk incineration to further remove carbon, and assessing the storage of SSR to improve solution stability.