Pozzolanic and Hydration of Highly Reactive Treated Rice Straw Ash (RSA) for Interfacial Transitional Zone (ITZ) Improvement in Cement Mortar

Abstract

For utilizing rice straw as pozzolan in the mortar production, it is required to develop an amorphous silica rich material to replace cement. At the same time, it is an excellent alternative, instead of burning the rice straw after the harvesting process. Silica is a beneficial additive to cement mix by accelerating the cement hydration process due to its high reactivity to improve the mortar strength. Thus, the research aims to develop rice straw ash (RSA) as a highly reactive silica-rich pozzolan. This study focuses on extracting the high amorphous silica through thermochemical pretreatment using a low concentration of hydrochloric acid (HCl) and continued with the incineration process at a controlled temperature. The response surface methodology (RSM) through the Design Expert software was used to determine the sample number involved in the thermochemical pretreatment and incineration process since both processes had a few factors with a large range. Then, the treated RSA (TRSA) undergoing the grinding process using a ball mill. Lastly, the minimum amount of TRSA was evaluated in the mortar with partial replacement levels varying from 1% to 5. As a result, the TRSA is a highly reactive pozzolan since the total percentage of reactive compound content (silicon dioxide (SiO2), aluminium oxide (Al2O3), and iron (III) oxide (Fe2O3)) fulfilled the ASTM C618 standard requirement (>70%) when treated using 0.06 M of HCl solution heated at 70? for about 2 hours and incinerated at 600? for about 1 hour. TRSA was achieved to be an amorphous silica rich pozzolan through XRD and FTIR analysis. TEM analysis also conducted and further confirmed the TRSA had a high amorphous silica content. TRSA with the nano-sized (4.505 nm to 6.278 nm) in the high amorphous silica state produces a good pozzolan and causes an excellent pozzolanic reaction in developing the mortar strength. The strength activity index (SAI) test for pozzolanic reactivity proves the TRSA meets the requirement of ASTM C311, having more than 75% of the SAI value. In addition, the composition of 4% TRSA as cement replacement material was the highest and improved by 60.27% in mortar strength and ITZ gap compared to the conventional mortar throughout 90 days. Overall, the strength of TRSA-based cement mortar showed an excellent performance compared to the conventional mortar and non-treated RSA (NTRSA). Hence, the TRSA is considered a high-quality pozzolanic material incorporated with a small amount of concrete production.