Implementing a Slow-Cooling Method for Thermal Treatment of RHA to Use as a Secondary Precursor in Alkali-Activated Mortar

Abstract

Alkali-activated binder (AAB), a contemporary construction technology, aims at decelerating the cement demand. The lowered rate of cement demand will reduce the pace of cement production and also bring down the associated environmental concerns. The current experimental work attempts to investigate the effect of utilizing thermally treated rice husk ash (RHA) as a secondary precursor in ground granulated blast furnace slag (GGBFS) based alkali-activated mortar (AAM). The RHA was subjected to thermal treatment which utilizes sustained heat from slow-cooling technique for obtaining the ash with high pozzolanic activity. Therefore, for determining optimum thermal treatment controls, two different temperatures (500°C and 600°C) and four retention times (0.5, 1.0, 2.0, and 4.0 h) were used. The RHA was subjected to the desired level of temperature and retention time, and then the ash was slowly cooled by retaining it inside the furnace. The cooling rate was 0.5°C/min. The pozzolanic activity, the phase changes and the percentage carbon content in RHA was studied through pozzolanic activity test, x-ray diffraction (XRD), and scanning electron microscopy–energy dispersion spectroscopy (SEM-EDS). The ash treated at 500°C temperature and 1.0 h retention time had the greatest pozzolanic activity among all variants. RHA with highest pozzolanic activity was used in four different percentages (5%, 10%, 15%, and 20%) in GGBFS based AAM. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) activators were used to cast one control and four test mixes (TM). The results showed that 10% RHA inclusion in AAM, increases the compressive strength (7 days), consistency, initial and final setting time by 61.39%, 35.21%, 488.2%, and 310.25% respectively. The Addition of RHA as replacement to GGBFS improves the workability, setting time and strength, making the AAM more suitable for construction industry.