Optimization of the manufacturing process and properties of alkali-activated palm oil fuel ash-based cold-bonded aggregates

Abstract

Tons of palm oil fuel ash (POFA) are currently being disposed of at landfills or left untreated in the environment, taking up valuable land space and posing significant hazard to the environment. To address this issue, this study investigates the production of artificial lightweight aggregates (LWAs) using POFA as a raw material through a cold-bonded one-part alkali-activation method. High-volume of weakly pozzolanic POFA and different combinations of GGBS (0%, 10%, 30%) as precursors, and Na2SiO3.5H2O (9% and 12%) as the activator were used to produce the artificial LWAs. The granulation process was systematically investigated, where the influence of granulation parameters (the ratio of POFA and GGBS, activator content, water content, rotation angle, and rotation speed) on granulation efficiency and granulation duration were evaluated. The physical properties including loose bulk density, water absorption, and crushing strength were also investigated. In addition, the phase change after alkali-activation was evaluated. Results showed that the water demand for the aggregates with different combination ranged from 0.3 to 0.46. Increasing the GGBS and Na2SiO3.5H2O content improved the granulation efficiency up to 87.4% and shortened the granulation duration to 7 min. Response surface methodology (RSM) modeling revealed that the optimum rotation angle and rotation speed were 55° and 50 rpm, respectively, resulting in a maximum granulation efficiency of 88.2%. The loose bulk density of POFA-based alkali-activated aggregates (PFAAs) was 595.4–730.3 kg/m3, meeting the requirement of LWAs in EN13055. After 28 days curing, the PFAAs with the GGBS replacement of 30% and 12% Na2SiO3.5H2O exhibited crushing strength and water absorption of 2.4 MPa and 22.4%, respectively. Moreover, a stronger alkali-activation was achieved with 30% GGBS replacement, which improved the performance of PFAAs, as evidenced by the phase analysis.