Alkali-activated rice husk ash-foamed composites: Correlation between pore structure, hydration, and hardening properties

Abstract

Solid waste recycling plays a crucial role in environmental protection and energy conservation. This study explores the impact of the modulus of the alkaline activator on the dry density, water absorption rate, thermal conductivity, electromagnetic wave absorption, and compressive and flexural strength of rice husk ash (RHA)-foamed composites. Additionally, the foamed composite's micropore structure and hydration characteristics were characterized. For the first time, the study reveals the correlation between the pore structure, hydration products, and hardening properties of alkali-activated RHA-foamed composites. The study found that decreasing the modulus of the alkaline activator increased the amount of OH⁻ ions available in the gel, and the number of micropores (r ≤ .1 µm) in the foamed composites increased from 7.1903% to 21.3156%. This resulted in the refinement of pore sizes and optimization of heat transfer paths. Meanwhile, increasing the C–S–H gel composition in the hydrated products improved its compressive and flexural strength. When the alkali modulus reaches 1, 28 days foamed composites display compressive strength of 8.33 MPa and thermal conductivity of .1404 W/(m·K). Furthermore, the superior pore structure improved the electromagnetic wave absorption of the foamed composites, yielding a reflection loss value of −12.02 dB.