Enhancing thermal insulation, mechanical strength, and durability of one-part fly ash-based geopolymer foam concrete using lime and mahogany sawdust

Abstract

The development of sustainable and energy-efficient construction materials is crucial for reducing environmental impact and improving building performance. This study investigates the effects of slaked lime (LM) and mahogany sawdust (MS) as partial replacements for fly ash (FA) and silica sand (SS) in one-part geopolymer foam concrete (GFC). Twelve mixtures were tested for fresh properties (flowability, density), mechanical performance (compressive and flexural strength), thermal insulation (thermal conductivity), and durability (water absorption, porosity, sorptivity, high-temperature resistance, freeze-thaw, and sulfate resistance). The results revealed that increasing LM content enhanced compressive strength, with the highest strength of 6.22 MPa achieved at 50 % LM and 100 % MS, representing a 202.92 % improvement compared to the reference mixture (2.06 MPa). Although the maximum compressive strength (6.22 MPa) is lower than conventional concrete, the developed GFCs are intended for non-structural, lightweight, and thermally insulating applications, where low density and high thermal performance are prioritized over structural load-bearing capacity. Flexural strength followed a similar trend, reaching 0.39 MPa, marking a 129.41 % increase over the reference. The incorporation of MS contributed to weight reduction, with the lowest oven-dry density recorded at 556 kg/m3 for the reference mixture, while the highest density was 1587 kg/m3 at 100 % MS and 50 % LM, showing a 185.32 % increase. Thermal conductivity values ranged from 0.113 W/mK (reference) to 0.197 W/mK (100 % MS, 50 % LM), indicating improved insulation properties at lower LM content. This corresponds to a 74.34 % increase in thermal conductivity, highlighting the densification effect of LM and MS incorporation. Water absorption and sorptivity decreased significantly with higher LM levels, with sorptivity dropping from 32.52 kg/m2 (reference) to 10.87 kg/m2 (100 % MS, 50 % LM). High-temperature resistance tests revealed that strength increased by up to 33.6 % at 200 degrees C but declined significantly at 800 degrees C, with the highest loss (46 %) occurring in high-MS-content mixtures. Freeze-thaw resistance was optimal at 0 % MS, where strength increased after 25 cycles, but higher MS content led to up to 57.6 % strength loss after 50 cycles. These findings demonstrate that an optimized LM-MS balance enhances mechanical, thermal, and durability performance, making geopolymer foam concrete a viable alternative for sustainable construction.