Sustainable geopolymer foam concrete with recycled crumb rubber and dual fiber reinforcement of polypropylene and glass fibers: A comprehensive study

Abstract

This study examines the thermal, mechanical, and durability performance of fly ash-based geopolymer foam concrete (GFC). It incorporates recycled crumb rubber (CR) as a lightweight aggregate and is reinforced with polypropylene fibers (PPF) and glass fibers (GF). The goal is to develop sustainable, high-performance GFC for energy-efficient and eco-friendly construction. Seven mixtures were tested with varying fiber types and dosages: PPF (1 % and 2 %), GF (1 % and 2 %), and hybrid reinforcement (0.5 % and 1 % each of PPF and GF). The results show significant improvements in key properties. The developed GFC achieved compressive strength of up to 8 MPa, aligning with commercial foam concrete (5–10 MPa) and geopolymer-based foams (2–12 MPa). While it does not represent a breakthrough in durability, the material offers superior lightweight properties, enhanced thermal insulation, and greater sustainability compared to conventional alternatives. Compared to the reference, the compressive strength increased by 198 % in the mixture containing 2 % GF, while mixtures with 1 % and 2 % PPF exhibited 33 % and 14.9 % increases, respectively. Hybrid reinforcement at 1 % PPF and 1 % GF achieved a balanced 45.4 % improvement. Flexural strength gains were most notable in mixtures with 2 % GF, showing a 261 % increase over the reference. Thermal conductivity ranged between 0.438 and 0.548 W/mK, with the lowest value achieved in the mixture with 1 % PPF (2.23 % lower than the reference). Dry density varied from 967 to 1188 kg/m³, with the highest value observed in the 2 % GF mixture (20.1 % higher than the reference). Porosity and water absorption were lowest in the 2 % GF mixture, showing reductions of 31.1 % and 47.4 %, respectively. High-temperature resistance tests indicated that GF-reinforced mixtures exhibited greater stability at moderate temperatures, with strength loss reductions of up to 63.2 % at 200 °C, but experienced degradation at 600 °C. Microstructural analysis confirmed improved matrix integrity, reduced porosity, and enhanced fiber-matrix bonding in fiber-reinforced mixtures. This study demonstrates the feasibility of integrating CR, PPF, and GF to develop high-performance, lightweight, and eco-friendly GFC, offering significant potential for sustainable construction applications.