From Industrial Waste to Sustainable Infrastructure: Engineered Geopolymer Lightweight Aggregates for Low Carbon Concrete

Abstract

The extensive consumption of natural aggregates and cement in concrete production has intensified concerns regarding resource depletion and environmental sustainability, creating a growing need for alternative construction materials derived from industrial by-products. This study investigates the feasibility of producing geopolymer lightweight aggregates (GLWA) from fly ash (FA), rice husk ash (RHA), ground granulated blast-furnace slag (GGBFS), and metakaolin (MK) through alkali activation and incorporating them into geopolymer lightweight aggregate concrete (GLWAC). Four aggregate formulations were developed and evaluated in terms of particle density, crushing strength, water absorption, and heavy metal leaching behavior. The resulting aggregates were subsequently used as coarse aggregates in lightweight concrete mixtures, and their effects on fresh, mechanical, and durability-related properties were examined through flowability, compressive strength, splitting tensile strength, ultrasonic pulse velocity (UPV), and electrical resistivity measurements.
The results demonstrated that aggregate composition significantly influenced both aggregate quality and concrete performance. The GGBFS-containing aggregate exhibited the highest particle density (1.52 g/cm³), crushing strength (48.0 kgf/cm²), and lowest water absorption (13%), leading to the highest compressive strength and UPV among the GLWAC mixtures. In contrast, the RHA-containing aggregate showed greater porosity and lower mechanical performance due to its higher water absorption. All geopolymer aggregates exhibited negligible heavy metal leaching, confirming their environmental compatibility. Furthermore, the developed GLWAC mixtures achieved satisfactory self-consolidating characteristics and durability performance, with electrical resistivity values indicating moderate-to-good resistance against ionic transport.
The findings demonstrate that engineered geopolymer lightweight aggregates produced from industrial residues can simultaneously enhance resource efficiency, reduce dependence on natural aggregates, and deliver balanced mechanical and durability performance, highlighting their potential for sustainable and low carbon concrete applications.