Development and performance evaluation of self-compacting lightweight alkali-activated concrete incorporating hydroton clay balls

Abstract

Alkali-activated concrete has emerged as a promising alternative in construction due to its enhanced performance characteristics and reduced carbon footprint. This study introduces a novel category of self-compacting lightweight alkali-activated concrete using hydroton clay balls (lightweight expanded clay aggregate, LECA) as coarse aggregate and manufactured sand as fine aggregate. The research investigates the influence of fly ash content in the binder and maximum aggregate size (MAS) on the mechanical properties of the concrete mixes. Three series of mixes were developed with MAS varying at 10 mm, 12.5 mm, and 16 mm, and fly ash proportions at 0 %, 30 %, and 50 %. A novel pre-treatment method involving geopolymer slurry was employed to enhance the stability of LECA by mitigating water absorption, crucial for achieving self-compacting properties. The lightweight concrete mixes demonstrated excellent filling and passing abilities, adhering to EFNARC guidelines, with the mix L10FA50 (smallest MAS and highest fly ash) achieving the highest workability. Compared to the normal-weight mix N16G100, the mix L10FA50 recorded 17 % higher slump flow, 45 % better sieve segregation resistance, and 34 % faster V-Funnel flow times. Dry densities of lightweight mixes ranged from 1851 to 1943 kg/m³, about 19–20 % lower than normal-weight concretes. The pre-treated LECA enhanced the mechanical performance of lightweight mixes, achieving maximum compressive strengths of up to 49.17 MPa, splitting tensile strengths of 3.40 MPa, flexural strengths of 8.60 MPa, and fracture energy of 161.51 N/m, approximately 65 % of the normal-weight mixes. Higher strength gains were particularly notable with higher GGBFS content and larger MAS. The microstructural analysis confirmed dense morphologies with C-S-H and C-A-S-H gel formations, contributing to improved strength. This research establishes the feasibility and performance benefits of utilizing LECA in alkali-activated concrete formulations for sustainable construction practices with enhanced mechanical and microstructural properties. © 2025 Institution of Structural Engineers