Long-term structural behaviour of marine-conditioned geopolymer concrete cast with geopolymer-coated recycled concrete aggregates and basalt fibres

Purpose This study aims to investigate the novel long-term performance characteristics of a pioneering self-compacting geopolymer concrete (SCGC) incorporating recycled concrete aggregates (RCA) and basalt fibres (BF) under harsh environments and simulated marine conditions. The SCGC is a low-carbon concrete formulated using binders such as fly ash, slag, micro fly ash and a solid alkali activator (sodium metasilicate), making it a one-part geopolymer concrete (GPC). This research also highlights the significance of coating RCA with geopolymer slurry to enhance its performance under both long-term marine and ambient conditions. Design/methodology/approach Cylinder and steel-reinforced beam samples were cast using SCGC incorporating geopolymer-coated RCA and hybrid-length BF. These were compared to control samples cast with only natural coarse aggregate. The concrete’s mechanical and structural properties were evaluated after 6 and 12 months of exposure to wet-dry seawater cycles, while beams were subjected to sustained loading. A three-point bending test was performed on beams to analyse the load-deflection behaviour, crack patterns and failure modes. Additionally, scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to study the microstructure and chemical properties of samples. Findings After one year, marine-conditioned samples with natural aggregate, coated RCA and coated RCA with BF showed strength gains of 44, 48 and 39%, respectively. Tensile strength increased by 43 and 20% for mixes with natural aggregates and coated RCA, while ambient-conditioned samples showed no significant gains. However, BF increased chloride penetration, causing fibre degradation and a 5.6% drop in ultimate load capacity after 12 months compared to their performance at 6 months. Despite this, fibre-reinforced mixes outperformed ambient-conditioned samples, with chloride ingress having minimal impact on mixes with sole RCA or natural aggregates. Research limitations/implications The reproduction of marine environmental conditions, including the wet and dry cycles used in this study, may not fully capture the complexities of real-world marine exposure. Originality/value It is the first to investigate SCGC employing geopolymer-coated RCA as the sole coarse aggregate type, combined with BF, under extended tidal marine exposure. It examines both the mechanical properties: compressive strength, splitting tensile strength and modulus of elasticity and the structural behaviour of reinforced beams under sustained load.