Enhancing long-term alkaline durability of epoxy-coated flax textile for internal concrete reinforcement: Surface modification & matrix integration with rice husk ash

This study aims to explore innovative strategies to enhance the alkaline resistance of epoxy-coated flax textile as internal reinforcement in concrete environments by modifying its surface with rice husk ash and incorporating rice husk ash into the cementitious matrix. Epoxy-coated flax textiles were exposed to simulated concrete pore solution at 20 ± 2 °C and accelerated in-situ concrete condition at 50 °C. Results showed that both untreated and rice husk ash-modified epoxy-coated flax rods experienced significant reductions in tensile load capacity (by 49 % and 59 %, respectively), stiffness (by 29 % and 30 %) and strain capacity (by 33 % and 46 %) after 30 weeks of exposure to simulated concrete pore solution. Flax fibre extracted from epoxy-coated flax rods exhibited a continuous decrease in hemicellulose and wax content, whereas those from the modified rods retained detectable hemicellulose after 30-week exposure. This indicates a slower alkaline hydrolysis of flax fibre resulted from surface treatment. The pozzolanic reaction of rice husk ash contributed to this effect by consuming Ca(OH)₂ and limiting calcium migration onto the fibres. In accelerated in-situ concrete condition, only normal epoxy-coated flax textile reinforced recycled aggregate concretes showed significant reduction in tensile strength, with a 32 % decrease compared to its original strength. The flax fibre extracted from this group exhibited calcium deposition and a reduction in cellulose content of up to 8 % compared to fibres from other samples. In contrast, the samples incorporating either surface treatment or matrix modification with rice husk ash showed no significant changes in tensile strength throughout the exposure period, with all p-values exceeding 0.05. Notably, samples combining both approaches demonstrated a 16 % improvement in tensile strength after 30 weeks. This study presents novel method for mitigating alkaline degradation in cellulosic fibres within harsh cementitious environments by utilising agricultural residues. These findings support the development of lightweight, sustainable construction elements such as building exteriors, roofing systems, and decorative components. • Innovative approaches are proposed to improve alkaline resistance of flax fibre polymer in concrete. • Long-term accelerated in-situ ageing tests were conducted. • FTIR, SEM-EDX and TGA tests were conducted to explore long-term degradation and mechanisms. • The proposed approaches are applicable for different natural fibres in concrete.