Durability assessment and reliability modelling of CFRP composites under simulated long-term exposure to acidic, alkaline, and aqueous environments

• Accelerated ageing used to study CFRP in water, acid, and alkaline solutions. • Tensile strength degradation linked to matrix and fibre matrix interface damage. • Weibull statistics applied for reliability and hazard assessment of CFRP sheets. • Environment specific reduction factors derived for design in aggressive conditions. • Proposed factors improve on ACI 440.2R by accounting for exposure environment. A detailed experimental programme was conducted to investigate the durability of unidirectional Carbon Fibre Reinforced Polymer (CFRP) sheets exposed to water, acidic (pH = 1), and alkaline (pH = 12.6) environments under accelerated ageing. Immersion periods of up to 12 weeks at elevated temperature were used to simulate long-term degradation mechanisms relevant to practical applications such as underwater structures, sewer networks, and industrial plants. Residual tensile strength, failure mechanisms, and microstructural changes were examined at the end of exposure. After 12 weeks, CFRP sheets retained 84.1 % of their tensile strength in water, 73.8 % in acid, and 66.7 % in alkaline solution, demonstrating that alkaline environments cause the most severe degradation. SEM analysis revealed microcracking within the resin matrix and fibre matrix interface, together with the formation of expansive products in acidic and alkaline environments, as the principal damage mechanisms . While elevated temperature accelerated degradation, the extent was mainly dictated by the environment’s aggressiveness. A reliability-based model was developed using the two parameter Weibull distribution to quantify the variability of strength degradation and associated hazard under each exposure condition. The model provides a rational framework for assessing the service reliability of CFRP strengthened structures in chemically aggressive environments. Based on inferential probability theory, environment specific reduction factors of 0.90, 0.82, and 0.80 were derived for water, acidic, and alkaline exposures, respectively. These values address a key gap in current design practice by offering a statistically grounded alternative to the single oversimplified factor (0.85) prescribed in ACI 440.2R, irrespective of service environment.