Experimental Study on Flexural Strengthening of Damaged Reinforced Concrete Bridge Decks Using CFRP Laminates in Nigerian Conditions

Carbon fibre reinforced polymer laminates offer an effective and minimally intrusive method for restoring and enhancing the flexural capacity of deteriorated reinforced concrete bridge decks, yet their performance under Nigerian climatic exposure conditions and with locally available adhesive systems has not been adequately characterised. This study presents an experimental investigation of flexural strengthening of pre-damaged reinforced concrete beam specimens representing bridge deck soffits, using CFRP laminates applied with ambient-temperature epoxy adhesive systems in the high-humidity coastal conditions of Lagos in the South West geopolitical zone. Twelve beam specimens were pre-damaged to approximately 60 percent of their theoretical ultimate flexural capacity by monotonic loading before CFRP laminate application. Specimens were strengthened with one, two, and three layers of unidirectional CFRP and tested to failure after exposure regimes representing ambient, 50-cycle wet-dry chloride immersion, and ultraviolet radiation conditioning. Failure modes, ultimate load recovery, stiffness restoration, and CFRP-concrete interface performance were recorded. Results indicate that one-layer CFRP strengthening restored ultimate flexural capacity to 94 percent of the undamaged control under ambient conditions. Wet-dry chloride conditioning reduced CFRP effectiveness by 11 percent for single-layer systems, primarily through adhesive degradation at the CFRP-concrete interface as confirmed by scanning electron microscopy. Ultraviolet conditioning had a negligible effect on flexural performance. Three-layer CFRP configurations induced premature plate end debonding failure before yielding of internal steel, limiting capacity recovery relative to two-layer systems. The study provides empirically grounded CFRP specification guidance for bridge deck rehabilitation in Nigerian coastal conditions. Keywords: CFRP strengthening, bridge deck rehabilitation, flexural capacity, Lagos, bonded laminates.