Experimental investigation of corrosion effects on the structural performance of RC slabs incorporating distributed fibre optic sensing

Research aims and scopes:

This research investigates the influence of reinforcement corrosion on the structural behaviour, deterioration mechanisms, and damage development of reinforced concrete (RC) slabs, with particular emphasis on two-way slab systems representative of ageing bridge deck. The principal aim is to establish a clearer relationship between the severity and spatial distribution of corrosion and changes in structural performance, including load-carrying capacity, stiffness, deformation, cracking, strain distribution, and failure mechanism. A further objective is to evaluate whether advanced sensing and measurement techniques can provide reliable indicators of corrosion-induced deterioration and structural damage.

The experimental programme considers both single- and double-layer reinforced concrete slabs subjected to different levels of accelerated reinforcement corrosion. This enables the effects of reinforcement configuration and corrosion severity to be examined systematically. Particular attention is given to the transition between punching, combined flexural–punching, and flexural failure mechanisms as corrosion progresses, and to understanding how deterioration of the reinforcement and steel–concrete interaction contributes to this behaviour.

The scope also includes the application of distributed fibre-optic sensing (DFOS) alongside conventional strain gauges and displacement measurements to characterise the evolution and spatial localisation of structural response. Dynamic hammer testing is investigated as a complementary global damage assessment technique by relating changes in dominant vibration frequency to stiffness degradation. Following structural testing, the reinforcement is extracted and subjected to high-resolution three-dimensional scanning, allowing corrosion morphology, local section loss, residual cross-sectional properties, and pitting characteristics to be quantified. These measurements provide a direct connection between the physical corrosion condition of individual reinforcement bars and the measured structural response of the slabs.

Main body of work:

The experimental programme consists of 1.7 m × 1.7 m × 0.15 m two-way RC slabs with either single-layer or double-layer reinforcement. For each reinforcement configuration, an uncorroded control specimen and slabs subjected to different corrosion levels were tested. Corrosion was introduced using an accelerated electrochemical procedure with a saline electrolyte and externally applied direct current. The achieved corrosion levels were subsequently quantified using gravimetric measurements and detailed three-dimensional scanning of the extracted reinforcement.

The slabs were tested under central concentrated loading using a 300 × 300 mm loading plate under displacement-controlled conditions. Their behaviour was monitored using LVDTs, conventional strain gauges and DFOS installed on the reinforcement. The measurements were used to evaluate load–deflection behaviour, stiffness degradation, reinforcement strain development, crack localisation, deformation patterns and redistribution of structural response. The results show that corrosion can substantially modify the governing structural mechanism rather than simply causing a proportional reduction in ultimate strength. The uncorroded specimens generally exhibited relatively brittle punching or flexural–punching behaviour, whereas increasing corrosion promoted earlier reinforcement mobilisation, reduced stiffness and a transition towards a more deformation-dominated flexural failure mechanism. The influence was particularly important in double-layer slabs, where corrosion of both reinforcement layers affected the overall load-carrying mechanism and produced a significant reduction in capacity.

The DFOS measurements provide continuous spatial strain information that cannot be obtained using discrete conventional strain gauges. They enable the development of strain localisation, cracking and redistribution around damaged regions to be followed throughout loading. Complementary hammer-impact testing demonstrates that reductions in dominant vibration frequency can be associated with progressive structural stiffness loss, providing a potential global indicator of damage development.

Finally, three-dimensional scanning of the extracted reinforcement is used to characterise the actual corrosion geometry. A digital processing methodology is being employed to distinguish the regular rib geometry of deformed reinforcement from corrosion-induced surface loss, allowing the remaining structural core area, local section loss, pit depth and residual sectional properties to be quantified along individual bars. By integrating structural testing, distributed sensing, dynamic measurements and detailed post-test corrosion characterisation, the work aims to establish a comprehensive framework for understanding and ultimately modelling the residual behaviour of corroded RC slabs. The experimental results will also provide the basis for subsequent nonlinear numerical modelling, including detailed finite-element and nonlinear grillage approaches for assessment of corrosion-damaged slab systems.