Structural performance of repaired reinforced concrete beams with damaged compression zones: an experimental study using digital image correlation

Abstract This study investigates the repair effectiveness of reinforced concrete (RC) beams with crushed compression zones and reduced tensile reinforcement. The aim was to evaluate the restoration of load-bearing capacity and flexural performance after repair using polymer-modified mortar. The experimental program included four-point bending tests, high-precision displacement monitoring, and digital image correlation (DIC). Experimental results were compared with predictions obtained from a nonlinear sectional deformation model and with reference beams having reduced reinforcement but no damaged compression zone. The repaired beams reached a reinforcement yield moment of 8.62-8.97 kNm and an ultimate bending moment of 9.5 kNm. The strain in the repaired compression zone remained below the ultimate strain capacity of the repair mortar, indicating stable composite action between the original concrete and the repair material. The repair method increased the reinforcement yield moment by approximately 35%, confirming effective restoration of the compression zone and improved structural performance. The results demonstrate the usefulness of DIC for assessing repaired RC beams and support the application of polymer-modified repair systems for beams with damaged compression zones.