An investigation of concrete stress-strain behavior by the image analysis method

Concrete is a composite load-bearing building material. The deformation behavior of load-bearing materials under load is vital for the building system. Investigation of these brittle and quasi-brittle behavior patterns at various load levels provides an advantage in the evaluation of mechanical properties. In this study, the deformations occurring within the concrete samples in different stress-strain regions were investigated using an image analysis technique. The experimental samples experienced elastic-limit loading for two hours to clearly monitor the deformations at elastic, plastic, and breaking points. For the microstructure studies, the samples were prepared with epoxy for image analysis. Thin-sections were taken from each series of epoxy-impregnated concrete test samples, examined under a microscope, and photographed. Deformation studies on the digital photographs were carried out by the image analysis method. The results show that crack formation and crack types change because of increased stress and deformations. Crack formations within the concrete are parallel to the loading direction and occurred mainly in the aggregate–cement-paste interface. At 85% of the ultimate stress, crack length was measured as 0.665-29.505 mm and crack width 0.180-4.128 mm, while the crack length was 0.305-32.688 mm and crack width were 0.106-2.906 mm at fracture stress.