Investigations on fracture in reinforced concrete beams in 3-point bending using continuous micro-CT scanning

This study explores a fracture process in rectangular reinforced concrete (RC) beams subjected to quasi static three-point bending. RC beams were short and long with included longitudinal reinforcement in the form of a steel or basalt bar. The ratio of the shear span to the effective depth was 1.5 and 0.75. The focus was on the load-deflection diagram and crack formation. Three-dimensional (3D) analyses of the size and distribution of pores and cracks were carried out with an X-ray micro-computed tomography system SkyScan 1173 of high resolution that is a very valuable non-destructive tool for studying a 3D material interior. The tomography system was connected with a quasi-static loading machine ISTRON 5569 to continuously follow fracture changes without loading breaks. The beams failed in shear due to a diagonal shear crack that was steeper with basalt reinforcement. The shear strength and flexural strength of RC beams with steel reinforcement were higher by about 10% than of RC beams with basalt reinforcement. The deflection corresponding to the maximum load of RC beams was higher by about 20-25% in RC beams with basalt reinforcement due to its lower basalt modulus of elasticity. The final volume of cracks in beams reinforced with basalt bars was higher by about 9-20% than in concrete beams reinforced with steel bars due to a higher beam deflection whereas the maximum crack width in concrete beams reinforced with basalt bars was higher by about 20-40% than in concrete beams reinforced with steel bars. The critical shear crack in RC beams with basalt reinforcement was wider by about 20-40% and steeper by about 10-45% as compared to concrete beams with steel reinforcement. The relationship between the crack volume and beam deflection was bi-linear. Both, aggregate breakage and crack branching occurred during beam bending. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the fracture process of reinforced concrete beams under quasi-static three-point bending, with a focus on crack formation and load-deflection diagrams. The use of basalt reinforcement resulted in steeper diagonal shear cracks, higher crack volume, and wider maximum crack width, as well as increased deflection and crack inclination. The relationship between crack volume and beam deflection was found to be bi-linear, with both aggregate breakage and crack branching observed during beam bending.