DYNAMIC MATERIAL CHARACTERIZATION OF CONCRETE

Abstract

The dynamic material behaviour of concrete has been studied by performing experiments under varying strain rate on a suitably designed and developed split-Hopkinson pressure bar apparatus. Three different grades of concrete, M35, M45 and M60, have been identified to investigate the deformation and strength characteristics of standard and high strength concretes under varying strain rate. The strength and fracture behavior thus studied under dynamic loading conditions has been compared with that of the quasi-static loading condition. A detailed experimental investigation has been conducted to explore the influence of the strain rate and the specimen size effect on the dynamic compressive and tensile properties. A systematic study was performed to characterize the dynamic compressive and tensile behavior including the compressive strength, tensile strength, dynamic increase factor, stress-strain curves, critical strain, ultimate strain, deformation and failure process, energy absorption capacity, and strength-time response. In addition, the specimen diameter effect on the compressive strength, tensile strength, dynamic increase factor, critical strain, and energy density was thoroughly discussed. The crack initiation, crack propagation, and failure mechanism were monitored with the help of high-speed photography performed by using a high-speed video camera, Phantom V411. Also, the tested specimens were analyzed to study the failure pattern, fragmentation, shape, and size of fragments under high strain rates. Weighing analysis was performed on the tested concrete specimens to investigate the strain rate effect on fine and coarse fragment quantity formed. The material characterization was initially performed under quasi-static loading on standard (M35, M45) and high-strength concrete (M60). The quasi-static compression and splitting tensile tests were conducted using the HEICO Compression Testing Machine (CTM). The quasi-static compression test was performed on the concrete cubes of 150 mm size as well as on the cylindrical specimens of aspect ratio (L/D) ≈1 (Diameter ≈ 29.5 mm, Length ≈ 30 mm). Similarly, the quasi-static splitting tensile test was performed using the Brazilian disc method on the cylindrical specimens of 29.5 mm and 45 mm diameter having L/D≈1 and L/D≈0.67 aspect ratios, respectively. In addition, the dynamic compressive and tensile behaviour was studied through the experiments carried out using the developed SHPB setup under varying strain rates on cylindrical specimens of diameter 29.5 mm and 45 mm maintaining a nearly constant length of 30 mm.