IMPACT BEHAVIOR OF PLAIN CONCRETE LOADED IN UNIAXIAL COMPRESSION

The uniaxial stress-strain response has been measured for air-dried plain-concrete cylinders, nominally 100 mm in diameter and 250 mm long, loaded in compression at both a slow static rate of about 10 microstrains per second and a much higher impact rate of between 5 and 10 strains per second. Design concrete strengths of 30 and 50 MPa were tested. Static loading was carried out in a hydraulic testing machine, and a guided free-falling mass was used for impact loading. The impact and static responses are compared to provide some insight into the behavior of concrete during hard-impact loading. Differences in behavior are identified for various strength and deformation characteristics. Although the maximum strength and corresponding axial strain, the energy-absorption capacity at failure, and the secant modulus all increase during impact loading, the initial tangent modulus does not appear to change very much. Other characteristics such as volumetric strain and Poisson's ratio are also studied. A simple physical model is used to help explain observed changes.