Experimental study of dynamic compressive properties of fibre reinforced concrete material with different fibres

This research conducts drop weight impact tests to study the dynamic compressive properties of fibre reinforced concrete (FRC) material with different types of fibres. The impact tests are conducted with an instrumented drop-weight impact system consisting of a hard steel drop weight, two 180 t fast response loadcells, a high-speed video camera, and a fast response data acquisition system. Seven fibre types with different shapes and material properties are considered in the study. They are synthetic fibres, undulated, cold rolled, flattened, hooked end, and two new spiral shape steel fibres developed in this study. A volume fraction of 1% fibre is used in all specimens. The concrete matrix for all FRC specimens is mixed to obtain a compressive strength of 35 MPa. The drop-weight impact experiments are conducted with two different drop heights in order to study the dynamic material properties at different strain rates. The impact forces on top and bottom of specimens are measured to investigate the axial inertia effects and the stress wave propagation effect. The high-speed video camera is used to capture the failure process, displacement and velocity responses of specimens, which are used to estimate the strain and strain rates of the specimen under impact loading. Strain gages are also used for direct strain measurements. The dynamic stress–strain relations and impact resistance of the tested specimens are compared. The influence of fibre shapes on the failure modes, strength and energy absorbing capability of FRC is discussed. The rate sensitivities of the compressive strength, Young’s modulus and toughness of FRC are also examined. The testing results demonstrate that the new spiral steel fibre proposed in this study provides better confinement to concrete matrix and thus better bonding to concrete material, therefore increases the dynamic resistance and energy absorption capacity (toughness) of FRC.