Experimental Studies on Dynamic Response of Hardened Cement Paste

This jpaper is concerned with the description and explanations of Hardened Cement Paste (HCP) response to dynamic (explosive) loading. An experimental testing technique has been developed to study the dynamic cracking of HCP samples, using cylindrical explosive microcharges. Following the initiation of the microcharge, radial cracks propagate and measurements of their growth may be conducted. Procedures to predefine the crack path have been investigated, like preparation of linear grooves along the sample. Predefining the crack path enabled relatively simple measurements of its propagation velocity. The dynamic crack propagation velocity was found to be relatively low, within the range of 70-200 m/sec. (about an order of magnitude lower than the theoretical value). The dynamic HCP failure process was found to be usually of multicrack type. Studies of microcharge intitiation near a samples boundary provided insight into the development of scabbing cracks and of their interaction with the radial cracks propagating towards the boundary. It has been found that crack interaction is strongly dependent on the relationship between the stress wave velocity and the crack propagation velocity.