Fragmentation from spallation of RC slabs due to airblast loads

Terrorist attacks using improvised explosive devices on reinforced concrete buildings create a rapid release of energy in the form of a shock wave. Most casualties and injuries resulting from such an attack are not caused by the blast itself, but rather by the disintegration and fragmentation of the RC member due to concrete spallation on the opposite side of the member and which is propelled at high velocities depending on the size of the fragments. Therefore, it is important to analyze the size distributions of the concrete fragments from spallation. In this paper, two RC specimens were tested under explosive loading in a blast chamber: the first, a reinforced concrete (RC) specimen; and the second, an identical RC specimen retrofitted with 6 near surface mounted (NSM) carbon fibre reinforced polymer (CFRP) plates on both the top and bottom faces. Both specimens were subjected to the equivalent 2.1 kg of TNT at a standoff distance of 0.6 m, resulting in significant scabbing of the concrete. All fragments resulting from the blast tests were collected and analyzed. A sieve analysis was carried out to investigate the size distributions of the fragments from the two specimens. It was found that the fragment size followed both a Weibull distribution and a Rosin–Rammler–Sperling–Bennet (RRSB) distribution. The distribution of the fragment shape factor was also studied. The fragment shape factors were distributed according to the lognormal distribution. Furthermore, the influence of fragment size distribution on energy density dissipation was evaluated.