The spallation of the concrete slabs or walls resulting from contact detonation constitutes risk to the personnel and equipment inside the structures because of the high speed concrete fragments even though the overall structures or structural members are not destroyed completely.Correctly predicting the damage caused by any potential contact detonation can lead to better fortification design to withstand the blast Ioadings.It is therefore of great significance to study the mechanism involved in the spallation of concrete slabs and walls.Existing studies on this topic often employ simplified material models and 1D wave analysis, which cannot reproduce the realistic response in the spallation process.Numerical simulations are therefore carried out under different contact blast Ioadings in the free air using LS-DYNA.Sophisticated concrete and reinforcing bar material models are adopted, taking into account the strain rate effect on both tension and compression.The erosion technique is used to model the fracture and failure of materials under tensile stress.Full processes of the deformation and dynamic damage of reinforced concrete (RC) slabs and plain concrete slabs are thus observed realistically.It is noted that with the increase of quantity of explosive, the dimensions of damage crater increase and the slabs experience four different damage patterns, namely explosive crater, spalling, perforation, and punching.Comparison between the simulation results of plain concrete slabs and those of RC slabs show that reinforcing bars can enhance the integrity and shearing resistance of the slabs to a certain extent, and meanwhile attenuate the ejection velocity and decrease the size of the concrete fragments.Therefore,optimizing reinforcement arrangement can improve the anti-spallation capability of the slabs and walls to a certain extent.