This paper simulates an impact-echo array technique for the two-dimensional imaging of defects in thick concrete structures. A finite difference time domain (FDTD) Model was employed for simulating the impact-echo method. The absorbing boundary conditions were employed in the FDTD for efficient calculation. The signals predicted using the FDTD models were then used for 2D image reconstruction of the cross-sectional region of the structure. The reconstruction algorithm uses time shifting (migration) of the signals based on point-source assumption for the impact sources. The images are represented in a typical "B-scan" format. Several types of defects were simulated, and parametric studies on the different parameters that influence the image quality during imaging of defects in concrete structures were examined.