Two earthquakes occurred on October 23 and November 9, 2011, in Van, Turkey, with magnitudes (Mw) of 7.2 and 5.6, respectively. The types of the damage and collapse that occurred in both earthquakes necessitate a detailed examination of the load-bearing elements, which essentially comprise the components of RC buildings, in terms of their material quality. For this purpose, the compressive strengths, X-ray diffraction (XRD), and scanning electron microscopy with X-ray microanalysis (SEM/EDS) were performed on concrete samples collected from the collapsed buildings, with a view to understand the role of the materials in the devastation caused by the earthquakes. Visual observations and the results of the tests showed that there were not only construction and manufacturing failures, but also the strength of the concrete was a crucial factor that contributed to the damage and collapse of the buildings. In addition to these conclusions, results obtained from XRD and SEM-EDS showed that compressive strength increased with the size of calcium-silicate-hydrate (C-S-H) peaks, but much less significantly with the Ca-Si (C/S) ratio. (C) 2016 American Society of Civil Engineers.