Granulated concrete samples obtained from the upper surface of deteriorated RC slabs under the surface asphalt layer of a road were examined by microscopic technique and chemical analyses. The muddy components in the granulated concrete were composed of fine-granulated cement pastes and externally invasive clays and asphalt. Deicing salts were thought to be involved in the granulation of concrete, because calcium hydroxide had completely disappeared from the cement pastes although carbonation was not observed. The granulation was considered to be triggered by cracks caused by re-bar corrosion or an alkali-silica reaction. It was estimated that the progress of granulation was due to a complex mechanism of physical action by repetition loads and chemical action by deicing salts.