Alkali-silica reaction affects the shale and an occasional quartz sand grain in the fine aggregate, but is not deemed to be significant cause of the deterioration. The field survey found no evidence of permanent expansion such as closure of joints, blowups, nor gel efflorescence. The cement paste pore structure adjacent to the shale grains appears filled with reaction product, with only minor cracking (about the length of the sand grain). The accommodation of reaction products by the cement paste pore structure may have limited expansive stresses created by the reaction of the shale with alkali hydroxides in the pore solution. Significant cracking associated with ASR may occasionally be found when a large (5 mm) shale aggregate is located in the upper-most 20 mm of the concrete.