With the decreasing use of river sand, crushed stone was brought into use as aggregate. Recently, alkali aggregate reaction as a cause of cracks in concrete construction has become a social problem. Aggregate made of certain kinds of pyroxene andesite reacts with the alkali ingredient contained in the concrete, which expands and cracks. This reaction has not been thoroughly explained yet. Frost damage during construction and water penetration cracks and then freezing cause frost damage, but on Gunkanjima the temperature rarely falls below zero. Perhaps the weathering of the island's buildings owes little to these two causes.