Studies on Durability and Deterioration of Reinforced Concrete Structures in Okinawa －Investigation of Existing Structures, 3. Iriomote Island－

摘要

The reinforced concrete structures, mainly bridges, in Iriomote Island are investigated from the view point of durability. The following items are clarified: 1) The average values of the specific weight and water content taken from the damaged portions of the concrete structures are 2.17 and 11.75%, respectively. 2) The above values show that the quality of concrete in Iriomete Island is the lowest one in the series of investigations made by authers. 3) Concrete materials except sand are transported via sea, and the island is remote from center region of Okinawa prefecture. The levels of construction and its administrative works of reinforced concrete structures are not so high to make good quality concrete in the island. 4) Average salt content of the concrete samples taken from the existing structures is 0.39% by mortar weight. This figure is enough large to corrode the reinforcing bars embedded in concrete. 5) The number of RC bridges built during 1951～1955 is 16, and 4 of which are destroyed or rebuilt, 11 of which are seriously deteriorated due to the corrosion of reinforcing bars in concrete. 8 RC bridges are built after 1968, two of which are lightly damaged by their reinforcing bar corrosions and the rest are safely maintained. 6) The main reasons of the above damages are the high content of salt in concrete and the low quality of concrete. 7) The school buildings of this island are not investigated enough. Two schools are observed and concrete samples are taken from their damaged portions. The average of their salt contents is 0.33% and not so different from the value of the bridges. 8) The high rate of damage of bridges in Iriomote Island must be lowered by appropriate measures, which should be applied as soon as possible.