MULTIPLE PROTECTION DESIGN FOR DURABLE CONCRETE BRIDGE DECK IN COLD REGIONS

Abstract

 “Reconstruction Roads” are the highways constructed to accelerate recovery from the Great East Japan earthquake that occurred in 2011. The total distance of Reconstruction Roads is approximately 360 km, which includes more than 250 bridges. Because Reconstruction Roads are located in a cold zone, durability against frost attack is necessary for their concrete structures. In addition to freezing and thawing effects, bridges also suffer from alkali silica reaction (ASR) and chloride attack from the use of deicing salt.
 During the construction of a reinforced concrete (RC) slab of the “Mukai sada-nai Bridge,” we designed the concrete and reinforcing materials to be durable. A multiple defense strategy is a key phrase in our durability design. To prevent possible deterioration, at least two countermeasures were applied. The use of fly ash is a core countermeasure because it is effective against both ASR and chloride attack. Air content was designed at 6% to achieve antifrost performance. An expansive agent was also used to reduce the risk of shrinkage cracks. Epoxy-coated reinforcing bars were used to resist corrosion. An RC slab was carefully constructed at the Mukai sada-nai Bridge. Wet curing continued for three months to obtain a pozzolanic reaction. The quality of the hardened concrete was checked by element tests and nondestructive tests. Additional costs to enhance durability were acceptable with regard to risk control. Success at the Mukai sada-nai Bridge was followed by the construction of other durable RC bridge decks on Reconstruction Roads.