New Deterioration Index and Overdesign Factor of Strength for Structural Concrete due to Freezing and Thawing Action
Naoki KATO, Kenji KOBAYASHI, Tetsukazu KIDA, Tsutomu KONDO, Makoto IMANO, Makoto SUDO, Shizuka IZAWA and Kiyoshi KATO
Abstract:It is the worldwide problem to improve the earthquake-proof and the durability of concrete structure; therefore, the many researches concerned have been carried out and good results already have been obtained. However, the enormous time and labor are spent in the event of evaluating the freezing and thawing deterioration. The practical evaluation method has been developed newly on the basis of the phenomenal fact of the durability deterioration. Thus, the surface deterioration index being able to be applied to the existing concrete structure has been obtained as the surface defect ratio due to the popping-out instead of the usual relative dynamic modulus of elasticity and the mass variation. Furthermore, the present paper deals with the relationships between the surface defect ratio, the compressive strength and the relative dynamic modulus of elasticity and also that the boundary relative dynamic modulus of elasticity ƒÀb=60% corresponds to the boundary surface defect ratio ƒ¿b=8.0% for the first time. Such an index indicates that the surface defect ratio is highly structure-sensitive in comparison with the mass variation. In addition, the overdesign factor of structural concrete strength has been clarified considering the durability deterioration. Key Words:Concrete, Popping-out, Durability, Meteology, Freezing and thawing action, Surface defect ratio, Elastic modulus, Repeated fatigue, Creep, Design strength, Overdesign factor