若材齢で凍結融解を受けた普通および軽量骨材コンクリートの塩化物イオン透過性

Abstract

The chloride permeability of normal weight and lightweight concretes subjected to freeze-thaw damage at the age of 3 days was evaluated by using the AASHTO T277 chloride permeability test method and the freeze-thaw test method similar to that recommended by JSCE-1986. The relative dynamic modulus of elasticity was obtained from the results of ultrasonic pulse velocity measurements for each specimen before and after the freezing and thawing test. The results showed that the chloride permeablity of the normal weight concretes having an air content of at least 7.6% changed little with the repeated cycles of freezing and thawing ranging from 18 to 44 cycles, irrespective of the presence and the type of mineral admixtures. It was found that the application of freeze-thaw cycles obviously decreased the values of the relative dynamic modulus of elasticity in the normal weight concretes, but that the reduction in the relative dynamic modulus of elasticity did not always result in an increase in the chloride permeablity of the concretes. The test results also indicated that most of lightweight concretes made with fully-saturated expanded shale aggregates exhibited an extremely high chloride permeability, when they were subjected to a single freeze-thaw cycle. Furthermore, the type of microcracks developing in the normal weight concretes under the repeated freeze-thaw cycles was discussed.