Durability of blast-furnace slag concrete mixed with expansive and swelling admixtures

South Korean concrete crack management standards deem cracks larger than 0.3 mm to be defects. However, concrete crack reduction technology is lacking and urgently needed to meet these standards. In this study, the durability characteristics of blast-furnace slag concrete with an expansion material and swelling admixtures were examined. We observed that expansion using the expansive material not only contributed to the initial expansion but also continued to act during drying shrinkage, maintaining a drying-shrinkage reduction rate of over 40 %. This expansion effect is shown in the initial stage and contributes to compensating for contraction by continuous expansion activity in the long term. In addition, the freeze-thaw resistance was observed to be higher in the case of a mixture substituted with 30 % fine blast-furnace slag powder than in the standard mixture using normal Portland cement, and the carbonation resistance showed that the carbonation penetration depth decreased as the curing time increased. Thus, to achieve crack control by initial drying shrinkage of the blast-furnace slag concrete, it is expected that the expansion material would effectively control cracking, and the use of this expansion material will be advantageous in securing better quality bentonite than hydroxy propyl methyl cellulose.