Experimental study on self-compacting concrete-filled steel tube samples containing shrinkage-controlling admixtures

Abstract

Once again, the earthquake disaster in Turkey and Syria indicates the significance of aseismic structures. Concrete-filled steel tube (CFT) columns are key components in such structures. In this study, the effect of shrinkage control admixtures on the performance of self-compacting mixes that are often used in CFT column construction was evaluated. They were confined to a 3 mm thick cylindrical hollow steel tube and the infilled concrete shrinkage was monitored with the embedment of a vibrating wire strain gauge. The concrete length of this compound was found to be reduced as the length of the confining tube expanded. However, this change in concrete length was reduced by 70% with the use of a commercial grade liquid mixture that reduces shrinkage in the early stages. A substantial reduction in concrete shrinkage was observed with the use of limestone powder and a compensating admixture for shrinkage. The use of limestone also improved the resistance of concrete to water permeation and chloride ion transport by pore filling effects. Although steel confinement reduced concrete shrinkage by 50% at 28 days, the addition of specialty admixtures is still highly recommended to avoid the effect of debonding, induced by the shrinkage discrepancy between confining steel and the inner concrete mass.