Early-age cracking resistance of ground granulated blast furnace slag concrete

Abstract

High-performance concrete (HPC) generally experiences rather high autogenous shrinkage. If restrained, residual tensile stress will be induced which may be sufficient to cause cracking. Ground granulated blast furnace slag (GGBFS) has been utilized as a mineral admixture to reduce shrinkage cracking in HPC. The restrained shrinkage cracking of concrete containing GGBFS appears to be less than that of concrete without slag. However, the data is limited, and the effect of the GGBFS on the restrained cracking resistance needs to be further investigated. Restrained ring tests on cracking resistance of HPC using GGBFS as 0%, 20%, 35%, and 50% by weight replacements of cement were performed. Four concrete mixtures with the same w/b ratio of 0.32 were placed in a 23 ± 1 °C, 60 ± 5% RH environment, and covered with vinyl and aluminum adhesive tape. The outer rings were removed at 24 h after casting to allow water evaporation through the height of the specimen. Test results showed that: (1) the residual tensile stress at the age of 14.25 days after casting decreased by 18.6%, 33.2%, and 40.9% when the amount of GGBFS increased from 0% to 20%, 35%, and 50%, respectively; (2) the stress rate decreased by 58.9%, 62.5%, and 66.8% when the amount of GGBFS increased from 0% to 20%, 35%, and 50%, respectively, indicating that the cracking resistance based on stress rate increased with increasing GGBFS replacement.