Influence of GGBS and SRA on Early-Age Shrinkage Cracking Potential of Self-compacting Concrete: Insights from Capillary Pressure

Shrinkage cracking is a prevalent failure mode in concrete structures, particularly those with low volume-to-surface ratios, compromising durability and increasing maintenance costs. Early-age concrete is more prone to shrinkage cracking due to insufficient strength development. Capillary pressure is recognized as the primary driver of shrinkage in concrete; however, conventional sensors can only measure capillary pressure up to 100 kPa for approximately seven hours post-casting, hindering a comprehensive understanding of the relationship between capillary pressure evolution, early-age shrinkage, and cracking potential. This study employs a novel high-capacity tensiometer (HCT) capable of monitoring capillary pressure in concrete up to 2000 kPa, thereby extending measurement capabilities. The effects of ground granulated blast furnace slag (GGBS) and shrinkage-reducing admixture (SRA) on capillary pressure evolution and shrinkage cracking potential were investigated. An extensive experimental program, including measurements of settlement, free and restrained shrinkage, elastic modulus, and tensile strength, was conducted alongside capillary pressure monitoring. Results show that significant shrinkage occurs during initial and final setting times when concrete remains in the plastic phase, with minimal capillary pressure evolution. With further development of capillary pressure, cracking was observed during the semi-plastic phase due to a marked reduction in strain capacity of concrete. The findings also indicate that although GGBS replacement reduces capillary pressure evolution, it is not an effective strategy for mitigating shrinkage cracking due to concurrent reductions in tensile strength. Notably, the effectiveness of SRA is inversely related to GGBS content, necessitating careful consideration in its application.