Measurements of strain and humidity within massive concrete cylinders related to the formation of ASR surface cracks

This study aims at proving the validity of a notion that the formation of non-expansive near-surface layer is responsible for surface cracking in ASR-affected concretes by a laboratory experiment. Relationship between the progress rate of the front of non-expansive layer toward inner portions and the formation of the first surface cracks was scrutinized by measuring relative humidity (R.H.) values and strains within a massive concrete cylinder (ϕ450 mm × 900 mm) with reactive aggregates under a dry environment. It was presumed from the measurements that a non-expansive layer of about 40 mm had been formed at the first cracking. Thereafter, the environmental humidity was raised to > 95% R.H. Pursuit of the growth of surface cracks and subsequent measurements of strains and R.H. values within the concrete cylinder under the moist environment suggested that the re-saturation continuously gave rise to the generation of tensile stresses in near-surface regions leading to active extension of surface cracks.