Evaluation of cracking behavior of concrete at early-age based on ring test

Two steel rings with the same external diameter, but the different thicknesses were used for the restrained ring tests on three kinds of concrete with different strength grade. The development of inner strain along the ring at three different height from top to bottom were recorded from concrete cast. The experimental results show that the development of inner surface strain of the steel ring coordinates well with the development of shrinkage stain of concrete. By tracking the inner surface strain of the steel ring the development of concrete shrinkage can be well found and the exact cracking time can be known. Regarding sensitivity of measurement, the thicker the steel ring, the higher the measuring sensitivity. For the given ring thickness, the measured strain at the middle of the ring is the largest and at top is the smallest. The higher the strength of concrete, the larger the inner strain can be measured. Meanwhile, the cracking tendency is high also.