Influence of ring size on the restrained shrinkage behavior of ultra high performance fiber reinforced concrete

In order to evaluate the restrained shrinkage behavior of ultra high performance fiber reinforced concrete (UHPFRC), ring-tests with three different wall thicknesses and two different diameters of inner steel ring were performed. Partially exposed free shrinkage and tensile tests were carried out simultaneously to assess the theoretical elastic stress, stress relaxation, degree of restraint and potential for cracking in the concrete. Test results indicated that the UHPFRC ring specimen with a thicker steel ring demonstrated a faster theoretical cracking time, higher stress relaxation and degree of restraint than that of a thinner steel ring, whereas those factors were rarely affected by the diameter of the inner steel ring. About 39-65 % of the theoretical elastic stress was relaxed by the sustained interface pressure. Since the actual residual tensile stress of all specimens was less than the tensile strength, the computed cracking potential varied from 0.43 to 0.7, and thus no shrinkage crack was observed. Finally, the degree of restraint provided a linear relationship with the ratio of steel and concrete wall thickness.