Advanced techniques for the study of shrinkage-induced cracking of concrete with recycled aggregates at early age

The present work analyses the impact of the substitution of natural coarse gravel and sand by recycled gravel and sand on the concrete behavior under free and restrained condition since setting. The methodology presented in this paper associates a Temperature Stress Testing Machine (TSTM) with free shrinkage tests and other experimental advanced techniques, such as direct tensile testing and the monitoring of elastic properties using repeated loading testing. It is observed that the cracking sensitivity decreased with recycled concrete content in spite of lower tensile strength. This is due to the major influence of relaxation, but also damage and coupling effects. These phenomena contributed to a decrease of the stresses with different magnitude and kinetics. For concretes with recycled gravels, the major stress reduction was attributed to relaxation. The reduction of elastic modulus due to damage appeared from the first 24 h while creep seemed to develop later, as tensile stress to strength ratio became higher. Concrete with recycled sand had a different behavior with earlier creep development and lower damage.SCOPUS: ar.j