Development of Strain-Induced Stresses in Early Age Concrete Composed of Recycled Gravel or Sand

This paper aims at identifying the effect of the substitution of natural coarse gravel and sand by recycled gravel and sand on the early age development of the volume change and the mechanical properties since setting. For this purpose, a new experimental testing protocol for the characterization of cementitious materials at early age is used. This new approach is based on the repeated application of thermal variation and loading using a newly developed testing device. The high porosity and absorption of the recycled aggregate and sand induce a strong reduction of the autogenous deformations, the modulus of elasticity and the strength during the hardening process. A significant increase of the basic creep phenomenon is observed when using recycled aggregate, especially with recycled sand and at very early age. An elastic and viscoelastic calculation of the restraint of the free deformations shows that the use of recycled gravel and sand decreases the risk of cracking in sealed condition.