On the Effect of Freeze-Thaw Cycles in Recycled-Aggregate Concrete and in its Bond with Steel Bars

Recycling Construction and Demolition Waste (CDW) is one of the main actions to be taken to make the building industry more sustainable, under both the economic and environmental standpoints. In this context, many technical and scientific papers and documents have been published in the last two decades on the physical and mechanical properties of Recycled Aggregate Concrete (RAC) and on how these properties may be affected by the peculiar features and engineering properties of Recycled Concrete Aggregate (RCA). Such an extended work, however, has been mainly limited to the material scale, to the detriment of the structural scale. Within this context, the paper is focused on RAC as a material, and on its bond with steel bars (which has structural implications), in the extreme conditions ensuing from freeze-and-thaw cycles. Tension stiffening (strictly related to steel-concrete bond) is investigated through tensile tests on RC specimens. Both recycled-aggregate concrete as such, and tension stiffening are also numerically modelled, and comparing experimental and numerical results allows to conclude that there is hardly any difference between the behaviors of natural-aggregate and recycled aggregate concrete. The concrete grade is C35 and the freeze-thaw cycles (up to 150 cycles) are characterized by a temperature variation from +4 °C to −18 °C and back to +4 °C in 5 hours.