Freeze-thaw resistance of normal and high strength recycled aggregate concrete

The reuse of Construction and Demolition Waste (CDW) employed as aggregates for new concrete production, leading to the so-called Recycled Aggregate Concrete (RAC), is an excellent solution from the environmental point of view. In fact, the influence on the use of Recycled Concrete Aggregate (RCA) on the resulting RAC's properties has been widely investigated in the recent years, but evaluation of concrete's performance should not be limited only to its behavior under "ordinary" conditions and the characterization of RAC in terms of durability become of extreme importance for structural application. For instance, in cold regions, the concrete's performance over time is closely related to its reaction to freeze-thaw cycles. As a matter of fact, when concrete is exposed to this type of attack, the porous structure tends to absorb water and, then, this water may turns into ice due to temperature variations. This process causes changes in the internal pore structure, reduction in mechanical the properties and appearance of cracks. In this context, this study investigates the mechanical and physical performance of different RAC mixtures after the exposure to fast freeze-thaw cycles. Specifically, normal and high strength mixtures (i.e., 35 and 60 MPa) with 100% RCAs were subjected to 150 cycles in which temperature variation from 4°C to -18°C was applied. The experimental results showed that degradation induced by freeze-thaw cycles was more pronounced in the normal strength concrete samples.