A novel mix design methodology for Recycled Aggregate Concrete

This paper proposes a conceptual formulation for predicting and controlling the compressive strength of Recycled Aggregate Concrete (RAC) mixtures, by explicitly taking into account the specific features of Recycled Concrete Aggregates (RCAs). In fact, since RCAs are significantly more porous than Natural Aggregates (NAs), the mix design rules commonly employed for ordinary structural concrete cannot be applied as such for RACs. Therefore, the formulation proposed herein is intended at generalising the aforementioned rules with the aim to take into account the higher porosity of RCAs. Although being a mainly conceptual methodology, the proposed formulation is supported by a wide set of experimental results: they unveil the influence of several aspects and parameters (such as source and processing procedures of RCAs, aggregate replacement ratio, water-to-cement ratio, water absorption capacity and initial moisture condition of aggregates) on the resulting compressive strength of RAC. Finally, the proposed mix design methodology demonstrates that the resulting compressive strength of RACs can be predicted by taking into account only one parameter (i.e., water absorption capacity) identifying the “quality” of RCAs. Further generalisations intended at controlling other physical and mechanical parameters of RAC are among the future development of this research.