6. Generalised Mix Design Rules for Concrete with Recycled Aggregates

A conceptual formulation for controlling the resulting mechanical properties of Recycled Aggregate Concretes (RACs) is proposed via a set of generalised mix-design rules intended at covering the specific features of Recycled Concrete Aggregates (RCAs). As a matter of fact‚ the RCAs are characterised by a higher porosity and water absorption capacity than ordinary aggregates and‚ thus‚ general mix-design rules for ordinary structural concrete cannot be applied to RACs as such. Therefore‚ the formulations proposed herein are intended at generalising those rules taking into account the key properties of RCAs‚ as they are possibly influenced by the alternative processing procedures‚ which can be applied when turning demolition debris into concrete aggregates. Particularly‚ these formulations aim at predicting both the final value and the time evolution of compressive strength of RACs depending on their production procedure and mixture composition. The proposed formulations are calibrated and validated on the results of various experimental campaigns covering the effect of several aspects and parameters‚ such as the processing procedures‚ the source for RCAs‚ the actual aggregate replacement ratio‚ the water-to-cement ratio‚ the water absorption capacity and the initial moisture condition of coarse recycled aggregates. Design charts of the proposed formulations show ease of the method as well as the potential of employing this rational design method for RAC.