Macro-mechanical models for evaluation of the elastic modulus of recycled aggregate concrete

Macro-mechanics is a rational basis for determining some of the mechanical properties of concrete based on its composition. In this investigation, well known macro-mechanical models for elastic modulus of Natural Aggregate Concrete (NAC) are adapted and generalized to make them applicable to Recycled Aggregate Concrete (RAC). Two sets of models are presented: (1) Phase-Based Models: where the elastic modulus is expressed in terms of the volume fractions and elastic moduli of relevant concrete mixture constituents, (2) Bulk-Based Models: where the elastic modulus is expressed in terms of the total mortar and aggregate volumes and elastic moduli of two limiting mixes, one with 0% and the other with 100% replacement of coarse natural aggregate by RCA. The detailed procedures are presented and the derived expressions for evaluating the elastic modulus are shown. To validate the proposed models, results of an experimental program involving many NAC and RAC mixes are used, with the mixes proportioned by either the traditional method of the American Concrete Institute (ACI) or by the Equivalent Mortar Volume (EMV) method developed by the writers. Reasonable agreement is observed between the computed and corresponding experimentally measured elastic moduli, with maximum difference of 12%.