Size Effects on Uniaxial Compression and Tension in Recycled Aggregate Concrete Fabricated Using Conventional and Equivalent Mortar Volume Techniques

The equivalent mortar volume (EMV) method, praised for being cost-effective and efficient in improving recycled aggregate concrete (RAC) with minimal natural aggregates, is nevertheless complex regarding the internal structural impacts on uniaxial mechanical properties and size effects. This study rigorously investigates these size effects on RAC’s uniaxial tensile and compressive behaviors, fabricated via conventional and EMV methodologies, through extensive experimental and numerical analyses. Two-dimensional random polygonal aggregate models and discrete element mesomodels with heterogeneous properties were initially developed. After calibration, the impacts of the water-to-cement ratio, recycled aggregate content, and fabrication methods on compressive and tensile strengths, elastic modulus, and peak strains were thoroughly evaluated. Ultimately, size reduction coefficients for tensile and compressive strengths are proposed for practical application. Key findings include the following: (1) The EMV method significantly augments RAC’s elastic modulus and compressive strength, with a lesser effect on tensile strength. (2) Compared to conventional RAC with the same water-to-cement ratio, RAC produced using the EMV method exhibits delayed compressive damage and less severe damage overall, while tensile damage remains unchanged. Both types show similar failure patterns and crack distributions. (3) The size effect on compressive strength in the EMV method-cast-RAC aligns with that of natural aggregate concrete (NAC) with a similar water-to-cement ratio, exhibiting greater sensitivity than conventional RAC. In contrast, the tensile strength size effect is more akin to conventional RAC and less pronounced than NAC. (4) For RAC fabricated using the EMV method, size reduction coefficients of 0.70 for compressive strength and 0.77 for tensile strength are recommended for sizes ranging from 50 mm to 400 mm.