Mechanical and Durability Properties of Optimally Treated Recycled Concrete Aggregates

The incorporation of Recycled Concrete Aggregates (RCA) aiming to produce Recycled Aggregate Concrete (RAC) mixtures tends to reduce CO2 emissions, cost and energy consumptions; however, the existence of old cement paste (adhered mortar) attached to the surface of RCA leads to inferior fresh, mechanical and durability properties compared to conventional concrete. This paper reports on a mechanical treatment method implemented to partially remove the adhered mortar in RCA samples placed inside a rotating concrete truck mixer. The impact of the RCA with the metallic walls was determined in terms of mass loss, circularity index and image analysis within different time frames. Based on the results, the optimum mechanical treatment duration was found to be 3 hours. Following, 17 different combination mixtures including partial or full replacement percentages of untreated, treated, coarse or fine RCA at 0.25 and 0.50 w/c ratios were investigated by means of mechanical and durability properties. For high w/c ratios, the inclusion of mechanically treated aggregates was more beneficial in terms of compressive strengths, while for low w/c ratio, the early-compressive strengths were enhanced. Even though the splitting tensile strengths were not significantly affected for low w/c concretes, the inclusion of treated aggregates reduced the chloride permeability and drying shrinkage of all mixtures.