Rheological and Mechanical Behavior of Concrete Mixtures with Recycled Concrete Aggregates

Abstract

This paper investigates the workability, compressive strength, and elastic modulus of normal strength concrete mixtures that use recycled concrete aggregates (RCA) as replacement for virgin coarse natural aggregates. To provide a regional geographical representation of the variability in material quality and properties, a total of 144 mixtures with 16 different RCA sources are used in the experimental program. Three RCA concrete mix design methods utilizing varying amounts of direct volume aggregate replacement, direct weight replacement, and equivalent mortar replacement are compared. It is found that the RCA material properties do not affect the workability of RCA concrete designed using the direct volume replacement method. However, for the equivalent mortar replacement method, there is a significant reduction in workability even when the maximum recommended amount of water reducer is used. The compressive strength and elastic modulus of concrete are not significantly affected by the mix design method. Depending on the RCA source, the compressive strength of RCA concrete is generally comparable to the strength of concrete with virgin aggregates. However, there is a greater effect in the elastic modulus as the amount of RCA is increased. The results suggest that the RCA material properties that most affect the mechanical behavior of concrete are the aggregate water absorption and deleterious material content.