The use of recycled concrete aggregate (RCA) in the U.S. has mostly been limited to non-structural applications such as roadway sub-base. To advance this sustainable material as replacement for coarse natural aggregates (e.g., gravel) in structural applications, a fundamental understanding of the behavior of RCA concrete is needed while also incorporating the variability in RCA properties. To this end, this dissertation investigates the short-term and long-term structural behavior of RCA concrete through material and member level experiments, accompanying analytical models, and statistical investigations. Three RCA concrete mix design methods utilizing up to 100% (i.e., full) direct volume aggregate replacement, direct weight replacement, and equivalent mortar replacement are compared. To represent the variability in material properties, sixteen RCA sources from the midwestern U.S are used.
The research vision is to use RCA with minimal deviation or additional processing from current practice for conventional reinforced concrete structures. The material level tests show that direct volume replacement is the best method to design RCA concrete mixes because this simple method results in a consistent volumetric yield and workability as conventional concrete. While there is a decrease in the concrete strength and stiffness as a result of RCA, the dissertation proposes design relationships to pre-qualify the RCA (using the aggregate water absorption and deleterious material content) to achieve specific concrete strength and stiffness performance criteria.
RCA has a much greater effect on concrete stiffness than strength; and thus, increased deflections may be a greater limitation. Based on creep and shrinkage experiments, the dissertation develops adjustment factors for conventional concrete creep and shrinkage models to predict the deformations of RCA concrete. These models are validated using the long-term deflections from eighteen reinforced concrete beam test specimens. The beams are subsequently tested under ultimate loads to experimentally and analytically investigate the flexural, shear, and bond failure in RCA concrete. The measured long-term beam deflections are also used to validate a new time-dependent concrete material model for the OpenSees structural analysis program. This model is then extended to parametric Monte Carlo investigations to determine the service-load behavior of beams and columns incorporating the variability in RCA properties.