Title: Parametric Service Load-Deflection Analyses of Reinforced Concrete Beams with Recycled Concrete Aggregates
Author(s): Adam M. Knaack and Yahya C. Kurama
Publication: Structural Journal
Appears on pages(s): 301-313
Keywords: immediate and time-dependent deflections; recycled concrete aggregates; reinforced concrete beams; sustained service loads
This paper describes a numerical parametric investigation on the effects of coarse recycled concrete aggregates (RCAs) on the time-dependent sustained service-load deflections of reinforced concrete beams. The varied parameters are the volumetric replacement of coarse aggregate, concrete compressive strength, beam geometry (length, depth, width), rotational restraint at beam ends, top and bottom longitudinal steel areas, ultimate shrinkage strain, ultimate creep coefficient, and ambient relative humidity. In addition, RCA quality is quantified and varied through the water absorption and deleterious material content (for example, wood and asphalt). The beams were analyzed using a time-dependent concrete material model that can capture cracking, shrinkage, and creep behavior. The results show that the deflections of beams with good-quality RCA (with low water absorption and deleterious material content) are not much greater than those for beams with natural aggregate (NA). Importantly, RCA amount and quality have larger effects on the deflections of beams with less cracking (that is, shorter and/or deeper beams) and for beams with increased rotational restraint, for which allowable deflection limits would be less likely to govern design. There are significant differences between the ACI 318 time-dependent deflection factor and the numerical simulation results, with ACI 318 generally providing overly conservative estimates of the time-dependent factor, except for beams with minimal or no cracking. It is also found that RCA has a greater effect on the time-dependent deflections than on the initial deflection.