Title: Sustained Service Load Behavior of Concrete Beams with Recycled Concrete Aggregates

Author(s): Adam M. Knaack and Yahya C. Kurama

Publication: Structural Journal

Volume: 112

Issue: 5

Appears on pages(s): 565-578

Keywords: beam deflections; neutral axis; recycled concrete aggregate (RCA); sustained load

DOI: 10.14359/51687799

Date: 9/1/2015

Abstract:
This paper describes an experimental investigation on the time-dependent sustained service-load behavior of normal-strength concrete beams with recycled concrete aggregates (RCA) used as replacement for coarse natural aggregates (NA). Eighteen beams were tested incorporating different aggregate replacement amounts, reinforcing details, concrete age at superimposed loading, and beams with and without cracking upon immediate load application. It is shown that increased amounts of RCA result in significant increases in both the immediate and long-term deflections of concrete beams, but this effect is smaller for beams with increased cracking. Greater creep and shrinkage deformations also cause a greater downward shifting of the neutral axis (that is, increase of the neutral axis depth) in RCA concrete beams as compared to NA concrete beams. ACI 318 and Eurocode generally gave good design estimates for the immediate deflections of the test specimens. In comparison, the long-term deflections were significantly underestimated for the uncracked beams. For the cracked beams, the long-term deflections were somewhat underestimated by ACI 318 and overestimated by Eurocode by approximately similar percent errors. The ability of the design methods to predict the measured deflections did not differ significantly between the NA concrete and RCA concrete beams.