Influence of Concrete Age on Compressive Behavior of FRP-Confined Concrete
This paper presents the results of an experimental study on the influence of concrete age on the compressive behavior of fiber reinforced polymer (FRP)-confined normal-strength (NSC) and high-strength concrete (HSC). The first part of the paper presents the results of 18 FRP-confined and 18 unconfined concrete specimens tested at 7 and 28 days. To extend the investigation with specimens with concrete ages up to 900 days, existing test results of FRP-confined concrete was assembled from the literature. Based on observations from both short-and long-term influences of concrete age on compressive behavior of FRP-confined concrete, a number of important findings were drawn and are presented in the second part of the paper. It was observed that, at a same level of FRP confinement and unconfined concrete strength, the stress-strain behavior of FRP-confined concrete changes with concrete age. This difference is particularly pronounced at the transition zone of the stress-strain curves. It is found that, in the short-term, the ultimate condition of FRP-confined concrete is not significantly affected by the age of concrete. However, in the long-term, slight decreases in the compressive strength and the ultimate axial strain are observed with an increase in concrete age.