Effect of aggregate sizes on dilation properties and stress-strain behavior of FRP-confined recycled aggregate concrete

Aggregate size plays a crucial role in determining the mesoscale uniformity and compactness of concrete, directly influencing its dilation characteristics. This dilation behavior, especially under axial load, has significant implications for the tri-axial stress conditions when the concrete undergoes passive confinement using Fiber-Reinforced Polymer (FRP). This study focuses on comprehensively investigating the stress-strain behavior and dilation properties of FRP-confined recycled aggregate concrete (RAC), with a specific emphasis on the effects of recycled aggregate (RA) sizes. A series of compression tests were conducted to examine the stress-strain response of FRP-confined RAC, shedding light on how the dilation properties are influenced by varying RA sizes. The results revealed notable differences in the physical properties (crushing index and water absorption ratio) of RA compared to natural aggregates, with these differences significantly impacting the unconfined concrete strength. Although, an increase in aggregate size demonstrated an improvement in FRP confinement efficiency, it did not bring about a change in the ultimate strength of FRP-confined concrete due to the interaction between the weakening of unconfined concrete strength and the increase in confinement efficiency. In addtion, the transition stress on the stress-strain curve proved highly dependent on both aggregate size and FRP confinement efficiency to RAC. Consequently, a new modified transition stress model, accounting for the effect of aggregate size and FRP confinement, was introduced. Incorporating this newly proposed transition stress model into the existing stress-strain expression yielded predicted stress-strain curves that closely matched the experimental results for FRP-confined RAC with varying RA sizes.