Behavior of different-sized FRP-confined square compound concrete columns containing recycled concrete lumps

Abstract

A new concrete recycling method is to crush demolished concrete into distinctly large recycled concrete lumps (RCLs), which are in a direct mix with fresh concrete, leading to the so-called compound concrete. Not only can this method decrease the recycling cost by simplifying the recycling process, it can also increase the recycling ratio. However, existing studies have demonstrated that such compound concrete is inferior to normal concrete. To improve the performance of compound concrete, an effective technique is to confine the compound concrete using fiber-reinforced polymer (FRP)–confining tubes, as demonstrated by a limited number of studies through tests on circular compound concrete columns. However, no studies have been done on FRP-confined rectangular compound concrete columns. Moreover, the possible column size effect in such columns has never been investigated; indeed, existing studies have revealed that FRP-confined rectangular normal concrete columns of different-sized specimens may exhibit obvious behavioral difference. Against this background, this paper presents the results of the first-ever experimental program on glass FRP (GFRP)–confined square compound concrete columns of three different sizes. The columns of different sizes had the same effective FRP confinement stiffness, and, therefore, the possible column size effect could be revealed. It was observed that the column size effect was obvious in the test columns in terms of compressive strength. Finally, three existing compressive strength models originally developed for FRP-confined normal concrete were evaluated using the present test results.