Development Length of Small-Diameter Basalt FRP Bars in Normal- and High-Strength Concrete

Abstract

Small-diameter fiber-reinforced polymer (FRP) bars have great potential in certain applications, such as concrete sandwich panels, ties, and shear connectors. In this study, the development lengths (Ld) of basalt FRP (BFRP) deformed bars of 4–8 mm diameter (db) will be determined through a series of 44 notched beam tests with concrete of 41–70 MPa compressive strength. The beams measured 101 × 203 mm in cross section and varied in length from 610 to 1,980 mm to accommodate various embedment lengths (Le). Depending on db, Le varied from 5 to 109 db and the clear concrete cover was 30 mm. Bond failure of the 4 and 6 mm bars was by pullout and that of the 8 mm bar was by concrete splitting. The bar axial stress at failure will be plotted against Le for each set and linear regression will be used to establish Ld based on the guaranteed tensile strength. It was shown that as concrete strength increased from 41 to 70 MPa, Ld reduced from 32 to 20 db for the 4 mm bar, from 30 to 25 db for the 6 mm bar, and from 52 to 23 db for the 8 mm bar. The average bond strength increased as the Le shortened, and as concrete strength increased. ACI 440.R1 (ACI 2015) and CAN/CSA S806 (CSA 2012) design guides grossly overestimated Ld of these small-diameter bars. Alternative equations are proposed for both splitting and pullout bond failure that provided more accurate predictions of Ld.