Development length of sand-coated GFRP bars embedded in Ultra-High performance concrete with very small cover

Abstract

The development length of sand-coated glass fiber reinforced polymer (GFRP) reinforcing bars embedded into ultra-high performance concrete (UHPC) with very small cover is evaluated in this study using twenty-eight notched beam specimens tested in flexure. The parameters included the type and percentage of short fibers in the UHPC mixture, namely 2% and 4% steel fibers and 2% and 3% polyvinyl alcohol (PVA) fibers. The embedment length of a 17.2 mm diameter (db) GFRP bar, a widely used size, was varied from 4db to 16db. The study focused on a very small clear concrete cover of 1.0db to simulate applications that would optimize the use of UHPC, taking advantage of its superior strength. The specimens experienced splitting bond failure as expected. The average bond strength (τu) was higher in UHPC with steel fibers than PVA fibers. It also increased with fiber content but reduced with embedment length. Consequently, the development length (Ld) was smaller in UHPC with steel fibers than PVA fibers and was also reduced as fiber content increased. The Ld values for UHPC with 4% steel, 2% steel, 3% PVA and 2% PVA were 20db, 29db, 35db and 55db, respectively. ACI440.1R-15 and CAN/CSA S806-12 design equations provided very conservative estimations for Ld, by factors of 1.5–5.7. An alternative simple equation has been suggested for Ld.