Bond behavior between GFRP bars and seawater sea-sand fiber-reinforced ultra-high strength concrete

To tackle the challenge of steel corrosion in conventional reinforced concrete (RC) structures, particularly in maritime environment, the implementation of glass fiber reinforced polymer (GFRP) bars in seawater sea-sand concrete (SSC) structures becomes increasingly popular due to their excellence corrosion resistance. However, the bond characteristics of GFRP bars in fiber reinforced ultra-high strength SSC have not been explored. To this end, a series of pull-out tests on 63 specimens were performed in this study to investigate the influences of different GFRP bar diameters of (i.e., 6 mm, 10 mm and 16 mm), anchorage lengths (i.e., 2.5 and 5 times of the bar diameter), concrete types (SSC and conventional concrete), and polyethylene (PE) fiber contents (i.e., 0, 0.5% and 1% volume fraction) on bond characteristics. The results show that similar to FRP-conventional concrete bond joints, larger bar diameter and longer anchorage length would lead to bond strength reductions for FRP-SSC bond joints. A 0.5% PE fiber addition in SSC would lead to a 3–10% increase in bond strength. However, further increase in PE content to 1% may not necessarily result in further increase in bond strength. Furthermore, the assessment of different design codes revealed that, although ACI440.1R-15 yielded relatively more accurate estimations for bond strength than other design codes, the bond strength could be overestimated if the bar diameter is greater than 16 mm or the anchorage length is less than 5 times the bar diameter.