Development Length of GFRP Reinforcing Bars in Concrete Containing Seawater

Abstract

As the world faces a growing problem of freshwater scarcity, the construction industry—which as a sector is among the largest consumers of freshwater globally, especially for concrete mixing, curing and cleaning must consider alternatives that can help solve the issues associated with water shortages while continuing to meet the construction industry’s essential needs. In many cases, the same regions experiencing severe water shortages are in relatively close proximity to the sea or ocean; in these areas, the concrete industry potentially has access to a practically unlimited source of water which is currently not widely viewed as a viable option. Although the use of seawater in concrete can result in some minor changes in its fresh and hardened properties, one of the main long-term challenges is related to the high concentration of chlorides which leads to depassivation of reinforcing steel and results in corrosion-induced deterioration. Therefore, a corrosion-resistant reinforcing material, such as fiber-reinforced polymer (FRP) bars, may provide an acceptable alternative for concrete structures when non-potable mixing water is used. The present research is part of a broader study exploring the viability of seawater concrete structures reinforced with glass FRP (GFRP) bars. In this work, an experimental program comprised of six beam anchorage specimens reinforced with 16 mm spiral GFRP bars were tested. Three control beams were fabricated using concrete made with regular tap water, while the remaining beams used concrete made with seawater. The embedment length of the GFRP bars in the anchorage regions ranged from 300 to 500 mm. A method is proposed for calibrating theoretical bond-slip relationships using strain readings along the embedded region. Using the calibrated model, the development length of the bars is estimated and compared with current design codes which were found to be conservative. The results of this study, in combination with other results not presented here, suggest that the use of seawater as mixing water in concrete has a negligible effect on the bond behavior and overall structural performance of GFRP-reinforced concrete elements. Further research on long-term performance is ongoing.