Enhancing adhesion of carbon-glass hybrid fibre-reinforced polymer tubes to seawater sea sand concrete through surface sand coating

The bond strength at the interface between seawater sea sand concrete (SWSSC) and fiber-reinforced polymer (FRP) tubes is critical but remains understudied. This paper examines the improvement of bond behaviour between SWSSC and carbon-glass hybrid FRP tubes using a surface sand coating technique. Four different grading of sand coating were used to alter the surface roughness. Push-out tests were conducted on the specimens to determine the bond strength and failure modes. It was found that increasing surface roughness through sand coating significantly enhances bond strength, making it up to 239 times stronger than that of uncoated samples. However, although the coating with the largest particle size and broader particle distribution showed a slightly higher bond strength compared to other types, the difference was not statistically significant. Therefore, it can be concluded that, regardless of the coating grading, sand coating significantly improves the bond strength with no notable difference in their effectiveness level. The findings of this study provide valuable insights into the use of hybrid FRP tubes with sand-coated surfaces, offering a practical solution for enhancing bond strength. These insights can inform future construction practices aimed at developing more durable, sustainable, and environmentally-friendly materials, helping to reduce the carbon footprint of the construction industry.