Deterioration of the FRP-to-concrete interface subject to moisture ingress: Effects of conditioning methods and silane treatment

Abstract

Please cite this article as: Amidi, S., Wang, J., Deterioration of the FRP-to-concrete interface subject to moisture ingress: effects of conditioning methods and silane treatment, Composite Structures (2016), doi: http://dx. AbstractFiber reinforced plastics (FRP) composites have emerged as one popular material in retrofit/rehabilitation of concrete structural members in last decades. The long-term durability of the FRP-to-concrete interface in aggressive environments plays a critical role in the success of this technique. An experimental program has been carried out in this study to examine the effect of moisture on the deterioration of the FRP-to-concrete interface. In addition to condition the specimens through fully submerging the specimens in water, a new method to condition the specimen through submerging only the bottom half of the specimen in water was used in this study. Testing results suggest that the fracture toughness of the FRP-to-concrete interface conditioned through half immersion is significantly higher than that of the interface conditioned through full immersion. Three possible responsible mechanisms have been identified: different moisture distributions along the epoxy-concrete interface induced by conditioning methods; faster moisture diffusion through the epoxy-concrete interface, and hygroscopic swelling stress induced by the swelling of the epoxy after absorbing moisture. The significant effect of the conditioning method on the durability of the FRP-to-concrete interface makes us postulate that the laboratory testing method based on full immersion of the specimen in water could exaggerate the deterioration of the interface induced by the moisture in real applications, in which the 1 Corresponding author. Tel.: +1 205 348 6786; fax: +1 205 348 0783. Email address: jwang@eng.ua.edu (J.Wang) 2 interface is exposed to air, rather than water. In such a case, neither the moisture diffusion along the epoxy-concrete interface nor the swelling of the interface is as significant as in the case of full immersion in water used in the laboratory testing. In addition, this study also evaluated the potential of silane coupling agent on enhancing the durability of the FRP-to-concrete interface in moisture conditions.

Performances, challenges and opportunities in strengthening reinforced concrete structures by using FRPs – A state-of-the-art review

“…Generally, plasticization, swelling, hydrolysis and differential stress may develop owing to moisture uptake [95,96]. Swelling of a polymer is proportional to its moisture content and increases with increasing relative humidity [97]. The swelling of a polymer matrix and the plasticization of its structure may be recovered after drying; the recovery depends on the constituents and quality of adhesives.…”

Recent developments in experimental and computational studies of hygrothermal effects on the bond between FRP and concrete

“…Use of saline coupling agents to improve the interfacial bond behavior between FRP and concrete has proved effective both under normal conditions 219,220 and under hygrothermal exposure. 221,222 Due to its ability to induce covalent bonds between the epoxy and concrete, a much stronger adhesion than the hydrogen bond between the epoxy and concrete results. 221 This helps in achieving a more durable FRP–concrete bond under water attack.…”

“…In addition to the use of saline treatment to improve the FRP–concrete bond, it has been shown that the use of a new conditioning method by partial submergence of only the bottom half (containing the FRP–concrete bond interface) of the test specimen is more effective in improving the fracture toughness than the case with full submergence of the specimens. 222…”

Evaluation of the Moisture Effect on the Material Interface Using Multiscale Modeling

“…moisture penetration, temperature change, chloride ion penetration, and alkalinity in its service life. Among these environmental effects, the moisture penetration is reported as one of the most critical factors which significantly reduces the load bearing capacity of the reinforced element from its designed value and causes unexpected failure of structures [1][2][3][4][5][6][7][8][9]. Under the moisture condition, deterioration of the mechanical property of composite system could be caused by the strength reduction of the FRP composites, plasticization of the polymer matrix or the degradation of interface between adhesion and substrate [10][11][12][13][14][15].…”