Gravimetric experimental study on moisture diffusion characteristic of pultruded FRP composite and adhesive materials

Pultruded FRP composite material was increasingly used in the applications of civil infrastructures, especially for bridge decks. Thus, the long-term life of these materials in hostile environments is critical. In this paper, experimental studies have been undertaken to characterise the moisture diffusion of pultruded FRP composite materials and adhesives. Gravimetric experiments were carried out for the rectangular FRP composite specimens, which were exposed to the vapour environmental condition and also immersed in water. Moisture uptake curves as a function of time were obtained. Correspondingly, based on the moisture diffusion theory, the diffusion coefficients of FRP composite material parallel to the pultrusion direction were identified. All the FRP specimens reached the moisture saturation level within two days. Comparing with the moisture diffusion process in different aging conditions, the conclusion can be drawn that the rates of moisture uptake are more sensitive to temperature and the moisture saturation levels of FRP material are only dominated by relative humidity and immersed water. For the gravimetric experiments of adhesive specimens，after 37 day environmental ageing, only polyurethane adhesive material reached the moisture equilibrium as 2.667% of the initial self-weight within 6 days. This value is much higher than that of FRP material in the same ageing condition of 40℃, 96% RH. But the moisture diffusion process into adhesives is quite slower.