On the response to hygrothermal aging of pultruded FRPs used in the civil engineering sector

Abstract

This paper presents the effects of hygrothermal aging on the durability of a pultruded flat sheet, immersed in distilled water at 25 °C, 40 °C, 60 °C or 80 °C for a period of 224 days. Elevated temperatures noticeably increase the moisture diffusion coefficient and moisture uptake behaviour. Measured changes in the tensile and in-plane shear mechanical properties were examined after 28, 56, 112 or 224 days. Tensile properties remained practically unaffected by aging whereas matrix dominated shear properties revealed an initial drop which was recovered to a substantial degree after further hygrothermal aging. Visco-elastic property changes due to the superimposing mechanisms of plasticization, additional cross-linking etc. were recorded. Scanning Electron Microscopy micrographs indicate that the fibre/matrix interface remained practically intact, even after the most aggressive hot/wet aging. X-ray Energy Dispersive Spectroscopy analysis showed no chemical degradation incidents on the fibre reinforcement surfaces and infrared spectroscopy revealed superficial chemical alteration in the aging matrix. Optical microscopy revealed matrix cracking in samples aged at 80 °C for 112 days. Lastly, Computed Tomography scans of un-aged material showed internal imperfections that undoubtedly enhanced moisture transport. After aging at 60 °C for 112 days, Computed Tomography detected preferentially situated water pockets. Keywords: Pultruded FRP, Hygrothermal aging, Moisture, Mechanical testing, Scanning Electron Microscopy, Computed Tomography