Is Hygrothermal Aging of Construction Polymer Composites a Reversible Process?

This paper presents the effects of wet/dry cycling loading on the moisture uptake behavior of a Fibre Reinforced Polymer (FRP) composite used in the civil engineering sector. FRP samples of various dimensions were cut from an 'off-the-shelf' pultruded flat sheet and conditioned in a cyclic hygrothermal environment. A series of 3 consecutive moisture absorption-desorption cycles lasting for 153 days were carried out to investigate the moisture uptake behavior of FRPs. The hygrothermal procedure consisted of immersion in 60°C distilled water until saturation and consecutively drying in a 60°C oven until equilibrium was reached. After the 1^st desorption cycle, it was found that FRP samples lose a significant amount of mass due to chemical decomposition, the extent of which increases as wet/dry cyclic loading progresses. The effective mass loss leads to a subsequent significant increase in the rate of moisture uptake. Mechanical behavior of the FRPs aged at 40°C, 60°C and 80°C for 224 days is examined at both 'wet' and 'dry' states to reveal the reversible and irreversible effects of moisture uptake. It was revealed that the effects of 40°C hygrothermal aging on mechanical performance are reversible when moisture is removed.