Mechanical properties of pultruded glass fiber reinforced plastic after freeze–thaw cycling

Abstract

The use of pultruded fiber-reinforced plastics in civil infrastructure requires the long-term prediction of their mechanical properties, which should be based on understanding and estimating the processes in the structure under action of aggressive environmental factors: humidity and freeze–thaw cycles. This article reports on results of short-term exposure to severe freeze–thaw cycling in the temperature range from –30°C to 20°C of polyester-based glass fiber reinforced plastic both dry and wet. The effect of freeze–thaw cycling of flat specimens cut from I-beam pultruded profile was estimated by use of three-point-bending tests and dilatometric investigation in the temperature range from 20°C to 125°C. It was found that freeze–thaw cycling results in an increase of flexural modulus and decrease of ultimate strength, and strain. The effect is more pronounced for dry material than of moistened, but it is comparable with the data spread. Linear thermal expansion coefficients in three principal axes of the composite are different: the highest is in transverse to fiber axis out-of-layers plane. The linear thermal expansion coefficients of wet material are higher than of dry. Heating up to 125°C and subsequent cooling results in a residual (shrinking) volume strain. The changes of flexural characteristics, linear thermal expansion coefficients, and shrinking strain after heating–cooling after freeze–thaw cycling are mediated by the change of moisture content in the material specimens.