Temperature as an Accelerating Factor for Long-Term Durability Testing of FRPs: Should There Be Any Limitations?

Abstract

Fiber-reinforced polymer ͑FRP͒ composites are increasingly being used in civil engineering applications due to their numerous advantages. Moreover, some environmental conditions can potentially enhance their long-term durability. Therefore, the study of their long-term behavior is crucial to ensure their durability. To perform durability study in a reasonable time limit, accelerating factor, such as high temperature, is generally used. However, the use of very high temperature of conditioning could amplify the reduction of the properties leading to conservative prediction of long-term properties. The present paper attempts to clarify the effects of high temperatures on the mechanical and barrier properties ͑moisture absorption͒ of GFRP's internal reinforcement, by presenting some experimental results and conclusions of laboratory accelerated studies.

Effect of Hot-Wet Aging on the Pin-Bearing Strength of a Pultruded Material with Polyester Matrix

“…Preliminary studies presented by Schutte (1994), Bank et al (1995, Chin et al (1997), Gentry et al (1998), Kellogg et al (1999), Liao et al (1999), Abeele et al (2001), Nishizaki and Meiarashi (2002), Karbhari and Zhang (2003) and Robert et al (2010) have involved the measurement of one or more property of flexural and tensile moduli and strengths, and fatigue resistance. Each study used a different accelerated aging condition, with a constant temperature in the range -50°C to 80°C; and immersion in water, or salt solution, or acetic acid, or ammonia; for a period of time from 12 hours up to 2 years.…”

“…When giving their study's conclusions, Nishizaki and Meiarashi wrote "Although it is hard to imagine that deterioration of glass FRP materials exposed in construction applications would be as rapid as that found for the specimens in the deterioration experiment exposure conditions, still, water and moisture levels are clearly factors contributing to the long-term deterioration of materials exposed to water". Robert, Wang, Cousin, and Benmokrane (2010) observed that many previous researchers were selecting high temperatures (up to 80°C) relative to the polymer resin's glass transition temperature (T g ) to get the maximum rate of aging (the highest possible acceleration factor from Equation (2)). The weakness with this approach, for the evaluation of the durability of a FRP reinforced with glass fibers, is that too high a temperature can cause additional material degradation (that could not be experienced in the field) because the chemical degradation mechanism had changed.…”

“…Knowing of this weakness, it can be observed that the outcome of forcing a high acceleration factor, by selecting a too high aging temperature, is to under estimate the actual durability. Robert et al (2010) also worked with a pultruded material having a vinyl ester based matrix.…”

“…Presented in Figure 10 of Robert et al (2010) ) were established, and it may be assumed that they are specific to the pultruded bar material, having a vinyl ester matrix. If the function, for Equation (2), in Figure 10 of Robert et al (2010) is assumed to be valid for 1525 series material (with a fire retardant polyester matrix) it can be estimated that aging for 3000 hours at 40 o C is equivalent to 3.5 service years in Canada, where the mean annual (service) temperature is 6 o C. Robert et al (2010) do, however, provide the following cautionary observations on the application of the Arrhenius equation curve.…”

“…If the function, for Equation (2), in Figure 10 of Robert et al (2010) is assumed to be valid for 1525 series material (with a fire retardant polyester matrix) it can be estimated that aging for 3000 hours at 40 o C is equivalent to 3.5 service years in Canada, where the mean annual (service) temperature is 6 o C. Robert et al (2010) do, however, provide the following cautionary observations on the application of the Arrhenius equation curve. "It has to be noted that in regions of large temperature variations such as Canada, one-year aging at an average temperature is not equivalent to one-year aging at temperatures varying around this median temperature.…”