PSI - Issue 64

Tom Argyle et al. / Procedia Structural Integrity 64 (2024) 1376–1385 Argyle et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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5.3. Effect of temperature on CFRP rod performance The glass transition temperature (Tg) is an important property of the adhesives. Above this temperature, the mechanical properties of the resin will significantly drop, and will transform from a hard-like material to a rubbery like material. Thus, due to the position of the CFRP system on the upper surface of the deck in the hogging regions it is an important aspect to be considered where the material is in close proximity to fresh asphalt material. It was, therefore, necessary to understand the distribution of temperatures within the resin when the hot asphalt is applied to the deck, to ascertain whether a) the heat induced in the resin would be sufficient to induce the Tg, and b) if the resin was affected, the subsequent effect on strengthening performance. A trial was carried out on a panel of approx. 500 mm x 500 mm x 100 mm with a 20 mm x 20 mm groove at the centre of the slab. The groove was filled with epoxy adhesive and CFRP rod and cured for 24 hours, and waterproofing was applied on top, to replicate the strengthening design. Thermocouples were embedded within the resin, located at the top (0 mm), middle (10 mm) and bottom of the groove (20 mm) and the temperatures was also recorded at the waterproofing.

Fig. 8. Sample used to determine the temperature of the adhesive level.

Based on a total surfacing thickness of 100mm, a 50mm Hot-Rolled Asphalt binder layer was applied on top of the waterproofing, and the temperatures were recorded until the asphalt temperature reached the ambient temperature. Once cooled, a 50mm Stone Mastic Asphalt wearing course layer was applied, and again the temperatures were recorded until the asphalt reached the ambient temperature. Figure 9 shows the temperatures recorded in the trial. During the application of the binder coarse layer the peak temperatures at the bottom and top of the resin reached 35ºC and 65ºC, respectively, for a short period of time. Note that these temperatures are also lower than the adhesive Tg = 65ºC. However, it is still above Tg – 15ºC = 50ºC. TR 55 (2013) suggests that the Tg of the adhesive should be at least 15ºC above its maximum operating temperature. The temperature at the top of the waterproof reached 110ºC, showing that it provides a good thermal insulation for the resin. Because of the insulation provided by the binder layer, the temperatures within the resin on application of the wearing course were significantly lower, with a peak temperature of 36°C.