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Pultrusion is an easy molding method of fiber-reinforced polymer (FRP) to obtain a long composite material with a uniform cross-section at relatively low cost. In some cases, pultruded FRPs are now used in bridges and deck projects. Since the application of pultruded FRP as a structural material is increasing, a study on the durability of pultruded FRP under outdoor conditions is necessary in terms of safety. Some studies have shown that pultruded glass fiber-reinforced polymer (GFRP) exhibits a slight reduction in mechanical properties during outdoor exposure. Since pultruded GFRP consists of multi-layers, the change of mechanical properties in each layer is important to understand. In this study, an outdoor exposure test on pultruded GFRP for 10 years was conducted with three types of pultruded GFRP, which have different laminate systems, including surface-coated specimens of each type. Changes of strength and elastic modulus due to outdoor exposure were discussed with a focus on the contribution of each layer based on the rule of mixtures.

The authors set out to investigate the durability of the bond between carbon fibre (CF) sheet reinforcement and concrete. They conducted an outdoor exposure test in a moderate climate for 14 years and an immersion test for 6 months on CF sheet bonded to concrete, and then evaluated the adhesive bond properties using the pull-off and peel methods. The pull-off strength slightly decreased after 14 years of exposure, but residual values still indicate quite good adhesive properties. The failure modes for both the initial specimens and the specimens after 14 years of exposure consisted of concrete substrate failures in all cases. This result suggests that the slight decrease in pull-off strength does not necessarily indicate a change in the properties of the bond between CF sheet and concrete. On the other hand, results of the peel tests showed different types of failure modes and seemed more discriminant than those of the pull-off method. As regards specimens immersed in water, pull-off results were in few cases consistent with the peel characterizations, showing significant evolutions in the strength and failure mode. But for most specimens, the two methods provided divergent trends. In the end, this study suggested that the peel test could be relevant for evaluating the durability of the bond between CF sheet and concrete, while the representativeness of the pull-off test remains a matter of discussion.

本研究は, 遮水シートの耐久性評価を目的とし, 室内促進暴露実験と実暴露実験を実施し, 遮水シートの力学特性 (硬さ, 引張強さ, 伸び率) や表面状態の変化を追跡評価したものである。室内促進暴露実験の結果, 伸び率は経過時間とともに徐々に低下し5, 000時間では初期値のおおむね80%程度となり, そのとき遮水シート表面には亀甲状の微小亀裂が発生していることが確認された。一方10年間の実暴露実験を行った遮水シートの力学特性の変化は小さく, ある種類の遮水シート表面には室内促進暴露実験と同様の亀甲状の微小亀裂が観察されたが, 最終処分場の標準的な供用期間である15年に対して遮水シートの耐久性は充分余力あるものと推測された。また両実験結果を比較検討した結果, 2, 000時間強の室内促進暴露実験の結果が実暴露実験10年間に相当することが確認された。さらに遮光性保護材を用いると, 遮水シートの劣化の主要因とされる紫外線を遮断することができ, 遮水シートの耐久性が大幅に向上することも確認できた。

Carbon black, used as a reinforcing filler for rubber materials, was evaluated for asphalt binders in pavements. Carbon black added to straight asphalt within 20 wt% caused an increase in the elastic modulus and a decrease in the viscosity of the asphalt, especially at temperatures higher than room temperature. Addition of carbon black raised the maximum service temperature of asphalt in the category of the binder performance grade according to the SHRP (Strategic Highway Research Program) specifications. On the other hand, addition of carbon black also increased the failure strain at low temperatures. Furthermore, addition of carbon black reduced the coefficient of thermal expansion (CTE) of asphalt to closer to that of aggregates. In asphalt mixtures, tensile stress occurs at the boundary between asphalt and aggregate with decreasing temperature due to the CTE difference. Addition of carbon black reduced this stress. Carbon black addition to asphalt has the potential to improve both deformation resistance in the high temperature region and crack resistance in the low temperature region, which were empirically considered to be contradictory. Therefore, carbon black is an effective filler for improving the durability of asphalt pavements.

FRP is used for corrosion protection and/or as structural members utilizing its anti-corrosion properties. Moreover, since the weight of a superstructure can be significantly reduced due to its specific strength, FRP is expected to offer structural functionalities such as rapid construction, substructure downsizing, and improved seismic performance. We constructed an FRP bridge made entirely of pultruded and hand-lay-up GFRP materials, and have been monitoring its functionality and durability. This paper reports the changes in structural load-bearing behavior during nine years of field exposure. Loading response of the FRP bridge after long-term exposure was almost the same as that just after its completion and deterioration in structural performance has not been observed in nine years. The results prove that FRP materials have good durability and functionality for long-term field exposure as structural materials for bridges.