Plastic Pipe Design # 2006 Washington DC
HDPE is used in bridge construction as part of the corrosion protection system of steel tendons in post-tensioned bridges. There are different types of HDPE sheathings that vary in thickness, number of layers and shape. Within this article these products and their applications will be presented. Furthermore, all the properties of the sheathings that are necessary to maintain a successful operation and a durable protection of the steel against corrosion and other influences are shown. HDPE sheathings are applied both for internal tendons (within the concrete section) as ducts or as sheathings and for external tendons as sheathings. In contrast to sheathings ducts have to fulfil lower demands on corrosion protection since they are not exposed directly to aggressive influences. Because of economical reasons and difficulties in construction on site a continuous deviation is impossible for external tendons. The tendons either can be arranged horizontally without deviation or deviation at a very short length at concrete deviators can be realized. At the deviators the soft PE-sheathings can be stressed seriously perpendicular to its axis by the hard steel. The deviation pressure may even lead to local plasticization and to a notable loss in thickness of the sheathings. Testing has been done at the laboratory of Technische Universität München with full scale deviation of 3 MN tendons with a radius of 4 m to investigate the influence of the pressure under the strands, shape of the strands, duration of loading (creep) and especially friction between strands and polyethylene on the wearing of the PE-sheathing at deviation points. This article not only presents the results of the tests but also gives an overview about the authors’ suggestions how to compensate for very high stresses by changing the design.