Bridge caps with carbon reinforcement Part of project VI.6-I: Testing of composite behavior on the composite body

Project duration: 2017 - 2018

As a significant component of the bridge superstructure, bridge caps have to fulfill a variety of functions and requirements. First and foremost, they serve to protect the load-bearing bridge structure from chemical, physical and weather-related effects. In addition, bridge caps also serve to attach passive protective devices and accommodate walkways and/or bicycle paths. Due to their exposed location and the particularly intensive stresses associated with them (temperature changes, freeze-thaw cycles, exposure to de-icing agents), bridge caps are considered to be particularly susceptible to damage, and adequate durability cannot be reliably achieved by current means. Therefore, bridge caps as "wearing parts" have to be renewed several times within the service life of the bridge so far. The essential problem in the dimensioning and structural design of bridge caps is to reconcile sufficient freeze-thaw resistance of the concrete with an effective limitation of the crack widths of the long-stretched, jointless components. For the latter, a low concrete strength is aimed at, so that primarily finely distributed cracks with small crack widths form as a result of shrinkage deformations, which are generally not relevant to durability. However, as a direct consequence of the limitation of concrete strength - and the necessary increase in water-cement ratio - bridge caps often exhibit insufficient freeze-thaw resistance. By using carbon reinforcement that is thinner, more closely meshed and less susceptible to corrosion than conventional steel reinforcement, the previous weak points in bridge caps could be largely mitigated and considerably more durable components could be produced. However, for the use of carbon reinforcement instead of steel reinforcement to succeed, the first sub-goal is to determine the necessary anchorage length of the carbon fiber mesh and to optimize the bond between the carbon fibers and the modified cap concrete. Furthermore, it has to be verified whether or to what extent the bond between reinforcement and concrete is affected under the typical freeze-thaw actions and the special boundary conditions in a cracked bridge cap. Based on these parameters, the second sub-objective is to optimally adjust the carbon reinforcement to the planned application. This includes, in particular, the practical verification of the anchorage length at the composite and the expansion body determined computationally on the basis of pull-out tests. Furthermore, the accuracy of the prediction of crack formation (crack spacing and crack width) generated by the respective model is to be verified by applying existing models.