C3-V1.6: Durability of bridge caps
Table of contents
Project data
Titel | Title TP C3-VI.6-2: Verbesserung der Dauerhaftigkeit von Brückenkappen durch den Einsatz von Carbonbewehrung als Teilvorhaben im Vorhaben C3-V-I.6: Brückenkappen mit Carbonbewehrung | TP C3-VI.6-2: Improvement of the durability of bridge caps through the use of carbon reinforcement as part of project C3-V-I.6: Bridge caps with carbon reinforcement Förderer | Funding Bundesministerium für Bildung und Forschung (BMBF); Projektträger: PT Jülich / C3 – Carbon Concrete Composite Zeitraum | Period 01.2017 – 11.2018 Leiter | Project manager Prof. Dr.-Ing. Dr.-Ing. E.h. Manfred Curbach Bearbeiter | Contributors Dipl.-Ing. Kristina Farwig, Dipl.-Ing. Robert Schneider Projektpartner | Project partner Lehrstuhl für Baustofftechnik, Ruhr-Universität Bochum |
Report in the annual report 2018
BRIDGE CAPS WITH CARBON REINFORCEMENT

Intact bridge cap on a motorway overpass
Bridge caps are used for the protection of load-bearing bridge structures. The exposed position of the caps means that they are exposed to heavy loads. They must not only be able to withstand impact loads, but also occurring hygric and thermal weather conditions. Since the concrete is usually applied seamlessly over the entire length of the cap, the obstruction of the displacement between the cap and the superstructure consequently results in restraining stresses with cracks in the concrete. The entry of chloride-containing water leads to corrosion of the reinforcement, which must be placed as close to the surface as possible in order to limit the crack width sufficiently.

Use of textile reinforcement for bridge caps
To keep the degree of longitudinal reinforcement as well as the crack widths low, special cap concretes with a high water-cement ratio and thus a lower concrete tensile strength are used. In addition, a high frost-thaw resistance is required for cap concretes. This contradictory approach to the construction of bridge caps means that frost damage of the concrete surface is frequently observed. Thus, the required serviceability, which implies a non-slip surface texture, can rarely be guaranteed for more than 50 years, so that the caps usually have to be renewed several times. The aim of the project is therefore to mitigate the weak points of the cap concretes by using carbon reinforcement and to be able to predict crack widths and distances by using a developed calculation tool.
The advantages of carbon fabrics are obvious. They are not only corrosion-resistant, but also have high rigidity and can be placed close to the surface. The bond between the reinforcement and the concrete is decisive for limiting the crack widths and distances. It can be tested experimentally. In expansion specimen tests crack widths and distances can be measured by photogrammetry. The tool is based on a force-crack-opening relationship determined in single pull-out tests, which can be used to calculate the required anchorage length, the minimum crack distance and the mean crack width to compare them with the test results.