TRC under compression – influence of biaxial load application

Table of contents

1. 1. 1. Project data 
      2. Report from the annual report 2021
      3. Report from the annual report 2020

Project data 

Titel | Title Experimentelle Untersuchungen des Tragverhaltens von Textilbeton unter Druckbeanspruchung – 2. Phase: Einfluss biaxialer Lasteintragung | Experimental investigation of the load bearing behaviour of textile reinforced concrete under compression load – 2nd Phase: Influence of biaxial load application Förderer | Funding Deutsche Forschungsgemeinschaft (DFG) Zeitraum | Period 03/2019 – 05/2023 Leiter | Project manager Prof. Dr.-Ing. Dr.-Ing. E.h. Manfred Curbach Bearbeiter | Contributor Dipl.-Ing. Peter Betz

Report from the annual report 2021

Carbon reinforced concrete comes under pressure

While previous research in carbon concrete has mainly focused on the tensile load-bearing behaviour of the composite material, knowledge of the compressive load-bearing behaviour is still rudimentary. In the first project phase, initial investigations were carried out concerning uniaxial compressive loading and various influencing factors were identified. The degree of reinforcement, for example, was found to have a major influence on the compressive load-bearing capacity, while the production method played a subordinate role. For the application on the structural element level, these investigations are only suitable to a limited extent, as uniaxial loads only occur in rare cases. In reality, there are usually multi-axial stress conditions.

Therefore, the second project phase deals with the validation of the previous findings for stress conditions that are closer to those present in a structural element by using biaxial tests. A distinction is made between biaxial compressive loads and compressive loads with transverse tension in the reinforcement plane. While the former involves the increase in compressive strength in special cases in reinforced concrete structures, the reduction of compressive strength in cracked components, i.e. compression zones with transverse tension, is essential for shear force and torsion design. For both types of loading, investigations were planned on the influence of the number of layers, yarn diameter, mesh size, impregnation, fabrication and orientation of the reinforcement. The majority of the biaxial compression tests have been successfully completed this year.

For successful project implementation, the selection of suitable load introduction systems is of particular importance. For the compressive forces, proven loading principle could be used, but for the introduction of tensile stresses, the development of a new anchoring fixture is necessary due to the limited space in the testing machine. In addition to a uniform introduction of tensile stresses, care must be taken to ensure that the compressive stress distribution is impaired as little as possible. In preliminary investigations, different anchorage systems with clamps and bolts, anchorage areas made of resin and concrete, as well as additionally sanded reinforcements were considered.

Report from the annual report 2020

Carbon reinforced concrete under compression

Many scientific areas of carbon concrete have been researched for years and show considerable progress in the regulation of the material. While models or modelling approaches exist e.g. bending, shear forces and torsion there is little knowledge about the behaviour of carbon concrete components under compressive loads. Initial findings under uniaxial compressive loading were obtained in the first phase of the project. The change of the manufacturing process, from cast specimens to hand-laminated insertion of the textile layers, led to a reduction of the load-bearing capacity. Furthermore, the influence of various parameters on the compressive strength of carbon concrete cubes was investigated, such as the spacing between the layers, the yarn thickness, the mesh size or a staggered arrangement of the textile layers. Based on these results, the focus of future research investigates to what extent these findings can be transferred to practically relevant components. A first step is being taken in this second phase of the project using multi-axial loaded carbon concrete disks with dimensions of 200 x 200 x 40 mm³. In most components, induced multi-axial stress states are present (for example due to torsional or shear loads).

For this reason, based on the knowledge from steel reinforced concrete constructions, possible increases in the load-bearing capacity due to compression-compression loads as well as reductions due to compression-tension loads are to be investigated. In addition to the structure of the textile reinforcement itself, which includes impregnation, layer spacing, mesh size and also the textile orientation, the manufacturing process and different stress ratios are to be varied during the tests. Based on the results from the second project phase, a numerical material model will be designed or the model from the first project phase will be extended. With the help of this model, virtual parameter studies can be conducted to plan large component tests in a further project phase and to be able to carry them out with as little effort as possible. Besides, these large-scale component tests are to verify the material model established at the end of this project phase.