Load bearing behaviour of TRC under uniaxial compression
Table of contents
Project data
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Titel | Title |
Report in the annual report 2018
CARBON REINFORCED CONCRETE UNDER COMPRESSION
Betonage der gering bewehrten Probekörper
The progressing development and introduction of carbon concrete to the construction industry has led to increased awareness regarding the importance of general standardization of the material, design, and construction methods. The standardization of carbon concrete would, in turn, promote the further development of this innovative building material. Simultaneously, it would reduce the cost for the technical approval process. For this purpose, carbon concrete has to be investigated and understood in all its phases.
There are already design models for load cases like bending, shear or torsion for both new structures and the strengthening of existing structures. However, for the complete understanding of carbon concrete, the behaviour of the material under uniaxial compression is important, and it has been studied in this project for a few years. Therefore, previous studies were expanded with a series of uniaxial tests. For example, the effect of different impregnation materials and methods was investigated. Additionally, fine-grained concrete cubes (40 × 40 × 40 mm³) with various reinforcement content, and even with single carbon yarns were tested. These additional tests led to a bigger pool of experimental data for the derivation of design models.
Versuchsstand mit Messvorrichtung
Besides the experimental tests, numerical investigations were conducted to get a better understanding of the load bearing mechanism in the reinforced specimen. A large parameter study showed the flow of the compression struts around the yarns, along with the transverse stresses introduced in the specimens during uniaxial compression loading, which are mainly responsible for the strength reduction. These results help to understand the load bearing behaviour of carbon concrete under compression and confirmed the experimental data.
Based on all these data, it was possible to derive calculation models to forecast the strength reduction of carbon-reinforced concrete. The present investigations showed that the main factor of the reduced concrete strength is the soft yarns, which introduced discontinuities to the concrete. Therefore, the models to calculate the strength reduction depended primary on the volume of the textile in the specimens or construction element.
Report in the year book 2017
TRC UNDER COMPRESSION
Fracture pattern of a TRC cube with inclined reinforcement layers
The progressive development and distribution of the innovative and resource-saving composite material textile reinforced concrete (TRC) lead to many new areas of application. As a result, there is a high demand for design models, material models for computational calculations or standardization. The base for these models is a complete understanding of the load bearing behaviour of TRC. For the behaviour under tension, bending, shear or torsion, models have been developed. However, the behaviour of TRC under compression is quite unknown. This specific material property is important for the design of compression struts in beam webs (shear forces), of compression zones in bending beams, of sections with a partial area under pressure, or columns.
To investigate the behaviour of TRC under uniaxial compression a wide range of tests was conducted. Unreinforced and reinforced finegrained concrete cubes (40 × 40 × 40 mm³) were used as test specimens. The test program includes many different parameters that may affect the behaviour of TRC. In particular, the inclination of the textile plane compared to the loading direction is of great importance. The tests on unreinforced and reinforced specimens manufactured by hand-lamination and conducted in 2016 were extended with tests on textile reinforced cubes manufactured by casting. Therefore, it was possible to investigate new parameters, like the manufacturing process, by comparing the new results to the existing data. With the last test series, the influence of the impregnation of the textiles was investigated. In particular, a flexible and a stiff coating system were compared.
From the test data, the first general conclusions were formulated. Furthermore, numerical simulations were performed to get a better understanding of the load bearing behaviour and the material mechanics of TRC, and the analytical data were compared to the experimental data. For example, the stress flow inside specimens with varying inclination angles between the textiles and the loading direction could be visualized and analyzed. One way to find a model to predict the strength of TRC under compression with different inclined textiles would be the adaption of special models of fractured rocks.
Report in the year book 2016
TRC under compression
Casting of carbon reinforced concrete specimens
The suitability of textile reinforcement for carrying of tension and shear forces in concrete structures has been demonstrated in the past. During investigations of the shear and the torsion behaviour of textile reinforced concrete (TRC) members, the question arose, if there can be possible a reduction of the strength of the compression strut. This question is the focus of this research project. In various areas of application, the behaviour of TRC under compression is of great interest; therefore, a detailed investigation of the performance of TRC under compression is indispensable.
To ensure the quality of the test program, the test set-up and the measurement equipment were optimized in the beginning of 2016. Not only was the effect of the load bearing brushes on the stress state in the small concrete specimen a crucial point of this process, but the simultaneous measurement of the longitudinal and lateral strain were also a challenge.
Parallel to the development of the test set-up, the production of the specimens, to be used in about 550 individual tests, was conducted. The experiments included unreinforced and textile reinforced cubic specimens with an edge length of 40 mm. By testing the unreinforced specimens, it was possible to determine the effect of the concrete placement methods that are commonly used in strengthening: hand-laminating and concrete pouring. Furthermore, such first tests served as reference for the tests on reinforced concrete specimens, which included textiles with various yarn thicknesses and mesh sizes. The different geometries of the textiles served to systematically investigate the effects of the textile reinforcement.
The hand-laminated, reinforced specimens were tested and evaluated in 2016 along with the unreinforced specimens.
With the help of measured stress-strain curves, various phenomena generated by the textile reinforcement could be investigated. These observations allow to formulate the behaviour of TRC under compression. By the end of 2016, the third test phase had been started with manufacturing of textile reinforced specimens by casting. These tests were conducted to gain a further understanding of the characteristic behaviour of TRC under compression.
Report in the year book 2015
TRC under compression
Experimental set-up with adjusted measuring instruments
During the past two decades, the new building material textile reinforced concrete (TRC) was developed and investigated intensively. Most of the studies focused on the load bearing behaviour under uniaxial and flexural tensile stress. Furthermore, these investigations led to basic design models for this kind of material. For the strengthening of structural components made of reinforced concrete, the tensile behaviour of textile reinforced concrete is decisive, but other areas of application require an understanding of the load bearing behaviour of the material under compression load. This structural behaviour is quite different to the known properties of steel reinforced concrete, because the textile reinforced structures cannot carry any loads in their longitudinal or transverse direction. For example, a few studies from Aachen and Cottbus showed a decreased compressive load capacity of TRC in comparison to that of fine grained concrete without fabric, but extensive investigations are still outstanding.
Therefore, this research project will carry out fundamental experimental investigations to clarify this kind of material behaviour. Especially the influence of main parameters like textile reinforcement and the angle between the textile layer and the load direction will be examined. This extensive test program is supposed to result in mathematical formulations for the main parameters describing the stress-strain behaviour of the new material. Moreover, the formulation of a simple design model for relevant load cases is of importance.
In the beginning of the project, the development of an experimental set-up and a measurement concept is a main concern. To minimize the friction between the load application system and the specimen, load bearing brushes will be used. Additionally, a wide range of measuring instruments, like strain gauges, linear variable differential transformers or photogrammetry, were tested, and it was possible to find an adapted measurement set-up for the test program. Recently, the production of unreinforced specimens in three different ways is being carried out to start the first phase of experiments. Besides, the selection of possible textile structures, for the second part of test program, is in progress which should start in January 2016.