C3-V1.2-I-a: Design and safety concepts

Table of contents

1. 1. 1. Project data
      2. Report in the annual report 2020
      3. Report in the annual report 2019
      4. Report I in the annual report 2018
      5. Report I in the annual report 2017
      6. Report II in the annual report 2017
      7. Report in the annual report 2016

Project data

Titel | Title TP C3-V1.2-I-a: Erstellung und Überprüfung von Sicherheits- und Bemessungskonzepten für Carbonbeton zur Erstellung eines normativen Regelwerkes im Verbundvorhaben C3-V1.2: Nachweis- und Prüfkonzepte für Normen und Zulassungen | TP C3-V1.2-I-a: Development and review of design and safety concepts for carbon concrete to formulation standards as part of the joint research project C3-V1.2: Verification and testing concepts for standards and approvals Förderer | Funding Bundesministerium für Bildung und Forschung (BMBF); Projektträger: PT Jülich / C³ – Carbon Concrete Composite Zeitraum | Period 01.2016 – 12.2020 Verbundvorhabenleiter | Leader of the joint research project Prof. Dr.-Ing. Dr.-Ing. E.h. Manfred Curbach Leiter Teilvorhaben | Subproject manager Prof. Dr.-Ing. Dr.-Ing. E.h. Manfred Curbach Bearbeiter | Contributors Prof. Dr.-Ing. habil. Ulrich Häußler-Combe, Dipl.-Ing. Robert Zobel, Dipl.-Ing. Alexander Schumann, Dipl.-Ing. Karoline Holz, Dipl.-Ing. Jörg Weselek Projektpartner | Project partners Institut für Massivbau; Institut für Baustoffe; Institut für Leichtbau und Kunststofftechnik; Institut für Textilmaschinen und Textile Hochleistungswerkstofftechnik, TU Dresden | Institut für Betonbau, HTWK Leipzig | Institut für Massivbau; Institut für Baustoffe, RWTH Aachen | DAfStb e. V., Berlin | Implenia Conctruction GmbH, Leipzig | DBV e. V., Berlin | Hentschke Bau GmbH, Bautzen | Lefatex Chemie GmbH, Brüggen-Bracht | LISt GmbH, Rochlitz | MFPA Leipzig GmbH | P-D Glasseiden GmbH Oschatz | VDZ gGmbH, Düsseldorf | Betonwerk Oschatz GmbH | TARKUS IngenieurSanierung GmbH, Berlin | Torkret GmbH, Essen | TUDATEX GmbH, Dresden | Baustoffprüflabor Müller & Lobisch GmbH, Dreiheide

Report in the annual report 2020

LOAD TEST FOR CARBON REINFORCED CONCRETE IN BRIDGE CONSTRUCTION

The project C3-V1.2 “Verification and testing concepts for standards and approvals” was one of the vital ones within the construction research project C³ – Carbon Concrete Composite. It aims for the first suggestion of technical regulations for carbon reinforced concrete. Additionally, there was an early ambition to realize these recommendations within a real project.

Therefore, the strengthening of a bridge construction with carbon reinforced concrete was intended. In summer 2020, after a long time of coordination with the building authorities, this strengthening was achieved and successfully  implemented. The construction, a slab bridge, is located at Kleinsaubernitz, Saxony, in the county Bautzen. The bridge of the street S 109, built in the 1950s, crosses the watercourse “Altes Fließ” with a span of approximately nine meters. The road serves as an alternative route for the nearby federal highway BAB A 4, as well as a connection to local companies; therefore, the traffic load is comparatively high. To be able to use the existing construction for more years under a rising amount of traffic, the awarding authority, the Landesamt für Straßenbau und Verkehr (LASUV), represented by the LISt Gesellschaft für Verkehrswesen und ingenieurtechnische Dienstleistungen mbH strived for an upgrade in a higher bridge class. The bridge class defines the permitted capacity for trucks and, after the strengthening, is now unlimited. This was made possible by a strengthening of carbon reinforced concrete with a thickness of 20 mm and four layers of carbon reinforcement.

It was the first application in bridge construction, therefore it was necessary to obtain a “Zustimmung in Einzelfall” (ZiE). Based on C3-V1.2 and the research on large structural members, the durability of the strengthening against cyclic load was proved. Additionally, the durability was also demonstrated by a test loading in-situ as postulated in the ZiE, and planned within the project. In cooperation with MFPA Leipzig, the bridge was loaded by two mobile cranes à 36 t, which was more than the previous load level. The superstructure works as predicted. Therefore, this example shows the possible advantages of strengthening structures with carbon reinforced concrete in the field of bridge constructions. In just three weeks, the strengthening measures were completed, including foundation and groundworks, strengthening construction, and post-assessment.
The construction work was carried out during the summer holiday period, and the short closure period during the construction work reduced the traffic restrictions to a minimum.

Report in the annual report 2019

REGULATIONS FOR CARBON REINFORCED CONCRETE KEEPS MOVING FORWARD

The project  C³-V1.2 is publishing the first proposal of regulations for the carbon reinforced concrete material by the project’s end. The partners from research and practice are working together in close collaboration. With 21 partners involved, the C³-V1.2 project it is the biggest part within the whole C³-project. The majority of the partners have finished their parts of the project successfully in the last year, so the first regulations in various fields – new buildings, strengthening of existing elements, construction with carbon reinforced concrete and for the single materials concrete and carbon reinforcement – are now available to the C³-consortium. The new rules and regulations are forming the basis for facilitating market entry of the material and the construction method. To check the functionality of the new regulations in real applications, an extension of the project was requested for three of the partners.

In 2020, an existing slab bridge made of reinforced concrete will be strengthened. With this, a higher bridge category will be achieved resisting higher traffic. Because of the novel construction methods, some complementing investigations were necessary to get individual approval (ZiE). A lot of experiments of the C³-project were already carried out and were referred. Small-scale tests, as well as few large-scale components with bending strengthening, were implemented with static and dynamic testing. The Institute of Concrete Structures executed the experimental program and the implementation in coordination with the project partner and designers. The essential building law must be created in the next step. Following the strengthening of the bridge, the effectivity of the method will be assessed in-situ, so that the load-bearing behaviour of the structure could be validated by the end of the project is completed.

Report I in the annual report 2018

REGULATIONS FOR CARBON REINFORCED CONCRETE

The project C3-V1.2 set itself the goal to present a first proposal for regulations for carbon reinforced concrete by the project’s end. Therefore, a multitude of associates from research and practice is required. In total, 17 partners are involved in this project making it one of the largest projects within the entire C³-project. It was originally scheduled to be completed by the middle of 2018, but had to be extended by one year to complete the extensive experimental investigations and to work on the regulations.

First, the foundation for setting up a set of rules was developed and a multitude of small-scale tests were carried out. This year, the experimental design and the implementation of the large-scale tests in cooperation with the project C3-V2.7 were imminent. For this purpose, the knowledge gained in the small-scale tests should be transferred to the large-scale components. This involves the bending and shear force strengthening of components with commercially available geometries. An extensive planning of the plates strengthened on bending as well as of the T-beams used to investigate the shear force strengthening had to be carried out at the beginning. This was followed by the base bodies’ production in a prefabricated concrete plant and the subsequent strengthening of the slabs and T-beams with carbon reinforced concrete. Afterwards, the carrying capacity of both the unstrengthened large-sized slabs and the slabs strengthened on bending were experimentally examined. With the help of the large-scale tests, it was demonstrated impressively that with a thin reinforcement layer of 10 mm thickness, the load capacities can be increased enormously compared to the unstrengthened component. The examination of the unstrengthened and the shear force strengthened T-beams are currently still in process.

In addition, plans to strengthen a complete bridge with carbon reinforced concrete are currently promoted to represent the project’s completion. An existing road bridge made of reinforced concrete is to be strengthened with carbon reinforced concrete trying to apply all results gathered during this project. Strengthening works are scheduled for early/mid 2019.

Report I in the annual report 2017

PREPARATION A STANDARD FOR BUILDING WITH CARBON CONCRETE

Most of the building projects with textile or carbon concrete were built by the use of approvals for the individual case. Besides such approvals, there are already some general type approvals for various applications of textile reinforced concrete, for example for strengthening measures of structural elements under bending, for  facade panels or sandwich wall elements. A general standard for carbon concrete does not exist nowadays. For wider use and acceptance of the construction material carbon reinforced concrete by building owners, structural engineers, and contractors such a standard is crucial. The main aim of this research project is, therefore, to transform research results into technical rules and to prepare a standard for carbon concrete accordingly.

At first, working documents for normative regulations were drawn up in cooperation between science and praxis. The working documents include, for example, rules for the design of building elements and strengthening, requirements on concrete and reinforcement and construction. In the working documents, a preferred stress-strain relation for the textile reinforcement, some engineering models, manufacturing tolerances for very thin building elements made of carbon concrete, or uniform test methods to determine material parameters is specified. To calculate the characteristic bond values for the design of anchorage lengths three test methods – single pull out test (SPO), double pull out test (DPO), and yarn pull out test (YPO) – were compared. As a result of strongly scattering material properties, the comparison shows that there is no single test method for all applicable cases. Therefore, boundary conditions for the three test methods were defined. The bond behaviour of carbon bars was also analyzed.

Furthermore, the influence of a fictitious preload on a structural member that should be strengthened for bending was investigated. It was found that the strains resulting from the preloading have an influence on the strain plane of the strengthened building element and thus on the type of failure, and possibly on the required cross-section area of the reinforcement.

The project goal is to make a major contribution to the establishment of carbon reinforced concrete so that the use of carbon concrete in construction will become a matter of course in the future.

Report II in the annual report 2017

ABOUT THE BOND AMONG CARBON RODS AND CONCRETE

Nowadays the bond behaviour between concrete and steel has been extensively investigated. In contrast to that, the investigation of the mechanism regarding the bond between carbon rods and concrete is still at its beginning. Since the bond behaviour has a decisive influence on the deformation properties and the load-bearing behaviour of a composite, it needs to be understood for carbon rods, too.

The reinforced concrete component’s bond behaviour is based on three mechanisms of action between steel and concrete matrix: adhesive, shearing and friction bond. According to current knowledge, the bond behaviour of carbon rods and concrete is related to the same mechanisms. But the comparison of the failure modes shows the appearance of additional effects, which affect the maximum bond strength significantly. Besides the known mechanisms, shearing of the concrete console, sudden blasting of the surrounding concrete, failure caused by shearing of the reinforcement ribs, failure by removing the inner rod core from the outer layer of the reinforcement element, and the combined failure of concrete and carbon rod can also occur.
In contrast to the behaviour observed for the bond between steel and concrete, in carbon concrete components the concrete is not necessarily the weakest component in this composite material. The bond strength and the mode of failure depend significantly on the individual components fibre and matrix of the carbon rods, their manufacturing, and the profiling’s surface geometry. Thus, the failure could not be described in a simplified way by rod extract or cleavage fracture as it is common in reinforced concrete structures.

In the context of the C3 project V1.2, carbon rods with different profiles were tested in a pullout configuration. The test series had the aim to identify and select the best performing ones, to be used in further investigations. Based on this test series, first conclusions about the bond behaviour between carbon rods and concrete could be made, for the various profile types, which are currently available on the market or have been newly developed by project partners. Furthermore, it could be shown, that the maximum bond strength depends strongly on the manufacturing, surface geometry as well as the rod’s matrix.

Report in the annual report 2016

Standards for carbon concrete

In order to establish carbon reinforced concrete itself, its widespread use and general acceptance, technical rules are of fundamental importance. Only through the establishment of general rules, applicable construction codes can be developed. Such practices would create the foundation for wider use and acceptance of the construction material carbon reinforced concrete by building owners, structural engineers and contractors. To establish such rules, extensive preliminary work is necessary. To reach these stated targets, a cooperation effort between industry and science will be made in the joint research project C3-V1.2 – Verification and testing concepts for standards and approvals.

The aim of the project C3-V1.2 is to establish the basics for robust regulations as well as for verifying, monitoring and testing concepts of carbon reinforced concrete. For this purpose, development of standardized verification and testing concepts will be carried out at first. Besides design methods, this also includes requirements for concrete and carbon as separate materials, for the composite material carbon concrete, as well as for building construction and testing. Afterwards, the development of standardized processes and testing concepts will begin. The aim is to determine uniform test methods with which the material parameters can be determined.

To verify the developed testing and verification methods, extensive experimental tests on carbon concrete components will then be performed. These experimental tests shall be carried out, based on relevant component-specific requirements regarding temperature and moisture, static and non-static loads, application and manufacturing processes. Lastly, three building component tests with practical dimensions (e.g. T-beam and precast wall element) will be finally investigated in the research project in order to demonstrate the suitability and the practicability of the developed verification and testing methods. These will be completed by way of practical projects (for example Strengthening of a bridge with carbon reinforced concrete).

We hope to make a huge contribution to the establishment of carbon reinforced concrete as a result of the project, so that in the future, the use of carbon concrete in civil engineering will move into the mainstream industry.