RILEM Technical Committee FTC : Durability and Service Life of Concrete under the Influence of Freeze-Thaw Cycles combined with Chloride Penetration (External organisation)

Faheem, A. (Member)

Activity: MembershipMembership of commitees, commissions, boards, councils, associations, organisations, or similar

Description

At this moment there are many different ways to design and predict service life of reinforced concrete structures. Three deteriorating processes are mainly considered separately: (a) number of freeze-thaw cycles, (b) chloride penetration through the concrete cover to reach the reinforcing steel, and (c) time dependent carbonation. For all three processes national and international standards exist. But the predicted service life is rarely reached in practice. Chloride penetration is usually described by a diffusion process although migration of chloride is a very complex process including adsorption on the internal surface of hardened cement paste, convection with capillary absorbed salt solution with a pronounced filter effect, and chemical reactions. In addition in practice there is a great number of drying and rewetting cycles every year. With the results published in the final report of RILEM TC 246-TDC it could be shown that service life of reinforced concrete structures can be considerably shortened under the influence of combined actions, as for instance chloride penetration and an applied mechanical load. That means that prediction of service life based on one deteriorating process only cannot be considered to be conservative. It could be shown that chloride penetration is accelerated significantly in case a tensile stress is applied. One conclusion of RILEM TC 246-TDC is that the influence of combined actions has to be studied in order to make service life prediction more realistic. There is a great number of potential combinations and step by step the most influential combinations will have to be investigated. With this new RILEM TC the influence of a combination of freeze-thaw cycles, applied mechanical load, and chloride penetration shall be investigated. Freeze-thaw cycles modify the structure of the nano-pores. If freeze-thaw cycles are imposed under applied load, the material becomes anisotropic. There is a dominant direction for chloride penetration. Based on the expected results durability prediction will become more realistic and service life can be extended systematically. The expected results of the new RILEM TC will also have an enormous economical effect.

° Durability of concrete under combined freeze-thaw cycles, chloride penetration and mechanical load shall be studied experimentally in different laboratories. It is planned to carry out comparative test series, which shall be predefined in detail. Different types of concrete shall be included, such as standard concrete, high strength concrete, and fibre reinforced concrete. Results of different test series shall be analysed and compared with existing or newly developed materials models. Conclusions of the obtained results shall be compared with observations of real structures in different climatic environment.

This project may be considered to be a follow up project and a supplement of RILEM TC 246-TDC and it shall be carried out in close contact with the new RILEM TC chaired by Professor Nele De Belie: Carbonation of Concrete with Supplementary Cementitious Materials, and two newly proposed RILEM TCs, (1) Controlled Expansion of Concrete by Adding MgO-based Expansive Agents Taking the Combined Influence of Composition and Size of Concrete Elements into Consideration, and (2) Test Method for Concrete Durability under Combined Role of Sulphate and Chloride Ions.

° The rate of chloride penetration is accelerated in the direction parallel to the applied stress and it is slowed down in the direction normal to the applied stress. This effect is relevant for the prediction of service life of reinforced concrete structures, but it has been neglected totally so far. This specific influence on chloride penetration shall be considered in particular.

° RILEM TC 246-TDC was a first attempt to study the influence of combined actions such as applied load and chloride diffusion on durability and service life of reinforced concrete structures. It was clear, right from the beginning, that many more results will be needed to make service life design under the influence of combined actions more realistic and more reliable. This new RILEM TC can contribute essential new results and a number of similar TCs must follow to provide us with the necessary data for well-based reliable service life design of reinforced concrete structures.
Period27 Aug 201927 Aug 2020
Held atInternational Union of Laboratories and Experts in Construction Materials, Systems and Structures, France
Degree of RecognitionInternational