205-DSC : Durability of Self-Compacting Concrete
Technical Committee 205-DSC
Within concrete research, self-compacting concrete is reported to be the 'hot topic'. Many research projects are being carried out world-wide, and this on aspects like rheology, workability, casting, mechanical properties, durability… RILEM has been very active within the field of Self-Compacting Concrete, by the organisation of RILEM Technical Committees (former Committee TC-SCC on Self-Compacting Concrete chaired by A. Skarendahl, Actual Committee TC-CSC on Casting of Self-Compacting Concrete chaired by A. Skarendahl), and by the organisation of International Symposia (Stockholm 1999, Reykjavik 2003, Chicago 2005 (scheduled)). The actual RILEM Committee TC-CSC on Casting of Self-Compacting Concrete is finalising its work. The last meeting is planned during the RILEM Spring Meeting in Chicago, March 2004. Within this Technical Committee, the specific aspects of casting Self-Compacting Concrete are focused on, like mixing and transportation, placing, curing, quality assessment, … A Report on this subjects will again provide some interesting information for researchers, practitioners, etc… Together with the earlier state-of-the-art report on SCC, some valuable information has already been published by RILEM. It is the feeling and conviction of the members of the actual RILEM TC-CSC that by finalising the work on Casting of Self-Compacting Concrete, some important issues concerning SCC will still remain. One main topic in this respect is related to the Durability of Self-Compacting Concrete. Because of the different mix design in comparison with traditional concrete, different durability characteristics might be expected. The degradation mechanisms of a cementitious material are greatly influenced by the permeability of the material for potentially aggressive substances. As the pore structure might be different for SCC in comparison with traditional concrete, some changes in durability behaviour might be noticed. At this moment however, it is unclear how significant these differences will be with regard to the concrete practice. A fundamental bottleneck in this discussion is the lack of fundamental insight in the transport behaviour of potentially aggressive substances in SCC. This situation leads to some kind of durability paradox with respect to the use of SCC. While durability problems related to the bad vibration of traditional concrete have led to the development of SCC, it seems that SCC is now being used in structures without having a good insight in the durability behaviour of this new cementitious material! In scientific literature up to now, it seems that the durability of SCC is almost entirely studied in comparison with conventional concrete. Most of the scientific articles published in literature give the results of some experimental analysis on some SCC-mixes, and make a comparison with some traditional concrete reference mixes. The results are often very valuable, although a lot of contradicting conclusions can be found. The main problem in this approach is the fact that traditional concrete reference mixes are sometimes chosen on basis of a same compressive strength, sometimes on basis of a same water-cement ratio, etc… This is leading to conclusions which can not be generalised, as e.g. same strength does not mean same material structure, same pore sizes, same transport mechanisms, etc… The obtained conclusions of these parametric studies are only valid within the boundary conditions of the actual research project in which they were obtained. A more fundamental approach is looking at the durability of Self-Compacting Concrete by studying its pore structure and air-void system, and by investigating the transport mechanisms. As seen on the most recent International Symposium on SCC, Iceland August 2003, some research institutes are now studying the durability of SCC following this more fundamental approach. It is expected that this more fundamental approach will lead to more general conclusions, and will shed some more light on the specifics of SCC with respect to durability behaviour. The proposed new RILEM Technical Committee on Durability of Self-Compacting Concrete would focus on the Durability of Self-Compacting Concrete, by first gathering the available information concerning pore structure, air-void system and transport mechanism. The available durability results will then be studied and summarised keeping in mind the fundamental mechanisms and driving forces. In this way some more general view on durability of Self-Compacting Concrete will be obtained. All relevant durability issues will be considered, like carbonation, chloride penetration, frost resistance, ASR, sulphate attack, thaumasite formation, fire resistance, etc… It is not the intention to give a review on these durability aspects for concrete in general. The aim however is to point at the specifics related to the use of SCC, e.g. due to the addition of a large amount of limestone filler, etc…
Terms of reference
The committee will comprise a selected membership of those organisations and research centres world-wide that have been active in searching for a basic understanding and modelling of microstructure, pore structure, air-void system, transport mechanism and degradation of Self-Compacting Concrete. It will include universities, research institutes, material suppliers, contractors, building owners, public agencies … The members will also be recruited from participants in international symposiums and workshops on the topic of SCC, and from RILEM TC-CSC "Casting of Self-Compacting Concrete". The state-of-the-art-report on Durability of Self-Compacting Concrete will be based on the following input: * The RILEM State-of-the-art-report on SCC * The proceedings of major international symposiums on SCC (Stockholm, Tokyo, Reykjavik, …) * Collection of data from relevant work, as published in international scientific journals * The committee will represent a majority of ongoing research projects in this field. The committee will gather, as far as possible, the results of relevant parts of these project Estimated duration of the work is 3 years. The new Committee could start its activities in the fall of 2004, after the finalisation of the work of the actual Committee TC-CSC.
The work will be an extension of the work in RILEM TC-CSC "Casting of Self-Compacting Concrete". The work will provide input to relevant standardisation-work in the field of SCC. The TC fits into the RILEM's technical programme, in particular the items "Performance, maintenance and repair of building materials and structures during the service life".
The main deliverables are : * STAR on Durability of SCC * a symposium
Group of users
- academics working with fundamental materials properties and numerical simulation of materials properties - testing laboratories - industrialists working with e.g. materials development - structure designers
Specific use of the results
The results will contribute to a more precise durability design of concrete structures with self-compacting concrete. The potential durability risks related to the use of SCC, if any, will be made clear. Otherwise, the advantages of using SCC with respect to a possibly increased service life will be outlined. This will contribute to a more advanced use of SCC within concrete construction. Also, the work will improve the fundamental understanding of degrading processes in SCC, with respect to microstructure and transport mechanisms, which is a requisite to design more robust concretes and to the further development of SCC.