220-FLM : Modelling of life time of concrete under different types of frost and de-icing salt attack
Technical Committee 220-FLM
In previous RILEM TCs 117 FDC and 176 IDC the two types of frost damage - scaling and internal damage - have been studied intensively. RILEM recommendations for test procedures have been worked out and assessed in round robin tests of the TC members and related organisations. Due to this it is possible to simulate frost attack in laboratory reproducibly and precisely. The mechanisms both leading to damage and protecting concrete are much better understood. Especially the water uptake during freeze thaw cycles proves to be relevant and characteristic for different concrete types. It is now the task to adopt these findings to behaviour in practise. * Material properties must be better understood: A) New constituents (chemical admixtures, additives, binder replacement etc.) allow a wide range of new concrete technology where long term behaviour is unknown and must be replaced be appropriate prediction in laboratory testing. B) Lack of resources demands for special materials - recycling. C) Reduction of CO2 emission demands new cements blended with fly ashes etc. * The frost and de-icing attack is different in different structures. Especially uptake of water or de-icing salt solution is significantly changed under slightly modified practical conditions. The correlation between real structures and laboratory testing must be defined much better. * Service life prediction and modelling becomes increasingly important for practical conditions. The necessary basis has been investigated in the previous TCs. * The modelling needs both application of the laboratory testing to the new types of concrete and adoption to the behaviour under real conditions. The knowledge of the physics and chemistry of microstructures must be combined with the need of application. Modelling of concrete and of fracture mechanisms must be represented in the TC as well as practical experience with modern technology and special structures. * Limits of scope: It is not the task of the committee to study other types of environmental attack. The scope of concrete types is restricted to usual modern concretes. A close cooperation with the TC dealing with high performance concrete is planned.
Terms of reference
There exists already a solid basis of both fundamental and applied knowledge due to the work of the recent finished TC 176 IDC. The members of the TC 176 IDC were involved in research programs covering the topic. Both laboratory testing, outdoor exposure and numerical modelling on the basis of surface physics and chemistry can be performed. Numerical methods will be improved by additional members. A state of the art review can be found in the RILEM Proceedings 24 and 25 organised by the RILEM TC 176 IDC together with RILEM TC 178 TMC and TC FHP, as well as in the proceedings of “International workshop on durability of high-performance concrete and final CONLIFE workshop”, to which a lot of members of this new established TC FLM have contributed These proceedings have been published in September 2004.
Detailed working programme
- Year 1: Distribution of research tasks and appointment of working groups start of modelling work (macroscopic) - Year 2 and 3: Continuation of modelling work (microscopic) and start of laboratory testing (new types of concrete, constituents (see topics above)) - Year 3 and 4: Correlation of lab testing results and modelling work (theory); intensification of appropriate modelling both of macroscopic and microscopic behaviour - Year 4: Final report and symposium
The work is closely linked with the results of RILEM TC 117 FDC and RILEM TC 176 IDC, as well as to the recently finished European research project CONLIFE, which also covered the topic. A close cooperation with other RILEM TCs such as RILEM TC 178 FHP and RILEM TC DSC should improve the results and widen the aspects. In Germany the topic is covered by a common research project supported by DAfStb and German research foundation (DFG).
The following achievements are expected: 1.) Improvement of knowledge of the following aspects: 1.1) Modelling of frost attack especially of uptake of liquid during a freeze thaw cycle, of the onset of damage and the appropriate protection of structures. 1.2) Appropriate use new concrete technology 1.3) Save development of environmentally friendly concretes. 1.4) Prediction and modelling of service life. 2.) Basis of modelling with respect to normal as well as high-strength concrete: 2.1) Nano- and Mesoscopic aspects 2.2) Transport of liquid and dissolved ions (de-icing agents) as well as vapour 2.3 Self-desciccation 2.4) Damage mechanisms 2.5) Influence of constituents (Binder, Admixtures, Additives) 3.) Numerical Modelling 3.1) Transport 3.2) Damage 3.3) Fracture mechanics 3.4) Probabilistic models 4.) Long-term and self-repair So that finally: - Appropriate use new concrete technology - Save development of environmentally friendly concretes - Prediction and modelling of service life is possible. Detailed working programme The TC has started in March 2004, nearly after end of the TC 176 IDC. The duration will not exceed 2007. By end of 2007 a symposium as well as a TC publication is planned.
Group of users
- Academics and scientists interested to improve the fundamental knowledge of sub-micro structural behaviour. - Practitioners who want to adopt new technologies without loosing long term behaviour. - Industries developing new products especially chemical additives and admixtures.
Specific use of the results
Service life prediction is essential for a future development in concrete technology. New products, recycling and new cements to reduce CO2 emission can only be used if the lacking long term experience is replaced by a solid testing and prediction which models the practical behaviour of real structures appropriate so that laboratory testing is a solid tool for prediction.