In charge of theme 3 (WG3)
Emmanuel ROZIERE – GeM Nantes (Emmanuel.Roziere@ec-nantes.fr)
Patrick ROUGEAU – CERIB (p.rougeau@cerib.com)
The objective of this theme “Reference concretes” is to define concrete formulations to study during the project so as to provide to the various laboratories samples allowing to carry out experiments on specimens and on concrete samples. The characterization of these formulations will guide the choice of reference concretes in the comparative approach and the choice of acceptable performance levels for the absolute approach.
The choice of the reference concretes is a key point in the performantial comparative approach, as the concrete to qualify is validated if its durability performance is at least as good as the one of the reference concrete. It is therefore essential to clarify the methods of definition of the reference concrete relating to various exposure classes in order to ensure that the appropriate safety margin is satisfactory. An analysis of the feedback and normative provisions is necessary, as well as the use of predictive models.
The objective is to establish rules to optimize the choice of reference concrete (comparative approach) as a function of the exposure classes, the duration of use, types of cement and used additions, and coatings.
Formulations types
This is to define a range of formulations, intended to be subjected to durability tests defined previously, allowing both to evaluate the sensitivity of the durability tests and to optimize the definition of reference concrete as a function of considered exposure classes.
The performantial approach aims to promote sustainable and low environmental impacts concretes and more generally to contribute to the optimization of the formulas, relying on different durability tests. It is therefore necessary to deepen the response to these tests for which there is a lower feedback, for example: with CEM III, CEM V, concrete high content additions, concrete with a cement matrix at very low content of calcium (carbonation behaviour), self-leveling concrete.
Taking into account variability
Whatever for absolute approach (acceptance of concrete on the basis of its properties with regard to threshold values) or well comparison (acceptance of concrete to qualify on the basis of its properties compared to those of a reference concrete), it appears necessary to define a methodology that incorporates the difficulties previously discussed by probabilistic approaches.
It is necessary in particular to provide answers to questions concerning the procedures for validation of a composition in the laboratory study phase:
- How to integrate the variability of the characteristics of the concrete on the basis of the batch?
- How to take into account the uncertainty due to experimental procedures?
The answers to these questions are the expected deliverables.