R 15 S U M I~ A B S T R A C TUarticle pr&ente une nouvelle m&hode d'aide 5 la formulation des b&ons adjuvant&. Elle consiste 5 concevoir, ~ partir d'une composition de b&on, un mortier, dit mortier de b&on 6quivalent (MBE), dont les pro-pri&& rhdologiques sont corr61ables 5 celles du b&on. Le but est de diminuer le nombre de gfich6es de b&on. La d6marche de mise au point de la m&hode, son champ d'application et ses limites sont pr&ent&. Le mode op6ratoire ainsi que le mat&iel n&essaire sont d&aill&. Un exemple de corr61ation entre les propri&& rh6ologiques mesur&s sur MBE et celles mesur&s sur le b&on associ6 est pr&ent& Parall~lement aux suivis rh6ologiques, des suivis thermiques sur MBE peuvent &re effectu&. Ils permettent d'anticiper les effets de diff&ents adjuvants sur le temps de prise du b&on. On montre que les d&alages observ& par suivi thermique traduisent bien les &arts de r&istances aux tr~s courtes &h&nces. En associant suivis rh6ologiques et suivis thermiques, la m&hode MBE permet de s61ectionner rapidement parmi diff&ents adjuvants celui qui r@ond le mieux aux exigences d'efficacitd (rapport dosage/cofit), de maintien rh6ologique et de d6lai de d&offrage.This paper deals with a new method to design concrete containing admixture. Its principle is to design a mortar, deduced fiom the concrete composition and called concrete equivalent mortar (CEM), for which the rheological properties display correlation with those of concrete. The aim is to reduce the amount of concrete batches. This article pwsents the scientific approach which has led to this method, its field application and limits. The test procedure and the apparatus are detailed. An example of correlation between the theological properties measured on CEM and on the corresponding concrete is presented. After monitoringfluidity versus time relationship, thermal measurements on GEM were carried out. These measurements allow to anticipate the effects of different admixtures on the setting time. One shows that the setting delays obtained on CEM are in good agreement with the difference of compressive strengths measured at early age. With rheological and thermal results, the CEM method permits to select between numerous admixtures, which is the most likely to fit in with the specifications of effectiveness (proportion/cost ratio), capacity of keeping the rheological properties over time and delay of formwork removal.

Prolonging the service life of nuclear power plants and more stringent safety requirements are increasing the need for miniature mechanical tests such as the Small Punch Test (SPT). This test was initially developed in the early 1980s at MIT and further developments with more extensive use were achieved by EPRI with a continuous program between 1990 and 1999. The present investigation is first based on a finite element simulation benchmark between EPRI and CEA. This provided a reciprocal validation of the numerical simulation of this test for an A533 B steel at room temperature. The loading mode progressively evolves from bending towards biaxial membrane loading of the specimen. Strain energy density was also computed as the failure criterion and the maximum value observed at experimental crack initiation is about 116 MJ/m3. A parametric finite element study was undertaken in order to evaluate the influence of factors such as specimen thickness, friction, yield strength, strain hardening coefficient, etc. Starting from this parametric study, an automatic routine was built which estimates the elastic-plastic Ramberg-Osgood stress strain relation. The need for standardization of this test will be underlined.

The article presents the results of work by the AFREM/HPC group on the formulation of high-performance concretes. This is an updating of LCPC's grout method. The goal is a methodology making it possible, for a given binder (or mixture of binders), to determine the saturation doses of a certain number of superplasticizers and compare them in terms of their effectiveness and the duration of the rheological behaviour they impart. The innovations with respect to the old method are the following: i) the starting concrete can vary over a broader range, ii) part of the sand is added in the grout, iii) mixing and measurement are better codified, and iv) the method of determining the saturation proportion is objective. The method has successfully passed tests of repeatability and reproducibility (between the six member laboratories of the group). Ri~SUMi~ L'article pr&ente le r&ultat du travail du groupe AFREM/BHP sur la formulation des b~tons h hautes performances. Il s' agit d' une remise a jour de la m~thode des coulis du LCPC. Le but en est de fournir une m&hodologie permettant, pour un liant (ou m~lange de liants) donnS, de d&erminer les doses de saturation d'un certain hombre de superplast~'ants, de comparer leurs efficacit& respectives et leur propension h con)&er un comportement rh&logique stable dans le temps. Les nouveaut& introduites, par rapport l'ancienne m&hode, sont les suivantes : i) b~ton initial pouvant varier clans une plus large gamme, ii) introduction d'une partie du sable clans le coulis, iii) malaxage et mesure mieux codifi&, iv) m~thode objective de d~termination de la dose de saturation. La m~thode a fait l'objet d'essais de r~p~tabilit8 et de reproductibilit~ (entre les six laboratoires membres du groupe) satisfaisants.

Charpy-V test results are widely used for the surveillance program of RPV (Reactor Pressure Vessel) embrittlement by neutron irradiation. Service life extension of nuclear power plants and more stringent safety requirements are increasing the request for small test specimens such as subsize Charpy. Furthermore, the empirical correlation formulas between conventional Charpy-V and fracture toughness are often questionable. Therefore, prior to use of reduced size specimens, different hypotheses have to be validated and this can only be achieved by combining tests and finite element simulations. The material of interest is a nuclear RPV low alloy ferritic steel 16MND5 (eq. A508 C13). Instrumented impact tests were performed on Charpy-V and subsize Charpy over a wide range of temperatures. The hyperbolic tangent curve from W. Oldfield [1] was fitted to the results. Then, correlation formulas are evaluated and commented. In a first step, the aim of the finite element simulations is to get a clear description of the global mechanical behavior of the specimens. A complete description of dynamic impact tests is not required for fracture mechanics purposes. A quasi-static simulation taking into account strain rate effect on the material response is sufficient. However, a 3D analysis is required even for cleavage failure mode. The second step is related to the transferability of fracture criteria. This task has been initiated at low temperatures using the Beremin cleavage model [2] and in the ductile regime using the Rousselier porous model [3]. The finite element results are compared to the experimental one. These results show good transferability potential.