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In this paper, we aim to achieve a probabilistic modelling of the compressive strength of concrete using three response surface models (RSM) and the artificial neural network (ANN) method. The input random variables for the three RSM and for the ANN are cement content, water content, measure of slump and air content, while the output for all the models is the compressive strength of concrete at 28 days. More than 800 cylindrical specimens 16 $$\times$$ 32 cm were tested. The experimental data are used to check the reliability of the suggested probabilistic models and their prediction capability. It is shown that the use of these new RSM is as simple as that of any of the basic formulas, yet they provide an improved tool for the prediction of concrete strength and for concrete proportioning. It is also shown that the concrete compressive strength can be readily and accurately estimated from the established ANN.

A simple thermohydromechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. Comptes Rendus Geoscience, ISSN : 1631-0713, DOI: 10.1016/j.crte.2010.09.006, Issue : 12, Volume : 342, pp. 892-900, December 2010.

A simple thermo-hydro-mechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN : 0363-9061, DOI: 10.1002/nag.952, Issue : 12, Volume : 35, pp. 1299–1317, 25 AOUT 2011.

International audience

19 p.; National audience; Companies in Algeria have restricted budgets devoted to the formulation of concrete. Therefore, very few research studies are interested by the concrete composition in accordance to its purpose. Hence, this work is a part of an approved research program assigned to clarify the impact of certain parameters on the quality of concrete. This experimental program consists of more than 700 cylindrical specimens of 16x32 cm that were made using local materials. Excluding the durability indicators towards the concrete, the compressive strength is the most significant property to be considered (Mounanga et al.,2006). The obtained results concern consistency and content airproperties of the concrete at fresh state and compressive strength of hardened concrete at 28 days. Thus, the influence of the air content percentage on the concrete consistency is studied. Moreover, the influence of these two parameters on the compressive strength of the hardened concrete is also presented. The experimental results obtained constitute a data bank, which allows comparing through a statistical analysis, the model established by Féret (Baron & Ollivier, 1996) and the results of the tests.; La formulation d’un béton correspond au processus de sélection des constituants et de leurs proportions pour fabriquer un matériau possédant certaines propriétés minimales précises, notamment en ce qui concerne la consistance, la résistance et la durabilité. Les entreprises en Algérie, n’ont que des budgets relativement restreints à consacrer à la formulation des bétons. A cet effet, très peu d’études de recherche y sont consacrées, pour mettre l’accent sur les aspects liés à la composition des bétons en fonction de leurs emplois. On est parti de cet état de fait, en vue d’étudier ---dans le cadre d’un programme de recherche agréé--- l’influence du pourcentage de l’air occlus dans le béton sur sa consistance ainsi que l’influence de ces deux paramètres (affaissement et pourcentage d’air occlus) sur la résistance à la compression des bétons durcis. Cela constitue du point de vue de l’ingénieur la propriété la plus importante du matériau, si l’on exclut les indicateurs de durabilité (Mounanga et al., 2006). Pour ce faire, un programme expérimental pour la confection de plus de 700 éprouvettes cylindriques de 16x32 cm a été planifié, en utilisant les matériaux locaux, à savoir: le ciment de Béni-Saf, ainsi que les granulats de l’Entreprise Nationale Algérienne des Granulats (E.N.G). Les bétons ont été formulés à l’aide de la méthode de Dreux-Gorisse. Deux cures ont été adoptées pour les éprouvettes confectionnées, cure à l’air libre ou immersion dans l’eau. Ce travail présente les résultats d’études concernant d’une part, les propriétés du béton à l’état frais (consistance, air occlus) et d’autre part, la résistance à la compression à 28 jours du béton durci. L’ensemble des résultats expérimentaux obtenus a constitué une banque de données. Cette dernière a permis de comparer, à travers une analyse statistique, le modèle établi par Féret (Baron & Ollivier, 1996) et les résultats des essais.