Apports combinés de l'expérimentation et de la modélisation à la compréhension de l'alcali-réaction et de ses effets mécaniques

A theoretical approach has been combined with an experimental one in order to better understand the mechanical behaviour of a concrete affected by Alkali-Aggregate Reaction (AAR), and more precisely by Alkali-Silica Reaction. The interest of a model, based on the mechanics of reactive porous media, first appears with the design of the experimental program, which involves more than six hundred samples. A first simple model has affected the choice of the main parameters (external water supply, temperature and stress) and also led us to consider a link between the mechanical consequences and the internal causes of AAR. Experimental data on deformations, cracking, weight variations and mechanical properties have been gathered. Furthermore, various techniques have allowed us to study the evolution of the material microstructure: scanning electron microscopy, visualization of the reaction products by fluorescence of the uranyle ion, mineralogical calculations. The main results are as follows: - The state of stress does not affect the development of the physico-chemical mechanisms involved in AAR. A method, based on 'imposed chemical deformations', may thus be proposed for calculting the structures concerned. - Osmotic pressure (or imbibition) appears to play a secondary role on the swelling owing to AAR, which results from the location of the reaction products. - The quantity of water available when the products are formed is a major factor of the swelling amplitude and kinetics. - Swelling can reach 0.1%, using only the water still available after cement hydration. - If the loss of water reaches a critical value, AAR simply stops, waiting for further water supply.- The intrinsic swelling heterogeneity was quantified; it emphasized the interest of a probabilistic framework for modelling AAR. - Monitoring the evolution of the mechanical properties showed that the compressive and splitting tensile strengths are not affected by AAR, whereas the Young's modulus decreases by about 30%, because of cracking. - The causes of the free swelling anisotropy are related to the casting direction and concrete anisotropy, regardless of AAR. - The S-shaped deformation curves are due to the increase in the porous space while concrete swells, making diffusion easier and hence accelerating the physicochemical mechanisms. - The swelling acceleration stage greatly determines the deformation kinetics of an AAR-affected concrete. External water supply and, above all, temperature have a major influence on the duration of this stage. All these results have enabled us to identify the parameters of a more advanced model describing the free swelling of a concrete similar to that of many affected structures in Northern France.Ce travail allie une approche théorique, basée sur la mécanique des milieux poreux réactifs, à une approche expérimentale importante, afin de mieux comprendre le fonctionnement d'un béton atteint d'alcali-réaction (plus précisément, de réaction alcali-silice). L'intérêt de la modélisation se manifeste dès la conception du programme d'essais, en orientant le choix des principaux paramètres - apports d'eau, température et contraintes - et en induisant une méthodologie d'étude qui établit un parallèle entre les effets macroscopiques et les causes microscopiques de l'alcali-réaction. Le volet expérimental a porté sur les déformations, fissurations, variations de poids et caractéristiques mécaniques de plus de six cents éprouvettes, en gonflement libre ou sous contrainte uniaxiale. Parallèlement, l'évolution de la microstructure du matériau a été étudiée par différentes techniques: microscope électronique à balayage, visualisation des produits de réaction par fluorescence des ions uranyle, calculs minéralogiques. Les principaux résultats expérimentaux ont été établis sur des bétons ordinaires à base de granulats calcaires (réactifs ou non) et de ciment Portland artificiel. Ils concernent principalement : - l'absence d'influence de l'état de contrainte du matériau sur l'évolution des processus physico-chimiques constituant l'alcali-réaction, ce qui permet d'envisager un calcul d'ouvrage par une approche de type 'déformations chimiques imposées', - le caractère secondaire, sur le plan du gonflement macroscopique, des phénomènes de nature osmotique, et la prépondérance de l'effet de la localisation des produits de réaction, - le rôle primordial, vis-à-vis du gonflement, de la quantité d'eau disponible au moment de la formation des produits de réaction, - la possibilité d'obtention de déformations atteignant 0,1% à partir de la seule eau de gâchage non utilisée par l'hydratation du ciment, - l'indépendance des phénomènes de transport d'eau par rapport à la présence d'alcaliréaction, - l'existence d'un seuil de dessiccation en dessous duquel l'alcali-réaction est bloquée jusqu'à l'arrivée de nouveaux apports d'eau, - la quantification de l'hétérogénéité intrinsèque, justifiant l'introduction d'un aléa sur le gonflement asymptotique, - le suivi de l'évolution des caractéristiques mécaniques, montrant le maintien des résistances en compression et en traction par fendage et une chute de l'ordre de 30% du module d'Young, liée à la fissuration des éprouvettes, - l'explication de l'origine de l'anisotropie du gonflement libre, due au sens du coulage et à l'anisotropie du béton, indépendamment de l'alcali-réaction, - la compréhension des causes de la forme sigmoïdale des courbes de gonflement, résultant de l'augmentation de l'espace poreux au fur et à mesure du développement de l'alcali-réaction et donc de la plus grande facilité de diffusion, - la mise en évidence de l'importance de la phase d'accélération des phénomènes (notion de temps de latence), dont la durée dépend des apports d'eau extérieurs, mais surtout de la température (dont l'effet est essentiellement cinétique). Ces résultats ont permis d'identifier les ordres de grandeur des paramètres fondamentaux d'une loi de comportement décrivant l'évolution d'un béton du même type que celui de plusieurs ouvrages atteints d'alcali-réaction, dans le Nord de la France

La certification ACQPA pour les revêtements par peinture des bétons de tunnels et de ponts

Cet article donne des éléments techniques et réglementaires, à l'attention de différentes "cibles", sur la certification des bétons de tunnels et de ponts

Classification automatique de défauts sur des images de tunnels par forêts d'arbres aléatoires

Format électronique, article courtInternational audienc

Apports combines de l'experimentation et de la modelisation a la comprehension de l'alcali-reaction et de ses effets mecaniques

Available from INIST (FR), Document Supply Service, under shelf-number : 22859, issue : a.1998 n.28 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Equipment and Procedure Description

This chapter collects the description of the main creep testing procedures in fibre-reinforced concrete (FRC) as well as the equipment used by each participant laboratory in the round-robin test (RRT). The description of each procedure was directly provided by the participants and follows the same structure for each participant where institution identification and contact information was included. Each participant summarised the most significant data such as specimen?s size, load configuration, parameters or environmental conditions in a quite useful table. Moreover, the participants included description and close-up pictures of the creep frames construction, the support boundary conditions, and the measurement devices used. Finally, the participants provided a complete description of the specific complete creep test procedure followed.Fil: Llano Torre, Aitor. Universidad Politécnica de Valencia; EspañaFil: Cavalaro, Sergio H. P.. University of Loughborough; Reino UnidoFil: Kusterle, Wolfgang. University of Applied Sciences; AlemaniaFil: Moro, Sandro. Master Builders Solutions; ItaliaFil: Zerbino, Raul Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería; ArgentinaFil: Gettu, Ravindra. Indian Institute of Technology Madras. Department of Civil Engineering; IndiaFil: Pauwels, Hans. Tohoku University. School of Engineering. Department of Architecture and Building Science; Japón. Bekaert; BélgicaFil: Nishiwaki, Tomoya. Tohoku University. School of Engineering. Department of Architecture and Building Science; JapónFil: Parmentier, Benoît. Belgium Building Research Institute; BélgicaFil: Buratti, Nicola. Universidad de Bologna; ItaliaFil: Toledo Filho, Romildo D.. Universidade Federal do Estado do Rio de Janeiro; BrasilFil: Charron, Jean-Philippe. Escuela Politécnica de Montreal; CanadáFil: Larive, Catherine. Centre d’Etudes des Tunnels; FranciaFil: Boshoff, William P.. University of Pretoria. Built Environment and Information Technology. Faculty of Engineering, ; SudáfricaFil: Bernard, E. Stefan. Technologies in Structural Engineering; AustraliaFil: Kompatscher, Michael. Versuchsstollen Hagerbach; Suiz

Database of the Round-Robin Test on Creep Behaviour in Cracked Sections of Fibre Reinforced Concrete organised by the RILEM Technical Committee 261-CCF

This database was obtained in an international Round-Robin Creep Test campaing promoted by the RILEM Technical Committee TC 261-CCF. The RRT database is open access available for the scientific community as supplementary material of the Round-Robin Test State-of-the-Art Report published by Springer in the RILEM State-of-the-Art Reports series to improve the global knowledge in the long-term deformations of the cracked FRC specimens. The database variables as well as the parameter organistaion are described in the Appendix C of the aforementioned book.[EN] The RILEM Technical Committee 261-CCF launched in 2015 an international Round-Robin Test (RRT) program to improve the knowledge on the long-term behaviour of cracked Fibre Reinforced Concrete (FRC) sections and assess all the different testing methodologies available. The participation of 19 international laboratories performing creep test following different methodologies in compliance with previously agreed conditions contributed to the success of the RRT. A convention regarding the data collection during the RRT was established to simplify the analysis of results. The RRT provided an extensive database of results from tests performed according to similar procedures and conditions agreed beforehand by the participants. More than 150 parameters and variables were defined and registered during the RRT realisation for each specimen. The long-term tests performed on 124 specimens for one year following four main creep methodologies provided a huge database with more than 15000 data. The analysis of this RRT should support the future proposal of standard test procedures and conditions, defining common criteria for future experimental programs for each test method as well as validation of models to consider creep in the design of FRC structures. The database of the RRT is offered open access to the scientific community as supplementary material of the Round-Robin Test State-of-the-Art Report published by Springer in the RILEM State-of-the-Art Reports series to improve the global knowledge in the long-term deformations of the cracked FRC specimens.This Round-Robin Test (RRT) has been supported by the fibre suppliers Master Builders Solutions (BASF), BEKAERT and ArcelorMittal Fibres. The RRT organizers wish to thank their financial support in the fabrication and delivery of the specimens all over the world. The RRT organizers gratefully thank to the following institutions their participation on this international experimental programme: Universitat Politècnica de València UPV, Universitat Politècnica de Catalunya UPC, OTH Regensburg, Master Builders Solutions (BASF), LEMIT-CIC and Facultad de Ingeniería UNLP, Indian Institute of Technology Madras IITM, NV BEKAERT SA, Tohoku University, ArcelorMittal Fibres, BBRI Belgium Building Research Institute, University of Bologna, Universidade Federal de Rio de Janeiro, École Polytechnique de Montréal, Politecnico di Milano, Sigma Béton, CETU Centre for Tunnel Studies, MEDDE, Stellenbosch University, TSE Technologies in Structural Engineering and VSH VersuchsStollen Hagerbach. The contribution of all TC members and external attendees during both face-to-face and on-line meetings as well as their proposals for the RRT experimental program, their contribution in both the book and the database, and the review of the many drafts of this database is greatly acknowledge. Last but not least, the TC chairman wish to thank to the RILEM Association their guidance during the Technical Committee lifetime and their support for the publication of the different works authored by the TC.Llano Torre, A.; Serna Ros, P.; Cavalaro, S.; Kusterle, W.; Moro, S.; Zerbino, RL.; Gettu, R.... (2021). Database of the Round-Robin Test on Creep Behaviour in Cracked Sections of Fibre Reinforced Concrete organised by the RILEM Technical Committee 261-CCF. https://doi.org/10.4995/Dataset/10251/16322