Experimental investigation of the variability of concrete durability properties

One of the main objectives of the APPLET project was to quantify the variability of concrete properties to allow for a probabilistic performance-based approach regarding the service lifetime prediction of concrete structures. The characterization of concrete variability was the subject of an experimental program which included a significant number of tests allowing the characterization of durability indicators or performance tests. Two construction sites were selected from which concrete specimens were periodically taken and tested by the different project partners. The obtained results (mechanical behavior, chloride migration, accelerated carbonation, gas permeability, desorption isotherms, porosity) are discussed and a statistical analysis was performed to characterize these results through appropriate probability density functions

A performance based approach for durability of concrete exposed to carbonation

International audienceCarbonation is a widespread degradation of concrete and may be coupled with more severe degradations. In order to change from prescriptive requirements to performance based specifications for durability, through the equivalent performance concept, it is necessary to find relevant performance tests and indicators. Concrete mixtures of the reported study were designed complying with required binder contents and water–cement ratios to investigate the effects of binder composition, aggregate type and curing conditions. Early drying severely affected performances, as well as cement replacement by low-calcium fly ash. Aggregates had indirect effects on actual water content and curing. Porosity, gas permeability and chloride diffusivity were found as unreliable indicators for carbonation, since they only characterise compactness of concrete. An accelerated carbonation test is proposed as a performance test, as it is sensitive enough and results were consistent with natural carbonation in the studied exposure conditions. Another indicator, based on chloride diffusivity/initial CaO content ratio, could provide useful data for given aggregate mixes and curing conditions, as it takes into account compactness of concrete and chemical reactivity of binder

Etude des bétons soumis au risque de carbonatation par le concept d'équivalence de performances

International audiencePerformance-based specifications have been introduced in the French standards through the equivalent performance concept. New concrete mixtures may be used provided that they are proved to be as durable as reference mixtures designed through prescriptive specifications. Our study deals with carbonation. It shows how some performances of reference concrete mixtures can vary even if binder content and water/binder ratio are kept constant.La nouvelle norme NF EN 206-1 introduit, alternativement aux valeurs limites de composition du béton, le concept de performance équivalente, qui permet de qualifier de nouvelles compositions de béton par comparaison avec un béton de référence conforme à l'approche prescriptive. L'étude porte sur les classes XC (carbonatation) et montre un exemple de variabilité des performances du béton de référence, à quantité de liant et d'eau constantes, ainsi que des limites des indicateurs de durabilité généraux dans l'estimation de la durabilité potentielle des bétons

Interés educativo

Declarar de interés educativo al Congreso Nacional de Profesores de Francés, 4, organizado por la Asociación de Profesores de Francés de la Provincia de Buenos Aires, que tendrá lugar del 16 al 18 de octubre de 1996, en Bahía Blanca, Provincia de Buenos Aire

Evaluation de la réactivité de plusieurs formules de béton vis-à-vis de la réaction sulfatique interne

JOA 2016, Journées techniques Ouvrages d'Art 2016, BORDEAUX, FRANCE, 25-/05/2016 - 26/05/2016La réaction sulfatique interne (RSI), connue depuis près de 40 ans en France, est une pathologie du béton qui peut se rencontrer encore aujourd'hui sur certains ouvrages anciens. Si les ouvrages construits depuis la parution des recommandations du LCPC en 2007 n'ont pas développé de désordres imputables à ce phénomène, ceux datant de plus de 10 ans peuvent présenter des désordres liés au développement tardif de cette réaction pathogène. Aujourd'hui, la composition des ciments évolue, notamment par l'incorporation d'additions minérales variées. Par ailleurs, l'actualisation récente de la norme NF EN 206/CN autorise une utilisation plus large de ciments de type CEMII/A-L et LL. Aussi, ces évolutions mènent à évaluer la réactivité de ces ciments vis-à-vis de la réaction sulfatique interne.Une étude a donc été menée à l'IFSTTAR à la demande de la FNTP pour évaluer l'efficacité de plusieurs additions minérales avec des ciments CEMI et CEMII/A-LL vis-à-vis de la RSI, en appliquant des traitements thermiques simulant ceux rencontrés par les pièces massives et en comparant ces formules à une formule témoin connue pour être très sensible à la RSI. Il a ainsi été montré l'efficacité des additions minérales pour inhiber cette pathologie aussi bien avec un CEMI qu'avec un CEMII/A-LL. Par ailleurs, l'utilisation d'un liant ternaire (CEMI + cendres volantes + fumées de silice) s'est également montré efficace. De plus, il a été établi les teneurs minimales à respecter pour se prémunir de la RSI en utilisation avec un CEMI ou un CEM II/A.Ces résultats seront à prendre en considération lors de la prochaine révision des recommandations pour la prévention des désordres dus à la réaction sulfatique interne

A Nuclear Role for miR-9 and Argonaute Proteins in Balancing Quiescent and Activated Neural Stem Cell States

Summary: Throughout life, adult neural stem cells (NSCs) produce new neurons and glia that contribute to crucial brain functions. Quiescence is an essential protective feature of adult NSCs; however, the establishment and maintenance of this state remain poorly understood. We demonstrate that in the adult zebrafish pallium, the brain-enriched miR-9 is expressed exclusively in a subset of quiescent NSCs, highlighting a heterogeneity within these cells, and is necessary to maintain NSC quiescence. Strikingly, miR-9, along with Argonaute proteins (Agos), is localized to the nucleus of quiescent NSCs, and manipulating their nuclear/cytoplasmic ratio impacts quiescence. Mechanistically, miR-9 permits efficient Notch signaling to promote quiescence, and we identify the RISC protein TNRC6 as a mediator of miR-9/Agos nuclear localization in vivo. We propose a conserved non-canonical role for nuclear miR-9/Agos in controlling the balance between NSC quiescence and activation, a key step in maintaining adult germinal pools. : An essential protective feature of adult neural stem cells is their relative quiescence. Katz et al. identify microRNA-9 as crucial factor that maintains adult NSCs quiescence and sets a heterogeneity within these cells, through a non-canonical nuclear mode of action. Keywords: neural stem cell, radial glia, quiescence, adult neurogenesis, telencephalon, miR-9, Argonaute, Notch, zebrafis

Design of portable rheometer with new vane geometry to estimate concrete rheological parameters

This paper presents the development of a portable vane rheometer to estimate concrete plastic viscosity and yield stress. The apparatus can be used not only in laboratory but also on construction site. In this study, new blade geometry was proposed to minimize the effect of segregation of concrete during testing, and also to expand the wide range of concrete work­ability with a slump of approximately from 7 cm to fluid concrete, and concrete with high plastic viscosity such as concrete with mineral additions. The used blade (U shaped and reversed) allows reducing the vibration of the apparatus, and ob­taining more stable measurements. The obtained results permit validating the rheometer test procedure and confirmed that the results are reliable, with a low coefficient of variation of 9% for repetitive test and of 5.8% for reproductive tests. First published online: 23 Jun 201

Effects of delayed ettringite formation on reinforced concrete structures

International audienceThe prediction and reassessment of mechanical behaviour of reinforced structures affected by delayed ettringite formation (DEF) is a major challenge for structure managers. Firstly, several experimental tests were performed in laboratory to study the influence of both uni and tri-axial reinforcements on DEF expansion. Strain decreases in reinforced directions were observed, proving that DEF expansion under restraint is anisotropic. Cracks were observed parallel to the restrained directions. No strain trans-fert occurs from restrained directions to other ones. Secondly, data provided by these results are used to fit a numerical finite element model taking into account both chemical and mechanical aspects of DEF. Finally, an element of a DEF damaged structure is modelled with the whole model and compared to on site observations

Effects of delayed ettringite formation on reinforced concrete structures

International audienceThe prediction and reassessment of mechanical behaviour of reinforced structures affected by delayed ettringite formation (DEF) is a major challenge for structure managers. Firstly, several experimental tests were performed in laboratory to study the influence of both uni and tri-axial reinforcements on DEF expansion. Strain decreases in reinforced directions were observed, proving that DEF expansion under restraint is anisotropic. Cracks were observed parallel to the restrained directions. No strain trans-fert occurs from restrained directions to other ones. Secondly, data provided by these results are used to fit a numerical finite element model taking into account both chemical and mechanical aspects of DEF. Finally, an element of a DEF damaged structure is modelled with the whole model and compared to on site observations