Among the various factors affecting DEF in concrete, the mineralogical composition is an interesting one because firstly of the industrial consequences and secondly because of the implications in the understanding of DEF in concrete. In this paper, two concretes were fixed with the same quantity of Portland cement CEMII/A L (with 6% of calcareous additions), the same water-cement ratio (0.57) and the same quantity of aggregates. Only the nature of the aggregates was different: calcareous or siliceous. The same thermic treatment was applied to the two concretes and DEF is generated in the two. However, amplitude and kinetics are very different, calcareous aggregates inducing a lower swelling. Finally, different explanations (mechanical, chemical and coupled) of these differences are discussed.

Delayed Ettringite Formation (DEF) in concrete is likely to develop in massive civil engineering structures such as bridges, nuclear plants, and dams with major security issues. In many cases, DEF pathology can lead to swelling and cracking which may significantly impact mass transfer and mechanical properties. It is then of major importance to build predictive tools for engineering conceptions and expertises. In this contribution, the chemical swelling evolution is integrated within the overall constitutive law of concrete that, besides, can experience other phenomena such like damage, plasticity, and long term creep, not all considered here. On another hand, as DEF is activated by environmental humidity above a certain threshold, we introduce the notion of effective time that takes into account the cumulative exposition above this threshold. Hence, a special care is taken with regards to the chemical irreversibility, together with the humidity-drying cycles. Computations are used to calibrate various sets of model parameters with the help of results from the literature, on the one hand, and from an experimental campaign where a calcareous aggregates-based concrete is studied, on the other hand. We show the efficiency of the developed numerical tool through a series of numerical examples.

Delayed Ettringite Formation (DEF) in concrete is likely to develop in massive civil engineering structures such as bridges, nuclear plants, and dams with major security issues. DEF pathology can lead to swelling and cracking which may significantly impact mass transfer and mechanical properties. It is then of major importance to build predictive tools for engineering conceptions and expertizes. In this contribution, the chemical swelling evolution is integrated within the overall constitutive law of concrete that, besides, can experience other phenomena such like damage, plasticity, and long term creep, not all considered here. On another hand, as DEF is activated by environmental humidity above a certain threshold, we use a notion of effective time that takes into account the cumulative exposition above this threshold. Hence, a special care is taken with regards to the chemical irreversibility, together with the humidity-drying cycles. The computations are used to calibrate the model parameters with the help of results from an experimental compaign where two kinds of concretes were studied; one with siliceous aggregates, and one with calcious aggregates. We show the efficiency of the developed numerical tool through a series of examples.

We show how a two-scales FE model—within a sequential approach—leads to consistently simulate the DEF macroscopic consequences: cracks pattern and opening, residual modulus decrease. The mesoscopic part of this model is adapted to heterogeneous materials and is based on two kinematics enrichments. The first one leads to a very fast meshing process along the randomly chosen set of aggregates and, the second leads to directly compute the cracks openings. Assuming DEF is driving to a progressive and homogeneous mortar expansion, we show how the macroscopic—concrete—expansion as well the cracks pattern are consistent with the experiments. For the latter we are interested in the characterization of the aggregates effect on the amplitude of DEF swelling, so that we focus on parameters such as the size and the volume fraction of granular inclusions.

In 2006, experiments were conducted on 90 concrete ski lift foundation elements. The concrete was contaminated with sulphates whose content by mass varied between 0.9% and 14%. The concrete was manufactured with type CEM I cement, limestone (calcium carbonate and dolomite) and siliceous aggregates with highly variable proportions of anhydrite. There was a considerable danger that the thaumasite form of sulphate attack would occur in these concretes because of their exposure to low temperatures (T <15°C). Tests were conducted on core samples taken from the structures to provoke the formation of thaumasite (immersion at 5°C) or ettringite (immersion at 20°C). After 900 days of monitoring, some concretes exhibited particularly severe deterioration. Conservation at low temperature led to severe swelling, failure and a marked loss of cohesion in some concretes with a high sulphate content (SO3 > 7% by weight). Development of the disorder is not only related to the total sulphate content. Factors that could not be characterised, such as the distribution and size of the anhydrite particles must also be taken into account. En 2006, une expertise est menée sur 90 fondations de remontées mécaniques. Des granulats de ces bétons sont pollués par des sulfates dont la teneur massique varie entre 0,9% et 14%. Le béton est formulé avec un ciment de type CEM I dosé à plus de 400 kg m–3, des granulats calcaires (calciques et dolomitiques) et siliceux, comportant de l’anhydrite dans des proportions très variables. Le risque d’attaque sulfatique par la formation de thaumasite dans ces bétons est important du fait de leur exposition à de basses températures (T < 15°C). Des essais sont réalisés sur des carottes extraites des fondations en vue de favoriser la formation de thaumasite (immersion à 5°C) ou d’ettringite (immersion à 20°C). Après 900 jours de suivi, certains bétons sont particulièrement endommagés. Le maintien à basse température a provoqué un gonflement important et une forte décohésion de certains bétons riches en sulfates (SO3> 7% g/g) jusqu’à leur ruine. Le développement de la pathologie n’est pas uniquement lié à la teneur en sulfates totaux. Des facteurs que nous n’avons pas pu caractériser, tels que la distribution et la taille des grains d’anhydrite, doivent également être pris en compte.

These recommendations deal with civil engineering structures and buildings comprising elements of important size that are in contact with water or subjected to a humid environment. They present the different levels of prevention that have to be determined according to the category of the structure (or part of the structure) and to the environmental conditions to which it is exposed. For each of the four levels of prevention selected, associated precautions are applied and associated verifications are carried out. The recommendations also present preventive measures related to the design and erection of the structures, the mix-design and the manufacture of the concrete as well as to its pouring. These preventive measures aim at avoiding the prolonged contact of the critical elements with water during the service life of the structure, at limiting the maximum temperature reached within the concrete of the critical elements, and at controlling the heating treatments of the precast elements. Résumé Les présentes recommandations concernent les structures de génie civil et les bâtiments qui comportent des éléments de grande dimension en contact avec l’eau ou exposés à un environnement humide. Elles présentent les différentes niveaux de prévention qui sont à déterminer en fonction de la catégorie de la structure (ou de la partie de structure) et les conditions environnementales dans lesquelles elle se trouve. A chacun des quatre niveaux de prévention sélectionnés, sont associées des précautions et des vérifications à mener. Les recommandations présentent également des mesures préventives relatives à la conception et à l’exécution des structures, ainsi qu’à la formulation, la fabrication et la mise en œuvre des bétons. Les mesures préventives visent à éviter le contact prolongé des éléments critiques avec l’eau pendant la durée de service de la structure, à limiter la température maximale atteinte au cœur des bétons des éléments critiques, et à contrôler les traitements thermiques des éléments préfabriqués.

Delayed Ettringite Formation (DEF) in concrete is likely to lead to swelling and cracking in structures which have undergone early age heating to a temperature of over 65°C. Application of a method that accelerates this process has made it possible to study the impact of cement properties on DEF. For two temperatures reached by the concrete (75°C or 85°C), the study considers a domain defined by the sulphate content [2.6–3.6%], the alkali content [0.5–1%] and the Blaine specific area [3330–4635cm2/g] of the cement. The impact of these parameters and the interactions between them on swelling are discussed. Monitoring of the dynamic elastic modulus of the concretes shows that this property may be reduced by DEF, but that it may increase again once the swelling process has ceased, probably due to the gradual filling of voids by ettringite formed under conditions of limited supersaturation.

The degradation of concrete structures caused by delayed ettringite formation (DEF) is a problem that affects many concrete structures worldwide [1]. This pathology is due to the formation of expansive ettringite inside the material and is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by DEF. Hence, there is an urgent need to find preventive methods that may enable the inhibition of DEF in new constructions. This paper presents the findings of a long-term study [2,3] on the expansion rate and microstructure of heat-cured concretes with different amounts of mineral additions, like fly ash, metakaolin, ground granulated blast-furnace slag, silica fume and limestone filler. For this purpose different concrete compositions were produced using the same binder, water/binder (w/b) ratios and aggregate type. The concretes were prepared and subjected to a heat-curing cycle and subsequently to two drying-humidification cycles. After these cycles the concrete specimens were immersed in water for long-term storage at 20 ± 2°C. Length changes of specimens were measured at regular intervals. The microstructures of old heat curing specimens were investigated by optical microscopy and SEM-EDS analysis. The results of the blended-concrete compositions were compared with control compositions, and the conclusions were extracted.

Os autores agradecem a Fundacao para a Ciencia e Tecnologia (FCT) o apoio financeiro no âmbito do projecto EXREACT (Mitigacao de reaccoes deleterias expansivas internas em estruturas de betao, PTDC/CTM/65243/2006), e ao projecto DURATINET (Durable Tranport Infrastructures in the Atlantic Area Network) do Programa Operacional Espaco Atlântico 2007-2013, co-financiado pelo FEDER.

The consequences of Delayed Ettringite Formation (DEF) on the mechanical properties of concrete still remain imperfectly known. It is generally recognised that this pathology can decrease the strength of the material and its Young modulus.The comparative study between the expansion of concrete and the evolution of its dynamic modulus carried out in this study on a great number of samples, demonstrates that two types of swelling behaviours can be observed: a linear and a sigmoidal.A relationship between modulus and expansion rate is highlighted but it only remains in the case of linear swelling, which does not generate any significant damage.In the case of sigmoidal swelling, the damage process starts for expansions greater than 0.1% that can consequently reduce by 60% the dynamic modulus and by 65% the compressive strength. The relationship between modulus and expansion rate established for linear swelling cases is temporary verified for sigmoid swelling ones at the inflection point. At this point, the supersaturation is assumed to be mostly consumed and cannot further damage the matrix. Thereafter, the phase of stabilization of the expansion begins, and can be concomitant with a rehealing of the matrix induced by the continuation of cement hydration.

Many studies have shown the effect of different parameters on the expansion induced by delayed ettringite formation (DEF), but there is not yet a general agreement on their relative effects due to discrepancies on experimental results generally attributed to different experimental conditions. The aim of this study is to assess the coupling effects between some of the main parameters of this reaction using the experimental design method. The main interactions concern two factors: temperature and duration of heating during curing. Each interaction has been subjected to statistical tests in order to be validated. The resulting empirical models can reflect the experimental fields and therefore provide useful information about the risk of expansion related to␣DEF, knowing the temperature and the duration of curing, the alkali content of the concrete, the aggregate nature and the water to cement ratio.

The purpose of this work was to provide information allowing a better understanding of the mechanisms involved in the physical adsorption of Cl- and SO42- anions on C-S-H. It is found that the charge of the electrolytes has a very marked influence on both the maximum quantity adsorbed and the affinity of the ions for the surface. The relationship between free and adsorbed anions may be described by the Langmuir equation. The zeta potential decreases in absolute value as the sodium hydroxyde concentration or temperature increase. To try to explain the adsorption mechanisms, we applied the model known as of triple diffuse layer of Stem and Grahame at the C-S-H/NaOH interface. Adsorption phenomena result probably from anionic exchange mechanisms at the level of the outer Stern layer.

L'objectif de ce travail etait d'apporter des elements d'information dans la comprehension des mecanismes d'adsorption physique des anions Cl - et SO 4 2- sur les parois des C-S-H. Il apparait que la charge de l'electrolyte a une influence tres marquee a la fois sur la quantite maximale adsorbee et sur l'affinite des anions pour la surface. La relation entre les anions libres et adsorbes peut etre decrite par l'equation de Langmuir. Le potentiel zeta decroit en valeur absolue lorsque la concentration en hydroxyde de sodium ou la temperature augmentent. Pour essayer d'expliquer les mecanismes d'adsorption, nous avons applique le modele de la triple couche de Stem et Grahame a l'interface C-S-H/NaOH. Le phenomene d'adsorption resulte probablement de mecanismes d'echange anionique au niveau de la couche externe de Stem.

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Un essai basé sur des cycles dont le séchage est réalisé à 38°C peut donc être envisagé. Des études complémentaires permettront de l'optimiser et de le valider.A test based on cycles whose drying is carried out at 38°C, applied to concretes can thus be considered. Complementary studies are still needed to optimize and validate this test.