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The research presented in this thesis seeks to examine and understand the mechanism of fire spalling role played by the external compressive loading during heating. Concrete cube (200 x 200 x 200 mm3) and slab (800 x 800 x 100 mm3) specimens made with CEM II and CEM III cements (B40-II and B40-III: fc28days ≈ 40 MPa) were exposed to ISO 834-1 fire curve under different levels of external uniaxial (for cube) and biaxial (for slab) compressive stress. Additionally, the effect of external compressive loading (confining pressure and uniaxial load) on the residual gas permeability of concretes have been investigated. In order to better analyse the experimental results and to provide more insight into the mechanism behind the fire spalling behaviour of concrete, numerical computations were carried out by using the existing thermo-mechanical model implemented in a finite element code CAST3M. The experimental results have clearly shown that the loaded specimens (uniaxial and biaxial) are more prone to spalling than unloaded specimens, with increasing amounts of spalling for higher values of applied compressive stress. Part of the tests, but not all have shown that B40-II (3% of slag) exhibited higher spalling than the B40-III (43% of slag).From this study on two ordinary concretes, it highlights that a certain level of external compressive stress (uniaxial or biaxial) was necessary to induce spalling. A possibility is that the applied compressive stress prevents the creation of cracks naturally due to thermal mismatch between cement paste and aggregates and thermal gradients. For unloaded specimen, the creation of cracks increases the permeability and naturally prevents the pore pressure to exceed a value that favours spalling.During a real fire, concrete structural members are always loaded or restrained. The presence of compressive loading during heating significantly increases the compressive stress (decreases the tensile stress) and the magnitude of pore pressure, which increase the risk of fire spalling. Then, the applied compressive stress is a very important key factor that the fire resistance design of concrete structures should take into account when considering spalling. Hence, it is recommended that the fire spalling test should not be carried out only on unloaded specimens, especially for the ordinary concrete.; La recherche présentée dans cette thèse vise à examiner le mécanisme d’écaillage des bétons exposés au feu et comprendre l’influence du chargement mécanique appliqué en compression durant le chauffage. Des cubes (200 x 200 x 200 mm3) et des dalles (800 x 800 x 100 mm3) de béton fabriqués avec des ciments CEM II et CEM III (B40-II et B40-III: fc28days ≈ 40 MPa) ont été exposés à un feu ISO 834-1 sous différents niveaux de chargement uniaxial (cubes) et biaxial (dalles). En outre, l'effet du chargement mécanique (pression de confinement et charge uniaxiale) sur la perméabilité résiduelle au gaz a été étudié. Afin de mieux analyser les résultats expérimentaux et comprendre les mécanismes à l’origine de l'écaillage, des calculs numériques ont été réalisés en utilisant un modèle thermo-mécanique du code aux éléments finis CAST3M. Les résultats expérimentaux ont clairement montré que les éprouvettes chargées (uniaxial et biaxial) présentent un risque d’écaillage plus important que les éprouvettes non chargées. L’écaillage augmente avec le niveau de contrainte appliquée. Une partie des essais mais pas tous, ont montré que le B40-II (3% de laitier) présente un écaillage plus important que celui du béton B40-III (43% de laitiers).À partir de cette étude sur deux bétons ordinaires, il peut être mis en évidence qu'un certain niveau de contrainte de compression externe (uniaxiale ou biaxiale) est nécessaire pour induire l'écaillage du béton ordinaire. Les pressions des pores se combine avec les contraintes thermiques dûes aux gradients thermiques. Les contraintes de compression appliquées empêchent la création de certaines fissures générées par l'incompatibilité des déformations thermiques de la pâte de ciment et des granulats et des gradients thermiques. Pour l'échantillon non chargé, la création de fissures augmente la perméabilité et empêche naturellement le développement des pressions de pores.Pendant un feu réel, les membres structurels en béton sont toujours chargés ou retenus. La présence d'un chargement compressif pendant le chauffage augmente considérablement le stress de compression (diminue le stress de traction) et la grandeur de la pression des pores, ce qui augmente le risque d'écaillage. Ensuite, le stress compressif appliqué est un facteur clé très important que la conception de la résistance au feu des structures en béton devrait prendre en compte lors de l'écaillage. Par conséquent, il est recommandé que les essais d'écaillage ne soient pas effectués uniquement sur des échantillons non chargés.

The research presented in this thesis seeks to examine and understand the mechanism of fire spalling role played by the external compressive loading during heating. Concrete cube (200 x 200 x 200 mm3) and slab (800 x 800 x 100 mm3) specimens made with CEM II and CEM III cements (B40-II and B40-III: fc28days ≈ 40 MPa) were exposed to ISO 834-1 fire curve under different levels of external uniaxial (for cube) and biaxial (for slab) compressive stress. Additionally, the effect of external compressive loading (confining pressure and uniaxial load) on the residual gas permeability of concretes have been investigated. In order to better analyse the experimental results and to provide more insight into the mechanism behind the fire spalling behaviour of concrete, numerical computations were carried out by using the existing thermo-mechanical model implemented in a finite element code CAST3M. The experimental results have clearly shown that the loaded specimens (uniaxial and biaxial) are more prone to spalling than unloaded specimens, with increasing amounts of spalling for higher values of applied compressive stress. Part of the tests, but not all have shown that B40-II (3% of slag) exhibited higher spalling than the B40-III (43% of slag).From this study on two ordinary concretes, it highlights that a certain level of external compressive stress (uniaxial or biaxial) was necessary to induce spalling. A possibility is that the applied compressive stress prevents the creation of cracks naturally due to thermal mismatch between cement paste and aggregates and thermal gradients. For unloaded specimen, the creation of cracks increases the permeability and naturally prevents the pore pressure to exceed a value that favours spalling.During a real fire, concrete structural members are always loaded or restrained. The presence of compressive loading during heating significantly increases the compressive stress (decreases the tensile stress) and the magnitude of pore pressure, which increase the risk of fire spalling. Then, the applied compressive stress is a very important key factor that the fire resistance design of concrete structures should take into account when considering spalling. Hence, it is recommended that the fire spalling test should not be carried out only on unloaded specimens, especially for the ordinary concrete.; La recherche présentée dans cette thèse vise à examiner le mécanisme d’écaillage des bétons exposés au feu et comprendre l’influence du chargement mécanique appliqué en compression durant le chauffage. Des cubes (200 x 200 x 200 mm3) et des dalles (800 x 800 x 100 mm3) de béton fabriqués avec des ciments CEM II et CEM III (B40-II et B40-III: fc28days ≈ 40 MPa) ont été exposés à un feu ISO 834-1 sous différents niveaux de chargement uniaxial (cubes) et biaxial (dalles). En outre, l'effet du chargement mécanique (pression de confinement et charge uniaxiale) sur la perméabilité résiduelle au gaz a été étudié. Afin de mieux analyser les résultats expérimentaux et comprendre les mécanismes à l’origine de l'écaillage, des calculs numériques ont été réalisés en utilisant un modèle thermo-mécanique du code aux éléments finis CAST3M. Les résultats expérimentaux ont clairement montré que les éprouvettes chargées (uniaxial et biaxial) présentent un risque d’écaillage plus important que les éprouvettes non chargées. L’écaillage augmente avec le niveau de contrainte appliquée. Une partie des essais mais pas tous, ont montré que le B40-II (3% de laitier) présente un écaillage plus important que celui du béton B40-III (43% de laitiers).À partir de cette étude sur deux bétons ordinaires, il peut être mis en évidence qu'un certain niveau de contrainte de compression externe (uniaxiale ou biaxiale) est nécessaire pour induire l'écaillage du béton ordinaire. Les pressions des pores se combine avec les contraintes thermiques dûes aux gradients thermiques. Les contraintes de compression appliquées empêchent la création de certaines fissures générées par l'incompatibilité des déformations thermiques de la pâte de ciment et des granulats et des gradients thermiques. Pour l'échantillon non chargé, la création de fissures augmente la perméabilité et empêche naturellement le développement des pressions de pores.Pendant un feu réel, les membres structurels en béton sont toujours chargés ou retenus. La présence d'un chargement compressif pendant le chauffage augmente considérablement le stress de compression (diminue le stress de traction) et la grandeur de la pression des pores, ce qui augmente le risque d'écaillage. Ensuite, le stress compressif appliqué est un facteur clé très important que la conception de la résistance au feu des structures en béton devrait prendre en compte lors de l'écaillage. Par conséquent, il est recommandé que les essais d'écaillage ne soient pas effectués uniquement sur des échantillons non chargés.

The use of building materials with an artificial reef feature could improve the marine ecosystem of the Channel. In addition, the shellfish activity of neighboring regions generates byproducts that can be valued as aggregates. The aim of this study is to incorporate sea shells in concrete that can be used in marine infrastructures to create new marine habitats. The research focuses on the one hand, the influence of the incorporation of sea shells on the properties of different concretes (ordinary, self-compacting and porous) and on the other hand, the evolution of their properties in the marine environment in relation to the aggressive agents and the colonization. The incorporation of crushed sea shells in ordinary and self-compacting concrete causes a severe increase in the entrained air which decreases their mechanical properties. In the porous concrete, crushed sea shells influence their porosity. The monitoring of submerged concretes confirms that the studied concretes are suitable substrates for the growth of marine organisms. However, immersion and environmental conditions are overriding factors taking into account the type of concrete and the presence of sea shells. Whereas a high concrete porosity can promote superiorcolonization, it is unfavorable from the viewpoint of the durability of these materials. Nevertheless, the covering of concrete by algae-like organisms can slow the deterioration of these materials by the aggressive agents of seawater., L’utilisation de matériaux de construction avec une fonctionnalité de récif artificiel pourrait améliorer l’écosystème marin de la Manche. Par ailleurs, l’activité conchylicole des régions limitrophes génère des coproduits qui peuvent être valorisés en tant que granulats. L’objectif de cette étude est d’incorporer des coquilles de mollusques dans des bétons pouvant être utilisés dans des infrastructures maritimes pour créer de nouveaux habitats marins. Les recherches se focalisent sur, d’un côté, l’influence de l’incorporation de coquilles sur les propriétés des différents bétons (ordinaire, auto-plaçant et poreux) et d’un autre côté, l’évolution de leurs propriétés en milieu marin vis-à-vis des agents agressifs et de la colonisation. L’incorporation de coquilles concassées dans les bétons ordinaires et auto-plaçants élaborés entraîne une forte augmentation de l’air occlus qui diminue leurs propriétés mécaniques. Dans les bétons poreux élaborés, les coquilles concassées influencent leur porosité. Le suivi des bétons immergés confirme que les bétons étudiés sont des substrats adéquats pour le développement des organismes marins. Cependant, les conditions d'immersion et environnementales du milieu sont des facteurs prépondérants compte tenu du type de béton et de la présence de coquilles marines. Les caractéristiques des bétons telles que la porosité, qui favorisent une colonisation supérieure, sont défavorables du point de vue de la durabilité de ces matériaux. Néanmoins, le recouvrement des bétons par des organismes de type algue peut freiner la détérioration de ces matériaux par les agents agressifs de l'eau de mer.

This thesis deals with the influence of the porosity and the saturation ratio on concrete behavior under severe stress. This work is part of a more general study of the vulnerability of massive reinforced concrete frame. In this context, studies focuses particularly on the behavior of the material and structures under impact. 3SR laboratory has a large capacity triaxial press, called GIGA, to achieve stress levels of the order of GPa, applied quasi-statically on concrete samples. Experimental studies on a reference concrete (R30A7) show the major influence of water on the behavior of highly confined concrete (VU, 2009). These same studies also show that the influence of Water/Cement ratio, high in simple compression test, decreases with increasing confinement. The first objective of this thesis is to better understand the effect of porosity on the behavior of concrete under high confinement. In this context two concretes are formulated. One with a reduced porosity relative to the reference concrete R30A7, and the other one with a greater porosity. The results of test campaigns show that the porosity don't play an important role under strong confinement (400 MPa). At the other hand, the deformability of the concrete remains dependent on the overall porosity of the material. The second objective of this thesis is to improve the knowledge of the effects of water on the behavior of concrete. For this, test on both saturated concrete made previously, are carried out. The results show the same effects of water than those observed on the R30A7 but also influenced by the porosity of the material. Tests on wet concrete are made to complete this study. Finally, this thesis proposes the development of triaxial tests with measurement of pore pressure and the development of a radial stress sensor specially adpated for strong confinement., Ce mémoire de thèse traite de l'influence de la porosité et de l'eau libre qu'elle est susceptible de contenir sur le comportement du béton sous sollicitations sévères. Ces travaux s'inscrivent dans le cadre d'étude plus général de la vulnérabilité des ouvrages massifs en béton armé. Dans ce contexte on s'intéresse particulièrement au comportement du matériau et des structures sous impact. Le laboratoire 3SR dispose d'une presse triaxiale de grande capacité, baptisée GIGA, permettant d'atteindre des niveaux de contrainte de l'ordre du GPa , appliqués de manière quasi-statique, sur des échantillons de béton. Des études expérimentales sur un béton de référence (R30A7) montrent l'influence majeure de l'eau sur le comportement du béton fortement confiné (VU, 2009). Ces mêmes travaux montrent par ailleurs que l'influence du rapport Eau/Ciment, importante en compression simple diminue avec l'augmentation du confinement. Le premier objectif de ces travaux de thèse est de mieux comprendre l'effet de la porosité sur le comportement du béton sous forts confinements. Dans cette optique deux bétons sont formulés. L'un avec une porosité diminuée par rapport au béton de référence R30A7 et l'autre avec un porosité plus importante. Les résultats des campagnes d'essais montrent qu'effectivement la porosité ne joue plus de rôle prépondérant à forts confinements (400 MPa) sur la résistance du béton. En revanche la déformabilité du béton reste dépendante de la porosité globale du matériau. Le deuxième objectifs de cette thèse est d'approfondir la connaissance des effets de l'eau sur le comportement du béton. Pour cela, des essais sur les deux bétons saturés précédemment formulés sont réalisés. Les résultats montrent les mêmes effets de l'eau que ceux observés sur le R30A7 mais influencés également par la porosité du matériau. Des essais sur béton humides sont également réalisés afin de compléter cette étude. Enfin, cette thèse propose le développement d'essais triaxiaux avec mesure de la pression interstitielle et le développement d'un capteur de déformation radiale adapté aux essais sous forts confinements.

International audience; Nanoporosities play a most significant role in the durability of cementitious materials, so that nanoscale features are a promising target for SHM. However, to this day, no sensor features the resolution required to investigate non-destructively these nanofeatures. To fill in this loophole, we are devising a SHM-targeted, carbon nanotubes and graphene based capacitive ultrasonic nanotransducer for microporosity assessment in concrete. In this paper, we report on the feasibility of the key building block of the proposed sensor: we have fabricated ultra-thin graphene and single-walled carbon nanotubes membranes. A breakthrough laser vibrometry experiment shows that the membranes can feature above-nanometer amplitudes of vibration over a large range of frequencies spanning from 100 kHz to 5 MHz. A detailed numerical model of the nanotransducer shows that upon embedding in a cementitious material it could determine the volume and content of the porosity in its vicinity. Such information would be invaluable in the evaluation of structural durability.

International audience; The prediction of the service lifetime of civil engineering structures needs an appropriate comprehension and quantification of the physical, chemical and mechanical processes associated with the durability of structural reinforced concrete. In particular, the porosity is an essential property involved in degradation of concretes. Also, the development of a probabilistic approach could enhance estimations of service lifetime. Experimental tests are therefore performed in the framework of project APPLET and aim at quantifying variabilities linked to concrete itself and its setting in a real structure. A spatial variability and the effect of the drying protocol for the measurement of porosity have been highlighted.La prédiction de la durée de vie d’un ouvrage de génie civil requiert une compréhension et une quantification appropriée des processus et grandeurs physiques, chimiques et mécaniques associés à la durabilité des bétons armés de structure. En particulier, la porosité ouverte est un élément important dans les processus de dégradation des bétons. D’autre part, le développement d’une approche probabiliste permettrait d’affiner les estimations de durée de service. A cet effet, des essais réalisés dans le cadre du projet APPLET visent à déterminer les variabilités susceptibles d’être induites par le protocole expérimental, mais aussi les variabilités liées au béton et à sa mise en œuvre dans un ouvrage réel. Une analyse de ces variabilités est conduite, et met en évidence une variabilité spatiale du matériau ainsi que le rôle majeur des protocoles de séchage retenus pour la détermination de la porosité.

This thesis focuses on the behavior of concrete under severe triaxial loading. The stress levels studied are, more accurately, those caused by a missile impact. The broader context of this study is to improve the understanding of infrastructures under dynamic loading type impact, which can generate mean stresses in the concrete of the order of GPa. Quasi-static tests are needed to characterize the behavior of a material in a homogeneous state of stress. The work presented in this thesis proposes the investigation of damage mechanisms of concrete during triaxial loading tests. For this, two innovative machines are used : a large capacity triaxial press and an X-ray computed tomography instrument. The process of conducting tests is to scan concrete samples in the undamaged state and after each loading cycle (load-unload) performed by mean of the triaxial press. The images from these tomographic examinations allow to assess the evolution of the mesostructure of concrete (scale where aggregates and macropores appear) for different loading paths and loading levels. Two samples were tested according to this process. The first one, at relatively low confinement (50 MPa), shows that the mechanisms leading to failure are very localized and mainly initiated at the microscopic scale. The second one, tested at a very high confinement (650 MPa), has a diffuse damage with also a localized failure mechanism. A mesoscopic discrete element model is also presented in this manuscript. The originality of this approach lies in the predictive model developed on one hand, the behavior of mortar, aggregates or their interaction is identified a priori or from tests on mortar and rock. On the other hand, the method of constructing the discrete element mesh is based on the 3D segmentation of tomographic images what allows a comparison between fracture facies of both experiment and numerical specimens. This model leads to a good prediction of the triaxial behavior of concrete and appears to be a promising tool to study damage mechanisms and the influence of parameters of concrete composition., Ce mémoire de thèse s'intéresse au comportement du béton sous chargement triaxial sévère, et plus précisément, aux mécanismes de dégradation associés. Le cadre plus général de cette étude est l'amélioration de la tenue des infrastructures soumises à des chargements dynamiques de type impact, pouvant générer des contraintes moyennes dans le béton de l'ordre du GPa. Des essais quasi-statiques sont nécessaires pour caractériser le comportement d'un matériau dans un état de contraintes homogènes. Les travaux présentés dans ce manuscrit proposent d'investiguer les mécanismes de dégradation du béton lors d'essais triaxiaux. Pour cela, deux machines innovantes sont utilisées : une presse triaxiale de grande capacité (Giga) et un tomographe à rayons X. Le processus de réalisation des essais consiste à scanner des échantillons de béton à l'état vierge et après chaque cycle de chargement (charge-décharge) effectué avec la presse triaxiale. Les images issues de ces examens tomographiques permettent d'évaluer la modification de la mésostructure du béton (échelle où les granulats et les macropores apparaissent) selon différents trajets et niveaux de chargement. Deux échantillons ont été testés triaxialement selon ce processus. Le premier, à relativement faible confinement (50 MPa), montre que les mécanismes menant à la rupture sont fortement localisés et principalement initiés à l'échelle microscopique. Le deuxième, testé à un très fort confinement (650 MPa), présente un endommagement diffus avec également un mécanisme de rupture localisé. Un modèle mésoscopique, utilisant la méthode aux éléments discrets, est également présenté dans ce manuscrit. L'originalité de cette approche réside d'une part dans le caractère prédictif du modèle développé, le comportement du mortier, des granulats ou de leur interaction étant identifié a priori ou à partir d'essais réalisés sur mortier et roche. D'autre part, la méthode de construction du maillage éléments discrets s'appuie sur la segmentation 3D d'images tomographiques ce qui permet une comparaison des faciès de ruptures expérimentaux et numériques. Ce modèle aboutit à une bonne prédiction du comportement triaxial du béton, et semble être un outil prometteur d'étude des mécanismes d'endommagement et de l'influence de paramètres de composition du béton.

In this thesis, we present an experimental study including, besides the destructive measurements usually implemented for the characterization of cementitious materials, non-destructive techniques using ultrasonic wave propagation in a frequency range from 50kHz to 600kHz. The objective is to study the correlations between hydraulic, mechanical properties and linear ultrasonic parameters (velocity and attenuation) of cement paste. This study specifically addresses the relationship between porosity and ultrasonic velocity of the different types of waves (body waves and Rayleigh wave). The studied materials are cement pastes with variable porosity, made up with different water / cement ratios and with different concentrations of air entrainer. To take into account the effect of water content, measurements are made at different states of saturation: saturated state, 70% saturation, 30% saturation and dry state. The data collected allows the creation of a database of experimental data involving physical, mechanical and ultrasonic parameters of cement paste. In the final part of this thesis, relationships between ultrasonic velocity and porosity based on macroscopic and microscopic approaches are presented and compared with measurements, Dans cette thèse, les travaux présentés s’appuient sur une démarche expérimentale utilisant, outre les mesures destructives habituellement mises en œuvre pour la caractérisation des matériaux cimentaires, les techniques non destructives exploitant la propagation des ondes ultrasonores à des fréquences comprises entre 50 kHz et 600 kHz. L’objectif est d’étudier les corrélations entre les propriétés hydrauliques et mécaniques de la pâte de ciment et les paramètres linéaires des ondes ultrasonores (vitesse et atténuation). L’étude concerne plus particulièrement les relations entre la porosité et la vitesse ultrasonore des différents types d’onde (ondes de volume et onde de Rayleigh). Les matériaux étudiés sont des pâtes de ciment à porosité variable, confectionnées avec différents rapports E/C et avec différents dosages en entraineur d’air. Afin de prendre en compte l’effet de la teneur en eau, les mesures sont effectuées à différents états de saturation : état saturée, 70% de saturation, 30% de saturation et l’état sec. Les données recueillies permettent la constitution d’une base des données expérimentale regroupant les caractéristiques physiques, mécaniques et ultrasonores de la pâte de ciment. Dans la dernière partie de cette thèse, les relations entre les vitesses ultrasonores et la porosité basées sur deux approches macroscopique et microscopique sont présentées et confrontées aux mesures

The carbonation is a pathology which affects cement-based materials such as concretes and mortars.The carbonated skin of material becomes brittle and losses the protection of inner steels againstcorrosion. The corrosion products generate a degradation of the concrete which may lead to thecollapse of the structure.Six types of adjuvant concretes and two cement pastes have been designed by a rheological study inorder to study the effect of accelerated and natural carbonation on the sustainability of concretes andcement pastes based on algerian resources. For this purpose, several investigation methods were usedwith both macroscopic and microscopic scales.In conclusion, the empirical rheological model developed herein can be used to formulate concretesresistant to carbonation. The study of carbonation shows that the accelerated protocol may be lessaggressive than the natural one, especially for dense cement pastes. In this case, the acceleratedcarbonation of the surface tends to fill up the superficial microporosity of the concrete, slowing downthe production of carbon dioxide, contrary to the natural carbonation which acts more diffusely withoutcompletely obstructing the pores. The lesser compact is the concrete, the more effective is theaccelerated protocol.; La carbonatation est une pathologie qui affecte les matériaux à base de ciment tels que les bétons et lesmortiers. Les zones carbonatées du matériau deviennent fragiles et perdent ainsi leur pouvoir deprotection des aciers contre la corrosion. Les produits de corrosion engendrent alors une dégradation dubéton pouvant aboutir à la ruine de la structure.Six types de bétons adjuvantés et deux pâtes de ciments ont été formulés grâce à une étude rhéologiqueafin d’étudier l’effet de la carbonatation accélérée et naturelle sur la durabilité des bétons et des pâtesde ciments à base de ressources algériennes. Pour ce faire, plusieurs méthodes d’investigation sontutilisées, aussi bien à l’échelle macroscopique que microscopique.En conclusion, le modèle rhéologique empirique développé peut être utilisé pour formuler des bétonsrésistants à la carbonatation. L’étude de la carbonatation démontre que le protocole accéléré, peut serévéler moins agressifs que la carbonatation naturelle, notamment pour des pâtes de ciment denses.Dans ce cas, la carbonatation accélérée de la surface tend à combler la microporosité superficielle dubéton, freinant ainsi la diffusion du dioxyde de carbone, contrairement à la carbonatation naturelle quiagit de manière plus diffuse sans totalement obstruer la porosité. Moins les bétons sont compacts, plusle protocole accéléré s’avère effectif.

Portland cement pastes made at a water/cement ratio of 0.25 were precured at 4 deg. C for 3 to 15 hr and then cured in simulated seawater at -2.0 and 2 deg. C for ages up to 180 days. Compressive strength, morphology, rate of hydration and porosity of the pastes were determined and interrelationships were established.

Several hydrated portland cement systems have been studied at DBR in a wide range of porosities. These systems include room-temperature hydrated paste, autoclaved paste, autoclaved with addition of sulfur and silica, hot-pressed samples and compacts of synthetic 14A tobermorite. Measurements included compressive strength, Young's modulus, product density, porosity and helium inflow, by which the various systems were characterized. It was concluded that, at a given porosity, an optimum proportion of higher density crystalline material and poorly aligned and ill-crystallized material yields the best strength but the quantity of poorly-crystallized material required decreases with porosity.

Modulus of elasticity and microhardness measurements were made on compacts of four sulfur preparations having different crystallinities morphologies and a wide range of porosities. Compacts amde from Crystex — a high polymeric sulfur — had mechanical properties inferior to those of other preparations studied. Annealing compacts resulted in a large increase in microhardness. Measurements of modulus of elasticity and microhardness of sulfur compacts reinforced with poly (ethylene terephthalate) fibers were made for a wide range of porosities.

The dependence of fracture mechanics terms (gamma[T], K[c], G[c] and J[c]) on relative humidity and porosity is determined for hardened Portland cement paste (HCP). The cardinal features of the fracture term/humidity curves and fracture term/porosity curves are discussed. Large hysteresis in fracture term/relative humidity curves is observed, the magnitude depending on the drying history of HCP. Meniscus effects, aging and moisture-assisted stress corrosion processes are thought to contribute to fracture of HCP. Unhydrated Portland cement, Ca(OH)[2] particles, and pores with specific size distributions in the HCP system possibly act as crack arrestors.

Compressive strength, modulus of elasticity, and microhardness measurements were made on a variety of autoclaved cement-silica preparations covering a wide range of porosity. A spectrum of linear log mechanical property — porosity functions was observed. Analysis demonstrated that the slopes of these functions were dependent on the preparation silica content and density of the hydrated product. The slopes of the lines for each mechanical property bore a constant ratio with slopes calculated from the corresponding lines of the other two mechanical properties. This resulted in expressions interrelating mechanical properties which were independent of porosity and valid for all preparations studied. Compressive strength and microhardness for preparations studied were shown to be directly related.

Cement matrices were prepared by autoclaving portland cement-silica mixtures having various percentages by weight of silica, with water-to-cement ratios of from 0.22 to 0.45. Normal cement paste samples were also made for comparison. Samples were heated to 100°C in vacuum for 24 h before impregnation with methyl methacrylate monomer (MMA), which was then polymerized; impregnation was repeated for complete impregnation. Young's modulus and microhardness were measured as a function of volume fraction of PMMA and results compared with those obtained from similar samples conditioned to 11% RH. Autoclaved impregnated and unimpregnated specimens and room-temperature-cured cement paste specimens at both conditions were exposed to 100% RH and their length changes measured for up to four years. Permeation to water vapour in the impregnated specimens, although decreased, still occurs and impregnation increased long-term expansion on exposure. Expansion on exposure to 100% RH is much larger for D-dried than for 11% RH-conditioned matrices; the latter produced stronger bodies on impregnation.

Mechanical properties of Ca(OH)[2] are compared with those of Portland cement paste at different porosities. Intrinsic values of modulus of elasticity (E) and microhardness (H) for Ca(OH)[2] compacts were obtained by extrapolating to zero porosity log E and log H versus porosity curves. The values for the Ca(OH)[2] and Portland cement paste systems are of similar magnitude. Flexural strength values for both systems were also determined to be of similar magnitude for the porosity range studied. Fracture terms (K[c], J[c], G[ c], gamma [T]) were determined. K[c] and gamma [T] versus porosity plots for both systems revealed that these fracture terms are of similar magnitude in the porosity range common to both.

The dimensional changes and the thermograms of cement specimens were determined during temperature cycles (+5 degrees to -60 degrees C, 0.33 degrees C/min). In each case, freezing processes at -8 degrees and -40 degrees C and melting processes at -11 degrees and 0 degrees C were observed. The results could be explained by a theory previously developed for the porous-glass-water system. At the higher temperature, freezing occurs on the outer surface of the specimen; at the lower temperature, it occurs in the pores after redistribution of the water. Because water does not freeze in pores filled on adsorption, it migrates out of these pores when the relative humidity (expressed in terms of the vapor pressure of undercooled water), unavoidably decreases on cooling. Expansion is deleterious when the water content of the paste is significantly greater than the equilibrium value at the prevailing relative humidity. The effects of the water/cement ratio, degree of saturation, air entrainment, sample dimensions, and cooling rate were consistent with the theory.

Two series of compacts are studied, one d-dried before and one after compaction. Measurements of absolute density, helium flow characteristics and Young's modulus indicate that high pressures can force the layers of d-dried material closer together, giving a Young's modulus double that displayed when no interlayer water is present and identical to that when spaces are occupied by water molecules. Water can re-enter between the layers, however, and on redrying Young's modulus is reduced by 50 per cent to the normal value for the d-dried material. The interlayer water must be regarded as part of the solid.

The length change theory proposed by Flood and Heyding for microporous solids is applied to cement paste in considering the effect of porosity and compressibility on the solid phase. The theory is also used to estimate the dependence of modulus of elasticity on humidity and is in general agreement with experiment. Some insight into microstructural change and its effect on length change is provided by estimates of a structure factor, κ. For humidities up to 56%, values of κ are approximately constant, but major changes in structure occur at higher humidities.

The effectiveness of dicyclopentadiene (DCPD)-modified sulphur in improving the durability of impregnated portland cement systems is assessed. Portland cement paste and porous vycor glass samples were impregnated with modified and unmodified sulphur and some samples were heated to 180 degrees C. Comparison of the measured modulus of elasticity with values calculated from mixture rules provided a qualitative measure of the adhesion between matrix and impregnant. Changes in length and modulus of elasticity with time of exposure at 100 per cent RH were monitored and formed the basis of durability assessment. Samples impregnated with DCPD-modified sulphur and heated at 180 degrees C showed the least distress. It is concluded that two factors control durability: interaction of the matrix with the impregnant, which influences the rate of ingress of water to the interface, and interaction between water and solid surfaces at the interface.

Some of the more important techniques used to measure porosity and pore-size distribution are discussed. The techniques used to measure porosity are the inelastic neutron-scattering method and the helium inflow and helium pycnometric technique. With the neutron scattering technique, the free and bound water can be distinguished. Helium inflow shows the collapse of layered structure when the bound water is eliminated, making it possible to separate the space between the interlayer space. Nitrogen adsorption, capillary condensation and mercury porosimetry provide both the total value of pore volume, which corresponds to the value obtained using helium pycnometry, and pore-size distribution, which correlates in all cases. With capillary condensation, however, some authors have obtained steeper curves and a much higher pore volume under 100 degrees A., 7th International Congress on the Chemistry of Cement, 1980, Paris, France

The interaction of aliphatic alcohols with Portland cement paste, C3S paste, and CSH is assessed by surface area measurements, pore structure determinations, X-ray diffraction analysis, thermal analysis, and helium inflow measurements. The implications of modifications to the microstructure of the cement systems following treatment with the alcohols are discussed.

The validity of the equation E = E[01] exp(-bP) is tested. This relates Young's modulus of a porous body to its porosity; E[01] represents the modulus of the zero porosity material and can be determined by extrapolation. Impregnation of the porous body with sulphur, and use of the Reuss equation E[c] = 1/(V[1]/E[01] + V[2]/E[02]) provides an alternate method for determining E[01]. Both methods are applied for seven different Portland cement systems. The results differ from each other by 5 to 23 per cent.

Properties such as porosity, pore-size distribution, surface area and drying shrinkage are determined for silica fume-portland cement blends (0–30% silica fume) cured from 1 to 180 days at w/ (c+sf) of 0.25 and 0.45. Porosity was measured by helium, mercury and water techniques. It is shown that in paste blends a discontinuous pore structure is formed after as little as seven days of curing due to reaction of Ca(OH) 2 with silica fume. The pores are not so large as those in mortars owing to the lack of interface effects. Total porosities of the blends can only be measured by a water technique, whereas for plain cement pastes other techniques are applicable.

Cement mortars containing 0% and 10% silica fume were prepared with a water/ (cement + silica fume) ratio of 0.60 and 0.70. Sand/cement ratios of 0, 0.5, 1.0, 1.5, 1.8, 2.0, 2.25 and 3.0 were used. Results indicate a large increase in frost resistance for specimens with 10% silica fume plus ( sand)/(cement + silica fume) ratio or >= 2.25 at w/(c +sf) of 0.60, with the greatest resistance for a sand/(cement + silica fume) ratio of 3.0. The improved frost resistance was attributed to the formation of pores in the 97,000--875 nm range at the sand--cement interface.

Measurements of compressive strength, modulus of elasticity, and microhardness were made on magnesium oxychloride cement systems having a wide range of porosity. Analysis of the plots of log mechanical property versus porosity gave expressions interrelating mechanical properties which were independent of porosity. Comparison of these results with those of the portland cement system show that magnesium oxychloride cement paste has a higher value of modulus of elasticity and microhardness over the porosity range studied. Microhardness of magnesium oxychloride cement paste is also greater than that for all gypsum plaster preparations in the porosity range studied. Mechanical behaviour of magnesium oxychloride cement compacts is improved when heated in water at 85°C. It appears that this heat treatment results in formation of a porous body consisting mainly of Mg(OH) 2 . Among the systems magnesium oxychloride, portland cement, gypsum and magnesium hydroxide, it appears that magnesium hydroxide forms the strongest bodies.

Pore structure and the surface area of the pores are the most important characteristics controlling the properties of porous materials. Many techniques, based largely on nitrogen or water vapour isotherms or mercury porosimetry, have been used to determine the pore structure of solids. Values obtained from these methods have been relatively reliable for materials with pore structures that remain stable on removal or addition of water.

Modulus of elasticity and microhardness measurements were made on magnesium oxysulfate systems (paste and compacted) having a wide range of porosity. Three sets of compacts were made; each set was made with particles having a different size range (5 to 150 μm; 150 to 300 μm; 300 to 600 μm). The log mechanical property versus porosity curves for paste samples were linear. The curves for compacted samples had a change in slope at 7.5 per cent porosity. At porosities less than 7.5 per cent, the data for paste and compacted samples were on the same curve. Tat higher porosities microhardness values for compacted samples were greater than those for paste samples; modulus of elasticity values were less. Compacted samples made with finest particles had higher values for mechanical properties at a given porosity. The mechanical behaviour of these systems was explained on the basis of the relative contribution of porosity, pore size distribution, interparticular bonds and strength of the solid phase.

Hydrated blast furnace slag and fly-ash cement blends have been shown to be very impermeable. Porosity measurements of these materials by methanol and helium pycnometry have been less than the values obtained by Hg intrusion to 410 MPa. Results of the three techniques for hydrated portland cement were the same. A technique was used in which mercury could be removed by distillation after Hg intrusion, and intrusion was then repeated. This was performed on several cements and cement blends. Pore-size distribution for the hydrated cement changed marginally but both blended materials changed markedly, displaying a coarser pore distribution. It was concluded that the latter bodies are composed of relatively large, but discontinuous pores, into which Hg enters by breaking through the pore structure.

Three mixes, a reference cement, one fly-ash blend containing 35% fly-ash, and one with 70% slag, were cured in water at 21, 35 and 55 degrees C at a w/c = 0.45. After 2, 7, 14, 28, 90, 180, 365, and 550 days Ca(OH)[2] content, porosity, pore size distribution, compressive strength, Young's modulus and microhardness of the products were determined. The logarithms of these mechanical properties were plotted against porosity. Higher temperature increased the rate of reaction of the reference cement for up to two days, then retarded it. This acceleration period was considerably extended for the cement blends. Mechanical properties at zero porosity were generally improved in blends hydrated at room temperature; and all blends had a finer pore and lower Ca(OH)[2] content than the cement specimen., Materials Research Society Annual Meeting, Symposium N, November 16, 1981, Boston, Massachusetts, United States

The nature of adherence in hydrated cement is examined and discussed with reference to the role of adsorbed water and interlayer water in the structure. Young's modulus and microhardness values are used to compare the structural characteristics of various cements under a number of conditions, particularly the effect of "d-drying" on hydrated cement. The technique of cold compaction for the preparation of model specimens of porous materials is also examined., Proceedings of the 7th International Congress on the Chemistry of Cement: 1980, Paris, France

Porosity measurements using both mercury intrusion and helium pycnometric methods are reported for several different hydrated cementitious systems. Significant differences in porosity values, where they arise, are explained in terms of microstructural limitations of the matrix material. Several mechanisms that affect mercury intrusion results are discussed.

Thermal and mechanical properties at elevated temperatures are given for various building materials. The thermal properties include thermal conductivity, specific heat, thermal expansion and density. The mechanical properties include strength and modulus of elasticity of the materials. Creep is also discussed. The various materials considered are lightweight and normal weight concrete, steel, claybrick, wood and gypsum., Reprinted from: SFPE Handbook of Fire Protection Engineering 1988, Section 1, Chapter 26, p. 1-378 - 1-391. ISBN: 0877653534

Porous bodies formed by autoclaving portland cement-silica mixtures and by normally curing portland cement were characterized by measuring Young's modulus, microhardness and porosity. These bodies were impregnated almost completely with molten sulphur. The bodies were characterized again. It was found that the mechanical properties of the composites could be described by a form of Reuss' mixing law. Equations relating the improvement of the mechanical properties of the composite to the properties of the porous body were derived for both Young's modulus and microhardness.

In northern latitudes frost action is undoubtedly the main cause of concrete deterioration. In spite of considerable improvement in building practices the consequences of freezing and thawing are still of great concern, and at times the situation becomes serious. For example, the adoption, some years ago, of the "bare pavement" policy by most highway authorities has led to deterioration of bridges, highways and sidewalks through the use of deicing salts in vast quantities. Another difficulty is the marginal quality aggregates that have come into use in some regions after frost resistant supplies have been exhausted. In the present review some aspects of the mechanism of frost action will be discussed., Seminaire: Durabilite des Betons et des Pierres: 17 November 1981, St-Remy-Les-Chevreuse, France

The pore system of hydrated cement paste is very complex and changes with the type of drying. Solid volume, helium inflow, and length change measurements over different relative humidity conditions permit surface area and hydraulic radii to be measured. It is shown that the system is composed of (1) gross pores into which nitrogen methanol and other fluids can readily enter, and (2) interlayer spaces that separate layers and are only about the diameter of one water molecule apart.

Normal portland cement mixed separately with two types of fly-ash and ground quartz to produce blends containing 35 per cent additive and a mix containing 70 per cent slag were cured in water at 21, 35 and 55 degrees C at a w/c = 0.45. After 2, 7, 14, 28, 90, 180, 365, and 550 days, Ca(OH)[2] content, pore size distribution, compressive strength, Young' s modulus and microhardness of the products were determined. Density and porosity were measured by mercury intrusion, helium pycnometry and methanol saturation. Mortars were also prepared using these blends. After curing for 15 or 240 days they were exposed to a salt solution containing 27.5% CaCl[2], 3.9% MgCl[2], 1.8% NaCl and 0.1% NaHCO[3]. The porosities of the hydrated blends were higher when measured by mercury intrusion and had a higher percentage of fine pores. Densities of the products calculated from these pore measurements gave more realistic values. Higher temperatures increased the early rate of reaction of the cement, then retarded it, but the acceleration period was extended for the cement blends. Factors responsible for durability were found to be pore volume above 88 nm diam and Ca(OH)[2] content., Fly Ash, Silica Fume, Slag and other Mineral By-Products in Concrete : Proceedings of the 1st CANMET/ACI International Conference: 31 July 1983, Montebello, Que, Canada

The effects of total porosity, average pore size, pore-size distribution and the size and density of crystallites are discussd in terms of the relationship between structure and mechanical properties. Several equations and their applicability are discussed. Pore reduction by impregnation is compared and the mechanism is explained in terms of the modification of stress concentrations and the filling of the pores. It is possible to predict mechanical properties using the mechanical characteristics corresponding to zero porosity as a basic parameter., Proceedings of the 7th International Congress on the Chemistry of Cement: 1980, Paris, France

Microhardness and Young's modulus of discs 1.3 mm thick were measured on several autoclaved Portland cement/silica systems, normally hydrated Portland cement and porous glass, representing a wide range of porosity and pore-size distributions. These samples subsequently were fully impregnated with sulfur. It was found that the results could be adequately described by the Reuss model mixing- rule, assuming that good bonding was achieved between the matrix and the impregnant and that the impregnant had similar properties when in the pores as when outside, as bulk. Systems were also studied for which some or all the assumptions did not hold, e.g. porous glass impregated with sulfur, and hydrated Portland cement impregnated with methyl methacrylate., Hydraulic Cement Pastes : Their Structure and Properties: 08 April 1976, Sheffield, England

The chief aim of this work was to observe any change in the mechanical properties of cement pastes and compacts when water is sorbed. Thin discs of normal cement paste were cut from 1 1/4-in. diameter cylinders made of 0.3 to 0.7 w/c ratios. Compacts of similar shape were prepared from bottle- hydrated cement at pressures of 15,000, 40,000 and 110,000 psi. All samples were conditioned to different levels of RH from 0 to 98 percent and back to 0; at each level the modulus of elasticity of all samples and the strength of some were determined by means of a miniature testing machine, which is described. Special precautions were taken to avoid any carbonation of the samples by conditioning them over solutions of sodium hydroxide and measuring in gloved conditioned boxes. No change in elastic modulus occurred between 0 and 50 percent RH, but an increase was observed above 50 percent RH. This was maintained on desorption, and appeared to be associated with entry of interlayer water in the tobermorite gel, which supports the mechanism of length change previously proposed by the authors. The maximum fracture-strength for samples of given porosity was attained at 0 percent RH, and the largest reduction of strength was observed from 0 to 15 percent RH. Plots of Young's modulus vs porosity and fracture-strength vs porosity gave common curves for compacts and pastes.

The relation between hardness, modulus of elasticity and porosity was investigated in three different systems prepared from normal Type I portland cement. This study was undertaken to obtain some data on the structure of cement- stone, particularly with regard to the nature of the interparticle bonds and their effect on mechanical properties. The study also enabled the evaluation of the possible use of compacts in cement research. The three cement systems, designated as I, II, and III, cement pastes ( I) in which porosity varied from 40% to 70% and the degree of hydration from 73% to 98% (w/c ratio 0.40 to 1.20), compacted cement pastes (II) in which porosity varied within the range of 25% to 60%, and compacts of bottle hydrated cement (III) in which the porosity varied from 20% to 55% and the degree of hydration from 0% to 90% (i.e., unhydrated cement compacts were included). Test results generally supported the concept that the strength of the cement-stone is mainly derived from a particular type of interparticle bond.

The interrelation of hardness, modulus of elasticity, and porosity was investigated in four gypsum systems. Results suggest that intergrowth and interlocking of crystals significantly affect mechanical behavior, at least hardness and modulus of elasticity, E. In addition, both properties are related to porosity, p. This relation can be described empirically by the exponential expression E = Eo exp (— p).

Measurementswere made on samples initially conditioned at 11% R. H. and dried in stages to the d-dry condition. Helium flow measurements, although less quantitatively, are qualitatively similar to those found for hydrated portland cement. It was con concluded that the narrow spaces into which helium flowed are interlayer spaces, not fixed-dimension narrow-necked pores. In the measurement of density it was shown that if aqueous solution is used on d-dried samples, account will have to be made for the fact that re-entrance of interlayer water occurs. However, if the material is dried only to 11% R. H. density can be measured by helium, methanol or aqueous Ca(OH)2 solution. The value varies only from 2.35 to 2.37 gm/cc for the hydrated C3S.

Changes in the dimensions and heat content of the porous, 96% silica glass-water system were determined as temperature was cycled between +5 degrees and -40 degrees C at a rate of 0.33 degrees C/min. The results are explained by the fact that the maximum experimentally realizable relative pressure, based on that of undercooled water, becomes less than unity below 0 degrees C and diminishes with declining temperature. As a result, the adsorbate content decreases by migration of water to the outer surface, where it freezes between 0 degrees and -8 degrees C. At lower temperatures (- 20 degrees C) water drains from the smaller capillaries into larger voids and solidifies. An account is given of the anomalies of the extension isosteres, including hysteresis. In contrast with previous studies, the results obtained with porous glass and organic adsorbates are similar to those of the glass-water system and can be explained by the same theory.

The mechanical properties of hydrated Portland cement, are largely dependent on its pore structure. This paper describes these relationships and shows the difficulties in firmly establishing them because of (a) the instability of the material under any form of stress and drying and (b) the existence of interlayer spaces which play an important part in volume stability and elastic moduli of the material. A new technique, the helium flow method, is described, where relative changes to the dimensions of very small pores, due to removal of sorbed water may be traced. This technique involves measuring the flow of helium as a function of time into the vacated spaces of the material as water is removed and returned. Simultaneously, volume change, porosity and density of the material are measured as a function of weight change. Results obtained by this technique are presented showing the unique behaviour of this "porosity" and how density of the sorbed water can be computed. Results that show the effect of this "porosity" on Young's modulus are also presented., RILEM/IUPAC 1973 International Symposium on Pore Structure and Properties of Materials, September 18, 1973, Prague, Czechoslovakia

In order that it may be possible to differentiate between adsorbed water and water chemically bound in hydrated Portland cement, a study was conducted of the dimensional-change sorption characteristics at low relative vapour pressures. By use of compacts of bottle-hydrated cement fabricated at loads between 5000 and 65, 000 lb., equilibrium as well as dynamic values were obtained for dimensional change and moisture change relationships below 20% R.H. The apparatus enabled experiments to be performed in high vacuum. For the first rewetting and second drying it was found that for equilibrium points from 7.2 to 17-6 and 17-7 to 7-9% R.H. the plots of ( Δl/l) vs (ΔW/W) were both linear. After degassing the specimens beyond 7.9% R.H., the dynamic points continued along the straight line traced out by the equilibrium points in the plot mentioned and a sharp transition point was obtained. The vapour pressure in the region of this transition point, referred to as datum point, was less than 10 μ. Further degassing produced another linear region. It was concluded with supporting evidence from work on other porous materials that the datum point where the transition between the linear portions of the curve occurs, will yield a good estimate of the true value for adsorbed water and will thus approximate to the point for zero adsorbed water; it will also separate the processes of desorption and dehydration. This establishes therefore a method for determining the adsorbed water in hydrated cement. The results obtained from the compacts of bottle-hydrated cement indicate that by this method the surface area, as calculated from the B.E.T. theory, will be considerably lower than that obtained from the high value for the evaporable water (determined by the method of Copeland & Hayes).

The vapour pressure and extension isotherms of the water- porous 96% silica glass were determined at +1.5, -6.4, -14. 6, -25.4 and -35.3 degrees C. Isotherms obtained at these temperatures coincided if the amount of adsorbed water, a, was plotted against the relative pressure with reference to that of undercooled water. This demonstrates that the isothermally adsorbed water is in a liquid-like state and confirms that the drastic reduction of a with declining temperature is due to a decrease of the maximum relative pressure that can be realized experimentally. In contrast to previous studies, a minimum in the extension isotherm at low concentration was found, indicating that adjacent hydrogen-bonded silanol groups of the glass may not be the site of water adsorption as has been assumed in the past. Examination of the pertinent literature suggests that a minimum of the extension isotherm is obtained on the adsorption of most substances if the experimental temperature is not higher than the bulk boiling point. The contraction effect and the secondary hysteresis at low coverages are assumed to be caused by microporosity.