Showing papers in "Materials and Structures in 1985"
801 citations
TL;DR: In this article, the significance of fracture energy in the strength of concrete structures is discussed and it is demonstrated that GF in some cases, for example for shear failure of beams and slabs without shear reinforcement, is a material property which may be as important as normal strength properties.
Abstract: RILEM Technical Committee 50-Fracture Mechanics of Concrete, has put forward a proposal for a recommendation for the determination of the fracture energy GF of mortar and concrete. The significance of GF in the strength of concrete structures is discussed and it is demonstrated that GF in some cases, for example for shear failure of beams and slabs without shear reinforcement, is a material property which may be as important as normal strength properties. For the measurements of energy absorption a three-point bend test on a notched beam has been proposed. The choice of test specimen and of evaluation method is discussed.
603 citations
TL;DR: In this paper, a rate-type aging creep law based on the Maxwell chain is generalized to variable humidity and is calibrated by extensive comparisons with test data from the literature, including the Pickett effect, which is the apparent increase in creep due to drying simultaneous with loading.
Abstract: The previously formulated rate-type aging creep law based on Maxwell chain is generalized to variable humidity and is calibrated by extensive comparisons with test data from the literature. The main object of attention is the Pickett effect, i.e., the apparent increase in creep due to drying simultaneous with loading. This effect is shown to have four sources, in their decreasing order of importance: (1) stress-induced shrinkage, (2) tensile strain softening due to progressive cracking, (3) irreversibility of unloading contraction after tensile strainsoftening, and (4) increase of material stiffness due to aging (hydration). The model, which is a special case of a previously advanced thermodynamic theory, depends on only one hypothesis about the microscopic physical mechanism of creep: The creep rate depends on the magnitude of the flux of microdiffusion of water between the macropores (capillary pores) and the micropores in the cement gel. By assuming this microdiffusion to be infinitely fast, the effect is reduced to a dependence of creep viscosities on the time rate of pore humidity, and this is further shown to be equivalent to stress-induced shrinkage, in which the shrinkage coefficient defining the ratio of the increments of shrinkage strain and pore relative humidity depends on stress. In three dimensions, the shrinkage coefficient thus becomes a tensor. For thermodynamic reasons, there must also exist stress-induced thermal expansion. Although tensile cracking is found to make significant contribution to the Pickett effect, it is far from sufficient to explain in fully. The theory agrees with test data on basic creep, creep of specimens with reduced water content at hygral equilibrium (predried), shrinkage, swelling, and creep at drying under compression, tension, or bending. The strainsoftening model used for tensile cracking is the same as that used previously to fit test data from fracture tests, direct tensile tests, and deflection tests of reinforced beams.
252 citations
TL;DR: In this article, the RILEM Technical Committee 50 (Fracture Mechanics of Concrete) put forward a proposal for a recommendation for the determination of the fracture energy GF of mortar and concrete.
Abstract: RILEM Technical Committee 50—Fracture Mechanics of Concrete, has put forward a proposal for a recommendation for the determination of the fracture energy GF of mortar and concrete. In connection with the above three comparative test series were arranged in order to collect information and experience regarding the proposed method. 14 laboratories from 9 countries were involved and about 700 beams were tested. This paper gives a condensed summary of the results.
205 citations
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TL;DR: The authors expose le fait que les different mecanismes qui sont a l'origine du comportement du beton sont si complexes and si dependants les uns des autres qu'il est impossible de les etudier exclusivement par voie experimentale.
Abstract: Tout d'abord, nous avons expose le fait que les differents mecanismes qui sont a l'origine du comportement du beton sont si complexes et si dependants les uns des autres qu'il est impossible de les etudier exclusivement par voie experimentale.
146 citations
TL;DR: In this article, the corrosion behavior of steel in hardened cement pastes containing various proportions of microsilica and sodium chloride has been studied by corrosion potential and linear polarisation measurements.
Abstract: The corrosion behaviour of steel in hardened cement pastes containing various proportions of microsilica and sodium chloride has been studied by corrosion potential and linear polarisation measurements. Replacement of increasing proportions of Portland cement with microsilica in pastes of constant total chloride content and water content caused the ratio of free chloride ion concentration to hydroxyl ion concentration in the pore water to increase. This tended to destabilise the passivity of steel during the early stages of hydration but the effect became less significant as curing progressed. It is suggested that the growth of anodic pits may be restrained in microsilica cement pastes owing to the fine pore structure of the material which limits the mobility of chloride ions near the surface of embedded steel.
62 citations
TL;DR: The bond characteristics of reinforcing steels are determined with the well known Pullout Test and Beam Test recommended by RILEM/CEB/FIP as discussed by the authors, which can be used to determine the bond properties of reinforcement steels.
Abstract: The bond characteristics of the reinforcing steels are determined with the well known Pullout Test and/or Beam Test recommended by RILEM/CEB/FIP.
37 citations
TL;DR: In this article, the authors discuss the development of accelerated tests and mathematical models for predicting the durability of concrete, and the advantages and disadvantages of accelerated testing and mathematical modeling in terms of the degradation mechanisms affecting concrete.
Abstract: This paper discusses development of accelerated tests and mathematical models for predicting the durability of concrete. Durability, service life, and degradation factors are defined and accelerated test methods are contrasted to conventional comparative methods. Factors and mechanisms of concrete degradation are reviewed, as are efforts to quantify these phenomena. Deterministic and stochastic models are discussed. Procedures for developing accelerated tests are presented and applied to a hypothetical example involving freeze-thaw damage. Advantages and disadvantages of accelerated testing and mathematical modeling are discussed in terms of the degradation mechanisms affecting concrete. Examples given of the modeling approach and service life prediction include the prediction of the strength and maturity of concrete, acid attack on cement, sulphate attack, and the effect of scaling and corrosion on load-bearing capacity of concrete.
27 citations
TL;DR: In this article, the failure mechanism of the pullout test is yet not understood, and several theories have been forwarded to analyze the test's failure mechanism and its effect on the strength of concrete.
Abstract: Pullout tests are increasingly being used to determine thein situ strength of concrete. Several studies have shown that a close correlation exists between the maximum pullout load and compressive strength of concrete. However, the failure mechanism of the pullout test is yet not understood. Conflicting theories have been forwarded to analyze the pullout test.
25 citations
TL;DR: In this article, a Mercury intrusion porosimetry was performed for aggregates used for concrete in Kuwait, and curves which were established helped to identify the types of rocks used.
Abstract: Mercury intrusion porosimetry was performed for aggregates used for concrete in Kuwait. The curves which were established helped to identify the types of rocks used. Microstructural flows in the form of pores whose diameter is larger than 100 nm were associated with certain identifiable rocks. Such pores are considered as a source of weakness for concrete and as a factor which adversely affects its durability.
16 citations
TL;DR: In this article, the authors generalized the previously published BP Model for prediction of concrete creep and shrinkage to cover the increase of creep caused by the cyclic component of environmental relative humidity, and proposed a simple formula, which is partly empirical, partly based on the diffusion theory, is proposed and calibrated by comparisons with test data from the literature.
Abstract: The previously published BP Model for prediction of concrete creep and shrinkage is generalized to cover the increase of creep caused by the cyclic component of environmental relative humidity. A simple formula, which is partly empirical, partly based on the diffusion theory, is proposed and is calibrated by comparisons with test data from the literature.
TL;DR: In this paper, two clay deposits from Lagos in Nigeria were used to develop cement-stabilized blocks and the optimal cube crushing strength was determined at the optimum water/cement ratios for different cement/clay-soil mixes which ranged from 5∶1 to 1∶15.
Abstract: Two clay deposits from Lagos in Nigeria were used to develop cement-stabilized blocks. Crushing strengths were determined at the optimum water/cement ratios for different cement/clay-soil mixes which ranged from 5∶1 to 1∶15. The optimal cube crushing strength (Y
2) decreased with increasing water/cement ratio (X) in a power relation as follows: Oregun Soil:Y
2=16,329.29X
−0.147. Alausa Soil:Y
2=6,307.42X
−0.580. Over 80% of the cube strength was developed by the fourteenth day (100% at 28 days). A comparison of the results with those of the British Statutory Minimum Compressive strength in bricks for various walls showed that the cement/clay soil mixes may be used for both load and non-load bearing walls of one or two storey houses.
TL;DR: In this paper, a theory for predicting the service life of r.c. structures is proposed and a way to evolve a theory based on basic data can be found scattered in the literature.
Abstract: The development in recent years with increasing air pollution, increasing need of energy saving and last not least the growing number of damage in old structures leads to a raising demand to calculate the durability of structures, too. The paper has been prepared by request of the RILEM Technical Committee 45-LTO to show that, in principle, it is possible to evolve a theory for predicting the service life of r.c. structures and to sketch a way how that could be achieved. A lot of necessary basic data can be found scattered in the literature. To collect these data will be the first step to take.
TL;DR: In this paper, the authors present l'etude de l'influence de la nature du materiau associe sur la croissance des cristaux de portlandite a leur voisinage.
Abstract: Les proprietes de l’aureole de transition, zone interfaciale entre la pâte de ciment Portland et les materiaux associes, dependent de nombreux parametres parmi lesquels l’orientation des cristaux de portlandite. En effet une orientation preferentielle de cristaux voisins selon leur plan de clivage favorise la propagation des fissures dans l’aureole de transition. Nous presentons ici l’etude de l’influence de la nature du materiau associe au ciment Portland (granulat inerte ou reactif, materiau poreux, armature en acier ordinaire ou galvanisee) sur la croissance des cristaux de portlandite a leur voisinage.
TL;DR: In this article, the authors proposed a method to determine the crack spacing and maximum crackwidth in reinforced concrete flexural members, based on a statistical analysis of the test results of Hognestad, Clark and Baseet al.
Abstract: A method is proposed to determine the crack spacing and maximum crackwidth in reinforced concrete flexural members. The constants appearing in the proposed method are determined from a statistical analysis of the the test results of Hognestad, Clark and Baseet al. Experimental crackwidth values are compared with the crackwidth values computed from the equations given by CP110, Model Code, Gergely and Lutz and the proposed method and the results are discussed.
TL;DR: In this paper, the authors propose a solution approchee au probleme de l'equilibre elastique of l'assemblage colle a double recouvrement.
Abstract: L'objet de l'article est de proposer une solution approchee au probleme de l'equilibre elastique de l'assemblage colle a double recouvrement. Dans une premiere partie le montage experimental est decrit: grâce a un dispositif bien precis les phenomenes secondaires dus a la flexion des substrats, qui peuvent avoir une influence non negligeable sur l'apparition parasite du pelage, sont elimines. Les resultats theoriques, bases sur une analyse par developpements asymptotiques, sont presentes: l'essentiel de l'apport par rapport aux travaux anterieurs tient dans la mise en evidence d'une couche limite au voisinage des extremites du raccordement; ce phenomene essentiel a deux consequences improtantes: 1o il existe un champ, de contraintes a distance suffisante des extremites du recouvrement, regi physiquement par les memes lois que celles qui ont ete admises jusqu'a maintenant, mais dont la nature est influencee par les conditions a la limite «moyennes», qui interviennent dans les couches limites—ce qui explique en particulier le caractere, jusqu'a present heuristique, des methodes de calculs employees dans les ouvrages technologiques; 2o il existe un champ de, contraintes a proximite des extremites du recouvrement qui est tres largement different de celui deduit des methodes heuristiques precedentes; on constate que la contrainte de cisaillement a un module beaucoup plus faible et par contre que la contrainte de decollement joue un role essentiel dans la rupture de l'eprouvette a l'extremite du raccordement.
TL;DR: In this article, three distinct cracking patterns were identified when a crack advancing from a notch in cement paste intersected a steel fiber placed perpendicular to it, in which the fiber caused a shift in the crack path, accompanied by microcracking and by separation of the main crack into several branches.
Abstract: Fracture patterns, produced when a crack advancing from a notch in cement paste intersected a steel fiber placed perpendicular to it, were studied by SEM methods. The specimens were small notched compact tension specimens that could be wedge loaded within the scanning electron microscope chamber using a wet cell. Three distinct cracking patterns were identified. In most cases the fiber caused a shift in the crack path, accompanied by microcracking and by separation of the main crack into several branches. Observations of the surface of the groove under the steel fiber indicated that the offsetting segment of the crack path in the matrix under the fiber was tortuous, and in many cases it was characterized by branching, discontinuities, and microcracks. The microstructure of the interface region consisted of CH-rich duplex film at the actual interface, backed by a highly porous zone consisting mainly of C-S-H. The offsetting crack segments tended to damage the preexisting interface zone microstructure under the steel fibers.
TL;DR: In this paper, a compilation of methods for characterizing the stability of bitumen emulsions is presented, which covers both methods for measuring stability during transport, storage and handling of an emulsion, in addition to measures for measuring breaking and hardening in various applications.
Abstract: A compilation of methods for characterizing the stability of bitumen emulsions is presented. The compilation covers both methods for measuring stability during transport, storage and handling of an emulsion, in addition to methods for measuring breaking and hardening in various applications. A general description of each test method is given. The concepts of “breaking” and “curing” are defined. Factors which may affect the stability of an emulsion are described. General views on the value of certain test methods and the orientation of further development work considered necessary in this area are expressed.
TL;DR: In this paper, the authors reviewed some of the recent non-proprietary research on the durability of building materials carried out in the US and emphasized the need for international collaboration in durability research.
Abstract: This paper is based on the text of a talk given at a RILEM Seminar on Durability of Building Materials. It reviews some of the recent non-proprietary research on the durability of building materials carried out in the US. It also reviews activities in RILEM which have stimulated the generation or dissemination of knowledge on durability of building materials. The paper emphasizes the need for international collaboration in durability research.
TL;DR: In this article, the cohesion of fresh cement mortars was measured with a device currently used for shear test on clays, the Laboratory Vane, and the results showed that fresh mortars were more stable than fresh clays.
Abstract: The cohesion of fresh cement mortars was measured with a device currently used for shear test on clays, the Laboratory Vane.
TL;DR: In this paper, a nouveau modele, a la fois simple and adapte a des calculs analytiques non iteratifs, est propose.
Abstract: Les methodes analytiques modrenes de calcul des fleches des structures en beton arme, ainsi que les modelisations par elements finis du comportement non lineaire du beton arme considerent la contribution du beton tendu en phase fissuree a la rigidite d'ensemble de la structure. La plupart des theories proposees a ce jour dans ces domaines font appel a la relation liant la deformation moyenne d'une armature enrobee de beton fissure et la deformation que prendrait cette meme armature au droit d'une fissure. Les auteurs, constatant que tres peu de donnees experimentales supportent les differents modeles releves dans la litterature, ont experimente des tirants en beton arme avec, comme parametre de l'etude, le pourcentage geometrique d'armature. La deformation moyenne des tirants, mesuree sur de grandes bases, est comparee a differents modeles rencontres dans la litterature. Un nouveau modele, a la fois simple et adapte a des calculs analytiques non iteratifs, est propose.
TL;DR: A comparative study on a limited number of existing abrasion tests for concrete has been done, with the intention that it should serve as a basis for the preparation of a recommendation for a standard test or tests.
Abstract: A comparative study on a limited number of existing abrasion tests for concrete has been done, with the intention that it should serve as a basis for the preparation of a recommendation for a standard test or tests. A summary and classification of the tests is presented, together with a critical evaluation. In view of the number of different tests currently being used in various countries, it is clear that no single test has yet been devised that adequately measures the wear resistance of concrete under all conditions. Since concrete is subjected to different kinds of wear, it seems likely that a number of tests, each suited to a particular mode of abrasion, will be required. Further experimental evidence on the correlation of test data with practical performance is required before firm recommendations can be made.
TL;DR: Des mortiers prepares avec different types de ciments (ciments Portland, ciments au laitier and ciment alumineux) ont sejourne pendant 15 annees dans l'eau douce agressive d'une source issue du massif vosgien (TH=1 a 1,5° francais and 13 a 15 mg/l de CO2 agressif).
Abstract: Des mortiers prepares avec differents types de ciments (ciments Portland, ciments au laitier et ciment alumineux) ont sejourne pendant 15 annees dans l'eau douce agressive d'une source issue du massif vosgien (TH=1 a 1,5° francais et 13 a 15 mg/l de CO2 agressif).
TL;DR: In this article, a caracteristique qui augmente en meme temps que la compacite et ne varie pas, du point de vue pratique, for les betons âges de plus de 14 jours.
Abstract: Dans cette etude nous donnons de nouvelles interpretations de l'indice sclerometrique de Schmidt et de la vitesse de propagation des ultra-sons, qui pourront etre exprimees de la facon suivante:
-La vitesse de propagation des ultra-sons nous renseigne sur la compacite du beton. C'est une caracteristique qui augmente en meme temps que la compacite et ne varie pas, du point de vue pratique, pour les betons âges de plus de14 jours.
-L'indice sclerometrique, qui montre la cohesion du beton a la suite de l'hydratation progressive du ciment, augmente avec le temps, mais ne se trouve pas affecte par la compacite du beton.
TL;DR: In this paper, it was shown that failure of large size concrete elements can be predicted realistically on the basis of linear elastic fracture mechanics, and that the role of subcritical crack growth on fracture toughness needs further investigation.
Abstract: It has often been questioned whether linear elastic fracture mechanics can be applied to describe crack propagation and failure of concrete. An important argument is that most test results are obtained on specimens too small to be representative of a material with a composite structure such as concrete. Large specimens with four different geometries have been prepared and tested. Crack length was increased under controlled conditions to at least 250 mm. It was found that fracture toughness increases initially as a crack propagates, but that a length-independent value is reached asymptotically. Within the range of accuracy, asymptotic values obtained with the four different geometries were the same. It is concluded that failure of large size concrete elements can be predicted realistically on the basis of linear elastic fracture mechanics. For comparatively small specimens, however, an approach which takes total fracture energy into consideration (for instance the fictitious crack model) is more appropriate. It is pointed out that the role of subcritical crack growth on fracture toughness needs further investigation.
TL;DR: In this paper, the authors present several accelerated testing techniques for concrete quality control, which can be performed on hardened concrete cylinders or cubes in one or two days, as compared to the usual 28 days.
Abstract: Quality control of concrete has taken many forms in past years. The most traditional method has been to conduct compression tests on hardened cylinders or cubes. Although this has been a satisfactory method, it has one major deficiency, and that is the testing is done after the concrete has set. If the concrete does not meet specifications, then costly and time consuming reconstruction must take place. Several accelerated testing techniques have been developed recently, and although these tests are accomplished in one or two days, as compared to the usual 28 days, they still are conducted on hardened concrete. The ideal test, of course, is a test that can be conducted on the plastic or fresh concrete. It is these methods of analysis that are being discussed in this paper.
TL;DR: Les mouvements de l'eau interstitielle d'un mortier d'enduit lies a l'evaporation d'une part and l'absorption capillaire par le support d'autre part affectent le processus d'hydratation du liant and levolution des caracteristiques mecaniques du mortier as mentioned in this paper.
Abstract: Les mouvements de l'eau interstitielle d'un mortier d'enduit lies a l'evaporation d'une part et a l'absorption capillaire par le support d'autre part affectent le processus d'hydratation du liant et l'evolution des caracteristiques mecaniques du mortier.