Showing papers in "Materials and Structures in 1995"
TL;DR: The mechanism of chloride-induced corrosion of steel embedded in concrete, the ingress of chlorides into the concrete, and the threshold chloride content for corrosion to occur are discussed in this paper.
Abstract: The mechanism of chloride-induced corrosion of steel embedded in concrete, the ingress of chlorides into the concrete, and the threshold chloride content for corrosion to occur are discussed. The binding of chloride ions by cement compounds and the associated effect of using different cements, both Portland and blended, as well as other factors influencing corrosion, are considered. Tests for the penetrability of concrete to chlorides are described. Finally, the prevention of corrosion is discussed.
396 citations
TL;DR: In this paper, the influence of matrix properties on composite pseudo-strain-hardening has been studied and a new class of ECCs with improved elastic modulus by the addition of fine aggregates to the cementitious matrix is proposed.
Abstract: Pseudo-strain-hardening behaviour under direct tensile loading in short fibre reinforced cement composites designed with quantitative guidance from micromechanics has been demonstrated experimentally, and conditions for the ductile behaviour of such engineered cementitious composites (ECC) have been formulated theoretically. In this paper special focus is placed on the influence of matrix properties on composite pseudo-strain-hardening. An experimental program is undertaken to study the dependence of the matrix properties on its mix compositions governed by water/cement and the sand/cement ratios. The theoretical and experimental knowledge thus obtained are combined to propose an innovative procedure for the design of composites using different types of matrix. The study is motivated by the need to develop a new class of ECCs with improved elastic modulus by the addition of fine aggregates to the cementitious matrix. Finally, a new composite is designed, and shown experimentally to exhibit the desirable features of pseudo-strain-hardening behaviour and improved elastic modulus.
370 citations
TL;DR: In this paper, the state of the art in test methods for polymer modified bitumens is presented, and a general description of each non-standardized test procedure is given.
Abstract: Polymer of road applications and their effects of functional properties (permanent deformation, fatigue cracking, low temperature cracking, stripping, wear resistance and ageing) of asphalt pavements are described. The state of the art in test methods for polymer modified bitumens is presented. The methods are classified as standardized or non-standardized. A general description of each non-standardized test procedure is given. Current or proposed specification models for polymer modified bitumens are summarized. The present situation regarding test methods and specifications of polymer modified bitumens and the need for further development are discussed.
304 citations
TL;DR: In this paper, the authors show that the nominal tensile strength of concrete structures is constant for relatively large sizes, whereas it decreases with the size for relatively small sizes, and that for smaller scales a self-similar distribution of Griffith cracks is prevalent, whereas for larger scales the disorder is not visible, the size of defects and heterogeneities being limited.
Abstract: The nominal tensile strength of concrete structures is constant for relatively large sizes, whereas it decreases with the size for relatively small sizes. When, as usually occurs, the experimental investigation does not exceed one order of magnitude in the scale range, a unique tangential slope in the bilogarithmic strength versus size diagram is found. On the other hand, when the scale range extends over more than one order of magnitude, a continuous transition from slope −1/2 to zero slope may appear. This means that for smaller scales a self-similar distribution of Griffith cracks is prevalent, whereas for larger scales the disorder is not visible, the size of the defects and heterogeneities being limited. In practice there may be a dimensional transition from disorder to order. The assumption of multifractality for the damaged material microstructure represents the basis for the so-called multifractal scaling law. This is a best-fit method that imposes the concavity of the bilogarithmic curve upwards, in contrast to the size effect law of Bažant. The relevant results in the literature for ranges in scale extending over more than one order of magnitude are analysed.
218 citations
TL;DR: In this article, a dilatometer designed specifically for measuring autogenous deformation in cement paste is described, which restricts moisture loss and ensures that the hardening cement paste suffers insignificant restraint.
Abstract: Different techniques for measuring autogenous deformation in cement paste are discussed, and a newly developed dilatometer designed specially for measuring this deformation is described. A particular characteristic of the dilatometer is the encapsulation of the cement paste in corrugated moulds. This restricts moisture loss and ensures that the hardening cement paste suffers insignificant restraint. In addition, the encapsulation permits measurements to commence shortly after casting.
200 citations
TL;DR: In this paper, the authors presented a RILEM Recommendation inMater Struct.28 (1995) 357-365, calibrated by a computerized data bank comprising practically all the relevant test data obtained in various laboratories throughout the world.
Abstract: Model B3 for creep and shrinkage prediction in the design of concrete structures, presented as a RILEM Recommendation inMater Struct.28 (1995) 357–365, is calibrated by a computerized data bank comprising practically all the relevant test data obtained in various laboratories throughout the world. The coefficients of variation of deviations of the model from the data are distinctly smaller than for the latest CEB model, and much smaller than for the previous ACI model (which was developed in the mid-1960's). The effect of concrete composition and design strength on the model parameters is identified as the main source of error. The model is simpler than the previous models (BP and BP-KX) developed at Northwestern University, yet it has comparable accuracy and is more rational.
191 citations
TL;DR: In this article, the main issues relevant to tensile bond testing, namely material properties, surface conditions, geometry, loading and the effects of material mismatch, are discussed, with an emphasis on the core pull-off technique.
Abstract: The development and maintenance of a sound band is an essential requirement of a concrete patch repair. Tensile bond tests are increasing in popularity as a means of measuring this adhesive property, both on site for quality control and in the laboratory for materials evaluation. This paper discusses the main issues relevant to tensile bond testing, namely material properties, surface conditions, geometry, loading and the effects of material mismatch. Analytical and experimental work is presented, along with the results of other researchers, with an emphasis on the core pull-off technique. The latter is shown to be a good method for evaluating bond strength provided that appropriate precautions are taken to minimize the influence of flaws and stress concentrations, and that the effects of mismatch in repair and substrate properties (particularly modulus, shrinkage and thermal expansion) are fully understood.
143 citations
TL;DR: In this article, the origin of gypsum, its genesis, varieties and properties are discussed, and the focus is then on the most common binding material produced from it, plaster of Paris (β-hemihydrate), known in France as ‘plâtre de Paris’, in the USA as 'calcined gypsuma' and in Germany as 'Stuckgips'.
Abstract: Calcium sulfate, commonly known as natural gypsum, is found in nature in different forms, mainly as the dihydrate (CaSO4 · 2H2O) and anhydrite (CaSO4). They are products of partial or total evaporation of inland seas and lakes. Both the dihydrate and the anhydrite occur in nature in a variety of forms. The origin of gypsum, its genesis, varieties and properties are discussed, and the focus is then on the most common binding material produced from it, plaster of Paris (β-hemihydrate), known in France as ‘plâtre de Paris’, in the USA as ‘calcined gypsum’, and in Germany as ‘Stuckgips’. Details are given of the properties of gypsum paste (setting, expansion, and adhesion) and of hardened gypsum (strength, bulk weight, thermal expansion, volume and linear changes under humidity fluctuations, moisture absorption, paintability, corrosivity, thermal and acoustic insulation behaviour, and fire resistance).
136 citations
TL;DR: In this paper, a post mortem on concrete fracture surfaces of specimens broken in direct tension has been carried out, yielding non-integer (fractal) dimensions of profiles, which are then related to the normalized fracture energy of the material.
Abstract: Experimental evidence of the fractality of fracture surfaces has been widely recognized in the case of concrete, ceramics and other disordered materials. An investigationpost mortem on concrete fracture surfaces of specimens broken in direct tension has been carried out, yielding non-integer (fractal) dimensions of profiles, which are then related to the ‘renormalized fracture energy’ of the material. No unique value for the fractal dimension can be defined: the assumption of multifractality for the damaged, material microstructure produces a dimensional increment of the dissipation space with respect to the number 2, and represents the basis for the so-called multifractal scaling law. A transition from extreme Brownian disorder (slope 1/2) to extreme order (zero slope) may be evidenced in the bilogarithmic diagram: the nominal fracture energyGF increases with specimen size by following a nonlinear trend. Two extreme scaling regimes can be identified, namely the fractal (disordered) regime, corresponding to the smallest sizes, and the homogeneous (ordered) regime, corresponding to the largest sizes, for which an asymptotic constant value ofGF is reached.
128 citations
TL;DR: In this article, the shrinkage half-time is calibrated by simultaneous measurements of water loss, which circumvents the ill-posedness of shrinkage extrapolation problem and allows a more realistic assessment of the creep and shrinkage effects in concrete structures.
Abstract: Following statistical evaluation in part 1, this part deals with the improvement of prediction by updating one or two parameters of the model on the basis of short term tests and theoretical derivation of some formulae. The updating of model parameters is particularly important for high strength concretes and other special concretes containing various admixtures, superplasticizers, water-reducing agents and pozzolanic materials. For the updating of shrinkage prediction, a new method is presented in which the shrinkage half-time is calibrated by simultaneous measurements of water loss. This approach circumvents the ill-posedness of the shrinkage extrapolation problem. Theoretical justifications of various aspects of the model are given and a new formula for the additional creep due to drying (or stress-induced shrinkage) is derived. The new model should allow a more realistic assessment of the creep and shrinkage effects in concrete structures, which significantly affect durability and long term serviceability of civil engineering infrastructure.
118 citations
TL;DR: In this paper, the authors investigated the bond relationship between glass fibre reinforced plastic bars with polyester matrix and concrete in order to obtain information concerning the possible use of these bars for the reinforcement of concrete constructions, where the use of ordinary steel bars could have certain disadvantages due to the possibility of corrosion.
Abstract: The bond relationships between glass fibre reinforced plastic bars with polyester matrix and concrete is investigated in order to obtain information concerning the possible use of these bars for the reinforcement of concrete constructions, where the use of ordinary steel bars could have certain disadvantages due to the possibility of corrosion The results obtained are used to develop a model of the stress-slip relationship and to estimate the anchorage lengths needed to embed these bars in concrete casts
TL;DR: In this article, a set of structural models for calcium silicate hydrate (C-S-H) gel and computational techniques for their validation have been developed, which is a first step in a multi-scale approach to computing the drying shrinkage of model cement-based materials.
Abstract: The nanostructure of calcium silicate hydrate (C-S-H) gel contributes to many physical properties of concrete, including the important engineering properties of creep and shrinkage. A set of structural models for this gel and computational techniques for their validation have been developed. The basic nanostructure of C-S-H is conceived as a self-similar agglomeration of spherical particles at two levels (diameters of 5 nm and 40 nm). Computational techniques are presented for simulating transmission electron microscopy images and computing sorption characteristics of the model nanostructures. Agreement with available experimental data is reasonable. The development of these nanostructural models is a first step in a multi-scale approach to computing the drying shrinkage of model cement-based materials. Such an approach will provide a better understanding of the relationships between microstructure and the shrinkage behaviour of these systems.
Journal Article•
TL;DR: In this paper, an experimental-numerical approach is presented to rationalize the plethora of results, sometimes contradictory, reflecting the chrracterization of an epoxy bonded steel-concrete interface.
Abstract: An experimental—numerical approach is presented to rationalize the plethora of results, sometimes contradictory, reflecting the chrracterization of an epoxy bonded steel—concrete interface. Based on data from a specially designed half-beam specimen and experimental results from other specimen geometries, combined with their respective nonlinear finite element idealizations, a classical Mohr—Coulomb failure law together with a tension cut-off are suggested for the steel—glue—concrete interface. This description can then be used in a finite element simulation of a plated reinforced concrete beam.
TL;DR: Moretti et al. as mentioned in this paper measured the amount of energy required to drill a small cavity in a mortar layer and found the correlation between the drilling work and the mortar compressive strength.
Abstract: The determination of mortar load capacity in masonryin situ is not an established technique. An indirect method is described in this paper and, like the earlier one by Gucci, N. and Moretti, A., Boll. Ingegneri Toscana No. 9 (1989), is based on the measurement of the amount of energy required to drill a small cavity in a mortar layer. The instrumentation, designed and built for this purpose, has been the subject of an experimental study aimed at setting up the parameters of measurement and finding the correlation between the drilling work and the mortar compressive strength. The results obtained are reported and discussed, and a first theoretical interpretation is given.
TL;DR: In this article, a model is derived for the stress-crack width relationship for randomly oriented short fiber composites which takes hybrid fiber systems and possible fibre rupture into account. And this model can be included in a structural model for the prediction of crack widths in reinforced concrete structures.
Abstract: The stress-crack width relationship has been shown to be the key to an understanding of fracture propagation in and mechanical behaviour in tension of fibre reinforced concrete materials and structures. A model is derived for the stress-crack width relationship for randomly oriented short fibre composites which takes hybrid fibre systems and possible fibre rupture into account. It is shown how this stress-crack width relationship can be included in a structural model for the prediction of crack widths in reinforced concrete structures. With this combination of models a rational design tool for the design of composite materials and structures has been established. It is shown how different fibre systems can be tested for structural applicability and how combined material and structural optimization can take place.
TL;DR: In this article, the rheological behavior of fresh high performance concrete was investigated by use of a coaxial cylinder viscometer (BML Viscometer), after a series of experiments it was observed that the equipment used was not very suitable for concrete mixes with slump values of less than approximately 10 cm.
Abstract: The rheological behaviour of fresh high performance concrete was investigated by use of a coaxial cylinder viscometer (BML Viscometer). After a series of experiments it was observed that the equipment used was not very suitable for concrete mixes with slump values of less than approximately 10 cm. Also, for almost all mixes with a slump of less than 20 cm, plug flow occurred. By use of nonlinear regression analysis, however, a method for the determination of the two Bingham constants is proposed, even when plug flow occurs. Using these Bingham constants, the predicted slump values obtained from a chart established by computer simulation showed good correlation with those observed experimentally. A model for the prediction of plastic viscosity based on Farris' theory is also proposed. With two adjustable parameters the model gave a good description of the various concrete mixes tested.
TL;DR: In this paper, the minimum crack width that can be detected using the impact-echo method was determined by estimating the crack opening displacements for each impact echo test location, and the relationship between surface displacement and the real crack opening displacement was established using the results of nonlinear fracture analyses.
Abstract: To determine the minimum crack width that can be detected using the impact-echo method, two types of laboratory experiment on concrete plate specimens were conducted. In each experiment, a crack was propagated through the plate parallel to the plate surfaces, while surface displacement caused by crack opening was measured and impact-echo tests were performed along the crack trajectory. The relationship between the surface displacement and the real crack opening displacement was established using the results of nonlinear fracture analyses (reported elsewhere). The minimum crack width was determined by estimating the crack opening displacements for each impact-echo test location.
TL;DR: In this article, the modulus of elasticity and compressive strength of concretes is investigated. But the effect of the aggregate of the elasticity-compressive strength is not taken into account.
Abstract: To determine the modulus of elasticity of concrete precisely is very important for structures that require strict control of the deformability. International codes propose a wide variety of formulae which establish a relationship between modulus of elasticity and compressive strength. Most of these codes are valid up to 50 MPa, the usual limit for normal concretes. A research programme has been carried out to establish the modulus of elasticity-compressive strength curve for low and high strength concretes. The effect of the aggregate also has been studied. This is an important factor to take into account, sometimes more important than the concrete strength itself or even age. A model code formula provides good correlation with experiment up to a compressive strength of 120 MPa. Other aggregates not considered for this code have been studied and results given. Also, the influence of age on the modulus of elasticity is discussed.
TL;DR: In this article, the authors used nonlinear fracture analysis to determine the minimum crack width that can be detected using the impact-echo method, two types of laboratory experiment on concrete plate specimens were conducted.
Abstract: To determine the minimum crack width that can be detected using the impact-echo method, two types of laboratory experiment on concrete plate specimens were conducted. In each experiment, a crack was propagated through the plate parallel to the plate surfaces, while surface displacements caused by the crack opening were measured and impact-echo tests were performed along the crack trajectory. The relationship between the surface displacements and the real crack-opening displacements was established using the results of nonlinear fracture analyses. The minimum crack width was determined by estimating the crack-opening displacements for each impact-echo test location. As a result of this work, the minimum crack width which can be detected was found to be 0.025 mm, and the minimum crack width for which stress waves are not transmitted across the crack faces was found to be 0.08 mm. This paper describes how crack-opening displacements were determined using nonlinear fracture analyses.
TL;DR: In this paper, microfibre reinforced cement composites reinforced with high volume fractions of carbon, steel and polypropylene fibres were tested in uniaxial tension.
Abstract: Microfibre reinforced cement composites reinforced with high volume fractions of carbon, steel and polypropylene fibres were tested in uniaxial tension. Composites investigated included those with only one type of fibre (mono-fibre composites) and those with two or more types of fibres (hybrid-fibre composites) in the same mix. Considerable strengthening, toughening and stiffening of the host matrix due to microfibre reinforcement were observed. In the hybrid-fibre composites, different fibres appear to act as additive phases; i.e., they maintain their individual reinforcing capabilities. The composites were also impact tested in uniaxial tension using a newly designed instrumented impact machine. When compared with static test results, considerable sensitivity to stress rate was noted; composites were found to be stronger and tougher under impact and the improvements were more pronounced at higher fibre volume fractions. The potential of these composites for use in thin sheet products and other similar applications is recognized, and the need for continued research is stressed.
TL;DR: In this article, the results of an investigation into the interfacial properties of composite materials based on plain and silica fume pastes, and andesite, dolomite and granite rocks used as commercial concrete aggregates were presented.
Abstract: The results are presented of an investigation into the interfacial properties of composite materials based on plain and silica fume pastes, and andesite, dolomite and granite rocks used as commercial concrete aggregates. Microstructural studies are reported, and the observations are shown to assist qualitatively in the interpretation of mechanical test results. Fracture properties of the various combinations show that the mechanical response of the composites is material specific. In general, andesites develop superior interfacial bond properties, and the use of silica fume tends to embrittle composites. For the mix proportions and materials used in this study, no direct (micrographic) evidence of a transition zone between interface and bulk paste could be observed.
TL;DR: In this paper, the evolution of the conductivite thermique in fonction of the temperature is discussed, and two modeles d'estimation of the thermique du beton cellulaire autoclave are presented.
Abstract: Pour mesurer simultanement sur quatre echantillons l'evolution de la conductivite thermique en fonction de la temperature, un dispositif experimental specifique, entierement pilote par ordinateur, a ete developpe en integrant quatre sondes a chocs thermiques ‘monotiges’ dans une etuve chaud/froid. Nous avons choisi d'explorer la gamme des temperatures comprises entre 0 et 60°C. Une serie de teneurs en eau entre l'etat sature et l'etat sec ont ete realisees par sechage progressif au four a micro-ondes. Sept echantillons de beton cellulaire autoclave avec des masses volumiques allant de 270 a 630 kg m−3 ont ete selectionnes et leurs relations conductivite thermique-teneur en eau-temperature completement determinees. Sur la base de ces resultats, deux modeles d'estimation de la conductivite thermique du beton cellulaire autoclave en fonction de ses caracteristiques et de son etat hygrothermique ont pu etre construits et valides; l'un necessite la connaissance des proprietes thermiques de la ‘matrice solide’ microporeuse entourant la macroporosite cellulaire, l'autre se place a une autre echelle en considerant, cette fois, les proprietes du ‘grain’ solide non-poreux. Ces deux modeles presentent des caracteres predictifs equivalents et l'on choisira l'un ou l'autre suivant les donnees dont on dispose.
TL;DR: In this article, the authors performed a mode identification study on cracks produced during mixed mode loading of concrete and found that the locations of cracks were found to agree very well with the surface crack patterns for a variety of loading paths.
Abstract: The results are reported of a mode identification study on cracks produced during mixed mode loading of concrete. The locations of cracks were found to agree very well with the surface crack patterns for a variety of loading paths. The classification of cracks into mode I and mode II were conducted using a simplified moment tensor analysis. The results indicated that, in general, cracking occurs in mode I, even when the loading is pure shear. Mode II deformations generally follow the mode I cracks, as the crack interface is subjected to shear.
TL;DR: In this article, an appareil simple a fabriquer and a utiliser is presented for mesurer la permeabilite de betons, i.e., a developpe un permeametre de laboratoire a air a charge variable.
Abstract: Pour mesurer la permeabilite de betons, on a developpe un permeametre de laboratoire a air a charge variable. On decrit son principe, son fonctionnement (tres simple) et le mode de calcul de la permeabilite. On peut utiliser pour cela une theorie complete ou simplifiee. L'utilisation de la theorie simplifiee conduit a une sous-estimation systematique de la permeabilite de l'ordre de 25%. D'autre part, les resultats obtenus avec ce type de permeametre sont voisins de ceux obtenus avec le permeametre a change constante. Le permeametre a presente est un appareil simple a fabriquer et a utiliser.
TL;DR: Toutlemonde et al. as mentioned in this paper presented the experimental program and first results of shock-tube tests on concrete slabs and drew conclusions concerning the role of free water (i.e., evaporable or non-chemically bonded) in the pores of concrete, which can explain the loading rate effects that have been observed.
Abstract: This article presents the experimental program and first results of shock-tube tests on concrete slabs. It follows the description of the test in Toutlemonde, F., Boulay, C. and Gourraud, C., ‘Shock-tube tests of concrete slabs’, Mater. Struct.26 (1993) 38–42. The plan of experiments carried out in1991–1992 was performed to get better control of the shock (blast, impact, impulsive loading) resistance of concrete structures. Some conclusions are drawn concerning the role of free water (i.e., evaporable, or non-chemically bonded) in the pores of concrete, which can explain the loading rate effects that have been observed.
TL;DR: One-dimensional water transport in cores of different concrete types with a moulded surface at one end was investigated by simple measurement of mass changes during suction and by evaporation tests.
Abstract: One-dimensional water transport in cores of different concrete types with a moulded surface at one end was investigated by the simple measurement of mass changes during suction and by evaporation tests. Non-destructive methods (magnetic resonance imaging (MRI) and x-ray tomography) were applied successfully to the localization of water distribution within the concrete during such tests. Before the suction test was carried out, all samples were stored for 18 months under constant climatic conditions (35% RH, 70% RH, or 90% RH) to avoid inhomogeneous humidity distributions. They were then sealed with aluminium tape (epoxy in the MRI measurement) on all faces except the moulded surface, thus guaranteeing one-dimensional flow.
TL;DR: In this article, the authors investigated the strength of unsealed concrete and mortar incorporating quarzitic aggregate and bound by Portland cement and subjected to high temperature and biaxial stresses.
Abstract: The mechanical behaviour of normal weight concrete subjected to high temperature and biaxial stress is not well understood. The investigation reported is twofold. The strength is studied of unsealed concrete and mortar incorporating quarzitic aggregate and bound by Portland cement and subjected to high temperature and biaxial stresses. This involves short-term tests and includes the influence of the composition. Additionally a mechanical model is developed for the failure of concrete subjected to these stresses which incorporates not only the main variable temperature, but also compositional variables which have a significant influence on the strength of concrete at high temperatures.