Luc Taerwe

General hydration model for portland cement and blast furnace slag cement

This paper focusses on the evolution of the heat of hydration of hardening concrete or cement based materials. Based on isothermal and adiabatic hydration tests a new general hydration model is developed, valid both for portland cement and blast furnace slag cement. This hydration model enables the calculation of the heat production rate as a function of the actual temperature and the degree of hydration.

fib model code for concrete structures 2010

The fib Model Code 2010 is the most comprehensive code on concrete structures, including their complete life cycle: conceptual design, dimensioning, construction, conservation and dismantlement. It is expected to become an important document for both national and international code committees, practitioners and researchers.

CHEMICAL, MICROBIOLOGICAL AND IN SITU TEST METHODS FOR BIOGENIC SULFURIC ACID CORROSION OF CONCRETE

Abstract Biogenic sulfuric acid corrosion is often a problem in sewer environment: it can lead to a fast degradation of the concrete structures. Since the involvement of bacteria in the corrosion process was discovered, considerable microbiological research has been devoted to the understanding of the corrosive process. Mechanical engineers have focused on experiments comparing the resistance of several concrete mixes against biogenic sulfuric acid corrosion. Because of a lack of standardised methods, different test methods have been used, and various parameters have been modified to evaluate the resistance of the materials. The research done on sulfuric acid corrosion of concrete can roughly be divided in three groups: chemical tests, microbial simulation tests, and exposure tests in situ. In this article, an overview of the recent developments in the test methods for biogenic sulfuric acid corrosion and the obtained results are presented. Possible differences between biogenic sulfuric acid corrosion and chemical sulfuric acid corrosion are delineated.

Axial load behavior of large-scale columns confined with fiber-reinforced polymer composites

Confinement of concrete is an efficient technique used to increase the load-carrying capacity and ductility of concrete columns and is of interest for upgrading columns, piers, and chimneys. This article reports on an experimental and analytical study of axially-loaded large-scale columns confined with fiber-reinforced polymer (FRP) wrapping reinforcement; this work updates previous studies on smaller-scale columns. The effective circumferential FRP failure strain and the effect of increasing confining action were investigated. The authors compared the different existing compressive strength models to their study results. The authors then present a revision of an existing model developed previously by the second author. This revised model addresses the effective FRP failure strain that is attributed to localized stress concentrations near failure due to nonhomogenous deformations of the damaged concrete. The authors note that the wrapping configuration of the confinement has a considerable influence on the effectiveness of the FRP wrapping. The authors conclude that although the available models were developed based on small-size cylinders, four models seem to predict the ultimate strength of large-scale columns fairly accurately (Miyauchi et al, Saafi et al, Samaan et al, and Toutanji Revised).

Chemical and microbiological tests to simulate sulfuric acid corrosion of polymer-modified concrete

Abstract In certain industrial activities sulfuric acid is used during the production process, which may cause degradation of concrete structures. Another important phenomenon where sulfuric acid is responsible for concrete corrosion is biogenic sulfuric acid corrosion, which occurs often in sewer systems. Because previous investigations have already pointed out the difference between purely chemical sulfuric acid corrosion and biogenic sulfuric acid corrosion two different tests were performed: a chemical test and a microbiological test. Five different concrete compositions were used in the tests, including a reference mixture with high sulfate resistant portland cement and four different polymer cement concrete with a styrene–acrylic ester polymer, an acrylic polymer, a styrene butadiene polymer and a vinylcopolymer, respectively. The concrete composition with the styrene–acrylic ester polymer showed in both tests a higher resistance than the reference mixture while the compositions with the acrylic polymer and the styrene butadiene polymer had a lower resistance than the reference mixture. The concrete composition with the vinylcopolymer did not induce the same results in both tests. The results of the chemical test indicated a slight increase in resistance compared with the reference mixture while the opposite was noticed for the microbiological test.

TESTS ON AXIALLY LOADED CONCRETE COLUMNS CONFINED BY FIBER REINFORCED POLYMER SHEET WRAPPING

Wrapping of columns by means of FRP (Fiber Reinforced Polymer) reinforcement enhances the structural behavior of concrete columns considerably. At the Magnel Laboratory for Concrete Research a test program is set-up to evaluate some specific problems in the modeling of FRP confined concrete, i.e., effective circumferential FRP failure strain and effect of increasing confining action. Parameters studies are FRP type, bonded or unbonded wrapping application, column shape and strengthening lay-out. Both wrapped cylinders and wrapped columns are investigated. An analytical verification of the test results is performed according to different models. From the test results obtained so far, the efficiency of this strengthening technique has been demonstrated, both in terms of structural performance and ease-of-application. Quality of the application (voids, protrusion, etc.) and the wrapping concept (bonded or unbonded, partial wrapping, etc.) influence the strengthening effect.

INFLUENCE OF POLYMER ADDITION ON BIOGENIC SULFURIC ACID ATTACK OF CONCRETE

A simple and reproducible microbiological simulation procedure in combination with a chemical procedure was used to test concrete for its potential resistance towards biogenic sulfuric acid. Concerning fundamental aspects of the corrosion reaction, it was shown that particularly the penetration of H2S inside the concrete crevices accelerated the corrosion process. The influence of different polymer types and silica fume additions on the resistance of the concrete samples was determined. The addition of the styrene acrylic ester polymer resulted in an increased resistance while the addition of the acrylic polymer or silica fume caused less resistant concrete. For the vinylcopolymer and the styrene butadiene polymer, no significant effect was observed on the resistance of the concrete samples. The results of the two different test methods confirmed the difference between corrosion due to purely chemical sulfuric acid and corrosion due to microbiologically produced sulfuric acid.

Random particle model for concrete based on Delaunay triangulation

In this paper, an efficient simulation method for obtaining a random particle model for concrete is outlined. First, the ‘take-and-place method’ and its extension, the ‘directed searching process’, are discussed briefly and the shortcomings are indicated. A new method, the ‘divide-and-fill method’, appears to be more convenient, especially when only a small computer is used. In this simulation method the available space (two-dimensional) is divided in separate areas, using a Delaunay triangulation. These areas are filled with particles taking into account a given grading curve and gravel content. Comparison with physical concrete sections, obtained by means of image analysis, shows that the results of this method closely represent reality. The divide-and-fill method also yields a finite-element mesh in a quasi-automatic way.ResumeCette publication traite d’une méthode de simulation efficace pour l’obtention d’un modèle à particules aléatoires pour le béton. On donne d’abord un aperçu de la méthode ‘prenez-et-placez’ et de son extension, la méthode du ‘procédé de placement dirigé’.La méthode prenez-et-placez produit un modèle numérique à troi dimensions. On réalise la structure composite en plaçant les granulats dans un ordre de grosseur décroissante. Les principles qui sont à l’origine de cette méthode sont d’une simplicité remarquable. Néanmoins on n’obtient de bons résultats qu’à l’aide d’un ordinateur assez puissant, même en considérant le ‘procédé de placement dirigé’. Ce procédé, qui est une forme primaire d’intelligence artificielle, tient compte des zones occupées pour la sélection de la position des granulats.Une méthode nouvelle qui, de plus, permet l’utilisation d’un PC ordinaire, est la méthode ‘divisez-et-remplissez’. Cette méthode donne un modèle de simulation à deux dimensions et procède en deux étapes. D’abord, on divise la section en triangles de Delaunay. Ensuite, on remplit ces triangles de particules en tenant compte de la distribution granulométrique et de la teneur en gravier. La courbe granulométrique bidimensionnelle peut être calculée facilement à partir de la courbe tridimensionnelle. La triangulation de Delaunay peut être réalisée sur la base d’un algorithme ‘divisez-et-vainquez’, avec un procédé dit ‘bubble’ et contrôle ‘swap’. La méthode divisez-et-remplissez donne quasi automatiquement un maillage d’éléments finis. La géométrie des granulats naturels roulés peut être décrite par une loi morphologique, basée sur la méthode développée par Beddow et Meloy.

Nondestructive determination of the steel fiber content in concrete slabs with an open-ended coaxial probe

A microwave nondestructive testing technique to measure the steel fiber content in hardened concrete slabs is presented. The technique is based on an open-ended coaxial probe reflectometry method for measuring the effective permittivity of the steel fiber reinforced concrete and on a classical homogenization approach for determining the fiber content. Two different full-wave models for the probe-aperture admittance as a function of the permittivity are applied: a spectral domain model for the forward problem and a rational function approximation for the inverse problem. A Maxwell-Garnett type of mixing rule is derived for randomly oriented conducting prolate spheroids in a dielectric host medium. A coaxial probe has been constructed, calibration aspects are discussed, and experimental results are presented for concrete slabs with various fiber contents. It can be concluded that the presented technique is a promising one.

Resistance to biogenic sulphuric acid corrosion of polymer-modified mortars

Abstract The use of polymer-modified mortar and concrete (PMM and PMC) is investigated to improve the durability of concrete sewer pipes. The aim of the research is to ameliorate the resistance of concrete to biogenic sulphuric acid attack through polymer modification. Prior to the durability tests, experimental research is carried out to reveal the influence of polymer modification on the physical and mechanical properties of mortar and concrete. The results of this research are presented in this paper. Due to the interaction of the cement hydrates and the polymer particles or film, an interpenetrating network originates in which the aggregates are embedded. The density, porosity and location of the polymer film depend on the type of polymer emulsion and on its minimum film-forming temperature (MFT). If air entrainment is restricted, an increased flexural strength is measured. Scanning electron microscope (SEM) analyses reveal the presence of polymer film and cement hydrates in the mortar. The polymer film causes a retardation of the cement hydration as well as a restriction of crystal growth.