Denys Breysse

Electrical resistivity measurement applied to cracking assessment on reinforced concrete structures in civil engineering

Abstract Non-destructive evaluation appears more and more important in the civil engineering economic stakes. In this context electrical resistivity measurements get sensitivity to parameters allowing to assess concrete structures conditions. This article analyses the ability of the resistivity measurement to study cracks in concrete. Its ability to detect and to locate cracks and spalling is shown with on site measurements on a damaged slab. Then specific studies on such disorders allow to distinguish the influence of their characteristics. The sensitivity of the method to cracks depth, according their moisture conditions, is assessed by computation. Experimental works on a reinforced concrete beam, ideally cracked, confirmed these results. Some assumptions based on measurements realised on a size-one structural component allow to assess the general influence of crack opening and bridging degree between crack lips. Qualitative results show the similar effects on measurement of various cracking parameters. Prospective works presented in the paper lead us to say that electrical resistivity method applied to civil engineering structures is a relevant tool for the assessment of structural damage.

A new image analysis technique for the quantitative assessment of microcracks in cement-based materials

Abstract The development of a new image analysis technique for the automatic detection and quantification of microcracking in cement-based materials is described. An impregnation technique is used to highlight microcracks and other microdefects (porosity, air bubbles) present in the concrete matrix. Microcrack observations of the polished samples are carried out using an optical microscope. The first step of the image analysis process consists of extracting the various defects from the observed image. The extraction process is essentially an automated thresholding operation carried out on the grey-level histogram. The second step consists of automatically sorting the various extracted defects on the basis of a certain number of shape factors. For the third step, an innovative technique is used to reconnect several neighboring microscopic fields. Finally, the characteristics of the cracking pattern are quantitatively determined using classical stereological techniques. The approximation of microcracks by straight lines enables researchers to draw maps of the sample crack network over an area of a few tens of square centimeters. Various tests were carried out to verify the accuracy and the reproducibility of the results yielded by the method. Results obtained for undamaged and mechanically loaded samples are also presented.

Image analysis for the automated study of microcracks in concrete

Abstract An image analysis technique for the automated detection and quantification (at the mesoscopic scale) of microcracks in cement-based materials is described. In order to highlight microcracks and other microdefects, the surface of the material is impregnated with a red or a fluorescent dye. Observations of the polished sample are carried out using an optical microscope. The image analysis algorithm developed for the segmentation of the microcracks includes a pretreatment of the color image, an automatic thresholding carried out on the gray level histogram and a treatment of the binary image. The resulting image is then treated using a shape analysis and edge corrections. The characteristics of the crack network are quantitatively determined using classical stereological methods. The technique enables the user to draw maps of the sample crack network over an area of several tens of square centimeters. Results obtained for undamaged and mechanically loaded samples are presented.

Development of a two-stage inspection process for the assessment of deteriorating infrastructure

Inspection-based maintenance strategies can provide an efficient tool for the management of ageing infrastructure subjected to deterioration. Many of these methods rely on quantitative data from inspections, rather than qualitative and subjective data. The focus of this paper is on the development of an inspection-based decision scheme, incorporating analysis on the effect of the cost and quality of NDT tools to assess the condition of infrastructure elements/networks during their lifetime. For the first time the two aspects of an inspection are considered, i.e. detection and sizing. Since each stage of an inspection is carried out for a distinct purpose, different parameters are used to represent each procedure and both have been incorporated into a maintenance management model. The separation of these procedures allows the interaction between the two inspection techniques to be studied. The inspection for detection process acts as a screening exercise to determine which defects require further inspection for sizing. A decision tool is developed that allows the owner/manager of the infrastructural element/network to choose the most cost-efficient maintenance management plan based on his/her specific requirements.

Cluster characterisation in a metal matrix composite

Abstract Inhomogeneities in the reinforcement of particulate metal matrix composites (PMMC) change their post elastic behaviour. Thus it is important to qualify and quantify particle clustering. Images of an Al–Si/SiC PMMC are analysed here in order to calculate interparticle distance, intercluster distance, and distance from isolated particles to clusters. This is done on six images at ×100 magnification, two images at ×200 magnification and one image at ×50 magnification. The analysis is done through increasing size dilatations. This is applied to the nine images but also to random images, allowing thus a comparison of the nine images and random ones. This gives four characteristic distances, and also the cluster size and the link between clustering and cracking. The particle and cluster alignment in the extrusion direction is also shown.

Influence of rest time on recovery and damage during fatigue tests on bituminous composites

Introducing rest periods during fatigue tests can significantly improve the remaining lifetime of bituminous mixes. An experimental protocol has been designed such as to study the range and kinetics of loss of stiffness and recovering of properties during rest periods. The range of the maximum recovery depends on the number of cycles previously applied. Recovery is not permanent and the loss of stiffness speeds up under repeated fatigue sequences. The speed of loss of stiffness seems to be a damage indicator. It evolves differently according to the fact that the specimen has (or not) previously been subjected to more aggressive solicitations. This points out the fact that the mix “keeps in memory” previous loadings.RésuméL’introduction de périodes de repos pendant les essais de fatique augmente significativement la durée de vie résiduelle des enrobés bitumineux. On a mis en place un protocole expérimental pour étudier l’intensité et la cinétique de la perte de raideur et de la récupération des propriétés pendant les périodes de repos. L’intensité de la récupération dépend du nombre de cycles préalablement appliqués. La récupération n’est pas pérenne et la perte de raideur s’accélère si l’on répète les séquences de fatigue. La vitesse de perte de raideur semble être un indicateur de l’endommagement. Elle évolue différemment selon que l’éprouvette a (ou n’a pas) été préalablement soumise à des sollicitations plus agressives. Ceci confirme que l’enrobé «garde en mémoire» les chargements précédents.

Electrical resistivity borehole measurements : Application to an urban tunnel site

This paper shows how it is possible to use wells drilled during geotechnical pre-investigation of a tunneling site to obtain a 2-D image of the resistivity close to a tunnel boring machine. An experimental apparatus is presented which makes it possible to perform single and borehole-to-borehole electrical measurements independent of the geological and hydrogeological context, which can be activated at any moment during the building of the tunnel. This apparatus is first demonstrated through its use on a test site. Numerical simulations and data inversion are used to analyse the experimental results. Finally, electrical resistivity tomography and single-borehole measurements on a tunneling site are presented. Experimental results show the viability of the apparatus and the efficiency of the inverse algorithm, and also highlight the limitations of the electrical resistivity tomography as a tool for geotechnical investigation in urban areas.

Influence of soil variability on differential settlements of structures

The paper addresses the interaction of a structure with spatially varying soil properties. In particular, the problem of a two-span continuous beam founded on a heterogeneous soil is solved analytically. The geometrical and stiffness characteristics of the structure interact strongly with the spatial properties of the heterogeneous soil. For a certain value of the correlation distance, a feature of the heterogeneous soil formation, the uncertainty and the risk of high values, not predicted with deterministic models, in estimating differential settlements and forces (bending moments, shear forces, etc.) on the structure becomes maximum. The analytical solution uses a series expansion of the soil properties relative to those of the structure. The error in the solution, due to the truncation of the series expansion, is estimated by relevant numerical results. The paper shows clearly that the forces on the structure founded on a heterogeneous soil can differ widely from those usually predicted by a deterministic model. Furthermore, a usual deterministic approach can underestimate the safety level of the structure significantly. # 2003 Elsevier Science Ltd. All rights reserved.

Effect of coarse aggregate on the workability of sandcrete

Abstract The results of an experimental study of the effect of a limited quantity of coarse aggregate on the workability of sandcrete are presented. This study has been conceived within an experimental design framework. Several parameters have been analyzed: aggregate content, aggregate size, aggregate shape and matrix strength (20- and 35-MPa matrices are cast). Statistical analysis shows that, for the 20-MPa matrix, aggregate content [gravel/sand ratio (G/S)

Investigation of the effect of the quality of inspection techniques on the optimal inspection interval for structures

Quantitative data from inspections are necessary to determine the state of a deteriorating structure and to identify the optimal maintenance strategy for the remaining life of the structure. This article presents the development of a two-stage inspection based maintenance management framework, which provides the owner/manager of a structure with a decision tool to optimise the service life costs of a structure. The two stages of an inspection are considered here, detection of defects present and sizing of detected defects. Using this framework, the optimal inspection interval for this study, based on the minimisation of the service life costs, is determined and the effect of inspection quality of the two techniques is studied. By modelling the detection and sizing stage of an inspection separately, the optimum combination of techniques can be determined.