Jean-François Lataste

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.

Study of electrical resistivity: variability assessment on two concretes: protocol study in laboratory and assessment on site

This article presents electrical resistivity measurement on concrete. The first part presents the study of a lighter protocol for measuring electrical resistivity, allowing investigations of a large number of specimens, without degradation of the quality of final results. The second part is based on measurements made on two concretes cast regularly during one year each, on two sites. Measurements done to assess the different variability sources distinguish variability linked to the measurement of those related to the material. The third part of the article compares the laboratory measurements to those made on site. Finally, all the results reflected the interests of the resistivity measurement because of low variability obtained, and consistency between results. Les travaux présentés portent sur la mesure de résistivité électrique sur les bétons. Une première partie présente l’étude d’un protocole de mesure électrique allégé, qui a permis de traiter un grand nombre d’éprouvette sans que la qualité finale des résultats n’en soit altérée. La seconde partie repose sur les mesures faites sur deux bétons coulés régulièrement sur deux chantiers durant une année. Les mesures réalisées permettent d’évaluer les différentes sources de variabilité des résistivités en distinguant les variabilités inhérentes à la mesure de celles liées au matériau. Une troisième partie de l’article confronte les mesures en laboratoires à celles réalisées sur site. L’ensemble des résultats traduit finalement l’intérêt de la mesure de résistivité du fait des faibles niveaux de variabilités obtenus, et de leur cohérence entre les différents résultats.

Shrinkage and swelling of clay soil: Comparison between laboratory and in situ measurements

ABSTRACT This paper presents the results of the shrinkage and swelling behavior of clay soils in a geological formation in the laboratory and in situ. Free swelling and drying tests on undisturbed samples, from an experimental site in the Gironde department (33) in France, have allowed theoretical displacements to be computed, starting from the free swelling parameter ϵg (%) and the linear shrinkage factor Rl (-). The computed displacements are of the order of millimeters in swelling and centimeters in shrinkage, whereas on the experimental site, they are of the order of millimeters during an annual cycle. However, following a second year of in situ measurements, we observed a cumulative settlement effect of the order of one centimeter. By comparing the results obtained, we revealed the influence of various factors, such as lithological variabilities at different scales, and repetitive shrinkage-swelling cycles, on the behavior of clay soils.

Quality of NDT measurements and accuracy of concrete physical properties quantitative assessment

ABSTRACT Assessing concrete condition is of major interest either for looking at weak or more damaged areas, or for reliability computations. NDT measurements provide a valuable way of offering a quick overview on the material condition. One of their main weaknesses is that their results cannot be directly linked with material properties. This paper presents how a collaborative research programme has been developed such as: (a) to select the best appropriate measurement techniques, (b) identify calibration laws enabling the quantitative material condition assessment, (c) identify possible valuable combinations of techniques. This strategy is applied to laboratory specimen data as well as to on site data. A focus is also placed on the reliability of the material condition assessment.

Study of fibre distribution and orientations in UHPFRC by electrical resistivity and mechanical tests

ABSTRACT This paper presents experimental tests carried out on steel fibre reinforced concrete samples, including mechanical tests as well as non-destructive technique (electrical resistivity) and non destructive technique on cores (X-ray). Electrical resistivity measurements are done as a blind test, to characterise the electrical anisotropy and deduce the distribution and the orientation of fibres. These results are compared to X-ray imaging to check the quality of the non destructive evaluation. Then, flexural and compressive strength are measured on specimens to assess the influence of fibre distribution on the concrete properties.

Auscultation non destructive du chevetre du pont de la Marque (59) : Combinaison de techniques

ABSTRACT This article was the result of a series of measurements on a bridge wall near Lille carried out by the various teams of a national project supported by the RGC&U, entitled “evaluation of the degradation of cover concrete and assistance to the diagnosis and the repair of the works” which the goal is to try to quantify what kind of improvement can be expected from the combination of non-destructive techniques in order to assess the structural state of existing reinforced concrete structures. Three techniques were employed: radar, resistivity and ultrasonic. The various teams implied in the project have tested the aptitude of each technique to detect the alkali-aggregate reaction but also to qualify the state of deterioration of the concrete by the combination of the results obtained by these various techniques.

Non destructive evaluation of concrete contamination by chloride: Comparison of methods

ABSTRACT This paper aims to analyse the sensitivity of some NDT methods (radar, resistivity and capacitive technique) to chloride contamination. In laboratory, four different concretes with different water to cement ratio and two kinds of aggregates were conditioned with different saturation degrees of two solutions (30 g/l or 120 g/l of NaCl). NDT measurements show that the attenuation of radar waves is sensitive to the presence of chlorides but depending on the saturation degree of the solution while velocity is not affected. Resistivity is also very sensitive. The real permittivity measured at low frequency with capacitive technique is modified by the presence of chlorides. All the techniques were carried out on a real site. From the analysis of laboratory results, an attempt of evaluation of both moisture content and level of chloride contamination is proposed and compared to values obtained from cores extracted on a very near area.

Quality of concrete condition assessment using several non-destructive techniques

Non-destructive techniques (NDT) are often seen as a practical and efficient way to assess the material and structural condition of existing reinforced concrete structures. However, assessment cannot be reduced to measurement and interpretation, and asset managers and structural engineers often need a quantitative assessment. A combination of several techniques can offer precious help. This article intends to show what kind of improvement can be expected from such a combination. Examples are taken from a series of on-site case studies and laboratory experiments. The focus is on the assessment of water content and concrete porosity as these material properties are key factors regarding their present condition as well as their durability in an aggressive marine environment. Material variability, uncertainties on measurements and model error condition the accuracy of the parameter estimation. Their relative contribution to the quality of material assessment is analysed.

Assessment of bonding, delamination and interfaces

Concrete can be viewed as a continuous, homogeneous and isotropic material when the investigation does not consider the microstructure scale (this level will not be considered in this report). “Interface”, as generally defined, is a physical limit between two materials. Such a limit can be viewed as an alteration of the mechanical continuity of concrete, and then, as a possible alteration of its mechanical and physical properties.

Study of fibre orientation and distribution in UHPFRC by electrical resistivity and mechanical tests

ABSTRACT This paper presents experimental tests carried out on steel fibre reinforced concrete samples, including mechanical tests as well as non-destructive technique (electrical resistivity) and non destructive technique on cores (X-ray). Electrical resistivity measurements are done as a blind test, to characterise the electrical anisotropy and deduce the distribution and the orientation of fibres. These results are compared to X-ray imaging to check the quality of the non destructive evaluation. Then, flexural and compressive strength are measured on specimens to assess the influence of fibre distribution on the concrete properties.