Zoubir Mehdi Sbartaï

Effect of concrete moisture on radar signal amplitude

The moisture content of concrete is a critical parameter for most of the physicochemical pathologies, such as steel reinforcement corrosion, alkali-aggregate reaction, and freezing-and-thawing cycles. Therefore, the detection of moisture is important for the diagnosis of concrete structures at early stages of deterioration. The present study was undertaken to assess the effect of the degree of saturation, water-cement ratio (w/c), and volumetric water content on the amplitude variation of direct and reflected radar waves. Four concretes with w/c of 0.5, 0.6, 0.7, and 0.78 were evaluated. Radar measurements were carried out on 72 samples saturated at 0, 20, 40, 60, 80, and 100%. Test results show that an increase in the degree of saturation leads to significant decrease in the amplitude of both direct and reflected waves. This is mainly attributed to the increase in complex permittivity related to the polarization and conduction mechanisms occurring in concrete. Generally, the radar measurements showed good repeatability, which was evaluated using the coefficient of variation, and the statistical dispersion of the direct wave amplitude was lower than that of the reflected wave. For dry and wet concrete, w/c did not appear as an influent parameter regarding the experimental results. A good correlation was found between the amplitude of direct and reflected waves for each degree of saturation. This suggests that the direct and reflected wave amplitudes provide similar information regarding the concrete moisture. Irrespectively of w/c and the depth of reflector, an empirical relationship between signal amplitude of direct wave and volumetric water content was established that can be used to estimate concrete moisture.

Evaluation of concrete water content and other durability indicators by electromagnetic measurements

In order to use non destructive techniques (NDT) for the survey of reinforced concrete structures, it is important to show their ability to measure the cover concrete characteristics related to durability, in particular the concrete water and chloride contents. For this purpose, tests with two electromagnetic methods (GPR and capacitive probes) and impact echo method were carried out on 81 slabs of 9 different concrete mixes. Concrete porosity was ranging between 12.5 and 18%. Measurements were carried out at five different water contents. A real structure was also tested in situ. The NDT results are compared to concrete performance indicators such as porosity and water content, as well as chloride profiles. The comparisons show the complementarity of the methods to perform a pertinent diagnosis of concrete structures.

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.

Non destructive evaluation of timber structures using GPR technique

This paper deals with the study of the GPR technique for timber structures evaluation. According to the electromagnetic (EM) theory, GPR waves propagation is governed by the EM properties of a dielectric material as wood, which is affected by various parameters such as moisture, as well as heterogeneities. This paper presents some laboratory measurements in the aim of studying the sensitivity of electromagnetic waves to moisture variation in wood material. Dielectric relative permittivity was measured using resonance technique at 1.26 GHz for Spruce and Pine wood samples. GPR measurements were also carried out using GSSI SIR 3000 system connected to 1.5 GHz antennas on several wood samples. The results of this study show the good relations between real/imaginary relative permittivity and moisture content of the different wood samples. Moreover, due to the dependence of wood permittivity to moisture, GPR features in time domains present some correlations with moisture content of wood material.

Assessment of Concrete by a Combination of Non-Destructive Techniques

Abstract: The evaluation of the properties of concrete is an important objective for managers and engineers of the diagnosis of structures. The contribution of non-destructive evaluation methods (NDE) is essential because it allows us to obtain information on the quality of the material or its durability without damaging the material examined. This evaluation includes two objectives: (a) an evaluation of mechanical indicators (modulus, mechanical strength, stress), and (b) an evaluation of durability indicators (water content, chloride content, porosity, carbonate depth, etc.).

Construction of Conversion Models of Observables into Indicators

Abstract: Non-destructive techniques can be used in concrete structures for detection, localization (1D, 2D or 3D) or quantification. These three sets of objectives correspond to objectives of increasing ambition: – in the first case, it is about detecting the presence of a defect, a singularity or a local variation of property: presence of a rebar, thickness change, compactness defect, etc. It is based on the sensitivity of the non-destructive measurement to the desired change; – in the second case, we aim to map an observable (the result of non-destructive measurement), for example the resistivity which varies according to the water content of the cover concrete, or the velocity of the radar wave. As in the first case, it exploits the sensitivity of the measurement to the expected contrast and can also take advantage of the velocity of acquisition of non-destructive measurements to rapidly map large areas; – the third objective is more ambitious and more difficult to satisfy: it is a matter of estimating a quantity, called an Indicator (I), from the non-destructive measurement of an Observable (O). The sensitivity of the value of I to any change of O is of course necessary, but it is also necessary to have a model M which will make it possible to deduce the value of I from the measurement of O in the form I = M(O).

Non destructive measurement data fusion for a better assessment of concrete

Non destructive techniques provide many quantitative information about concrete condition (observables), which must be processed such as to give way to the indicators which are looked for. An experimental database is defined and fed with a series of NDT measurements obtained through various techniques. The methodology requires: the selection of best observables, the expression of relationships between indicators and observables and the combination of information provided by various sources. Data fusion, which accounts for uncertainties arising at various levels, offers a promising way.

Combiner et fusionner les mesures de CND pour mieux estimer les propriétés du béton

ABSTRACT Non destructive techniques provide many quantitative information about concrete condition (observables), which must be processed such as to give way to the indicators which are looked for. An experimental database is defined and fed with a series of NDT measurements obtained through various techniques. The methodology requires: the selection of best observables, the expression of relationships between indicators and observables and the combination of information provided by various sources. Data fusion, which accounts for uncertainties arising at various levels, offers a promising way.