Stéphanie Bonnet

Quantification and uncertainty analysis of a structural monitoring device: detection of chloride in concrete using DC electrical resistivity measurement

In this work, we seek to assess and optimise the performance of an integrated chloride detection sensor based on the DC electrical resistivity measurement. We specifically seek to evaluate the detection threshold of chlorides. The main problem of the resistivity measurements in concrete is the dispersion of results mainly linked to the material heterogeneity and electrical contact limitations. To take into account the uncertainty of the measurement, we used a measurement device and sensors based on Geoelectrical Imaging methods. It gives richer information than the one delivered by conventional resistivity measurement sensors. Thus, it allows the use of statistical analysis and quality assessment methods. Before performing tests in concrete, we worked in a medium of known and homogenous resistivity in order to assess and optimise the performances of the acquisition system. Then we performed tests on concrete specimens containing different contents of chloride ions. Performance assessment of the resistivity probe is based on an analysis of receiver operating characteristic curves and the detection threshold of chlorides is calculated using the αδ method.

Experimental Study of Aggregates Size Effect on Strain, Damage and Permeability of Concrete

Two approaches can be used to study the size effect: one based on the change in sample size, and the other based on the variation in the aggregates size. The main objective of this research was to study the second approach. We studied 6 various concrete mixes and each test was repeated three times. For each material, uniaxial cyclic compressive tests have been performed to investigate the behaviour of concrete in a partially damaged state. The specimens were submitted to three levels of loading corresponding to 30, 60 and 80% of the maximal compressive strength. The damage indicator chosen is the decrease of Young’s modulus and the tightness indicator is the gas permeability. Results show that the concrete composition and more particularly the aggregate size have an important influence on the mechanical and transfer properties of concretes.

Sources of uncertainties for total chloride profile measurements in concrete: quantization and impact on probability assessment of corrosion initiation

Abstract Reliability methods have proved in the past that they were rational aid-tools for the safety assessment of existing structures, within which some uncertainties occurred. Condition assessment is usually carried out using on-site measurements, which are assumed perfect. However, it is now accepted that some significant uncertainties may affect the assessment of material properties using semi-destructive methods. The purpose of this paper is to present a method for the identification and evaluation of measurement uncertainties using a bias and a zero mean error modelled by a random variable. These uncertainties obtained are then modelled using a probabilistic model. In a marine environment, the main cause of reinforced concrete structure degradation is the corrosion due to chloride ingress. The chloride profiles are determined using a destructive method involving many steps where the experimenter plays a key role. In order to identify sources of errors, four researchers have performed repeatability tests. The total chloride content is expected to be the same for all the samples. The heterogeneity has been studied using statistical analysis. A value of the bias is provided and the model results are consistent with the original results. Finally, the impact of measurement errors on reliability and life-cycle assessment is discussed.

Chloride propagation in concrete harbour

Under the marine environment, the main cause of degradation of reinforced concrete structure is the corrosion of steel bars. It is due to the presence of chloride ions into the concrete porosity. When the chloride ions concentration reaches a critical value, steel bars are not protected and corrosion can start. This work studies the chloride propagation within a coasting concrete structure. This structure is a quay of the Nantes Saint-Nazaire harbour (P.A.N.S.N.) located in the estuary on the West Atlantic coast and built in 1971. In situ measurements of chloride profiles are realised for longitudinal and transversal beams and for slab in different locations and different orientations (north, south, east, west and under face). These profiles are determined by a destructive method using at the end the titration of chloride solution. The diffusion coefficients are calculated by using the Fick’s law and they permit to quantify the concrete quality in relationship with the location. A statistical distribution of these data was carried out in the aim to predict the service life of the structure by using a probabilistic model. A second part deals with the chloride kinetics in this structure which is not always immersed. The kinetics propagation is also compared with two models existing in the literature. This approach will be compared later to experimental tests realised in laboratory and will allow the development of an empirical chloride propagation law in this quay structure. This will be done also with other structures because this work is done in the frame of a European Interreg III B project called Medachs.

Bayesian Network Framework for Statistical Characterisation of Model Parameters from Accelerated Tests: Application to Chloride Ingress Into Concrete

Abstract This paper addresses the topic of long-term characterisation and probabilistic modelling of chloride ingress into reinforced concrete (RC) structures. Since the corrosion initiation stage may cover various decades, normal tests which simulate chloride penetration into concrete in laboratory conditions as the same as natural conditions, will require significant experimental times. Hence, long-term lifetime assessment of RC structures under chloride attack remains still a challenge. In practice, this problem is solved through the use of accelerated tests which speed up the chloride ingress rate and provide valuable mid- and long-term information on the chloride penetration process. Nevertheless, this information cannot be directly used for parameter statistical characterisation if the equivalent times required in natural conditions to reach the same chloride concentrations in the accelerated tests are unknown. Consequently, this study proposes a novel iterative approach based on Bayesian network updating to estimate chloride ingress model parameters from the data obtained under accelerated laboratory conditions. The Bayesian network structure and iterative approach are first tested with numerical evidences. Thereafter, the complete proposed methodology is verified with results from real experimental measurements. The results indicate that combining data from normal and accelerated tests significantly reduces the statistical characterisation error of model parameters.

Novel anticorrosive zinc phosphate coating for corrosion prevention of reinforced concrete

Deterioration of reinforcing concrete structures is a common problem among all the coast countries. Every year, several billion dollars are spent to repair and maintain reinforced concrete structures. Over time, the metal reinforcing bars used to improve the properties of concrete become susceptible to corrosion due to factors such as the presence of chloride and carbonation. Present work includes the use of novel anticorrosive coating. The use of zinc phosphate (ZP) coating has advantage of the low solubility of phosphates in medium- or high-pH solutions; also the resulting coating remains adhered to the metal surface even under extreme deformation. This study presents the efficiency of a new inhibitive pigment ZP containing zirconium compound obtained by chemical conversion (CC) method and cathodic protection to protect the steel rebars against localised corrosion in concrete. The corrosion behaviour of coated steel was assessed by open circuit potential, potentiodynamic polarisation and electrochemical impedance spectroscopy. Firstly, results demonstrated that the new coating show an adsorption on steel surface and provides an effective corrosion resistance compared to carbon steel rebar. Secondly, results showed that the increased weight of coating made by CC is consistent with the development of the polarisation resistance and corrosion potential of samples studied. Thirdly, a reduction in the corrosion rate is obtained once the coating covers the surface of the metal.

Comportement mécanique de poutres attaquées par la corrosion : Utilisation du code de calcul Eficos

ABSTRACT The aim of this study is to predict the mechanical behaviour of beams which were in sea water for 40 years. Mechanical experimentations were carried out after inspection of beams: loading in four-point bending and loading in direct tension. The mechanical behaviour of the beams is modelled before and after being corroded, with the software Eficos. The steel corrosion is taken into account only by a reduction in steel cross section because steels have no anchorage. A good correlation is obtained between simulations and experimental results for bending in the case of reinforced concrete.

Influence de la présence du chlore sur les propriétés à l'équilibre et de transfert de mortiers

ABSTRACT This work comes within the research framework of the LCPC “Transfer in concretes and Durability of constructions”. The durability of construction in sea areas depends on the penetration of chloride in porous media. The chloride ions affect some hydric properties. The influence of chloride content on isothermal sorption curves was studied at first. If we consider only the influence of chloride on the activity of the pore solution, the isothermal curves should be shifted to low relative humidity. This was checked by our experiments on mortars and an amount of shift could be calculated. Then experiments on unsaturated mortars have been leaded. Chloride do not seem to affect the hydric transport properties. The combined evolution of chloride and liquid content put in evidence, the slowing down of reaction speed of chloride with the solid matrix and that chloride do not move significantly during a first drying process.