Experimental study of cement grout: rheological behavior and sedimentation

International audienceThree basic elements (cement, water and admixture) usually make up injectable cement grouts used for prestressed cable coating, repair and consolidation of masonry, soil grouting, etc... The present study was divided into two parts. First, in order to characterize rheologically fresh cement paste with W/C ratios (water/cement ratio) varying between 0.35 and 1, an experimental study was carried out and has revealed that the cement past behaves like a shear-thinning material whatever W/C. second, to study the time evolution of their density, a gammadensitometer bench was used. Relying on the water content and the density measured, we demonstrate that the computation of the degree of hydration of cement is possible. The cement/geotechnics interdisciplinary approach proposed here has made it possible to obtain a large range of original results useful to improve our understanding of the sedimentation processes for cement pastes with different W/C ratios

Pieu sous charge latérale cyclique : incertitudes sur les mesures

L’effet des cycles de chargement horizontal en tête de pieu sur l’interaction sol-pieu est étudié sur modèles réduits centrifugés. L’évolution avec le nombre de cycles du déplacement au point d’application de la charge et du moment maximum est analysée avec une interpolation logarithmique en incluant un calcul d’incertitude

Chloride propagation in concrete harbour

International audienceUnder 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

Characterisation of internal erosion disturbances on sand/kaolinite samples

International audienceInternal erosion is one of the main causes of instabilities within hydraulic earthstructures: dike, levee or dam. Entrainment and transport of some particles affect the porosity and grain size distribution, which change the hydraulic and mechanical characteristics. These evolutions could induce instabilities: slidings, overtoppings or even failures. The difficulty of detection and the great dynamic of internal erosion demonstrate the necessity of experimental studies from the beginning of particle transport. We propose a parametric study on sand-kaolinite samples. The follow up of the effluent is performed by an optical sensor and by weighing the amount of particles torn away from the sample. These tests show that the internal erosion is initiated by the displacement of clay particles. If sufficient kaolinite content is taken away, the erosion of sand particles is induced. The evolution of the solid mass sample loss depends on the values of the different parameters tested