Modelling of Short-Term Interactions Between Concrete Support and the Excavated Damage Zone Around Galleries Drilled in Callovo–Oxfordian Claystone

peer reviewedProduction of energy from nuclear power plants generates high-level radioactive nuclear waste, harmful during dozens of thousand years. Deep geological disposal of nuclear waste represents the most reliable solutions for its safe isolation. Confinement of radioactive wastes relies on the multi-barrier concept in which isolation is provided by a series of engineered (canister, backfill) and natural (host rock) barriers. Few underground research laboratories have been built all over the world to test and validate storage solutions. The underground drilling process of disposal drifts may generate cracks, fractures/strain localisation in shear bands within the rock surrounding the gallery especially in argillaceous rocks. These degradations affect the hydro-mechanical properties of the material, such as permeability, e.g. creating a preferential flow path for radionuclide migration. Hydraulic conductivity increase within this zone must remain limited to preserve the natural barrier. In addition galleries are currently reinforced by different types of concrete supports such as shotcrete and/or prefab elements. Their purpose is twofold: avoiding partial collapse of the tunnel during drilling operations and limiting convergence of the surrounding rock. Properties of both concrete and rock mass are time dependent, due to shotcrete hydration and hydromechanical couplings within the host rock. By the use of a hydro-mechanical coupled Finite Element Code with a Second Gradient regularization, this paper aims at investigating and predicting support and rock interactions (convergence, stress field). The effect of shotcrete hydration evolution, spraying time and use of compressible wedges is studied in order to determine their relative influence

Hydration of slag-blended cements

International audienceIn this paper, the hydration of slag in blended cements is investigated through the measurement of hydration reaction indicators such as portlandite content, non-evaporable and free water, and hydration heat. Three substitution rates of cement by slag were used (30%, 50% and 70%). The tests were performed at two constant temperatures (20 °C and 40 °C) in order to assess the activation energy of the different components. A multiphasic hydratation model is proposed to take account of the difference of kinetics of each main phase (clinker and slag) and the hydration kinetic law proposed considers interactions between the two phases. It includes the activation of the dissolution of slag by alkalis released by the clinker phases in the pore solution, the portlandite consumption by slag and the effect of temperature and moisture content on the reaction kinetics. The model is able to simulate the evolution of hydration products and adjust the hydration product stoechimetry to the rates of slag and the current temperature automatically and instantaneously. Its reliability is shown through its ability to fit the whole experimental plan results with a single parameter set. Among these parameters are the hydration heat of slag and its water consumption. The model and its parameters should be useful to simulate other types of slag-blended cement