Architecture and management of a geological repository - Andra

4 – Waste disposal Packages4.1.5.4 GranulatesThe choice of granulates (sands and gravels) results from the objective of preventing alterationphenomena due to alkali silica reaction.Considering the time scales considered, particularly for the variant with reinforced retention capacity,the granulate must be a physicochemically stable limestone. Dolomitic limestones (containingMagnesium), or limestones with a high alkaline content, must be avoided. The limestone granulatesenvisaged must contain at least 95% calcium carbonate (CaCO 3 ). The impurities constituting theremaining 5% must also be free of any alkali silica reaction.The diameter of granulates must be limited (dimensional classification less than 12.5 millimetres) toimprove the concrete's mechanical strength and density. The granular section can also be refined toimprove the concrete's density to improve performance and facilitate concrete casting (injection,possibility of pumping). Finally, the granulates must be non-reactive.4.1.5.5 Fibres and possible reinforcementFibres and any reinforcement used aswer the mechanical reinforcement and durability needs of thecontainer.The use of stainless steel reinforcement rods and/or fibres avoids the risk of cracking linked to theexpansion of non-alloy steel corrosion products. It should be noted that the level of concentration ofchlorides in the water, which is likely to reach packages in a disposal context, will have no effect onstainless steel corrosion.The addition of fibres to the concrete improves the quality while reducing the risk of microcrackingand provides characteristics of ductility and tensile strength. A tensile strength of 5 MPa has thereforebeen targeted.However, the role of fibres only helps to stop crack initiation under traction if the physical propertiesof the concrete matrix are such that the material has high levels of ductility. Otherwise, the fibres onlyabsorb the stress after cracking has started.4.1.5.6 Formulation, industrial implementation tests and performance obtainedSeveral concrete formulations have been developed in the laboratory, then tested using industrialsuitability tests. During these tests, particular attention was paid to the "pumpability" of the concrete,linked to the size of the granulate and dimension and shape of the fibres. A self-placing concrete wastherefore sought, which does not need vibration to position it.Two types of formulations were developed:- an initial formulation basis was defined using CEM I with the addition of 10% silica fume on theone hand and limestone filler or fly ash on the other, for a total mass of cementitious materialclose to 500 kg/m3 and between 170 and 200 kg/m3 of water. The W/C ratio obtained is less than0.35. Granulates and sands are Boulonnais limestone for a total mass of around 1700 kg/m3. Thefibres are stainless steel hooked fibres for 30 kg/m3 (or 56 kg/m3 for the variant withoutreinforcement).- a second formulation basis was defined using CEM V with the addition of 5% silica fume for atotal mass of cementitious material close to 500 kg/m3 and a mass of water between 170 kg/m3.The water/cementitious material(W/C) ratio obtained is less than 0.35. The fibres are stainlesssteel straight fibres for 85 kg/m3.Furthermore, the specific formulation for the lid of the standard package (hydrogen porosity) wasdeveloped on the basis of CEM I with limestone filler but no silica fume and only 25 kg of stainlesssteel hooked fibres.The formulations developed and used to produce demonstration models allowed to reach the fixedobjectives.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM123/495