Maximization of reutilisation of concrete from decommissioned nuclear installations to preclude radioactive waste storage packages

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Several reasons argue for the complete recycling of concrete: - Statistics show that after water; concrete is the most widely used product in the world. This has two enormous consequences: -- Concrete is made from limestone and clay for the cement, silica for sand, and various rocks for aggregates. The quarries necessary to produce these materials are not only eyesores, they are slowly but surely eliminating hills at an alarming rate. Who will restore them, assuming this is even possible? -- Demolition concrete, which is becoming increasingly available as housing, office buildings and roads are brought up to standard, is used as rubble. Although rubble is not currently considered a pollutant, can we continue to allow the already enormous volumes to increase further, sterilising the ground on which they are dumped? Will we really allow ourselves to be submerged beneath a tide of waste materials? Rubble cannot be considered a natural material: its lifetime is very long, although it is affected by the burial conditions including the soil acidity and moisture. The lifetime of concrete is so long that it is routinely used to grout nuclear waste for over 300 years of high-integrity containment. - Why do we recycle glass, a product found in nature that is completely inoffensive and is produced in much smaller quantities than concrete. Why glass and not concrete? - When cement is produced from natural materials, the conversion of CaCO3 into CaO releases large quantities of a greenhouse gas: carbon dioxide (70 million tonnes in 1991). Complete recycling involves only dehydration and eliminates the need for this conversion step, with a corresponding reduction in the gas release. We found no references in the literature discussing complete recycling of concrete; undertaking research in this area therefore meant tackling a new problem. Basically, the issue was to determine whether the hydration of pure cement is a reversible process. Despite the lack of published work on the subject, the chemistry involved was promising. Demonstrating that pure hydrated cement can be reclinkered to restore or even improve its properties opened the way toward complete recycling of concrete. We could then address the difficult task of separating the three major components: aggregates, sand and cement. Although the adherence of fine hydrated cement particles to the sand and aggregates was only to be expected, as it constitutes the strength and cohesion of the concrete, it is also the Gordian knot of the separation process: for adequate separation to take place, it must be "undone". In this text, we describe work that was funded in part by the European Union, and which demonstrates three significant points: - Previously hydrated Portland cement can be reclinkered to obtain a fresh cement with at least equivalent properties. - All the components of legacy concrete (over 50 years old) can be recycled with a few additives to obtain a very good quality CLC mortar, which was our primary objective. - Complete recycling of this type only requires techniques well known to concrete professionals (crushing, heating, ball milling, sieving); its cost would thus certainly be near that of new concrete, and is only a question of scale. This Research addresses the issues of completely recycling concrete rubble. It ventures into unexplored territory that has been avoided by cement manufacturers, who have not undertaken any work in this area. CORDIS - the EU source of original scientific research - can alert the scientific community to the fact that the flow of concrete can and must be controlled. Without this awareness of an informed public, it will be extremely difficult to get the message across: the professionals of the concrete industry have other daily concerns.

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