Life cycle assessment of masonry mortars made with leftover recycled sand
Résumé
Ready-mix concrete plants have to manage excess production that is not used in construction sites. This surplus is about 4% that represents 3.5 million tons of concrete per year in France. This leftover concrete can be poured in tippers and when hardened, after crushing, the gravel part can be valorized in new concrete in replacement of natural gravels or in the construction of roads. However, the fine part is undesirable particularly because of the increase of needed water. So it is mixed with gravels for roads when possible otherwise it is used in quarry backfilling. Using such wastes for new building constructions allow to participate to circular economy. It is an important topic since in France, 440 million tons of mineral materials are necessary each year. Recycling is a way to reduce this overuse. However, it would be better to propose a valorization way with an added value. It is essential to remind that this kind of sand contains active particles of anhydrous cement. This study proposes in this way to use the fine part of leftover concrete to replace natural sand in masonry mortars. This valorization scenario has been chosen since the mechanical performances requested for such mortars are low, to face with the bad performances of such sands. This valorization can also bring benefits because of the reactive products inside and also because it is not necessary to dry it if it is stored in covered conditions, contrary to natural sand. This parameter is important for pre-mixed mortars, in order to avoid hydration reactions into the silos during the storage. The environmental interest has then been evaluated thanks to the life cycle assessment (LCA) method.