Durability of mortars with leftover recycled sand

Abstract

Abstract This study presents the durability of mortars made with leftover recycled sand. In order to take the outside storage of this young concrete into consideration, with its ensuing carbonation, two series of recycled sands are studied, one non-carbonated and the other carbonated. First, all the basic characteristics, such as water absorption, density, cement content, and thermogravimetric characteristics of the sands and their fractions are studied. Since the idea of recycling leftover sand is still new and not much studied, an indepth study of its fractions is necessary. The results show that recycled sand presents two layers: an old cement paste layer and a natural sand layer. It is the old cement paste layer that varies with the size and fractions, influencing the characteristics of the sands and the durability of their mortars. Second, many indicators of durability are studied (strength, air permeability, chloride ion migration, capillarity, carbonation and porosity accessible to water) according to the mortar composition, and are compared with those of reference mortars made with natural sand. The results demonstrate that, for both kinds of mixtures, the durability range is very close to the reference. However, a marked increase of durability was observed through the chloride ion migration index of the mortar with carbonated recycled sand. It can also be underlined that the mixture with carbonated recycled sand showed equal or even better performances than non-carbonated sand (better compressive strength index, migration index and carbonation index). Overall, this study demonstrates that the recycling of these kinds of leftover sand is possible.