Use of water absorption by concrete as a criterion of the durability of concrete - Application to recycled aggregate concrete

Aggregates produced bt the recycling of building wastes could be tired as l ocal substitute materials in construction, but their benefit to hydraulic c oncrete has Mot been Stilly exploited due to the fact that they are not "st andard" They are indeed suspected of having a very bad influence on the dur ability of concrete. As a matter of fact, transfer phenomena, including the absorption of water by capillarity, play an essential role in the durability of recycled aggreg ate concrete (RAC in short) considering their high total water/cement ratio . The influence of the RAC composition and the curing conditions on the wat er absorption process has been studied: the initial absorption, representin g the size of large capillaries and the absorptivity representing the volum e of the fine capillaries, have been measured. The RAC absorb a more important quantity of water than natural concretes do . They are therefore more vulnerable to various aggressions. Despite this f act, according to standard thresholds given in the literature, their qualit y can aptly be described as "average". River sand and coarse recycled aggre gate concrete that we call "mixed concrete" call also be considered for usa ge in average aggressive conditions.