Durability of concrete containing recycled concrete coarse and fine aggregates and milled waste glass in magnesium sulfate environment

Globally very large amounts of natural resources are being consumed every year due to the rapid growth of the demand for concrete in the construction industry. To address this problem recycling of demolished concrete has been introduced as a rational and practical solution for dealing with construction waste. In parallel to this, the use recycled materials in concrete, such as milled waste glass (MWG), has been widely examined with the aim of improving concrete strength and durability. In this study, the durability of concrete mixes containing recycled coarse aggregate (RCA) and recycled fine aggregate (RFA) as partial replacement (0% and 30%) of aggregates (gravel and sand), and MWG as partial replacement (0% and 30%) of cement was investigated. Concrete cubes were subjected to saturated magnesium sulfate solution, and the concrete durability was examined through a set of indicator parameters, including the expansion, mass variation, water absorption, and compressive strength of the concrete samples. A durability loss index (DLI) was introduced based on the aforementioned parameters to evaluate the durability of concretes in different groups. The results show that expansion and water absorption of concrete exposed to sulfate environment decreased with using RFA in the concrete mix by 17% and 26%, respectively, compared to conventional concrete. Also, the compressive strength results of sulfate-exposed specimens illustrate that simultaneous use of MWG with RCA and RFA can increase the sulfate durability of concrete in term of the compressive strength by 15% and 53%, respectively. In addition, DLI of mixes indicates that durability of concrete containing RCA, RFA and MWG may not be influenced much by the exposure of concrete to sulfate environment relative to normal concrete if appropriate mix proportions are adopted.