The AAR Susceptibility of Recycled Concrete and Natural Rock Aggregates After Pre-treatments

The AAR is a detrimental degradation where the natural aggregates play a major role. The increased use of concrete and recycled concrete requires a depth knowledge of the recycled aggregate concrete behaviour and the possible actions to improve the AAR resistance. A block of concrete with strength class C 30/37 was produced. The material was then crushed to obtain 0–32 mm recycled concrete aggregates (RCA). To reduce the porosity of the old cementitious hydrated paste around the aggregates, the RCA were treated with a nanosilica. At the same time, natural siliceous-based aggregates were heat treated up to 650 ℃. Then they were water and air quenched. The AAR reactivity of all aggregates was tested by preparing mortar samples, curing them in water vapour and successively in an autoclave at 150 ℃. The samples were immersed in an alkali-hydroxide solution. The recycled concretes with and without nanosilica and the natural aggregates pre-treated at 650 ℃ and water quenched exhibited a lower AAR susceptibility as compared to the concrete with the same natural aggregates. The heat treatment and quenching at 23 ℃ of the natural aggregates increased the mortar AAR expansion.