Identification of frost-susceptible recycled concrete aggregates for durability of concrete

Demolished concretes to be recycled show great diversity in property with regard to residual potential of resistance to the environmental effects such as frost action, when they are used in a new concrete as aggregate. There seems to exist no appropriate test method fitting specific characteristics of the recycled concrete aggregates with respect to the fair judgement of their unbound state frost durability. This fact rises another important prejudice against performance of recycled concrete aggregates compared to virgin alternatives. This study deals with reliable identification of frost susceptibility of recycled concrete aggregates. An unbound frost durability test with a mild pre-drying procedure (at 50 °C) was performed on recycled concrete aggregates originated from both air-entrained and non-air-entrained type of source concretes. The procedure distinctly identified the non-durable recycled coarse aggregates in parallel to freezing and thawing durability results of the concretes incorporating identical aggregates. Sulfate soundness test gave misleading results in judgement of the unbound state frost durability due to the highly disruptive physicochemical effect of the method on the recycled concrete aggregates, regardless of the air void characteristics of the materials.

Research highlights
► This study aims to develop an effective frost soundness test method for unbound recycled concrete aggregates.
► The proposed method sharply distinguishes the durable and non-durable recycled concrete aggregates.
► A pre-drying process at 50 °C is more relevant to the cement-bonded recycled aggregates.
► The sulfate soundness test yields misleading results when used for recycled concrete aggregates.