Effect of recycled aggregate treatment techniques on the durability of concrete: A comparative evaluation

Abstract

The utilization of recycled aggregates (RA) in new construction has been promoted by many countries but the structural use of recycled aggregate concrete (RAC) is limited owing to inferior durability performance. The focus of this work is to study the effect of different RA treatment techniques on the durability properties of RAC. For this purpose, five different RA treatment methods such as immersion in acetic acid, immersion in acetic acid with rubbing, accelerated carbonation, immersion in acetic acid with accelerated carbonation and immersion in lime with accelerated carbonation are considered during the study. To investigate the effect of different RA treatment techniques on the durability properties of RAC, different durability tests such as water absorption, permeability, chloride ingress, acid attack and carbonation are performed. Improved resistance against water absorption, chloride penetration, carbonation, and acid attack is noticed for RAC having treated RA than RAC having untreated RA. Chloride migration coefficient values of RAC having RA treated through immersion in acetic acid with mechanical rubbing and immersion in lime with accelerated carbonation are observed very close to that for NAC. Moreover, scanning electron microscopy and mercury intrusion porosimetry results also show the enhanced microstructure, dense ITZ and improved porosity for RAC having treated RA than RAC having untreated RA, justifying the positive effect of RA treatment on the durability of RAC. Based on the results, immersion in lime with accelerated carbonation and immersion in acetic acid with rubbing techniques can be used to enhance the durability of RAC. Furthermore, regression models between physical properties of coarse aggregates and different mechanical and durability properties of concrete show that the porosity of coarse aggregates can be used to predict the mechanical and durability performance of concrete effectively, which may be a step towards the design guidelines of durable and eco-friendly concrete.