Evaluation of Concrete Cover Depth for Green Concretes Exposed to Carbonation

Abstract

Carbonation resistance of fly ash concrete (FAC) and recycled aggregate concrete (RAC) has been extensively tested in the past decade, but there are still no recommendations for their application in codes of practice. Therefore, the main objective of this study was to determine the minimum concrete cover depth of RAC and FAC exposed to carbonation to satisfy the required service life. In this study the relationship between concrete compressive strength at 28 days (fcm) and inverse effective carbonation resistance (R–1ACC) was established. The analysis was carried out on all data available in the literature in order to establish this relationship for FAC and RAC made with different replacement percentages. After establishing a relationship between R–1ACC and fcm, a prediction of the service life was made using the fib-Bulletin 34 (2006) prediction model for all exposure classes to carbonation. For same concrete class, it can be concluded that in the case of RAC there was no significant difference in the duration of the service life compared with natural aggregate concrete, even at 100% replacement of natural aggregate with recycled ones. For concrete up to 35% of fly ash in total cementitious materials, concrete cover for satisfying the required service life of 50 years was 40% higher compared with Portland cement concrete, and more than two times higher in case of concrete with 40–70% fly ash.