Use of anthocyanin solutions in portland cement concrete to identify carbonation depth

Abstract

A method is proposed which comprises placing a portland cement concrete or mortar sample with a harmless solution, based on a variety of anthocyanins, which acts as an indicator yielding a color which is visibly different in zones where an alkaline reserve exists (pH ~ 12) (green) from that observed in carbonated areas (pH ≤ 9) (blue). We firstly experimented with various solutions containing anthocyanins extracted from flowers and fruits, after which food colors commercialized in the European Union were utilized seeking to prepare a reproducible method. The tested products are three food colors coming from grape, black carrot and red cabbage obtained by means of extraction and later dehydrated by spray dying. The solutions which seem most appropriate to us contain 2.5% of color dissolved in a liquid where alcohol and water are mixed at a 70/30 ratio.