Moving carbonation fronts in concrete: a moving-sharp-interface approach

We present a new modeling strategy for predicting the penetration of carbonation reaction fronts in concrete. The approach relies on the assumption that carbonation reaction concentrates macroscopically on an a priori unknown narrow strip (called reaction front) moving into concrete gradually changing its mechanical and chemical properties. We propose a moving-interface model to forecast the maximum penetration depth of gaseous CO2 in the porous concrete matrix. The main questions driving this research are: How fast does the carbonation front move? and How long does it take until the front reaches the reinforcement?. As model output, we determine simultaneously the position of the carbonation front and the profiles of the active concentrations. The model equations are solved using a specially-tailored finite element scheme and are validated relying on experimental data from the PhD thesis by D. Bunte Zum Karbonatisierungsbedingten Verlust der Dauerhaftigkeit von Außenbauteilen aus Stahlbeton, Ph.D. thesis, TU Braunschweig (1994). Our approach should be viewed as an alternative to the standard carbonation models. Keywords: Carbonation; Modeling; Moving-interface problem; Fast reaction; Finite element method