Numerical modelling of sulfuric acid attack on OPC and CAC materials

A reactive transport model was developed using HYTEC to simulate sulfuric acid attack on cementitious materials. The model was tested on ordinary Portland cement (OPC) and calcium aluminate cement (CAC) matrices using two sulfuric acid solutions at pH 3 and 1 for 100 days. The main results were that the cumulative leached Ca2+ per initial total Ca2+ was controlled by diffusion mechanisms as it increases linearly versus the square root of time. CAC exhibited a better performance, compared to OPC, at pH 3 while it suffered more deterioration at pH 1. Ettringite precipitation was observed in the decalcified zone with gypsum formation detected on surface only at pH 1. Moreover, the analyses of the solid phases’ profiles after 100 days revealed that the dissolution of AH3 in CAC material accounted for the severe deterioration of the matrix at pH 1. Moreover, an optimization of the numerical model to represent the associated laboratory test – BAC-test [Peyre-Lavigne et al. 2015, 2016] – using a 1D model was validated. Furthermore, a brief comparison of the results obtained by two different numerical models (Aquasim and HYTEC) was presented to highlight the main differences – such as database, reactions of hydrated phases and the diffusion in the porous medium – between the two approaches.