  We consider a two-scale reaction diffusion system able to capture the
corrosion of concrete with sulfates. Our aim here is to define and compute two
macroscopic corrosion indicators: typical pH drop and gypsum profiles.
Mathematically, the system is coupled, endowed with micro-macro transmission
conditions, and posed on two different spatially-separated scales: one
microscopic (pore scale) and one macroscopic (sewer pipe scale). We use a
logarithmic expression to compute values of pH from the volume averaged
concentration of sulfuric acid which is obtained by resolving numerically the
two-scale system (microscopic equations with direct feedback with the
macroscopic diffusion of one of the reactants). Furthermore, we also evaluate
the content of the main sulfatation reaction (corrosion) product---the
gypsum---and point out numerically a persistent kink in gypsum's concentration
profile. Finally, we illustrate numerically the position of the free boundary
separating corroded from not-yet-corroded regions.
