Concrete Carbonation & Rebar Depassivation

Reinforced concrete relies on a quiet chemical guarantee: the alkaline pore water inside sound concrete keeps embedded steel coated in a passive oxide film that all but stops corrosion. This simulation renders a real slab of concrete cover in 3D and drives it with the actual diffusion-reaction physics of carbonation — CO₂ entering from the exposed surface reacts with calcium hydroxide and pushes a carbonation front inward following the standard x_c = K√t law, visibly changing colour as the pore-water pH collapses from about 12.5 toward 8.5. Once that front reaches the rebar, the passive film breaks down, Faraday's law converts a corrosion current into a growing rust layer that bulges around the bar, and — once the expanding rust product exceeds its critical thickness — the concrete cover cracks. Four controls (CO₂ exposure, cover depth, water/cement ratio, and simulation time speed) let you see directly why cover depth and mix quality are the two levers engineers actually control to delay this failure mode by decades.