Concrete is highly corrosive, but not in the way most people expect. It won’t eat through materials like acid. Instead, fresh concrete is extremely alkaline, with a pH between 12.0 and 13.8, making it caustic enough to burn skin, dissolve certain metals, and cause lasting damage to anything in prolonged contact with it. Once cured and dry, concrete is far less reactive, but the wet or freshly poured form is a genuine chemical hazard.
Why Concrete Is So Alkaline
When cement mixes with water, a chemical reaction called hydration produces calcium hydroxide (also called portlandite) as a byproduct. This compound saturates the water in the mix and pushes the pH to around 12.5 on its own. Sodium and potassium ions naturally present in Portland cement push it even higher, sometimes above 13. For comparison, household bleach has a pH of about 12.5, and drain cleaner sits around 14. Fresh concrete falls squarely in that range.
This alkalinity isn’t a flaw. It’s actually what makes concrete work so well as a building material. But it also means that anything touching wet concrete, whether skin, aluminum flashing, or zinc-coated bolts, is sitting in a chemical bath strong enough to cause real damage.
What Concrete Does to Skin
Wet concrete causes alkali burns through two mechanisms working together. The calcium compounds in cement react with water and sweat on the skin to release hydroxide ions, which denature proteins and dissolve fats in a process called liquefactive necrosis. Unlike acid burns, which tend to create a barrier of damaged tissue that limits further penetration, alkali burns keep moving deeper into the skin. The reaction also generates heat, adding a mild thermal component to the injury.
What makes concrete burns particularly dangerous is that they’re often painless at first. The tissue damage progresses slowly, and the only early symptom is typically redness and warmth. Many workers don’t realize they’ve been injured until hours later. Burns can go unnoticed for up to 48 hours, by which point the damage has reached full thickness, meaning it extends through the entire depth of the skin. The most common scenario is a construction worker kneeling in wet concrete or getting it inside boots or gloves without immediately washing it off.
Beyond burns, Portland cement contains trace amounts of hexavalent chromium, a known skin sensitizer. Repeated contact can trigger allergic contact dermatitis, a chronic skin reaction that worsens with each exposure. OSHA has specifically flagged this as a hazard for workers who regularly handle wet cement.
Which Materials Concrete Corrodes
Concrete’s relationship with metals is complicated. Some metals it protects; others it actively destroys.
- Steel rebar: Concrete’s high pH actually helps steel. The alkaline environment causes a thin, stable oxide film to form on the steel surface, a process called passivation. This film keeps the corrosion rate extremely low, below 0.1 micrometers per year. That protective relationship is why steel-reinforced concrete works so well. Problems only start when the concrete cracks, carbonates over decades, or is exposed to chlorides (like road salt), which lower the pH and break down the protective film.
- Zinc and galvanized steel: Zinc reacts aggressively with the hydroxide ions in fresh concrete, producing hydrogen gas and zinc corrosion products. Research has shown that zinc in concrete can corrode at rates exceeding 4 micrometers per year, well above acceptable thresholds. The hydrogen gas production also creates pores at the interface between the metal and cement paste, weakening the bond. This is why embedding galvanized fasteners or coatings directly in wet concrete can be problematic.
- Aluminum: Highly susceptible to alkaline corrosion. Aluminum reacts with the calcium hydroxide in concrete, producing aluminum hydroxide and hydrogen gas. Aluminum conduit, flashing, or panels in direct contact with wet concrete will corrode unless a barrier coating separates the two materials.
Copper and brass are generally more resistant but can still degrade over long exposure periods. The general rule: any metal that reacts with strong bases will corrode in contact with fresh concrete.
How Long the Corrosive Phase Lasts
Concrete is most corrosive when it’s fresh and wet. As it cures over the first 28 days, free water is consumed by the hydration reaction, and the material becomes progressively less reactive. Fully cured, dry concrete still has an alkaline chemistry internally, but its surface is far less aggressive. Moisture reactivates some of that alkalinity, which is why old concrete that gets wet can still irritate skin or corrode vulnerable metals, just not as intensely as a fresh pour.
Over years and decades, a process called carbonation gradually lowers concrete’s pH. Carbon dioxide from the air reacts with the calcium hydroxide, converting it to calcium carbonate and dropping the pH toward 8 or 9. This is neutral enough that it no longer protects steel rebar, which is why older structures sometimes develop reinforcement corrosion problems. But for the question of whether concrete is corrosive to things it touches, the risk is concentrated in the first hours and days after mixing.
Protecting Yourself During Contact
If you’re working with wet concrete, full skin coverage is the priority. Waterproof gloves, long sleeves, and rubber boots with pants tucked over them prevent the most common burn scenarios. Eye protection matters too, since a splash of wet cement in the eye can cause serious corneal damage at that pH level.
If wet concrete does contact your skin, wash the area immediately with clean, cool water. Use a pH-neutral or slightly acidic soap rather than a standard bar soap, which can be alkaline itself. OSHA recommends considering a diluted vinegar rinse to neutralize any remaining caustic residue. Do not use waterless hand cleaners, alcohol-based gels, or abrasive scrubs, all of which can drive the alkaline compounds deeper into the skin or worsen irritation. Skin softening products should also be avoided on cement-exposed areas.
For protecting materials, the solution is usually a physical barrier. Aluminum or zinc surfaces that will contact concrete need a bituminous coating, epoxy layer, or plastic wrap between them and the wet mix. Once the concrete has fully cured and dried, the corrosion risk to adjacent materials drops significantly.