What Are Those Rust-Colored Orange Stains on Concrete Resembling Meteor Strikes?
At some point, you’ve walked down a sidewalk, parking lot or driveway and noticed round a bunch of those reddish-orange circles with wispy tails on them staining the concrete. These rust-colored marks look like a meteor shower rained down on the pavement. What caused these orange stains on concrete: Leaks from cars? Splatters from trees? Impurities in the pavement?
It’s probably a question you’ve never asked … but it has an interesting answer.
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Those orange stains on concrete aren’t from leaky cars
These comet-shaped marks do not actually come from the sky. They are rust spots often originating from within the asphalt itself. The discoloration can be due to the presence of metallic minerals called pyrites.
If the asphalt or concrete aggregate contain pyrites, which is prominent in certain river gravels, reactions can occur near the surface that is exposed to the weather elements and moisture. When the surface becomes wet or oxidizes, these minerals can collect and stain the asphalt. This chemical reaction sometimes causes the spot to swell and balloon a bit, filling with air that can lead it to crack. If the area is not treated once it reacts, the rust spot can continue to worsen and travel deeper below the surface as it’s exposed.
Depending on how tainted the concrete is with pyrites, dozens or even hundreds of these spots can appear.
If there’s a rampant amount of rust spots on a surface, there’s a chance that fertilizer could have been spilled there, and the remnants have become orange spots along the ground. But, more than likely, the orange stains on concrete are the product of metallic minerals oxidizing and rusting within the concrete.
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Sources: Magazine of Concrete Research via ICE Virtual Library, Concrete Construction, Sport Master
Aaron is unashamed to be a native Clevelander and the proud driver of a Hyundai Veloster Turbo (which recently replaced his 1995 Saturn SC-2). He gleefully utilizes his background in theater, literature, and communication to dramatically recite his own articles to nearby youth. Mr. Widmar happily resides in Dayton, Ohio with his magnificent wife, Vicki, but is often on the road with her exploring new destinations. Aaron has high aspirations for his writing career but often gets distracted pondering the profound nature of the human condition and forgets what he was writing… See more articles by Aaron.