Why Does Concrete Dry Faster Under Water? (Video)

“Greg Batista here once again to answer your online questions.

Iamthewalrus25 asks: Is it true that concrete actually cures better underwater?

Yes — and here’s why. Concrete doesn’t dry, it cures. The strength comes from hydration, a chemical reaction between cement and water. If concrete dries out too fast in the sun, hydration stops and strength is lost. Underwater, there’s always moisture available, so hydration continues uninterrupted. The U.S. Army Corps of Engineers has documented that underwater-cured concrete can be up to 20% stronger than air-cured mixes. Engineers also use anti-washout admixtures so the cement paste doesn’t disperse in water. That’s why we can pour piers, bridges, and seawalls directly underwater. In South Florida, where marine structures are common, engineers often prefer wet curing because it results in a denser, more durable product. Ironically, water — which most people think weakens concrete — actually helps it reach its full strength when controlled correctly.

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Authoritative references: U.S. Army Corps of Engineers – Concrete in Marine Environments; Portland Cement Association technical notes.

The author, Greg Batista, PE, CGC, SI is the owner of G. Batista Engineering & Construction and is a nationally-recognized engineer and contractor with more than 35 years of experience and offices in Fort Lauderdale, Florida.