Did Cement Or Concrete Fail In Oil Well?

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Was it "cement," as NPR has been reporting, or "concrete" that failed at the bottom of the BP well, causing millions of gallons of oil to be released into the Gulf of Mexico? Some listeners have written letters to ask. NPR Science Correspondent Richard Harris joins Melissa Block to explain the answer.

MICHELE NORRIS, host:

Time now for your email. Yesterday we reported on the failure of cement in BP's Macondo well in the Gulf of Mexico. Our science correspondent Richard Harris said part of the question is whether Halliburton knew the cement would not work.

RICHARD HARRIS: The spill commission says Halliburton's own tests were casting doubt on the cement's ability to set and harden at the bottom of the oil well. They did four tests, three of them suggested that the cement would be unstable. However, the commission says that one Halliburton test did show that the cement should set up and work.

MELISSA BLOCK, host:

Hmm. Well, that sent some of you to your keyboards. Lou Pupich(ph) of Newbury Park, California, wrote us an email with this subject line: Inquiring Mind. He asks, was it concrete or cement that failed in the BP tests?

And Grant Crosby of Anchorage, Alaska tells us we misrepresented the material. He writes: Cement, commonly known as Portland cement, along with aggregate -gravels, sand and water - are mixed to make concrete, which is what I think you're trying to say. It's a very common mistake, he says. But I figure as the leading news organization, in my book, you ought to start using concrete instead of cement. Using the words, we presume, not the material.

Well, NPR's Richard Harris is here now to answer this concern. Richard, I predicted this. You and I were having this conversation yesterday. I knew we would get letters on this to set us straight.

HARRIS: You're absolutely right. And it is true that people frequently confuse cement and concrete. In fact, we get letters practically every time that we talk about this. And the listener is correct. Concrete is a mixture of this gray cement powder, sand and gravel and of course water. And that's what sidewalks and foundations are made out of. But that is not what they pour down the oil wells in order to seal them up.

The stuff they use in that case is called cement, though it's actually a lot fancier than the Portland cement that's usually used to make concrete. It contains all sorts of special additives so it will stay runny long enough to get to its destination and then harden up at the bottom of the well when it gets there. Including, in this case, some nitrogen, which fluffed up the cement. It was actually part of the controversy about whether that should've been an additive in this particular case.

So, although it is true that the word grates on the ears of many a civil engineer, in this case, the stuff is called cement, not concrete.

BLOCK: Okay. Cement, not concrete, being used to seal the BP well.

HARRIS: That's right.

BLOCK: Okay. NPR science correspondent Richard Harris setting us straight on that. Thanks so much.

HARRIS: My pleasure.

BLOCK: And you can write to us at NPR.org. Just click on contact us at the bottom of the page.

HARRIS: As in contact cement?

(Soundbite of laughter)

BLOCK: No, that's a whole other thing.

(Soundbite of song, "Cement Mixer")

Mr. MEL TORME (Musician): (Singing) Cement mixer, put-ti, put-ti. A puddle o'veet, concrete. First you get some gravel, pour it in the vout, to mix a mess o'mortar you add cement and water and see the mellow roony come out.

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