Vijay

B&B beams - hairline cracks

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Got the first delivery of concrete B&B floor beams today and one has multiple hairline cracks (which the haulage driver very quickly pointed out before he made any attempt to offload) and another has one hairline crack up one side. How worried should I be about hairline cracks?

 

Cheers

 

Vijay

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I would be taking a picture and contacting the b&b manufacturer and also check the rest

John

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That's my exact plan but was more concerned that they just say it's fine and it's not ;)

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Concrete can develop fine surface cracks depending on various factors during curing. They don't affect strength, as I understand it. Whether this is what you have I don't know, sorry. 

 

Definitely one for the supplier

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Definitely worth checking, if they've been loaded/stacked or handled incorrectly they could have been damaged. I was told by our supplier that the beams can't handle very much unsupported overhang and if picked up incorrectly they can crack really easily.

Edited by bissoejosh
bad quote

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Just to update, the supplier are swapping the hairline cracked ones, even the one with a single hairline crack.

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The beams on beam-and-block are cast in the factory, and should therefore be quality controlled. The reinforcement bars they put into the beams are pre-tensioned, which means that they are pulled at each end before the concrete is cast around them. Once the concrete has set, the tensioners are released and the bars cut off flush with the ends of the beams. What this does is compresses the concrete because the bars are trying to regain their original (shorter) length. So the short answer is that you absolutely shouldn't have any cracks in the beams, and if you have, something's gone wrong in the factory. Also the driver's explanation doesn't stack up, since the concrete used is extremely strong.

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That was a good result, even if it shouldn't have happened in the first place. Bit of a pain if you have/had the next stages ready to go. Thanks for explanation @StructuralEngineer

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The driver was from an external haulage company, so only there to transport what he's asked. I think he just wanted to point it out rather than pass any blame ;)

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