Concrete hammer sound test reliability

[Jenifer Caplan]

Hi I would really love to understand why an engineering firm who is checking for delaminating is only using one way to check which is taking a hammer to every exterior surface area and if the sound changes they are marking it in a big box and stating it needs to be replaced even though there is really no difference in the should and no visual issues in the paint or cracking. I would love to get a professionals information regarding the accuracy of this method

 

[dik]

You can use tapping... in addition you can use chain drag, ultrasonics, GPR and for corrosion you can use half cell... The testing agency should be able to determine what is the best.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[IRstuff]

It sometimes boils down to cost and/or experience, just like a master mechanic can tell that you have a bearing that's going out, when you can only hear a cacophony of engine sounds.

As for cost, hammers are cheap, but the firm gets to charge their standard rate, and if the engineering firm expects to get the follow-on rehab business, then there's a bit of gray area whether they do their due diligence to verify.

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[Jenifer Caplan]

Yes so I am trying to figure out why there is no technology to determine the actual scope of work that needs to be done. It seems so rife with opinion vs validation? What is the best way to determine if the concrete needs repair?

 

[IRstuff]

best way to determine if the concrete needs repair

"Best" is often associated with "most costly" What you should consider is whether you want to get a PET scan each time you want find out if you've got a bacterial infection, vs. using a thermometer. The tools that are available are not mutually exclusive, but using the "best" will most likely cause future contracts to diminish, because you're going to force customers to pay for the "best" instrument to usually tell them that there's nothing wrong.

The engineer must always weigh "best" vs. "cost effective", and often the diagnosis is multistep; you use a hammer to find out if there's even a remote chance of needing use the "best" diagnosis tool to confirm. This is no different than a doctor trying to find out if you simply have a bacterial infection vs. hunting for cancers using a PET scan.

Something that has a specificity of 99% is great, but if it costs 100x more than a method with a 90% specificity, you have to question whether using the more expensive approach 99% of the time to find nothing is wrong is the right business model.

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[LittleWheels]

There is no 'best' diagnosis tool.

It takes time for reinforcement corrosion to progress far enough to crack and spall concrete. It is not an instantaneous process.

Half cell potential surveys should ideally be combined with resistivity surveys but even then, merely indicates the 'likelihood' of corrosion actually occurring. There is no certainty. I have found areas where there is a better than 90% expectation of ongoing corrosion but not actual corrosion visible when broken out. Equally, I have found corrosion where half cell potential results suggest no problem.

Delamination surveys (hammer tap, chain drag, ultrasonics) merely indicate where sufficient corrosion has probably occurred for concrete to begin to delaminate. They do not indicate where corrosion has commenced but has not progressed sufficiently for delamination to occur, though delamination may occur in the near future. It is commonplace for concrete repairs to be 150% or more of the surveyed delaminated area, because corrosion only becomes apparent around the boundaries of delaminated/ cracked concrete when broken out.