Swiss Hammer 1

[HectorB]

I have a Swiss Hammer (and the Anvil, too), but It's not calibrated. Actually, it reads 80.23 when the right reading should be 84.

How do I do the correction to accurate reanding?

 

[dirtdoctor]

Send it off to Soiltest, Durham-Geo, or the supplier you purchased it from. Most likely, you have a spring problem. If you insist on doing it yourself, change the spring and see what kind of reading you get. A knowledgeable repairman can put small spring crimpers to increase readout or loosen the spring to provide the correct anvil reading.

 

[gatorn10ac]

You can also use a known strength of concrete and take readings to compare and work up a correction factor. If the hammer is to far out then you may need to send it off and have it calibrated.

 

[dirtdoctor]

Comparing Swiss Hammer readings to concrete cylinders (or anything else for that matter) would have a higher variation than using the Hammer as is. The two tested reults would not be close - it's common knowledge that a Swiss Hammer reads higher than the actual strength of concrete. Swiss Hammer testing should only be used to provide a relative strength and should always (if possible) be compared to destructive test results, i.e., core testing. I see it all too often that Swiss Hammer results are used for acceptance testing when original test cylinder strengths are low.

 

[SirAl]

I agree with dirtdoctor that Swiss (rebound) hammer results should be used in a qualitative sence, and should be interpreted with caution and judgment. Converse to dirtdoctor's experience, I recall a situation where a contractor was very 'generous' with the application of release agent on his concrete form work. Subsequent to the pour, a very soft skin of concrete was exposed after the forms were removed. The quality of the concrete immediately fell into question and a rebound hammer was used to evaluate the concrete. Even after a seamingly appropriate amount of grinding to prepare each rebound test location, the test surface remained soft producing a low rebound result. Coring was undertaken and revealed that the problem was surfacial only.

 

[dirtdoctor]

Good point SirAl - I agree with you that when surface defects are of interest, a Swiss Hammer is a good tool. I was referring to its use as a means of determining the structural integrity of concrete. Pressure from concrete producers has caused many consultants to do testing that they know is not valid - I guess that's life for us slump monkey ringleaders.