Concrete spalling

[gosai]

The sidewalks has been poured 3 to 4 years back. Recently the sidewalk concrete spalled at several locations. In our opinion the spalling is a problem related to finishing and workmanship. The contractor is blaming deicing chemicals for the problem. Could any one provide more information on other factors cause spalling? Few photographs showing current conditions are attached. The concrete was exposed to freeze and thaw cycles during winter months.

Thanks to all

 

[dik]

Can you give us a hint about the concrete specs? strength, w/c, admixtures, slump, aggregate, air, exposure conditions if part of your locale, curing, etc. and conditions when the slab was cast? Some of the spalling appears at aggregate... any chance of ASR or ACR?

Dik

 

[gosai]

Specified strength is 4500 psi with 5 to 8 % air

 

[bridgebuster]

It's not "spalling", it's "scaling". Deicing salt is a possibility but normally, salt (calcium or sodium chloride) shouldn't cause air entrained concrete to scale. Although, there are some who hold that salt shouldn't be applied until the concrete has cured for at least a year. I think you're going to have a hard time making your case 3 to 4 years after placement. You could take a core and have a petrographic analysis and air content test done, but we're taking some $$.

There are several other causes for scaling: The mason(s) may have finished the concrete too soon - the bleed water was still on the surface; they may have overworked the finishing; or didn't cure it properly.

 

[dik]

As BB notes, there's more to it than just the strength and air content...What is the climate of exposure, too? Parts of the damage appeared too deep for scaling... Can you attach some close up photographs?

Dik

 

[dik]

Looked at the pix again... and maybe not too deep, looks like scaling... sorry BB.

Dik

 

[bridgebuster]

No problem dik. I took another look, near the top; the edges are broken off, which someone would call a spall.