Thread: Interior concrete slab damage

The concrete tilt-up commercial manufacturing structure built in 1987 has a slab-on-grade interior floor. The surface of the slab has deterioration that looks like deep spalling. The damage is not caused by freezing because it is located here in sunny Southern California. There is no evidence of chemical spills. Corroding metal is not visible at any of the damage locations. Some of the empty "divots" have evidence of efflorescence. I suspect vapor transmission from damp soil beneath the slab is reacting with the concrete's aggregate or chemistry. I have seen this at other locations here in SoCal. The divots, as I call the holes left behind when the surface blows off, range from roughly one inch to six inches wide, and a half inch to an inch and a half deep. A thousand or more of these divots are present, and more appear to be forming. I'd like to know if anyone has experience with damage like this on concrete in warm climates, and what the prognosis might be for a floor with this kind of ongoing problem.

Thanks for any insights you might provide.

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Are you sure that isn't physical damage from someone shooting nails or pins through some material that was laid out on the floor? Or a hydraulic ram slamming into the floor?
If not, I don't have a clue.

Your photos remind me of several bridge abutments on I-5 from my NM DOT inspection days that were rapidly deteriorating, starting just a few years after they were built (even though everything was designed and built according to current DOT specifications, and none of the other abutments on that particular contract were crumbling). Both abutments' exposed surfaces looked remarkably similar to your pix.

Our testing lab people took concrete samples and adjacent soil samples, and came back with a diagnosis of concrete sulfation. The process occurs when concrete is exposed to excessive iron pyrites in the soil or base course it's placed on, and results in swelling, possible crystallization and fracturing of the concrete when the sulfuric acid that's formed (when the iron sulfide oxidizes) combines with calcium carbonate in the concrete's cement. At the time (25 years ago), the fix for in-place concrete was to entirely remove and replace, using a mix made with Type V Portland cement (which has very high resistance to sulfation). We eventually did that, after trying some unsuccessful quick fixes, and completely replaced both abutments down to the piling. We also took the precaution of first placing a heavy vapor barrier between all new concrete and the surrounding soil. There might be less drastic remedies on the market today, such as a surface-quenching the slab with the right chemical, but I'm not familiar with any particular product that might work (been away from the industry too long). An alternative to complete replacement would be overlaying with a thin, bonded concrete overlay using a mix made with Type V cement. Much less expense, and considerably faster.

Originally Posted by John Kogel

Are you sure that isn't physical damage from someone shooting nails or pins through some material that was laid out on the floor? Or a hydraulic ram slamming into the floor?
If not, I don't have a clue.

Thanks, John. No, this is not impact damage. As you can see from the photo with my hand in it, we were able to slip a fingernail beneath the loose edge and simply pick up the fractured and separated piece of spalled concrete. I found scores of places where the spalling process is ongoing and a chunk of concrete could be easily worked loose from the slab.

Originally Posted by BridgeMan

. . .Our testing lab people took concrete samples and adjacent soil samples, and came back with a diagnosis of concrete sulfation. The process occurs when concrete is exposed to excessive iron pyrites in the soil or base course it's placed on, and results in swelling, possible crystallization and fracturing of the concrete when the sulfuric acid that's formed (when the iron sulfide oxidizes) combines with calcium carbonate in the concrete's cement. . . .

Thanks, BridgeMan. I think you are on to something that I have suspected all along: the concrete in this floor is probably reacting to to the chemistry of wet subsoil beneath the slab that is being transpired via vapor transmission through the slab. I don't know that iron pyrite is the culprit, but I suspect pressure spalling due to formation of salts or other chemical byproduct(s) within the concrete's structure. I wonder if a couple of core samples for compression testing and another for chemical analysis is in order? I have suggested this to my customer.

Craig

It appears from your photos most of the bad spots have that darker aggregate showing up. I too have many years of DOT experience in bridge design and pavement construction and I agree there is some type of chemical interaction with the concrete paste and/or aggregate. I would bet that Caltrans has seen this problem and could give you the exact cause. MoDOT in Missouri has experts at their central laboratory, construction and/or design divisions that can answer questions like yours. I am sure Caltrans has similar experts.

Try a search on google - such as this one that produced the following results.

http://www.oboa.on.ca/events/2009/se...n%20Repair.pdf

Concrete Technology and Construction | Durable Floors | Portland Cement Association (PCA)

Thanks, Randy and Claude. I spoke with an engineer close by and he confirmed the likelihood of a chemical reaction within the aggregate that is probably abetted by soil moisture and chemistry. No definitive answer, though I'll be interested to know the final determination and recommended corrective action.
I appreciate the reference information, Claude. Thanks for that. I searched Google extensively and did not find your excellent reference material.

What Bridge Man said. If I had a dollar for all the concrete slabs I've seen like this, oh boy!

Originally Posted by Jerry McCarthy

What Bridge Man said. If I had a dollar for all the concrete slabs I've seen like this, oh boy!

Slabs like these in warehouses are really tough on forklift tires.

Concentrated point loading use of wrong type of machinery skates upon unprotected slab surface will do the very same initital damage which may not be immediately apparent, subsequent activites and exposures (moisture + air/oxygen), floor sweeping, washing, condensation, and use reveal more areas "popping" over time. The pattern of split agregate, depth of the larger oval portion pictured and the patterns of the smaller divots througout as shown in the accompanying picture; as well as your description of the size ranges, depths, etc. and the shape of the larger with split aggregate, suggest same. DIY "rigging"/machinery-storage materials, i.e. moving of excessively heavy loads on small metal wheel machinery skates, and or jacks; upon unprotected slab of questionable strength, concentrated point loads+metal wheels+unprotected surface+stops and starts, non continuous motion, and changes in direction without adequate continuous forward motion (rotating upon skates not moving in a wide arc, point loaded rotation). Studded wheels/tires or chains on turning when not enough forward motion while heavily loaded similar damage patterns, esp when water added improperly when floating, or drying out too fast (prev winds and/or temps during and post pour) and not "curing" properly.

Occupancy/activity history & core sampling & analysis sound suggestion.