Slab spalling caused by fertilizer application? 1

[michael231]

One sub-freezing day this winter, a customer of mine, here in Atlanta, used fertilizer on his year-old driveway instead of de-icing compound. Shortly thereafter the areas of the driveway where the the fertilizer was the heaviest developed severe spalling. I have since heard that certain kinds of fertilizer can cause this condition. My customer maintains it is a flaw in the driveway pour (i.e. a warranty-service problem), even though the driveway was in excellent condition prior to this event. He contends that "some of his neighbors used fertilizer with no problems". Any comments?

 

[emmgjld]

The FIRST thing to determine is if the slab surface has 'spalled'(or delaminated) or is the surface has deteriorated due to chemical attack.

If the slab surface has spalled, then a pre-existing condition is present in the slab. The de-icing procedure probably caused the 'spalling' or delamination to occur rapidly rather than slowly. Several ACI & PCA publications deals with the several causes of 'spalling' and delamination. My experience in Colorado is that a variety of finishing techniques, coupled with weather and concrete mix proportions and additives, can result in slab surface deterioration. Ice (freeze-thaw)and aggresive De-icing usually just speeds up the process. Actually determining what went wrong can be a challange. The combinations of finishing, curing, weather, mix proportions and additions is quite large.

If the concrete surface has deteriorated due to chemical attack, the chemistry of the fertilizer will give indications. Please note that sulfate (gypsum) and I believe some compounds containing ammonia can be very hard on concrete. Again, ACI & PCA have a lot of information.

Good Luck

 

[Ron]

Single application chemical attack usually does not cause spalling. It is more likely that your concrete has bleed water channels and a lack of adequate entrained air that allowed water to penetrate the surface, freeze, and cause the spalling.

The differences between chemical attack and expansive spalling are readily apparent...chemicals usually attack the paste, while expansive spalling will usually split the aggregate as well as the paste.

 

[Jim6758]

When I was in the Air Force, we were required to use fertilizer rather than salt for runway and taxiway deicing due to the corrosive effect of salt on aircraft parts. These were generally urea based compounds and never created a problem with spalling.