Deteriorating Concrete Block on Ballasted Flat Roof PV System

[BroverCleveland]

Not electrical related, but on a project in Richmond, VA about 15-20 out of ~400 balalst blocks are in various stages of deterioration. My assumption is that some maybe some of them didn't cure properly, and now are experiencing water freeze/thaw cycles causing what you see here:


Clearly, it's not all of the blocks. Additionally, the half block sitting on top of the full block appears completely unscathed.
Anybody seen this before? Any ideas other than what I'm guessing with the freeze/thaw cycles?

 

[GoldDigger]

Concrete peckers?

 

[BandGap1.1eV]

Thats common to see on any CMU block thats not hydralically formed. ASTM C1884 or C1491 i think is the standard most racking manufacturers will reference for the blocks.

 

[hillbilly1]

Maybe the chemical they use to clean the solar panels? Doesn’t explain the top blocks being not affected though, unless maybe the bottom blocks sit in the chemical longer after they are cleaned?

 

[Hv&Lv]

Too little Portland during the mixing process, too much water added to the mix when it was poured, too little water added, etc..
Looks like a bad batch of blocks.

It happens occasionally

 

[grich]

We have several satellite dishes on Baird mounts sitting on the roof, and we are in the process of culling out the crumbling block. It's just water working on them...wicking up from the bottom of the sleds. I would expect the worst rot to be anywhere the block would be sitting in water longer during a rain event.

 

[BroverCleveland]

Thanks for the replies. @hillbilly1 we don't usually see module cleaning services around here. Too much rain to make it worthwhile. @grich that's an interesting idea I hadn't considered. I'm headed out there next week to replace the 20 that have started to fall apart and get an idea of how many others might be headed that direction. I'll see if the affected blocks are in puddle points. Ultimately, the customer is wanting all of the blocks on the roof replaced, which seems like an overreaction to 15-20 blocks deteriorating...