Neat idea, but I don't expect you to see anything after 30 days. If you don't, you haven't proven that blowing on carts doesn't cause damage -- only that blowing in carts doesn't cause visual damage within 30 days. I suppose if you wanted to get a bit more scientific you could use a multimeter or something and measure the conductivity before/after the spit batch and/or 30 day waiting period.

We all know that salting the roads during winter causes cars to rust, but not in 30 days.