Strange white powdry spot that seems to grow as it pits the slab?

by DJ Bee
(California)

I have a slab . This 12 inch round spot appeared. its literally eating the concrete. i have washed it with water and pine sol. I have used baking soda . I have used bleach.
I scrape it clean and in a few days this fine asbestos looking fibrous (like a bread mold) reappears. Its eating the concrete and leaving the aggregate alone. I have never seen anything like it(I am a building contractor). Its not a simple mold from water. There was some potassium from a water softener in the area and petro based lantern fuels in the area but no other chemicals were near this area. I'm stumped. if it doesn't stop I'm gonna have to cut the concrete out to halt the action and or remove the moldy fibrous bi-product. I'm not sure, the fiber if disturbed could be toxic? Its eating concrete that has been in place for 5 years. If anyone knows what this is I would be thankful to know.

A. It does look like some sort of reaction from an acid solution. We neutralize acid on concrete with baking soda and water mixture or ammonia and water mixtures. If you've already done that and it didn't work then I don't know what it might be. Sorry.