Metal granules (possibly slag) under my slab!?!?
I’m about 90 percent sure that instead of gravel, there are fine metallic particles under my cement slab downstairs.
House was built in 1968. I busted up a cement porch outside my back door and found these particles inbetween the slab and the dirt. They stick to a magnet, look rust colored, and are about the size of a grain of rice or smaller.
I also seen them when digging up my foundation along with the occasional black shiny rock that appears to be iron ore slag from pictures on the interwebs. The layer of these granules are probably 4-6” thick and sucked to dig through.
My slab is also cracked in heaved in most of my downstairs, so I’ll be able to confirm the slag is used there too when I bust it up.
Why did they use it instead of gravel, and does it need to be replaced with gravel?
Could that have been a factor in my slab heaving? I did find plugged up clay draintile as well.