Next, he moved all the garbage slag to the rear of the building, because the concrete engineer said it would be fine as long as there was enough gravel between it and the concrete, plus we put plastic down under the concrete before it was poured, too. He worked most of that day, and told me he'd be back Wednesday to finish prepping. He ended up with about 14 loads of gravel! unreal. But they used a bobcat compactor attachment that hammered this stuff into a concrete-like state. It felt so firm stepping on it. Much better than the loose slag, it was and is garbage.