I wonder what it'd cost to use a waste material like slag. Slag weighs like 90% of the weight of concrete and is 10% of the price--because we basically throw it

I wonder what it'd cost to use a waste material like slag. Slag weighs like 90% of the weight of concrete and is 10% of the price--because we basically throw it away. I guess the biggest cost would be containers to hold it. Even if the (cost container to hold slag + cost of slag) = (cost of equal weight concrete)--we're not using up concrete that could be used for things that actually need concrete. Here we just need something heavy that won't collapse when lifted. Plus, concrete releases co2 when poured. I guess co2 would have to be released to manufacture the containers--but even then...interesting thought.