Mixing enough concrete by hand for a slab is unfeasible. I assume you mean they mix it in a truck on site with the components brought and water from country used?
EWB Australia acknowledges the traditional custodians of country throughout Australia and recognise their continuing connection to land, waters and community. We pay our respects to them, their cultures and their land; to Elders both past and present; and to emerging leaders. We recognise that the Aboriginal & Torres Strait Islander people never ceded sovereignty of what we call Australia.