> He’s developed a machine that can mix substances that cities often pay to get rid off, such as gravel or building waste, along with cement to create low-cost

> He’s developed a machine that can mix substances that cities often pay to get rid off, such as gravel or building waste, along with cement to create low-cost concrete blocks. The cost saving comes from having to use only a sixth of the amount of cement that would otherwise have been needed if the concrete were used for building construction. Notwithstanding the misspelling of "of", it seems like if this becomes popular, such "waste" materials will increase in price, making the plan unviable at scale.