Depends on how much the inferiority of the concrete vs. that used for construction affects its durability and longevity. It needs to be able to withstand weigh

Depends on how much the inferiority of the concrete vs. that used for construction affects its durability and longevity. It needs to be able to withstand weight from blocks above, impact whenever it or an adjacent block is moved, and corrosion from any metallic material within. I could almost imagine these blocks needing to be tougher over time than something made from cement used in construction, to avoid crumbling under those conditions.