Reinforced Concrete Blocks are craftable building materials. It is one of the most durable building blocks in the game. Destroying a reinforced Concrete block will yield 25 Cobblestoen Rocks. Since A17 they will no longer downgrade to Concrete Blocks, instead they will just be destroyed.
Reinforced Concrete Blocks can be upgraded to Steel Blocks with ten (10) Forged Steel using any construction tool.