Concrete

====Concrete (or fine grain concrete) is a material obtained from the mixture of water, sand, gravel and stone particles. This material is cheap, easy to mold and resistant to external factors like fire or weather.==== ====Moreover, reinforced concreted is a mixture of fine grain concrete with steel bars. It was invented in 1849 by Joseph Monier for be used in railways ties, floors, bridges, etc. It's more resistant than concrete because steel is a hard metal.====