Why does concrete crack ?

Concrete , like all other materials , will slightly vhange in bolume when it dries out , In typical concrete this change amounts to abouts 500 millionths . Translated into dimesnions -this is about 1/16 of an inch in 10 feet ( 4cm in 3 meters ) . The reason that contractors put joints in concrete pavements and floors is to allow the concrete to crack in a neat , straight line a t the joint when the volume of the concrete change due to shringkage .