Concrete cancer is the common name for a failure mode of concrete. Water penetration causes the concrete reinforcement to rust and expand which in turn creates stresses on the surrounding concrete which can then spall (break away). The use or presence of Chloride based compounds, together with a reduction in alkalinity, can cause corrosion of the reinforcing steel bars then expansion and spalling. This deterioration is then accelerated by water ingress, which, again, causes the surface to spall.