Concrete is a composite material composed of aggregate bonded together with a fluid cement which hardens over time.Most use of the term concrete refers to Portland cement concrete or to concretes made with other hydraulic cements, such as ciment fondu.However, road surfaces are also a type of concrete, asphaltic concrete, where the cement material is bitumen. lower water-to-cement ratio yields a stronger, more durable concrete, whereas more water gives a freer-flowing concrete with a higher slump. Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.