Concrete has relatively high compressive strength (it doesn't crack under weight), but significantly lower tensile strength (it cracks when being pulled). The compressive strength is typically controlled with the ratio of water to cement when forming the concrete, and tensile strength is increased by additives, typically steel, to create reinforced concrete. In other words we can say concrete is made up of sand (which is a fine aggregate),ballast (which is a coarse aggregate), cement (can be referred to as a binder) and water (which is an additive).