Phosphonates are also used as concrete retarder. They delay the cement setting time, allowing a longer time to place the concrete or to spread the cement hydration heat on a longer period of time to avoid too high temperature and resulting cracks. They also have favourable dispersing properties and so are investigated as a possible new class of superplasticizers. However, presently, phosphonates are not commercially available as superplasticizers. Superplasticizers are concrete admixtures designed to increase the concrete fluidity and workability of concrete or to decrease its water-to-cement (w/c) ratio. By reducing the water content in concrete, it decreases its porosity, improving so the mechanical properties (compressive and tensile strength) and the durability of concrete (lower water, gas and solutes transport properties).