Due to the energy-intensive process of producing and transporting concrete, it is among the highest emitters of greenhouse gases of any building material. Several alternatives exist to lessen the environmental impact of this material, including the use of recycled concrete aggregate or reducing the cement content through supplementary cementitious materials (SCM), called fly ash and granulated blast furnace slag (slag), which require much less energy to make. Addressing another environmental impact of concrete, porous pavement supports pedestrian, recreational and light vehicular traffic, including parking, while allowing water to pass through and flow into the soil. Porous pavement including pervious concrete, porous asphalt, concrete pavers, and plastic grid systems can all reduce the volume of storm water and increase groundwater recharge, which ultimately improves aquatic habitat in stream and rivers.