This fact sheet examines the use of alternative cementitious materials in transportation. As the world’s second-most widely used material behind water, concrete is a core ingredient of American infrastructure, including its use to build roads and bridges on the National Highway System. Concrete, due to its long service life, has a low environmental cost; however, its major component, ordinary portland cement (OPC), in its manufacturing process, gives of a large amount of carbon dioxide; and by reducing or replacing OPC, significant sustainability improvements will result. To use less energy in cement production, the Exploratory Advanced Research (EAR) Program at the Federal Highway Administration (FHWA) is supporting research to increase access to potential replacements or alternatives for portland cement.