Dams require many materials to create stable structures that must withstand the pressures of the environment. While there are numerous materials such as soil, sand, and stone, which are primarily collected near the site of the dam, cement is the most commonly used building material. Though cement is only a fraction of the constituents in concrete, manufacturing a cubic yard of concrete (approximately 3900 lbs) is responsible for emitting about 400 lbs of CO2 (PCA). The production of cement accounts for 5% of the CO2 emissions by humans worldwide since its production process needs the use of much fossil fuel; however, this percentage may increase with the ever growing interest in mega dams. An example of the amount of concrete that can be used on a large-scale project is the Three Gorges Dam of China, which required 26.43 million cubic meters of concrete (Kennedy). Energy consumption is the biggest environmental concern with cement and concrete production. Cement production is one of the most energy intensive of all industrial manufacturing processes, including direct fuel use for mining and transporting raw materials, cement production takes about six million Btus for every ton of cement (BuildingGreen).
Another material that is needed during the construction of a dam is iron or steel. The steel making process is called smelting, which removes the oxygen from the metal. Fossil fuels are used to heat and break the elemental bonds in a heated furnace to create the iron or steel. ("Iron Smelting").
With China making the world's largest dams it is no surprise that they are the world's leading producer of cement, accounting for 37% of worldwide cement production but, using outdated and inefficient procedures to do so (PCA).