The third strategy for reducing the environmental impact of concrete is transforming its composition, primarily by reducing its cement content. As discussed above, it is the energy-intensity of cement that is the most problematic aspect of concrete. The primary means of achieving cement reduction is the substitution of waste flyash for Portland cement. Flyash is a waste by-product from coal-fired power plants. It is a pozzolanic material, very much like the pozzolan clay, created by volcanic activity, used by the Romans in their early forms of concrete. The US produces about 60 million tons of