flyash a year, with about 75 percent of it landfilledbasically 26 cubic miles (Mehta, 1998b). Flyash can substitute for up to 60 percent in a concrete mixture, and sometimes even more, depending on the application. Various studies have demonstrated that replacing 25% of the cement in concrete with fly-ash reduces energy consumption by 8.7%. This increase from the present 9% fly-ash would save 79 million MJ of energy in the U.S. alone (Glover, 2001). Flyash affects the plastic properties of concrete by improving workability, reducing water demand, reducing segregation and bleeding, and lowering heat of hydration. It increases concrete strength, reduces permeability, reduces corrosion of reinforcing steel, increases sulphate resistance, and reduces alkali-aggregate reaction. In short, it not only pays economic and environmental benefits, but it also improves the quality of concrete. Its only real drawback is a slightly slower setting time. Flyash concrete has been catching on with the rapid growth of the green building movement in the past several years. Nevertheless, it is still the object of negative bias by the mainstream building establishment. Part of the bias is due to sheer ignorance and the old view that it is dilute concrete. Part of it is that conventional practices change slowly in building, and the slightly longer curing time requires changes in scheduling. Studies and experimentationalong with builders direct experience of higher qualityare quickly breaking down these biases, and in fact, experimentation is growing with other cement substitutes like steel slag and rice hulls. There are certainly other measures that can be taken to reduce the energy-intensity and CO2 emissions of concrete, particularly those that improve of the efficiency of cement kiln operation. These include switching to lower-CO2 fuels such as natural gas