The manufacturing of cement requires a lot of energy, cement plants use several forms of energy, like coal, some use natural gas, and some also burn things like hazardous waste and tires. Cement plants are the 3rd largest emitter of mercury emissions. Mercury isn't the only thing coming out of the stacks at cement plants, they also give off things like sulfur dioxide, dioxins, and more.
I live just over two miles away from a cement plant that burns tires and other toxic things. They are classified as a high priority violator of the Clean Air Act by the EPA. Yet with many things made of concrete being marketed as green and the plant itself telling everyone it's green, it's an issue that is being overlooked. This cement plant even says it's recycling tires when it burns them for fuel and they say they are committed to environmental issues, they chair the local green committee and are sponsoring a green expo. All while polluting our air at an alarming rate.
Many people think I want to shut down the cement plant near me but that's not the case. If the one by me shut down they would have to make more cement somewhere else to meet demand and would just end up polluting another town. Cement can be made in a greener way but many of the cement companies don't want to invest in newer technology or even follow current laws as it cuts into profits. The way the law is now the fines often are smaller than what the company makes from breaking the law.
This issue is why when deciding if a product is eco-friendly or not, we must look at the manufacturing as well as the finished product. No product is perfect but we have to try and make informed choices. If you want to see how close you are to a cement plant check out Earthjustice's interactive cement kiln map.