While concrete with no net CO2 emissions is possible using these advances, it requires most of the concrete service lifetime to reach carbon neutrality and requires additional exposure of concrete wastes to air to absorb CO2. Carbonation is unlikely to be used unless it increases concrete strength. In some cases, concrete containing recycled aggregates has better properties than new concrete, while in other cases the strength or durability of the concrete is reduced. The use of concrete containing recycled aggregates may require modified processes to install and may require more expensive reinforcing materials or equipment 148 but could also reduce CO2 emissions by up to 50% over new concrete manufacture. Reducing the carbon footprint of concrete to zero, however, is likely to require replacement of concrete with other less carbon-intensive materials.