It isn’t often that you can equate coal-related products with energy efficiency, but when it comes to fly ash, it actually does help. This fine powder byproduct of coal plants is often used to replace natural materials in the production of concrete. Using fly ash reduces CO2 emissions. In fact, for every ton of cement replaced with fly ash, nearly one ton of CO2 is kept from entering the atmosphere.
Its primary benefits come from its durability and workability though. Replacing a certain percentage of Portland cement with fly ash imparts workability, allowing the concrete to be placed and finished more easily. Fly ash also reduces the internal porosity of the hydrated concrete improving its durability. This enables ready mix producers to differentiate themselves by offering contractors a product that is both durable and workable. Fly ash also typically replaces some cement at a reduced cost, helping ready-mix concrete producers to increase margins.
However, there are concerns now about fly ash shortage. Due to economical conditions, many power plants have been converted to use natural gas instead of coal in their operations. At some of the plants still burning coal, environmental concerns have led to the use of powdered activated carbon (PAC) to scrub mercury from the resultant gases before release to the atmosphere. The PAC is collected with the fly ash, and it can have a large impact on the efficacy of concrete admixtures , thus limiting its usefulness. Although good, clean fly ash is still available in some areas, trucking fly ash to regions that are seeking to use it can be cost-prohibitive.
This is spurring ready-mix producers to explore alternatives to fly ash, including slag, limestone fines, metakaolin, and silica fume. Chemical admixtures also help to enable the use of these alternate pozzolans. Ultimately, it is important to look for long-term solutions to the fly ash shortage, and to evaluate alternatives to fly ash.
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