Today’s construction and tomorrow’s environment can benefit greatly by using concrete designed with fly ash. Fly ash can transform ordinary concrete into “high performance concrete”. Fly ash has greater long-term durability and , therefore, concrete structures built with fly ash concrete will last longer.
Using fly ash as a resource, rather than disposing of it in landfills like a waste material, reduces the amount of other natural resources used in construction today. And since structures built with fly ash concrete will last longer, fewer resources will be depleted in the future. Using fly ash in this way exemplifies sustainable development.
Using fly ash in concrete is good for the environment in some obvious – and some not so obvious ways. Obviously, fly ash is an industrial by-product. If fly ash were not recycled, it would have to be disposed of in landfills.
Also, using fly ash in concrete means less cement is needed. The production of cement is energy intensive and releases large quantities of carbon dioxide (CO2) into the atmosphere. For every ton of cement produced, approximately one ton of CO2 is released into the atmosphere.
Fortunately, when fly ash is used in concrete, less cement is used. The energy that would have been required to produce that cement is saved. And for every ton of fly ash used in concrete, there is approximately one less ton of CO2 released into the atmosphere.
When concrete hardens, about 25% of the cement forms a by-product called calcium hydroxide. This compound contributes nothing to the strength of the concrete, it dissolves in water and may leach out of the concrete. Or worse, it could form combinations with other materials that could seep into the concrete and cause premature deterioration.
Fortunately, fly ash reacts with this calcium hydroxide, and chemically combines with it to form stable cemetious bonds. This pozzolanic reaction increases the durability of the concrete in two ways. First, since the fly ash chemically combines with the calcium hydroxide, it is tied-up and con not react with other materials that may seep into the concrete.
Also, as these extra bonds develop between the fly ash and the calcium hydroxide in the cementious paste matrix, the permeability of the concrete is reduced. Less water or other impurities can penetrate into the concrete to corrode reinforcing steel or otherwise damage the concrete.
Fly ash closely resembles the volcanic ashes used in the production of the earliest known hydraulic cements some 20,000 years ago, near the small Italian town of Pozzuoli (which later gave its name to our modern day pozzolans). The volcanic ashes were used in a number of well known Roman structures including the Coliseum and aqueducts which survive to date.
In addition to using in modern concrete, some other examples of how fly ash can be beneficially used in sustainable ways are in asphalt and in flowable fill.
Architects and engineers recognize fly ash concrete as a more durable and a more sustainable building material. Some of the many programs that have been created to encourage sustainable development and reward the beneficial reuse of environmentally friendly materials like fly ash include:
- The leadership in Energy and Environmental Design (LEED)
- Building for Environmental and Economic Sustainability (BEES)
- U.S. DOE Zero Energy Buildings
- U.S. EPA Whole Building Guide
- “Energy Star” label for buildings
- U.S. Green Building Council (USGBC)
Sustainable Development – building for the present without compromising the quality of life of future generations.