It mixes with flue gases that result when powdered coal is used to produce electric power. Since the oil crisis of the 1970s, the use of coal has increased. In 1992, 460 million metric tons of coal ash were produced worldwide. About 10 percent of this was produced as fly ash in the United States. In 1996, more than 7 million metric tons were used in concrete in the U.S. Economically, it makes sense to use as much of this low-cost ash as possible, especially if it can be used in concrete as a substitute for cement.

Here are a few benefits of Fly Ash:

1. Pocket and Planet Friendly
Because fly ash is initially a waste byproduct of coal-burning operations, FA-concrete is a cost-effective alternative to concrete made with only Portland cement as the binder. That alone is enough to pique the interest of concrete producers and contractors. Its versatility as a construction material makes it even more attractive. Because it has greater flowability, contractors find it reduces time at the job site. In addition, FA-concrete has shown improved strength and durability, which means that buildings, bridges, roads, and sewers have the potential for longer life.

Fly ash's "green" qualities provide yet another enticement. Cement production requires heat, which uses energy and releases copious amounts of carbon dioxide, a greenhouse gas, into the atmosphere. In contrast, fly ash is a plentiful waste product. The amount of fly ash generated annually is enormous, with the United States alone producing more than 60 million metric tons every year. By using fly ash as a construction material, contractors are recycling a waste product that would otherwise find its way into a landfill, and reducing the demand for cement.

2. Provides increased Strength for a longer time
The advantages of concrete made with fly ash (FA-concrete) grow from its physical and chemical characteristics. Fly ash particles are small, smooth, and round in shape, attributes that allow them to move readily around the aggregate to create an FA-concrete mixture with fewer voids. On the chemical side, fly ash makes a critical contribution by reacting with the lime (calcium hydroxide) that results when cement mixes with water. The fly ash reacts with the lime to make the same binder, called calcium silicate hydrate, that is created when cement and water mix. In other words, hydrated cement yields the concrete binder along with lime, and fly ash uses that lime to make more binder. Fly ash, therefore, can be used to replace at least some of the cement in a concrete mixture.

3. Protective Qualities
FA-concrete is also less susceptible to many of the common environmental stressors that take a toll on traditional concrete. Decreased permeability is the primary reason. FA-concrete can fend off surface assaults and sustain considerably less damage because it has fewer voids and consequently blocks deleterious substances from freely penetrating the concrete. A major concrete corrosive is salt, and particularly the chloride it contains. Salt can also have negative effects on the steel bars and latticework often imbedded in concrete as reinforcement. Both seawater vapor in coastal areas and deicing salt in colder regions can quickly ravage concrete.

The smooth, spherical, fly ash particles can maneuver around aggregate and fill voids without as much help from water. In addition, when FA-concrete is used in the proper mix proportions, microscopic voids remain. These tiny air pockets serve as safe storage vessels for freezing water in which it expand safely without compromising the concrete's integrity.

4. Quality Finished Product
Strength and durability are vital to a quality finished product, and so is appearance. In this aspect, FA-concrete again improves upon traditional concrete.

The augmented flowability of FA-concrete helps ensure that the concrete will more completely fill the formwork used to contain it in its plastic state until it sets or hardens. It will spread from top to bottom and to all edges of the formwork with less work, with an even consistency, and with fewer voids.

In addition, the appearance of concrete can be affected by excess lime. As mentioned earlier, Portland cement reacts with water to generate lime. As the lime leaches onto the surface of the concrete and evaporates, it leaves behind a milk-colored, powdery residue. On vertical and sloped concrete structures, streaks may occur.
In summary, fly ash has a wide range of attributes. It saves time and money, provides strength and durability, yields improved concrete flow and workability, and helps produce high-quality finished products. It is an excellent building and structural material.

Construction Information Initiative by Excellex Solution - http://www.excellexsolutions.com/