Through a partnership with Nova Scotia Power Inc., Shaw Resources has, over the last 20 years, supplied the Atlantic Canada Ready-Mix concrete Industry with high quality class "F" fly ash. Interuption in local fly ash required imports of fly ash into the region.
Fly ash is a fine, glassy powder recovered from the gases of burning coal during the production of electricity. When mixed with lime and water it forms a cementitious compound with properties very similar to those of Portland cement. Because of this similarity, fly ash can be used to replace a portion of cement in the concrete, providing some distinct quality advantages:
More workable concrete with enhanced flowability. Concrete made with increasing amounts of fly ash experiences higher slump with no change in water content. Less water results in reduced concrete shrinkage and cracking. fly ash's lubricating properties allow pump effort to be reduced by up to 30%. With the lower pump pressure, the need to add water on site is reduced. This ensures high quality concrete is delivered to the form.
The concrete is denser resulting in a tighter, smoother surface with less bleeding. fly ash concrete offers a distinct architectural benefit with improved textural consistency and sharper detail.
Typically, fly ash gains strength more slowly in the first few days, although with special considerations early design strengths can be achieved. When 28 day strengths are equal, the fly ash blend concrete will gain subsequent strength faster than the 100% Portland cement mix, and achieve higher ultimate strength.
The addition of fly ash produces a denser, less permeable concrete that reduces infiltration of damaging chemicals, such as salt and sulphate, thereby improving durability. Furthermore, fly ash's unique chemical properties help eliminate alkali aggregate reaction. Fly ash actually uses the available alkalis to produce increased strengths in the concrete, thereby removing the key link in the destructive alkali aggregate reaction.
Once simply blown into the air as a pollutant, fly ash is now a valuable resource used in the production of quality concrete. Furthermore, as a controlled by-product of electrical generation, fly ash is produced without any additional energy consumption. The production process for Portland cement, on the other hand, requires massive amounts of energy. By replacing a portion of the cement used in concrete with fly ash, substantial levels of energy consumption are avoided.
