In Concrete

TrowelphotoThe SEFA Group is committed to providing the highest quality product to its customers while giving unparalleled technical service. Our technical marketing staff is comprised of ACI certified concrete technicians and is involved in national and local concrete industry associations. We work in cooperative partnerships with all of our customers to maximize the beneficial utilization of coal combustion products in an environmentally friendly way.

The SEFA Group’s marketing philosophies center around the belief that the optimum amount of fly ash should be used in every yard of concrete produced. This can only be accomplished by developing close working relationships with our customers and utilities.

When designed properly, fly ash greatly improves both theplastic and the hardened characteristics of Portland cement concrete. The spherical nature of fly ash particles increases workability, even while using lower quantities of strength-reducing water than would be used in plain Portland cement concrete. Fly ash is also well graded, with a microscopic gradation that actually provides a buoyancy effect for the aggregates and lends cohesion to the mix, further improving workability and reducing segregation. Acting like tiny ball bearings within the mix, fly ash can aid in designing concrete suited to a wide variety of applications.

Because it has lower specific gravity than Portland cement, a pound of fly ash has approximately one third greater volume of fines than a pound of Portland cement. This enhances the finishability of concrete flatwork, and reduces bleeding because its gradation blocks water channels through the concrete.

The higher volume of fines found in fly ash also reduces segregation in the concrete mix, because fines hold the mix together. The increased workability and reduced segregation also makes concrete containing fly ash substantially more pumpable.

Adding fly ash to the concrete mix as a replacement for a portion of the Portland cement reduces the heat of hydration in the mix. This heat is a byproduct of the chemical reaction which takes place when water is added to Portland cement, contributing to “quick sets” in hot weather, which creates destructive thermal stresses in mass concrete structures like dams and large foundations. By using mix designs that include fly ash, engineers can better control the internal temperature rise created by the hydration of the cement.