Cement Substitutes

Fly Ash

Fly ash is a by-product of the combustion of coal and either collected from the bottom of the boiler or captured by filtration equipment in modern coal-fired power plants before it reaches the chimneys.

Initially, fly ash was either released into the atmosphere or disposed of in landfills. Then it was discovered that it can replace up to 50% of Portland cement in a concrete mix. Concrete with a high percentage of fly ash exhibits less bleeding and shrinkage than straight cement mix designs.  Fly ash can also significantly improve the workability of concrete.  

Benefits of Using Fly Ash - Initially, fly ash was disposed of in landfills until it was discovered that it can replace up to 50% of Portland cement in a concrete mix. Concrete with a high percentage of fly ash exhibits less bleeding and shrinkage than straight cement mix designs. 

 

Slag

Slag cement is an industrial by-product of an iron blast furnace. Slag diverted from the furnace is chilled and results into glassy granules that when grounded up into fine particles has desirable cementitious characteristics. 

The rule of thumb is that one ton of CO2 is released for every ton of Portland cement used in a concrete mixture. Substituting 50 percent slag can save between 165 and 374 pounds of CO2 per cubic yard of concrete.  Slag cement requires almost 90 percent less energy to produce than Portland cement so by using slag as a replacement in a mix design, the amount of embodied energy in a cubic yard of concrete is reduced by 30 to 48 percent. A ton of Portland cement requires about 1.6 tons of raw materials during mining operations. If 50 percent of slag cement is used instead of Portland cement, between 281 and 640 pounds of virgin material can be saved per cubic yard of concrete.

Slag is also known in the industry as having such benefits as improved workability, higher long-term compressive strength, consistent performance and easier finishability. The use of slag cement allows designers and architects to reduce the environmental footprint of concrete while ensuring improved performance and increased durability. 

Link to EPD

Benefits of Using Slag - The rule of thumb is that one ton of CO2 is released for every ton of Portland cement used in a concrete mixture. Substituting 50 percent slag can save between 165 and 374 pounds of CO2 per cubic yard of concrete.  Slag cement requires almost 90 percent less energy to produce than Portland cement so by using slag as a replacement in a mix design, the amount of embodied energy in a cubic yard of concrete is reduced by 30 to 48 percent. A ton of Portland cement requires about 1.6 tons of raw materials during mining operations. If 50 percent of slag cement is used instead of Portland cement, between 281 and 640 pounds of virgin material can be saved per cubic yard of concrete.