Concrete Admixtures in Decorative Concrete Work
How-to tips from the pros that save time and money. Admixtures are an important part of concrete mix design. They are those materials other than cement, water, and aggregate, and they are put into the mix just before or during the mixture to help it meet the design and finish needs of the installation.
by Cindy Grawl
Dallas, admixtures can be used in two ways: to improve concrete's ultimate durability and strength and to modify its behavior to make it easier to work with.
They can reduce the cost of concrete work, modify the qualities of the hardened concrete, and assure the quality of the concrete during the mix, transport, pour and set, while they help to modify setting times in response to weather or workability needs and make the concrete stronger and more durable.
According to the Portland Cement Association, Skokie, Illinois, the effectiveness of an admixture depends on the type and amount of cement used, water content, mixing time, slump, and the temperatures of concrete and air: Admixtures include the following broad categories:
- air entrainment chemicals that trap air in the mix, allowing it to withstand freeze-thaw cycles by giving water a place to go;
- water reducers to increase the slump and enhance the concrete's placeability without adding water and thus reducing the strength and permeability of the concrete; and
- accelerators and reducers to help modify set times and thus allow more time to do design work or keep the job on track with time constraints.
- other admixtures, says the PCA, can be used to color the concrete, inhibit corrosion, reduce shrinkage, enhance workability, damp proof and bond the concrete.
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