Admixtures are defined as any material added to a batch of concrete other than the required three ingredients: cement, water and aggregate. Admixtures alter the concrete’s quality, manageability, acceleration or retardation of setting time and other properties. They can help ensure a successful pour in both hot and cold temperatures. And admixtures can even help decrease cost and increase productivity in certain conditions.
Types of Admixtures
While there are many different products available, concrete admixtures break down into two types:
Chemical Admixtures: Modify the properties of finished concrete—such as waterproofing it—and protect wet concrete during mixing, transportation, placing and curing.
Mineral Admixtures: Can reduce concrete’s permeability and increase its strength. They can be used with Portland cement or with blended cement individually, or in combinations, depending on the desired concrete properties.
Anti-Hydro International has helped harden concrete and masonry structures all over the world, from the Hearst Tower in New York to the Sears Tower in Chicago. Its Anti-Hydro® admixture is a combination of organic and inorganic chemicals that react with Portland cement to produce better hydration. And better hydration reduces water requirements, bleed water and shrinkage. The result is a denser cement paste that cures harder.
But Anti-Hydro® doesn’t only harden concrete. It waterproofs it, too. It can be used when pouring a concrete floor to make it totally waterproof. Plus, Anti-Hydro® is relatively affordable, making it a common-sense choice when considering certain concrete projects. Simply put, Anti-Hydro® can both strengthen and waterproof finished concrete, a bonus for, say, basement and garage floors.
Concrete exposed to freeze-thaw cycles can benefit by adding air-entraining admixtures. Entrained air improves concrete’s resistance to damage caused by freezing and thawing, as well as to deicing chemicals. Grace Construction Products has a line of air-entrainment products that work well in the often-tumultuous weather patterns of the Intermountain West.
Water-reducing admixtures do just what the name implies: reduce the amount of water needed to mix concrete. Using these admixtures increases concrete’s workability at the same water-cement ratio. And that makes for a product that’s easier to pour and stronger when cured. In fact, water reducers have been proven to increase compressive and flexural strengths in concrete. Using water reducers can also retard the set time of concrete, making it a smart choice in hot-weather pours.
Concrete poured in near-freezing conditions can benefit from an accelerator admixture. These speed the setting time and, thus, the curing time begins sooner. Using accelerators in conjunction with good curing procedures protects the concrete from freezing. And it’s been shown that concrete is actually stronger overall when accelerators have been used during a pour.
From adding accelerators to speed up the setting time in cold temperatures to adding water reducers to retard setting in hot weather, admixtures make concrete easier to work with and can increase its strength.