What are Admixtures and Why are They Added to Concrete
Summary
Admixtures are used in concrete to enhance the performance of the mix in various ways. Generally added before or during the mixing process, admixtures can increase the strength the mix, accelerate or slow down the curing process among other benefits.
While workability, strength, and water tightness can be achieved by the use of adequate aggregate, Portland cement and by maintaining a good water-cement ratio, admixtures can often provide an added advantage. This is particularly true in extreme climates, or when the concrete is exposed to increased wear.
New types of admixtures are being experimented with today. Some provide environmental benefits and can help reduce pollution by reducing the need for Portland cement production. Other types of aggregates are being experimented with to allow concrete to self-heal or absorb pollution.
As these aggregates begin to gain more acceptance, they are likely to play a larger role in the construction of buildings, roads, and other types of concrete structures in the future.
Ingredients added to concrete, other than Portland cement, aggregates, or water, are referred to as admixtures. While not required, they are sometimes used selectively to improve the concrete mix.
Admixtures are used in concrete to alter its properties in various ways. Some common uses include improving workability, increasing or decreasing cure time, and increasing concrete strength. Admixtures can also be used for aesthetic reasons, such as to change the color of the cement.
Whenever possible, concrete workability, water tightness, and strength should be achieved by selecting suitable types of aggregate, Portland cement, and maintaining a good water-cement ratio.
When this is not possible or special circumstances exist, such as freezing weather, hot temperatures, increase wear, or prolonged exposure to deicing salts or other chemicals, admixtures can be helpful.
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