The basic ingredient in concrete is portland cement, which is mixed with water, and aggregates (sand, gravel, limestone).
Admixtures are natural or manufactured chemicals that are added to concrete before or during mixing. The most often used chemical admixtures are air-entraining admixtures, water reducers, retarders and accelerators:
Common Concrete Admixtures and Their Benefits
Admixtures are used in concrete for a number of reasons. Because admixtures modify the chemical makeup of concrete, it allows contractors the flexibility and workability to pour concrete to meet the project specifications, achieve strength requirements, or work in adverse weather conditions.
Water Reducing Admixtures (WRA)
Water Reducing Admixtures are used for two different reasons. (1) To lower water content in fresh concrete and to increase its strength. (The more water added to concrete will weaken the strength of the concrete once it has cured) (2) To obtain a higher slump without adding additional water and increasing workability.
High Range Water Reducers (Superplasticizers)
Plasticizers are used to increase strength and reduce permeability of concrete by reducing the water content in the mix. Plasticizers are useful in high-strength mixes because they increase the workability of the concrete. This admixture also increases the slump pumpability without adding water.
Small, uniform air bubbles are created with air-entraining admixtures. A major benefit of using air-entrainment admixtures is that they increase the durability of the hardened concrete especially in climates subject to freeze and thaw cycles. Air-entrainment also increases the workability of the concrete.
Retarding admixtures are used when it is necessary to slow the concrete setting time. Retarders are often used in hot weather conditions to counter the rapid setting caused by high temperatures. It allows for more time placing and finishing.
When you need concrete to set faster, accelerators are used. By speeding up the setting time, the curing process can start sooner and the concrete is ready earlier.
This is especially helpful during the winter months, since lower temperatures can slow the setting time. Whenever the curing process needs to be sped up, contractors can introduce accelerators to the mixture, not just during cold weather conditions.
Other Types of Concrete Admixtures
There are many types of admixtures on the market that can change and strengthen
concrete. For example, admixtures can be used to provide the following results:
- Protect Against Freeze Thaw Cycles Improve Durability
- Mid-Range water reducers
- High Strength Concrete
- Corrosion Protection
- Strength Enhancement
- Crack Control (shrinkage reduction)
- Finish Enhancement
- Fly-Ash (Making Concrete Stronger, More Durable, and Easier to Work With)
- Silica Fume (Early Strength and Reduced Permeability)
- Produce a fluid backfill, which flows easily and is self-leveling
Contact Liberty Ready Mix
For more information about admixtures or concrete services, contact us at 515-278-4807 or [email protected]. Our concrete experts can help you decide what you need for construction job. We’ve been pouring concrete in the Des Moines area since 2004 and are ready to work with you!