Published on 6/21/2018
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What are chemical admixtures?
Chemical admixtures are added to a concrete mix design during the batching process
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What are chemical admixtures?
Technically speaking Chemical admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement and are added to the concrete at the time of batching and mixing your concrete mix design at the ready mix concrete plant, before it is delivered to you. These so called admixtures can either speed up or slow down the time it takes for your concrete to set and harden. They can make your fresh concrete easier to work, place and finish, or they can increase or decrease the flowability of your concrete. By adding chemical admixtures at the batch plant concrete companies ensure your concrete mix design is fit for purpose and suitable for the temperature you are going to pour at. As an example many concrete plants add some accelerator to their mix designs during winter and retarder during the summer months, in order to either delay or prolong the setting time of your concrete accordingly.
However chemical admixtures are not simply added to concrete mix designs for your benefit, wherever possible they are included by concrete plants to reduce their cost of production during the batching phase. As an example water reducing chemical admixtures reduce the plants reliance on water, a costly ingredient when it comes to mixing concrete. The less water, the lower the cost of production.
Lets have a closer look at some of the most commonly used chemical admixtures:
- Accelerators are added to your mix design to speed up the hydration (hardening) of the concrete. Most accelerators contain some form of chloride, however the use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries, where nitrates may be favored. As outlined above, accelerating admixtures are especially useful for modifying the properties of concrete in cold weather.
- Retarders slow the hydration of concrete and are used in large or difficult pours where partial setting before the pour is complete is undesirable. As outlined above they are most useful during the hot summer months when concretor's require additional time to place your concrete before it hardens.
- Air entraing agents add and entrain tiny air bubbles in the concrete, which reduces damage during freeze-thaw cycles, increasing durability. However, entrained air entails a trade off with strength, as each 1% of air may decrease compressive strength by 5%.
- Water reducing agents such as plasticizers increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. A typical plasticizer is lignosulfonate. Plasticizers can be used to reduce the water content of a concrete while maintaining workability and are sometimes called water-reducers due to this use. Such treatment improves its strength and durability characteristics. Superplasticizers (also called high-range water-reducers) are a class of plasticizers that have fewer deleterious effects and can be used to increase workability more than is practical with traditional plasticizers.
- Pigments can be used to change the color of concrete, for aesthetics, and are commonly used in driveways and outdoor living areas
- Corrosion ihibitors are used to minimize the corrosion of steel and steel bars in concrete, which is useful in situations where concrete is poured in locations exposed to water or close to salt water
- Bonding agents are used to create a bond between old and new concrete (typically a type of polymer) with wide temperature tolerance and corrosion resistance.
- Pumping admixtures improve the pumpability of concrete by thickening the cement paste and reduce separation and bleeding.
So don't forget to let your concrete plant know the intricate details surrounding your next concrete pour. Is it to be poured in hot or cold weather, does it need to be pumped, and how many people do you have to finish the concrete. And how far away from the plant is your concrete pour. If it is a long drive you may need to add some retarder to your concrete mix design to ensure it doesn't start setting before you've even started placing it!
If you require further information on chemical admixtures don't hesitate to contact the leading chemical admixture suppliers in your region. The large manufacturers such as BASF, Sika, Mapei or Grace Chemicals often have teams of customer service representatives, chemists and sales reps only too willing to offer you the advice you need prior to pouring.
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Tags: accelerator admixture admixtures air entrainment chemicals cold weather concrete broker concreter concreting concretor hot weather plasticizers retarder water reducers
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