Six Types of Concrete Admixtures and When to Use Them

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Concrete is one of the essential materials in the construction industry. It has near-universal applications at worksites and is known for its strength and durability. However, even this staple material can be further modified to overcome some of its disadvantages or to suit the specific needs of your next construction project better. Here are some useful concrete admixtures and their applications:

Corrosion inhibitors

When your construction site needs a build that’s especially resistant to tension, reinforced concrete is often the best solution. But even after positioning and securing your steel rods with rebar ties and Sika epoxy products, the long-term durability of the reinforced concrete can still be compromised by corrosion through carbonation or chloride ingress. Corrosion-inhibiting admixtures use a substance such as calcium nitrite to prevent this process and can yield a service life of 30 to 40 years with minimal maintenance.

Air entrainment

Air bubbles forming in concrete might not yield a desirable look – and if appearance matters, you should be taking measures to prevent surface voids from marring the finish. But in the right conditions, air bubbles in fresh concrete make it more workable and resistant to freeze-thaw cycles. Air-entraining admixtures contain substances such as natural resins or sulfonated compounds, which get the balance just right by stabilizing air in tiny bubbles under 1 mm in size to retain the material’s overall strength.

Accelerating

Frequently used in winter, accelerating admixtures based on calcium formate or thiocyanates can make concrete set faster by 1-2 hours or more. The specific effects may vary based on type and application; you can speed up the setting time, rate of hardening, or early strength gain. This makes such admixtures especially useful when working in cold weather conditions, or on emergency repair jobs.

Retarding

Retarders such as gypsum or calcium sulfate delay the setting time of concrete without adversely impacting its long-term mechanical qualities; the resulting mix can even have better durability. You’ll appreciate this effect whenever you have to transport your concrete over longer distances, do extensive hand-finishing work, or add texture. Retarding admixtures also allow you to pour concrete at higher temperatures, making them a natural choice for working in hot climates.

Water-reducing

Adding chemicals such as polycarboxylic acid or salts of lignosulfonate acid will create a mixture that reduces the amount of water needed to achieve the desired consistency in your concrete. This increases the density and quality of your cement paste, which improves its strength and weather resistance while lowering permeability and maintaining the workable nature of the material. These water-reducing admixtures are especially useful when using specific aggregates in your concrete, and can also save costs by up to 10%.

Sometimes, admixtures called super-plasticizers, usually made from formaldehyde derivatives, are considered in this category. These result in very high-strength concrete, but must be worked with quickly; the high-slump effect can be lost after 30-60 minutes.

Shrinkage-reducing

Cement mix

When your work calls for strengthening or repairing existing structures, any risk of cracking or shrinkage must be avoided. Shrinkage-reducing admixtures use ethylene glycol derivatives to reduce the capillarity of the material. This prevents water evaporation from having the usual shrinkage effect you may notice in untreated mixtures.

On the surface, concrete structures might not look very different. But these small changes you could make to the composition can have significant effects on your work.

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