Using admixtures to get concrete to do what you want

An admixture is an ingredient used in concrete preparation, modifying the premixed concrete to enhance specific properties like concrete workability, durability and strength. The admixtures added to concrete depend on theparticular application.

Admixtures play different roles:

  • Accelerating concrete setting time
  • Reducing the segregation and water to cement ratio
  • Improving pumpability and accelerate the rate of strength development

You will need to specify to yourBrisbane concrete suppliers the areas you intend to apply the concrete so the right admixture is used.

What are the Different Admixtures?

 

We have seen that the choice of an admixture depends on the application area and its purpose. Now we will look at some of the different admixtures available on the market today.

1.  Water Reducing Admixtures

As you can tell from the name, water-reducing admixtures usually reduce water to create a concrete mixture. As a result, using a water-reducing admixture means you cut the amount of water you require to prepare the concrete. Consequently, using a water-reducing admixture means increased strength and workability along witheasier placement. Therefore, reducing the water to cement ratio in concrete preparation is an essential factor in making durable and high-quality concrete.

Water-reducing admixtures fall into three group’s namely, low, medium and high range. Determining the correct category for your application will depend on the percentage of water reduction desired.

2. Retarding Admixtures

Retarding admixtures slow the rate of concrete setting. By restricting the initial setting time, the concrete mixture stays in the fresh mix longer before hardening. The use of retarding admixtures is appropriate for various uses. The particular cases for retarding admixtures include:

  • Complex concrete placement or grouting
  • A specific architectural surface finish
  • Compensating for the accelerating effect of high temperature on the initial set
  • Prevention of cold joint formation in successive lifts

Organic and inorganic materials can aid the construction of the retarding admixtures.

3. Accelerating Admixtures

Accelerating admixtures are those admixtures when added to concrete, mortar or paste increase the rate of hydration of hydraulic cement and shorten the setting time while increasing the rate of early strength development.

Accelerating admixtures are more effective if applied under low temperature. Therefore, they serve best with superplasticisers where early age strength is required, mainly under lower temperatures.

4. Air-entraining admixtures

Air-entraining admixtures facilitate the development of microscopic air bubbles within the concrete during mixing. They add to thefreeze-thaw durability of concrete and increase its resistance to scaling caused by the deicing chemicals.

Generally, air-entraining admixtures are used in a cold-weather climatewhen the water within the concrete capillary poresfreeze and expand. If the concrete is critically saturated, the expansion of ice will exert pressure within the hardened concrete, causing cracking.

Usingair-entraining admixtures stops the formation of bubbles by stabilising the microscopic bubbles created when preparing concrete. Air-entraining admixtures reduce the surface tension of mixing water and promote the development of tiny bubbles. Stabilising the bubbles by forming a sturdy shell hinders the coalescence of bubbles and promotes the attraction to cement and aggregate particles.

Conclusion

Using admixtures imparts early strength in concrete. In addition, admixtures can improve the quality of concretewith proper application. Talk to approved concrete suppliers near you for the best concrete prices in Brisbane and the delivery of quality concrete suitable for your application.