If you want to change the properties of concrete, you need to use admixtures. That’s because concrete is composed of cement, water and aggregate, with admixtures typically added immediately before or during the mixing process.

There are lots of additives for cement, for example, there are admixtures for high-strength concrete, faster-setting concrete, water-repellent concrete, corrosion-resistant concrete and so on. You can increase its strength, durability or workability. You can also reduce or eliminate cracking due to water penetration, delay or accelerate the setting time, and prevent corrosion of reinforced steel. In short, admixtures give you more control over the concrete.

Most construction projects use a liquid admixture for concrete, which is added either before or during the mixing process, but they also come in powder form, such as those that repel water. The most popular admixtures for cement are accelerators and water retardants.

Accelerator Admixtures For Cement

Accelerators are one of the most commonly used admixtures for cement. That’s because accelerators make the concrete set faster whilst not compromising its strength. They are often used during the winter months when the cold temperatures slow down the curing and setting process of concrete.

They are also used when the forms need to be removed early because of a finishing process, such as stamping. Another frequent use is to make cast-in-place concrete benchtops for kitchens because you can’t wait two weeks for the concrete to set!

You might also have seen renovation shows where the builders or renovators bring in large heaters to make the concrete set faster – accelerators are a much cheaper and faster option. Another benefit is that when you reduce the set time of poured concrete, you also reduce the labour costs, so it’s a win-win situation!

Types of Waterproofing Admixtures For Concrete

Another common admixture used in concrete is one that reduces the porosity and water penetration of concrete blocks used in masonry construction. There are three different types of waterproofing admixtures for concrete:

  • Hydrophobic admixtures repel water by reducing the wetting capacity of the cement.
  • Pore-blocking admixtures fill any microscopic holes in the concrete to prevent water intrusion.
  • Crystalline admixtures are absorbed into the concrete to form a chemical barrier that prevents water entry into the concrete.

Waterproofing admixtures are frequently used in underground construction, water treatment plants, dams and reservoirs, marine structures, and so on.

We’ve already looked at accelerators and water repellents, so let’s check out the other main admixtures most likely to be used in building and construction.

Additives – Types and Functions

  • Retarders: Retarding admixtures used in concrete delay the setting times in high-temperature environments. They are invaluable when a longer working time is required for levelling, finishing or consolidating the freshly poured concrete.
  • Air Entrainers: These additives prevent cracking in cold climates during a freeze-thaw cycle. Essentially, these admixtures create microscopic air bubbles within the mixture, allowing trapped water to expand when it freezes. This prevents cracking and increases the workability and durability of the concrete.
  • Water Reducers: Also called plasticisers, these admixtures are designed to reduce the water required to mix concrete whilst maintaining its workability. There are high-range, mid-range and normal-range water reducers. High-range are the best admixtures for high strength concrete, mid-range are suitable for applications that need higher workability, and normal-range are a cost-effective option used when there are no stringent requirements.
  • Shrinkage Reducers: These additives reduce the potential for cracking as the concrete cures and shrinks. They are an excellent admixture for cement used in large slabs, bridge decks, airport runways, multi-story car parks, high-rise buildings, and so on.
  • Corrosion Inhibitors: These admixtures are used in concrete to reduce the potential for corrosion of embedded steel rebar and extend the life of the concrete. They are popular in coastal areas, cold, wet or humid climates, industrial areas, and underground structures.
  • Alkali-Silica Reactivity (ASR) Inhibitors: Otherwise known as concrete cancer, ASR is a reaction between highly alkaline cement and aggregate that contains silica, in the presence of moisture. This additive prevents severe cracking, loss of strength and failure of the concrete. It’s used in high-alkali concrete.
  • Viscosity & Rheology Modifiers: These admixtures increase the viscosity of concrete, so it’s easier to handle and pour. It’s used for precast elements, such as beams, slabs and wall panels, elevators and stairwells, dams, reinforced concrete pipes, and marine structures.
  • Silica Fume: A popular admixture used in concrete to increase its strength and durability. Used to create high-performance concrete for high-rise buildings, multi-story car parks, dams, and nuclear waste storage facilities. One of the best admixtures for high-strength concrete.

For help selecting the best admixtures for your next project, contact us at 8426 0352 or send an email.