What is Rapid Set Concrete?

Find out how rapid set concrete differs from regular concrete and when it is the most appropriate to use. In this article we outlines some of the differences between standard and rapid set concrete, when it’s appropriate to use, and some tips to help get you started!

Rapid set concrete is a fast-curing mixture of sand, cement, and special additives designed for projects where a strong and quick set is needed. It provides high durability and low shrinkage in an easy-to-use pre-mixed format. Its ideal use is to set fence posts, deck footings, and other small projects

The article below outlines some of the differences between standard and rapid set concrete, when it’s appropriate to use, and some tips to help get you started!

How does Rapid Set Concrete Work?

All types of concrete get strength from a chemical reaction called “curing” that occurs between the cement and water. Curing is different from concrete “setting” or “hardening.” For example, a concrete walkway can set and be walked on in within 24 hours, but it can take about a month to reach its maximum cured strength.

The curing process is an exothermic reaction, which is a chemical reaction that produces heat. If you’ve ever noticed that concrete is getting warm while it is hardening, that is the curing reaction going on inside.

Rapid set concrete works exactly the same as regular concrete. However, its cement ingredient ratios are slightly different that regular concrete and contain some additional additives which speed up the reaction and set much faster. However, it still takes about 28 days to fully cure.

What’s the Difference Between Standard and Rapid Set Concrete?

Rapid set and regular concrete are essentially the same product as they’re both made of sand, cement, and aggregate mixed with water. However, a different ratio of these ingredients, as well as some additional ingredients, is what makes rapid set concrete set faster and provide it with some different attributes as outlined below:

AttributeRapid SetRegular
Set Time1 hour24-48 hours
Full Cure28 days28 days
ShrinkageLowVery High
CrackingLowVery High
DurabilityHighLow

What Type of Cement Should I Use?

While you can use either rapid-setting or regular concrete for most applications, some projects are better suited for one product or the other.

The biggest consideration is how time-sensitive the project is. For example, for a project involving setting fence posts, using rapid set concrete can cut an eight-hour project down to 1-2 hours. However, for a large patio it would be best to use a slow setting regular concrete as you’ll need time to smooth it out. 

Another important factor is cost. You are paying for convenience with rapid set concrete as it is more expensive. While rapid-setting concrete is definitely convenient for a quick fence repair, a lower-cost standard concrete might be best for a larger scale project.

Regular concrete is better in hot weather. No matter what type of concrete you’re using, it will set faster in hot weather. If you’re using a fast-setting concrete and it’s hot out, you’ll have to work really fast or risk the concrete hardening too quickly. 

Rapid set concrete is not designed for any structural or load-bearing application. It is also not recommended for use with aluminum poles and posts unless they are properly primed and sealed.

What is the Best Use for Rapid Set Concrete?

Rapid set concrete in best used for:

  • Setting posts and poles – i.e. fences, mailboxes, deck footings
  • Small walkways and footpaths
  • Stairs and curbs
  • Minor repairs and small projects

Tips for Working with Rapid Set Concrete

Rapid set concrete is very easy to use, but there are a few tips and tricks to achieving success when working with it.

  • Check to see if the bag has hardened. If the bag is exposed to any humidity, it can begin to harden as it will be difficult to use.
  • Have all of your tools ready to go before you start mixing. This type of concrete sets very quickly, so ensure you’re fully ready to start working before you mix.
  • Break up any large clumps of mix before adding water. This will make the mixing process a lot easier! 
  • Always use cold water. Hot water will make the mix harden more quickly, so always use cool or cold water.
  • Add water a little bit at a time. The final consistency of the concrete should be a thick “sludge”. Adding too much water will create a “soupy” product that will not work properly. If you do add too much water, just add more mix until you reach the correct consistency.
  • Throw the mix out if it starts to set. Using concrete that is starting to harden will not work properly. Even if a small amount is needed to finish the job, always mix fresh concrete to complete the project. 
  • Wear gloves, long sleeve shirt, and a mask. Concrete contains lime which can be harmful to exposed skin. It is also a very fine powder that can be breathed in when pouring and can cause damage to the lungs. Protect yourself by wearing the proper protective equipment.