A fast setting concrete mix has the following ingredients included to speed up the set time:
If you need a concrete mix that will set up fast, plan to use at least a 4000 psi mix. This type of mix has more cement than most of the regular concrete mix designs.
More cement in the mix means more heat of hydration as the concrete sets up, speeding up the curing process.
Using warm water will also help speed up the set times, especially if you're pouring concrete in cold temperatures.
A water reducing admixture will help lower the water - cement ratio in the mix and still give you a workable mix to place your concrete. This helps with set times and improves the strength versus just using water.
Adding an accelerating admixture to the concrete will decrease set times by 10 - 30% in a lot of cases.
In the video above I'm using a 4000 psi concrete mix to pour this concrete floor. The concrete had 115 degree F water, 20oz of water reducer per yard of concrete, and we used two 50lb bags of calcium chloride in each truck load.
The outside temps were 32 degrees when we started pouring the floor. You can see the steam coming off the concrete as we get it spread out.
We started pouring at approximately 7 AM and we finished power troweling at 2 PM. The outside temperature never got above 41 degrees.
The most important ingredients for fast setting concrete are warm/hot water in the mix and using an accelerator like calcium chloride.
These two ingredients will speed up the set times of any concrete mix, whether it's ready-mix or a bag mix like Quikrete or Sakrete.
Using hot water to mix concrete will help speed up the set time by speeding up heat of hydration.
Heat of hydration is a chemical reaction that takes place when cement and water get mixed together.
If the water is COLD, there is less heat that develops and the concrete sets up slower.
If the mix water is HOT, there is more heat that develops, which makes the concrete set up much faster.
Outside, ambient air temperatures as well as mix water temperatures HOT or COLD play a very important role in how FAST of SLOW concrete sets up. Hot = Fast and Cold = Slow (in most cases)
The best and easiest way to make concrete set up faster is to use hot water to mix it with. If you use warm or really hot water, you'll see an increase in the set time.
The 2nd best way is to use an accelerator like flake calcium chloride. You can use this instead of hot water if hot water isn't available.
Most local hardware stores carry calcium chloride flakes/pellets in either 25lb or 50lb bags.
If you're using an 80lb bag mix, only start using about 2 Cups of calcium chloride flakes to see just how fast it starts setting up and adjust up or down from there.
The fastest drying cement mix and concrete mix is the brand called RAPID SET from CTS CEMENT.
They have a rapid setting cement mix called CEMENT ALL. This cement mix sets up in only a few minutes and cures hard enough to walk on in 20 - 30 minutes. It comes in a blue bag or blue box at HD.
CTS also has a rapid setting concrete mix called, you guessed it, RAPID SET CONCRETE MIX. This also sets up in only minutes and has 3/8" stone aggregate in it. It comes in a green bag and you can get it at HD.
I personally use both the Rapid Set Concrete Mix and Cement All for doing a lot of repairs and small concrete projects. Just beware, they both set up very fast.
They actually have a "set slowing admixture pack" to slow the set and give you more working time if you think you'll need it.
Quikrete has a RED bag called "Fast Setting Concrete MIx". They claim is hardens in 20 - 40 minutes and can be walked on in 2 hours.
You can use this 50lb quick drying bag mix for steps, sidewalks, slabs, and for setting fence posts or a mailbox post.
This concrete mix can be used to set posts without mixing. Just dump the dry ingredients around the post and sprinkle with water for it to harden.
This mix will reach 4000 psi in 28 days.
Quikrete also has a "High Early Strength" concrete mix called Quikrete 5000. It's not a rapid setting mix but does set up faster than their regular bag mixes. (I've used it for countertops)
This can be used for most anything; footings, slabs, walkways and floors. Just add some accelerator if you need it to cure faster. It'll reach 5000 psi in 28 days.
You can purchase either of these concrete mixes at Home Depot.
You guessed it, Sakrete has a 50lb bag called "Fast Setting Concrete MIx". (I see a trend here)
It'll harden in 30 minutes and you can walk on it in 6 hours & drive on it in 48 hours.
This can be used for setting posts, slabs, walkways, patios, curbs, and ramps.
It'll reach 4000 psi in 28 days. You can get this at Lowe's and most local hardware stores.
A fast setting additive for concrete mixes will greatly increase the set time and curing times of your concrete.
Quikrete has a 1.5 lb Concrete mix accelerator that comes in a green and black box. You can add 1 or 2 of these to a 60 or 80 lb bag mix to speed up the set time. Purchase this right at Home Depot.
Sakrete has a 1 gallon bottle of "Cement Mix Accelerator" you can add to their concrete mix to speed up set time.
How much you add and how fast they increase set times will also depend on how cold it is outside and how cold or warm the water is you use to mix with.
Another additive that'll increase set times is flake calcium chloride. Just mix about a cup or two in the mixing water before adding your bag mix concrete. Then mix the concrete and use at as you normally would. Just move a little faster:)
We use a 50 lb bag of calcium per 5 yards of concrete when we pour concrete floors. This increases set times a lot in colder weather. Add hot water to the mix and you have a rapid setting concrete mix.
Depending on which fast setting bag mix you choose, you'll have to add the correct amount of water to achieve the best results.
Each brand is very similar when it comes to adding mix water, here is the breakdown:
All these bag mixes have the mixing instructions right on the back of the bag.
The answer to that question is no, all these bag mixes are designed to reach 4000 psi at 28 days.
If you add more mixing water than the bags suggest then you could weaken the concrete. But just because it sets up faster doesn't mean it'll be a weaker mix.
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