How long does concrete take to dry? 4 Factors which affect it

Engineer Moid | April 8, 2020 | Concrete Notes | No Comments

How long does concrete take to dry?

The is the commonly asked question was how long does concrete take to dry? In the schedule of most construction projects, concrete drying time is a major factor. Drying is critical when the flooring system will be installed over the concrete slab and if the slab is not dry when the floor is installed then the floor will be damaged by excess moisture.

For the maximum strength, concrete takes 28 days to fully cure. It will be hard enough to walk after 24 or 48 hours and if the slap is under conditions you will need to allow 28 days of drying time for each inch of concrete thickness.

Concrete never stops curing because continual hardening occurs because cement particles react with the water. Cement is in contact with the moisture & minuscule bubbles and it will continue to for bonds. The concrete always hardening little more each day and also the cement bonds with water molecules and gets harder.

After 24 to 48 hours your concrete is hard enough to wall over it without leaving footprints and your concrete should be cured to at least 70% of its full strength after seven days. The concrete is fully hardened in 28 days.

The only way to know that concrete is dry is to test it and the most accurate test which is scientifically proven is situ RH test. To make more accurate projections and save time and money trend analysis helps you.

How Concrete Dries:

As the water evaporates from the surface the concrete dries. Due to water evaporation, water deep in the concrete moves through the capillaries to the surface to replace it and the surrounding air can hold more water vapor. Evaporation or drying of the concrete stops when the surrounding air cannot hold any more water vapor.

Speed Up Drying Time Of Concrete:

There are following points to speed up the drying time of concrete such as;

Too much amount of water can increase the drying time so, use the correct amount of water in the mix.

Over trowel or seal the surface can block the pores in the concrete & diminish moisture evaporation so do not over trowel or seal the surface and this can also increase the drying time.

Speed up the overall drying process of the slab by using dehumidifiers to remove moisture from the air.
Keep doors and windows close and fan circulating air once space is enclosed.
During warmer and sunnier weather pour the concrete and it will dry faster than in cooler weather.
While it is still wet add calcium chloride it helps the concrete to solidify faster.
Raise the temperature with the heater.
To trap escaping moisture place the plastic sheet over the concrete.

Testing Concrete For Dryness:

The way to know the successful in speeding up your concrete drying is to test the concrete for dryness and just by looking at the surface, you cannot tell it’s dry. The surface is always dryer than the center and also the moisture moves through the pores of the

Concrete to the surface and evaporate.

The researchers have developed a scientifically proven test for measuring moisture levels in slab and concrete moisture testing has been studied since 1960.

For measuring the RH of air trapped in the concrete the test requires sensor and these sensors are inserted into the slab at specific depths. The depth is 40% of the thickness for slabs drying from one side and the depth is 20% of the thickness for slab drying from two sides.

This test is known as the relative humidity test using in situ probes.

How To Know Concrete is Dry?

According to your best estimate when you think the concrete should be dry then the only thing you can do is testing. It will be dry but many times it won’t so give it more time and test again and continue this process until the test shows that the slab is dry and ready to receive the floor.

There is an option to use a moisture migration system if drying cannot be complete when the floor covering installed. To do an adequate job of sealing the moisture into the slab it is important to choose a high-quality product.

Factors Affecting the Concrete Drying:

Concrete drying time is not consistent across situations as there are several factors which can affect concrete drying time such as;

1: Moisture:

With water, it is cement interaction that causes the curing process and the concrete will cure more quickly if there is less water because there are few bonds to make. It may take longer to cure and you may see flaking on the top layer of concrete if there is too much water. After the finishing step, too much moisture will weaken the top layer and cause flaking.

2: Temperature:

Moisture evaporates faster when it is hotter and your concrete will cure faster. With specially designed concrete blanket you can cover your concrete to make it hotter so by doing this it will cure faster.

When trying to cure concrete in cold weather conditions this can be especially useful. The evaporation of moisture speeds upsetting time of the concrete and the hot temperature and wind accelerates the evaporation of moisture.

3: Mix Design:

You can add an accelerant to the mix if you need your concrete to cure faster.

Your full strength concrete may not be stronger as concrete allows you to cure to full strength normally while this speed up.

The mix design has a lot to do with the time of concrete settling and the area needs to be usable as soon as possible, such area will require accelerants. The accelerants do its job and speed up the settling time of the concrete and in the end, the accelerants will show a weaker overall strength but still meets the requirements of strength.

4: Concrete Blankets:

There are cool and hot blankets available these days for drying of concrete. If you want to dry your concrete you need concrete heating or concrete cooling blanket.

The cooling concrete blanket will keep newly poured concrete from the heat and it will work in both regular and hot conditions.