Speeding Up Concrete Drying and Concrete Curing
Proper concrete curing plays an important role in the durability of buildings and so does concrete drying. These processes can’t be rushed but there are techniques you can apply to speed them up. Some simple technologies are even available for expediting the processes, and you won’t have to buy them if they’re already installed in the building. All these faster cement drying and curing strategies are what we’re going to learn about today.
A project manager’s concern is mainly focused on construction crew management and progress tracking so the responsibility for cement pouring and curing is often passed on to concreting subcontractors. With new building projects becoming fast-paced, it would be helpful for concrete subcontractors to speed up their processes too.
Technology always plays a major role in accelerating things at the construction site. The use of subcontractor schedule software, for instance, can speed up the subcontractor’s activity tracking at the site, which is very important as modern buildings are mostly concrete. A lot of building phases rely on the cement pouring and curing process before they can proceed with a new phase. So it’s up to you — a concrete subcontractor — to finish the job faster without compromising quality.
What is Cement Curing?
Curing is a process taking place after cement pouring and finishing. It is a method used to maintain the right amount of moisture and to keep the desired temperature condition of the concrete. An adequate amount of moisture is needed for continued hydration at the depth and near the surface of the concrete as well as for volume stability, abrasion, development of strength, is mainly the maintenance of desired moisture and temperature conditions, both at depth and near the surface, for extended periods of time. Properly cured concrete has an adequate amount of moisture for continued hydration and development of strength, volume stability, resistance to freezing and thawing, and abrasion and scaling resistance.
In curing the cement, you’ll need to know the right curing time to ensure that your work develops optimum strength. The length of time needed for curing is dependent on these five factors:
- Size and shape of the member poured with cement
- Mixture proportions
- Ambient weather conditions
- Specified concrete strength
- Future exposure conditions
For instance, slabs on the ground like driveways, pavements, parking lots, floors, sidewalks, as well as structural concrete like columns, small footings, retaining walls, beams, slabs, and so on require at least seven days for ambient temperature over 40 degrees Fahrenheit for their curing period.
Generally, a minimum curing period should correspond to 70% of the concrete member’s compressive strength as recommended by the American Concrete Institute (ACI). Commonly, seven days is needed to achieve the 70% compressive strengths equivalent. However, the curing time can be lesser when concrete is placed under higher temperature. Similarly, a longer time will be needed to cure concrete under lower temperature. That said, the ACI Committee 308 suggests following these minimum curing periods for the following cement types:
· ASTM C 150 Type I needs seven days
· ASTM C 150 Type II needs ten days
· ASTM C 150 Type III needs three days
· ASTM C 150 Type IV and V needs 14 days
· ASTM C 595, C 845, C 1157 have variable curing periods
The Difference Between Curing and Drying
Before we go to the tips and techs used in speeding up curing time, let’s first differentiate these two terms that are often interchanged: curing and drying.
Curing and drying are two different concreting processes. In summary, the curing process only takes up to 28 days maximum to complete, while drying can take up months to complete.
In curing, you are basically trying to harden the concrete and can harden further even after the curing period. But like we said, in curing, you are trying to maintain proper hydration within the member. After curing, excess water may still be present and that should evaporate. This is why you need drying.
In drying, you will need to wait about 30 days for every inch of slab thickness given that the concrete member is under the right conditions. The concrete member should be exposed to low ambient relative humidity as well as consistent average temperature. This is why experts recommend turning on the HVAC to achieve these conditions. It’s different, though, when you are working outside where HVAC can’t be installed.
Concrete Curing Process
As we mentioned a while back, there are different types of concrete and their curing process may vary. However, these types have three common components namely cement, aggregate, and water.
To make up a concrete member, cement and water are mixed together and a chemical reaction occurs. This reaction is what binds them together and what causes them to harden. During the hardening process, concrete becomes porous and a certain amount of water becomes part of the concrete. Excess water then either evaporates or remains within the concrete.
Concrete Drying Process
This is where the excess water from the curing process is dried up. Generally, concrete dries as water inside it evaporates. Now, as water evaporates, the remaining water from deep down the concrete member moves up to the surface to replace the evaporated water. And this cycle continues for as long as the surrounding air can hold more water vapor. This is why it can take months before concrete drying completes.
Tips for Speeding Up Drying Before Cement Pour
Months of waiting before concrete totally dries up can be shortened. And you can start the process even before the cement pouring. Here’s how:
· When preparing your cement mixture, see to it that you use the correct amount of water. Too much excess water means longer evaporation period, hence longer drying time.
· Use a high cement content mix to speed up the drying time. But note that this can lead to cracking due to shrinkage.
· Don’t use lightweight aggregates as they can absorb a lot of water. Use synthetic aggregates instead as they don’t absorb water.
· Try to avoid the use of curing or sealing agents. They can inhibit evaporation from the surface of the concrete which lengthens the drying period.
Tips for Speeding Up Drying After Cement Pour
After finishing with the cement curing process, try, as much as possible, to enclose the work space. This is to prevent the concrete to absorb more moisture from the open surroundings.
Other than protecting the slab from moisture, it’s also important to consider other factors that can affect the drying process, including:
· Ambient relative humidity
· Air temperature
· Temperature of the slab itself
To ensure that moisture, relative humidity and temperatures won’t affect drying time, you can:
- Use HVAC
Relative humidity is important in the drying process because it controls evaporation. If it’s too high, then the concrete slab won’t dry. That said, you need to control relative humidity and you can do that by enclosing the space and installing HVAC. The cooling effect that an HVAC unit offers can maintain 50% relative humidity level. This level is perfect for concrete drying. On the other hand, heating can lower relative humidity. And as we mentioned earlier, you’d want a higher temperature to speed up the process. The heater of HVAC can do that most especially when you are pouring cement during the colder season.
- Use Dehumidifiers
There are specialized central dehumidifiers you can install at the construction site to speed up the concrete drying process. Portable dehumidifiers can also be used. They are useful when HVAC isn’t possible to be installed yet in a building, like during your first cement pouring.
- Test Concrete for Dryness
Never just assume that a concrete is already dry just by looking at it. Like we discussed, water can still be present deep within the slab even after you followed the recommended drying period.
To be sure, run a concrete moisture testing. This method has been used since the 1960s and it’s already proven effective and the basis for ASTM F2170 standard.
This testing method uses sensors to measure relative humidity of air inside the concrete. Sensors are inserted to either 40% or 20% of the slab’s thickness depending on which side of the slab is drying.
For this testing, you can use the Wagner Meters Rapid RH® L6 system. This situ relative humidity testing unit is known to conform with the ASTM F2170 standard. Once installed, allow it to test the slab for 24 hours where you take readings any time.
If the test shows that the concrete is not yet dry, then allow some more time for the drying process and use the techniques we mentioned above to speed it up.
But if you really need to install floor covering immediately, then you can use the last resort of moisture mitigation system. However, be sure to use a high-quality product to properly seal moisture in the slab and avoid future problems like weaker concrete or concrete deterioration.
New Technology for Concrete Dryness Testing
Small devices or sensors linked to apps are now available for more accurate data logging. You can use them to continuously monitor the moisture level within the concrete. They can also measure relative humidity and ambient temperature.
Like in construction crew management, data is also important in testing parts of your building, most especially the floor which will have to endure heavy foot traffic when it’s already open for occupancy.
Modern data loggers can send readings to you via an app so you won’t have to always visit the site for testing and reading. This data gives you a vital insight into the concrete drying process like the relative humidity at the site which greatly affects the drying period. Like a construction project management software, the data that this sensor-app system gives will later save you from liabilities when the schedule gets delayed.
Conclusion
There’s no other way to find out whether a concrete member is already dry or not unless you test it. Take advantage of the testing technologies so you can be sure that the drying process is completed before you close the project. Safety of occupants greatly relies on how parts of the building are made so unless you want to face litigation later on, be keen with your testing.
The simple techniques and tech used at the site like HVAC and dehumidifiers can speed up the process. If you need to follow a strict schedule or work on other concreting projects, you can use them to expedite concrete drying.
Concrete drying time has a major effect in a builders’ schedule as most activities at the site will come after concreting processes. By following our tips, you can greatly shorten the drying time and minimize errors.
