The ideal curing temperature is during concrete works is around 23°C.
Concrete is a mixture of water, cement, and various other ingredients. When concrete cures, it generates heat because the chemical reaction that takes place while the concrete hardens causes heat to be produced. This heat will continue to rise until all excess water has evaporated from the concrete mix. The concrete curing period varies depending on several factors, such as the size and thickness of the slab, air temperature, and humidity levels among many other variables. For example, large concrete surfaces take much longer to cure than smaller slabs because they have more volume in proportion to their surface area, so they retain more moisture. Sufficient moisture in the concrete elements slows down evaporation rates.
The ideal curing temperature during concrete works is around 23°C (68°F). That means if your project is in extremely cold or hot weather conditions, extra concrete curing conditions must be observed in order to realise properly cured concrete. For more information on water-cement ratio, minimum curing period etc, take a look at the Queensland Building and Construction Commission website.Colder climates slow down evaporation rates due to lower temperatures which means less evaporation also means a longer curing period. The ratio is exponential because the lower concrete temperature delays evaporation and slows down the chemical reaction, which in turn creates less heat.
Cold weather concreting projects may require more than 28 days for proper curing of slabs if they are cast in colder climates. Also, frost will delay the evaporation process pushing back when concrete can be used or even walked on.
This is done by misting the surface using a spray nozzle that emits a stream of water droplets to ensure the structural concrete has adequate moisture. Excessive dryness during the early hardening period causes shrinkage cracks. Water curing will, thus, protect concrete from surface cracking.
Radiant heaters or some other type of warm air blower can be used to add more heat to speed up evaporation rates. Precast concrete producers use steam curing to accelerate the curing of the precast concrete slab. Steam curing can cut the curing days from highs of 28 in very cold temperatures to only 3 days.
A tarpaulin, concrete blankets, plastic sheets Impervious paper, or any cover will help trap humidity in exposed surfaces on the slab reducing moisture loss and speeding up curing times. Coverings insulate concrete surfaces subjected to freezing temperatures to serve as effective insulation reducing heating costs.
Adding curing compounds is also a way of keeping the concrete wet, enhancing the curing process. You can use a curing compound like calcium chloride, wax, or acrylic liquids that assist the formed concrete surfaces attain the desired moisture.
Slabs larger than 800mm x 800mm should be covered for at least 7 days after screeding.Mark out areas on the concrete surface that will be covered with plastic sheeting to prevent them from drying too fast and causing cancer cracks. This is very important because if the slab dries too quickly, affecting cement hydration, it will shrink and cause plastic shrinkage cracking that may compromise the concrete surface or even its structural integrity.
The plastic sheeting should be taped onto the slab using duct tape with mastic asphalt patches on both ends of each seam. Using multiple layers will not speed up the curing process, and it will simply be a waste of money. The sheets must overlap by at least 100mm to prevent rain from seeping through the seams.Slope the ground around the covered slabs so that water can drain easily after it rains. This is done because leaving standing water on cement surfaces for prolonged periods may compromise their strength or even cause them to delaminate due to pressure exerted by hydrostatic forces in areas prone to flooding.
The next step is drying everything with blowers or some other source of warm air like propane gas heaters placed under tarps (the same ones used during screening ). Make sure that the blowers are kept at least 200mm away from the surface of the concrete; otherwise, this will create a "hot spot" and cause cracking.
The slabs should be inspected daily for cracks or other potential problems. As time passes, these problems will become more apparent, so they should be fixed as soon as possible to prevent them from getting worse. Also, if water starts accumulating under the plastic sheeting, it must be removed immediately because leaving it there for too long may compromise the integrity of the slabs.
If concrete is not cured, it will be very weak and susceptible to damage caused by water, frost or even foot traffic. If the concrete does not attain specified compressive strength during curing, its abrasion resistance capabilities will be compromised. It may also cause problems like delamination, heaving and even structural failure because of pressure exerted by hydrostatic forces in areas prone to flooding.
For the curing process of concrete to go smoothly in the entire curing period, the area where it is located must be dry and free from materials that will interfere with evaporation, such as gravel, mud or even standing water. Also, tools must be used properly while screening or screeding because failure to do so may cause problems during the curing process. And finally, make sure that no air pockets are left between slabs by tapping them initially with a rubber mallet and then finishing the job off using a hand tamper. This last step can either be done manually or mechanically, depending on how small the slabs being laid are. For slabs larger than 800mm x 800mm, this should occur within 7 days of pouring. A slab must be covered, especially in hot weather concreting, to prevent it from drying too quickly and causing cracks that may compromise either its surface or the integrity of the concrete structure. You can minimise plastic shrinkage cracking of fresh concrete by maintaining low concrete temperatures, moist curing the surface, or using saturated wet coverings. Make sure you slope the ground around the slabs so that water can drain away after it rains because standing water on cement surfaces for prolonged periods may cause delamination or structural failure because of pressure exerted by hydrostatic forces in areas prone to flooding. Last but not least, inspect your work daily for problems like cracking or other potential issues because if left unattended, these problems will get worse over time, compromising either the surface or even its structural integrity. And remember to always keep curing equipment out of the way of screeds, so they don't interfere with construction.
On the other hand, cement is composed primarily of calcium silicates (a compound made up of calcium, silicon and oxygen) known as clinker, which undergoes extreme heat treatment to cause it to bind together.
This creates a very hard and durable substance when mixed with water.
Screeding is a process used to create a perfectly smooth and level surface on freshly poured concrete. There are three main stages involved in screeding, listed below.
The screed's side edges will be held tightly against the edge of the forms with temporary stakes. The screed's side edges will be held tightly against the edge of the forms with temporary stakes.
This is also known as "skimming" because, during this time, the excess concrete mixture from the surface will be removed using either a hand float or power trowel. This can only be done after enough time has been allowed for it to dry slightly but not too much otherwise, it will start drying out and cracking.
Once enough material has been taken off, screens made out of mesh wire can then be dragged over the surface and pulled towards the user to remove any remaining high spots.