The concrete should be kept wet during the curing phase. The water reacts chemically with the chemicals in the cement mixture in a process known as “hydration.” Keeping the concrete moist causes many chemical reactions in the interior, resulting in the strongest concrete possible.
Many individuals are unaware of the significance of water in concrete, even after it has been added to the cement and aggregate combination. It’s possible that more water isn’t truly required during the curing process.
Did you know that after you add water to concrete, it never completely dries out? Water is so important to concrete that it refuses to let water molecules escape even when the concrete appears to be dry. There are various strong reasons to keep concrete wet during the curing process, as well as a variety of methods to accomplish so.
Water Chemical Reaction
Portland cement is one of the most widely utilized forms of cement worldwide. Concrete is made by mixing cement with water and aggregates (such as sand and gravel). Concrete’s main constituent is water. Concrete would never be able to generate the strength required to construct structures such as sidewalks or foundations without it.
Portland Cement is made up of five primary compounds that account for at least 90% of the whole mixture:
- Calcium silicate tricalcium (C3S)
- Silicate of dicalcium (C2S)
- Aluminate of tricalcium (C3A)
- Aluminoferrite tetracalcium (C4AF)
- Gypsum is a type of gypsum (CSH2)
Many chemical reactions occur when water is added to this mixture of compounds:
- Lime and heat are produced by tricalcium silicate and water. This greatly contributes to the concrete’s initial strength.
- Ettringite crystals and heat are formed when tricalcium aluminate interacts with gypsum.
- When all of the gypsums are gone, it interacts with water and any leftover Tricalcium aluminate to form monosulfate aluminate hydrate.
- Calcium silicate hydrates and heat are formed when dicalcium silicate combines with water. This contributes to the concrete’s long-term strength.
- Ettringite, lime, and alumina hydroxides are formed when tetra calcium aluminoferrite interacts with water and gypsum.
The resulting paste, when mixed with the aggregates, hardens as a result of its reaction with water, forming concrete that we walk on or that supports skyscrapers that are hundreds of stories tall. It all depends on the component proportions employed in the cement mixture.
For maximum strength, keep the concrete wet.
The concrete must cure once the cement has been poured and the forms have been removed. It would be a mistake to just let the concrete dry during the curing phase. Concrete does not gain its strength by drying.
The curing process in concrete will continue as long as the concrete contains water or moisture. However, there is a delicate balance to be struck while water-curing (also called moisture-curing). As long as there is water in concrete, it will continue to grow stronger; however, if it is water-cured for an extended period of time, the rate of strength gain will slow.
It’s usually a good idea to check the directions for each concrete mixture to see how long it’ll take to reach the specified design strength.
Water Curing Concrete Techniques
Before you start water-curing, ensure sure the water on the concrete’s surface has evaporated. When the water on top of the concrete evaporates, it indicates that it has become relatively durable. Depending on the temperature outside, this should take around an hour, but don’t forget about the concrete during this vital step.
Wet Covering, Ponding, and Fogging
Only horizontal and flat surfaces, such as slabs, are suitable for the ponding method of water-curing concrete. Ponding entails constructing a space on top of concrete to allow water to flood in and form a pond. You can achieve this by building walls or berms along the concrete’s edges to keep the water out. Sand, clay, or mortar are all possible materials.
This procedure necessitates a large amount of water. Because the water will evaporate, you must refill the pond at least 2 to 3 times every day, especially during the hot summer months. Water must be applied to the concrete’s borders on all sides. If even one location is overlooked, that spot may become weak and crack.
This approach is precisely as it appears for fogging (or “misting”). It’s as simple as spraying a thin mist or fog over the concrete surface to keep it moist. This procedure, like all curing processes, will aid in the prevention of concrete shrinkage cracking. This procedure should not leave standing water on the surface, as this can weaken and porous the concrete.
After the concrete has hardened enough, you can cover it with a wet covering that will not damage the cement. Burlap, straw, or canvas can be used as covers. Plastic sheets can also be used, but exercise caution. A plastic sheet on top of the concrete can develop creases, air pockets, or pooling water, resulting in blotching and uneven curing.
Temperatures must be above 50 degrees Fahrenheit for at least a week throughout the curing phase for all of these methods. Chemical reactions will slow down if it falls below that level. They will come to a complete stop at 45 degrees, and the concrete will lose all of its strength.
Another technique of curing concrete is steam curing. Curing in water vapor at atmospheric or higher pressures is known as steam curing. The enclosure temperatures are normally between 40 and 70°C (100 to 160°F) when cured at atmospheric pressure. When early strength increase is essential and heat is required for hydration, such as in cold weather, steam curing is utilized.
Concrete curing compound is a substance that aids in the preservation of the concrete’s moisture content. As a result, the concrete is adequately cured, resulting in the full development of concrete strength.
How Long Should Concrete Be Water-Cured?
A concrete mix that hasn’t been water-cured will dry up soon and lose its strength. This is why water-curing concrete for at least 20 days is critical. Most professionals and concrete manufacturing businesses recommend that you cure your concrete for 28 days (or a month).
The following is a general overview of the curing procedure:
For detailed curing procedures, see the paperwork for your specific concrete mix first.
- You should start and sustain the curing process within the first 24 hours of setting.
- The forms can be removed after roughly 48 hours, and you can walk on the concrete surface.
- Most concrete requires a minimum of four days to cure properly.
- This is only deemed a “partial cure” after 7 days. Heavy traffic, such as that caused by huge machinery, is acceptable.
- The concrete should have acquired its specified strength after 28 days and is now considered fully cured.
In a nutshell, water-curing concrete is critical to its strength and longevity. You can’t afford to skip this stage.