Concrete is an important building material used in many construction projects. It is made from a mixture of cement, sand, gravel, and water. One thing that is important to understand about concrete is that it goes through a curing process. The concrete curing time will allow the concrete to reach its full design strength.

What is Concrete Curing?

After the concrete is poured and finished, the concrete curing process begins. Curing means allowing the concrete to hydrate and harden. During this process, the concrete develops hardness and durability.

It is important for concrete to gain strength and become water-resistant. It involves maintaining proper moisture and temperature conditions for some time. The three basic methods used for curing are:

●       Water Curing, wetting the concrete surface with water

●       Spraying Curing Compounds

●       Covering the Concrete with Plastic Sheets or Straw

Curing allows the concrete to fully hydrate. Hydration refers to the chemical reactions between the cement and water that cause the concrete mixture to harden and bind together. Proper curing results in concrete that is stronger and more durable. Improper ways can result in weak spots and cracks.

Concrete Curing Time

The length of time needed for concrete to cure depends on several factors:

●       The Type of Cement Used

●       The Concrete Mix Onsite Design

●       Curing Conditions

●       The Size and Shape of the Concrete Slab

The curing process typically occurs over 4 weeks. It can be considered complete when the concrete reaches its specified compressive strength.

Let's look more in-depth at curing times.

●      Early Stages

The curing process begins immediately after the concrete is placed. In the first 24 hours after pouring, the concrete will go from a plastic state to being solid. However, the concrete is still very weak only reaching about 50% of its full strength in one day.

The critical time frame is within the first week. In 7 days, the concrete should be about 90% cured if proper curing conditions are met. Even though the concrete may feel hard at this point, the structure is still not at full strength.

●      Later Stages

Over the next 3 weeks, the remaining 10% of curing will occur. Most specifications consider concrete to be fully cured after 28 days. At this point, all hydration has occurred and the concrete has reached its full hardened state.

However, the concrete will continue to get harder over the first year. As it ages, density increases, and permeability drops.  After one year, concrete exhibits all its superior physical characteristics.

What Controls the Curing Rate?

●       Water-Cement Ratio:  More water equals faster setting concrete.

●       Cement Type: Different cement types hydrate at different rates.

●       Temperature: Heat accelerates curing while cold weather retards it.

●       Humidity: Adequate moisture ensures sufficient hydration.

Tips to Speed Up Curing

●       Use hot water when mixing:  Using hot water when initially mixing the concrete can accelerate the early strength gain. However, ensure the water isn't near boiling as that can cause other issues. The ideal hot water temperature range is 130-180°F (54-82°C).

●       Apply external heat:  Heating concrete slabs through hot air, infrared lamps or hydronic piping warms the concrete to optimal curing temperatures. This supplementary external heat shortens curing times. Keep temperatures between 50-90°F (10-32°C).

●       Insulate the concrete:  Using insulating blankets or foam boards helps retain heat released during hydration, allowing the concrete to cure faster. The higher temperature speeds reaction rates. Moreover, avoid excessive heat which causes unsoundness.

●       Use calcium chloride:  Adding a calcium chloride admixture improves early strength development. Additionally, this specialised accelerating admixture reacts with tricalcium aluminate to reduce initial setting times. Above all, dosage rates range from 1-2% by weight of cement.

●       Prevent moisture loss:  Concrete needs sufficient moisture for full hydration. Use wet burlap, plastic sheeting, or curing compounds to seal in moisture during the process. Preventing water evaporation means faster curing.

●       Use silica fume: Adding silica fume to the concrete mix design typically accelerates strength gain. Silica fume is a pozzolanic material that greatly increases concrete density and impermeability. The typical dosage rate is 5-10% by weight of cement.

●       Include set accelerating admixtures: Chemical accelerators can be added to shorten setting times. Alkali salts or soluble carbonates react and disrupt concrete dormancy which reduces curing durations. However, be careful of overuse causing cracking or excessive heat.

Conclusion

While concrete rapidly sets in the first week, full curing takes 28 days. Be patient as the concrete gains strength over time through concrete curing time. Your slab will perform reliably for decades with extra care taken to properly cure the concrete. Pro-Mix Concrete UK is here to help you with all your concrete needs including concrete pump hire. Trust us to provide the best service and top-quality concrete for your projects.

FAQs

How long should concrete be cured before removing formwork?

Formwork should remain in place for at least 24 hours after a concrete pour. This ensures the concrete has hardened sufficiently before removing supports.

When can foot traffic walk on new concrete?

Light foot traffic can walk on concrete after about 3 days. Allow one week before heavier loads or vehicles drive on a concrete road or sidewalk. This ensures the concrete has adequate strength.

Is it okay to get concrete wet while curing?

Yes, adding water keeps concrete moist during the curing time frame. Both wetting and drying cycles are fine. The key is limiting evaporation with consistent moisture.

What slows down concrete curing?

Cold weather can dramatically retard curing, taking months instead of weeks. Using less cement in the mix design or insufficient moisture also slows strength gain.

When is it safe to seal, paint, or cover concrete?

Those finishes should only be applied after curing is completed. This prevents any reactions with the sealants or trapped moisture issues.

Does concrete continue to cure and get harder over time?

Yes, the curing process allows concrete to gain additional hardness and strength over its first year. Density continues increasing while permeability drops.