Concrete Curing

It is critical to concrete’s long-term durability that it be kept as moist as possible for the first seven days after placement. In addition, it must be allowed sufficient drying time before being subjected to freezing temperatures or to de-icing salts. Curing concrete properly requires the correct control of moisture and temperature and without proper curing, concrete may only achieve 50% of its potential design strength. The logic behind the practice of a seven-day curing period rests on two facts:

Curing can be assisted in a number of ways:

A liquid curing agent is the most effective and convenient method. The curing agent should be applied as soon as finishing is complete. Curing agents form a membrane on the surface of the concrete in order to retain moisture. Once the curing agent has been applied, no further working of the concrete can be done. Use a spray or roller to apply curing agents.

Cold Weather Curing

Concrete can be placed safely throughout the colder months if precautions are taken. During colder weather, the mix should be adapted to the ambient temperature by heating the concrete, adding accelerators, and providing protection.

Concrete generates heat during hydration, the chemical process by which cement reacts with water to form a hard stable paste. Hydration is affected by initial concrete temperature, ambient air temperature, the dimensions of the concrete and mix design. The temperature of the concrete during and after placement is critical since concrete sets more slowly as the temperature drops. Finishing and form removal may be delayed in cool weather and strength development can be impaired if appropriate precautions are not taken.

Do not place concrete on frozen ground, on snow, or in freezing weather. If concrete freezes while in a saturated condition, surface problems like scaling, spalling or cracking can arise due to the expansion and contraction of frozen water inside the concrete. During freezing weather, water curing of concrete should be terminated 12 hours before the end of the protection period. Do not use a curing agent if there is any chance that the concrete will freeze during the curing period.

Concrete Sealing

After the concrete is fully cured, the application of a concrete sealer is recommended. The advantages of sealing concrete include:

Due to the porous finish of exposed aggregate concrete, a surface sealer is highly recommended.

Superplasticizers

Superplasticizers are admixtures that increase slump to make concrete easier to place. Superplasticizers disperse particles of cement throughout a concrete mix. The effect is the same as adding water, but without the detrimental side effects. In addition, they reduce water in the mixture to gain higher, earlier strengths.

As a contractor, superplasticizers can help you to build more economically and to produce higher quality concrete at the same time, since moderately flowing concrete can be placed more easily providing good consolidation around rebar and tight forms with minimal vibration. Combine superplasticizers with low initial slump concrete to produce a workable mix with higher earlier strength.

Use superplasticized concrete for floors, suspended slabs, toppings, walls, columns, and anywhere that higher slump concrete is required.