How long cement cure

The curing period for cold weather concrete is longer than the standard period due to reduced rate of strength gain. Compressive strength of concrete cured and maintained at 50 degrees Fahrenheit is expected to gain strength half as quickly as concrete cured at 73 degrees Fahrenheit.

In hot weather, curing and protection are critical due to rapid moisture loss from fresh concrete. The curing actually starts before concrete is placed by wetting substrate surfaces with water.

Sunscreens, windscreens, fogging, and evaporation retardants can be used for hot weather concrete placements. Since concrete strength gain in hot weather is faster, curing period may be reduced. Additional information can be found in ACI Joshua Gilman, P. Cement Industry Annual Yearbook U. Zemajtis, Ph. The length of adequate curing time is dependent on the following factors: Mixture proportions Specified strength Size and shape of concrete member Ambient weather conditions Future exposure conditions Slabs on ground e.

Figure 1. Moist Curing Time and Compressive Strength Gain Higher curing temperatures promote an early strength gain in concrete but may decrease its day strength. Figure 2. Effect of Curing Temperature on Compressive Strength There are three main functions of curing : 1 Maintaining mixing water in concrete during the early hardening process Ponding and immersion Ponding is typically used to cure flat surfaces on smaller jobs. Both documents provide standardized requirements for making, curing, protecting, and transporting concrete test specimens under field or laboratory conditions, respectively.

ASTM C provides procedures for evaluation of different mixtures in laboratory conditions. It is usually used in the initial stage of the project, or for research purposes. ASTM C31 is used for acceptance testing and can also be used as a decision tool for form or shoring removal.

Variation in standard curing of test specimens can dramatically affect measured concrete properties. According to the National Ready Mix Concrete Association 8 NRMCA , strength for concrete air cured for one day followed by 27 days moist cured will be approximately 8 percent lower than for concrete moist cured for the entire period.

In the process, the concrete becomes porous and a certain amount of this water becomes part of the concrete. Concrete dries as the water inside it evaporates through its surface. As this water evaporates through the surface, water from deep within the concrete moves through the capillaries and up to the surface to replace it. As long as the surrounding air can hold more water vapor, evaporation continues. Admixtures or the right balance of water can greatly help decrease drying times.

There are a few things you can do before you pour the concrete that will speed up the drying process:. Once the slab has cured, enclose the space as soon as possible to protect the slab from absorbing any additional moisture. While protecting the slab from additional moisture is important, there are a couple of other factors that affect drying after the pour:.

The ambient relative humidity is important because it controls whether water can evaporate from the slab. Enclosing the space allows you to use HVAC to control ambient conditions. In heating mode, they lower the relative humidity by raising the air temperature.

HVAC systems are also a great way to get air circulating around the concrete and thereby reducing drying time. To really speed up concrete drying time, enclose your slab and ensure the HVAC system is on. Some facilities have central dehumidifiers that can be used to speed up the drying process. You can also rent portable dehumidifiers and even fans. The only way to know if the concrete is dry is to test it. The test uses sensors — inserted into the concrete at specific depths — to measure the relative humidity of the air trapped in the concrete.

Pond curing is another great way to cure concrete, and the process is just as it sounds: You form temporary berms around a new concrete slab, and then flood the area inside them with one foot of water. Three days of pond curing does the work of seven days of moist curing, and without daily attention—just be sure the water level remains above the concrete slab.

Large-scale builders may use this method to speed up the construction process when pouring foundation slabs, for example, in order to get on to framing the structure. Available from DIY stores and ready-mix concrete companies, these contain soluble emulsions that form a protective film when sprayed directly onto the surface of newly poured concrete slabs or walls. Ultimately, the film provides a barrier or film to prevent water from evaporating, allowing it to cure at a consistent rate.

Some curing compounds are designed to disintegrate completely after a couple of weeks, while others should be removed by scrubbing after the curing process is complete. The goal of all concrete installation is to produce a high-quality product that resists cracking. While curing concrete will go a long way toward strengthening the finished project, many concrete slabs will crack anyway—despite all precautions—due to concrete shrinkage as water is used up in the hydration process as well as temperature fluctuations.

To preserve the beauty of the slab in the face of these challenges, do-it-yourselfers can place control joints at predetermined locations to guide the inevitable cracks. These joints should be cut in a quarter of the depth of the concrete slab during the very beginning of the curing process, within 24 hours of the initial pour. Using a metal jointing tool, the control joints can be easily and smoothly cut into the concrete surface as the appropriate distances in the slab.

Determine the maximum spacing between joints in feet by multiplying the planned concrete thickness in inches by 2. Feel free to place them closer together for added crack protection. Then, if your slab patio, driveway, or sidewalk cracks, it will most likely do so along a precut joint and can, therefore, go virtually unnoticed.