How long your concrete driveway should cure is only one factor to consider when pouring your new drive. Of course, the curing time is critical. If you don't maintain curing conditions long enough, the durability of your driveway will be compromised. But to be sure your new driveway lasts, you must also consider how environmental conditions will affect curing.
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Concrete is a mixture of Portland cement, sand and rock aggregate and water. When combined with water, cement reacts chemically to bind the aggregate into a monolithic solid. However, the chemical reaction--called hydration--between cement and water is affected by the ratio of cement to water, other substances that may be added to the concrete, and also by temperature and humidity.
Generally, less water in the concrete mix results in stronger concrete, but less water also makes concrete more difficult to work with, and a little more temperamental while curing. For driveways, a moderately strong concrete mix, designed to cure to 4000 psi compression strength, is adequate for most climates, while still being easy to work with. In climates that experience below freezing temperatures, an air-entrained mix infused with microscopic bubbles of air, facilitates curing and increase durability of the driveway.
The curing temperature of a curing concrete driveway is critical to its ultimate strength. Concrete that freezes while curing looses about 50 per cent of it's ultimate strength. Extreme heat or low humidity can cause surface evaporation, which arrests curing, resulting in weak, crumbly concrete. Also, a difference of more than -1.11 degrees C between the internal temperature of the concrete and the surface temperature, may result in deep cracks. Edges and corners are especially vulnerable to temperature fluctuations.
The hydration reaction between cement and water generates its own heat. To dissipate this heat and prevent surface evaporation, the concrete surface should be kept wet. Plastic sheeting may also be applied to minimise evaporation. Ambient temperatures around 22.8 degrees Celsius are considered ideal for maintaining an optimal concrete temperature of about 32.2 degrees Celsius. Ambient temperatures below 40 degrees, or above 32.2 degrees Celsius, require special precautions to ensure proper curing of the concrete driveway.
A concrete driveway may be walkable in a few hours, but it is not cured sufficiently to bear the weight of a vehicle. A minimum of three days initial curing, and a full week in some climates, will allow most concrete mixes to achieve 75 per cent of the concrete's ultimate strength. Usually, you can drive your car on the driveway at this point, but consult your concrete contractor or ready mix supplier first. Though curing actually continues for years, a concrete driveway achieves 90 per cent of it's final compression strength in 28 days.
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