Pouring concrete at night can help reduce the chances and effect of hydration caused by heat on the concrete. It will also reduce the evaporation of water on the concrete mixture as there are lower wind speeds and calmer wind conditions during the night.
Pouring concrete in the morning helps you avoid the warmest temperatures, which can affect the quality of your finished project. Starting early can help you complete your project quickly without risking your concrete hardening before you're finished.
Concrete is usually dry enough after 24 to 48 hours to walk on. For concrete to dry and reach its full strength, it typically takes about 28 days per inch of slab thickness. Once conditions are conducive for the concrete to cure at 85-90% relative humidity.
Rain can influence the surface appearance of the concrete and its internal strength. It can cause the concrete surface to become soft, which reduces the abrasion resistance and strength of concrete. At the same time, it increases the tendency for dusting and cracking to develop.
One of the most common methods for curing concrete is to hose it down frequently with water—five to 10 times per day, or as often as you can—for the first seven days. Known as “moist curing,” this allows the moisture in the concrete to evaporate slowly.
Concrete that is not moist-cured at all dries too rapidly, and reaches less than half its potential design strength. It will also have a greater number of shrinkage cracks.
Moist curing is a common method of concrete curing. It involves wetting the concrete slab often with water (5-7 times per day) for the first 7 days. This method ensures your concrete slab will be extremely strong and durable, because it allows the moisture to evaporate slowly, preventing cracks and shrinks.
As long as the concrete is given 4 to 8 hours after mixing and finishing to set up, rainwater won't affect it nearly as badly as it could. Some concrete mixes will actually benefit from rainwater on the surface because it's beneficial in aiding the hydration and curing process.
Plan to pour concrete before 10 a.m. or after 8 p.m. in order to avoid the hottest part of the day. If you are concerned about the temperature while working on a summer project, consider pouring concrete at night to give the mixture the best chance to harden and cure before the sun comes up.
Once the concrete has been finished (between 4-8 hours after pouring) and has set hard enough for walking on, the effects of rain should be minimal. The curing process is a chemical reaction, with ready mix concrete taking up to 28 days to fully cure.
The Issue with Pouring Concrete in Cold Weather
When temperatures dip below 40 °F, the chemical reactions that strengthen concrete slow down and can lead to weaker concrete. If concrete curing temperatures are below freezing, the water inside the concrete can freeze and expand, resulting in cracks in your surface.
If your concrete is exposed to the elements, you won't be surprised to learn that the concrete will dry faster in warmer, sunnier conditions. While this isn't always an option, choosing to start your project in summer is a surefire way to minimise curing time.
While Curing
When curing freshly-poured concrete, you must take precautions to prevent water evaporation caused by direct sunlight. For the duration of the curing process, which is typically 28 to 30 days, keep your concrete watered, covered, and sheltered from wind and sunlight.
Initial Setting Times for Concrete
In standard industrial cases, full strength concrete is recognized at 28 days. At seven days, you should have concrete that is cured to 70% full strength or greater. But to answer the question of, “How long does concrete take to set?” concrete setting time is generally 24 to 48 hours.
Many people ask whether you can safely pour ready mix concrete in the rain? The answer is yes, it is absolutely possible to pour in the rain, but ideally you should avoid. Rain presents challenges, so doesn't always mean that your schedule is out of the window, as long as you take proper action.
Curing plays an important role in strength development and durability of concrete. This is done by continuously wetting the exposed surface thereby preventing the loss of moisture from it. If water evaporates too quickly, it will weaken the finished product with stresses and cracking.
Many construction specialists recommend watering it down five to ten times per day, for the first week, starting 2-4 hours after it has been poured. The first two to four hours lets the concrete “finish”, which refers to the setting process.
Concrete typically takes 24 to 48 hours to dry enough for you to walk or drive on it. However, concrete drying is a continuous and fluid event, and usually reaches its full effective strength after about 28 days.
Most specifications for retail or commercial concrete slabs specify 4 to 6 inches of thickness. Owners and contractors have historically disputed whether a poured slab meets a specification because of its thickness.
Yes, you can pour fresh concrete over existing concrete. As long as your concrete is in mint condition, this task is doable. If you decide to pour a new mixture over an old slab, be sure it is at least 2 inches thick.
Concrete has to withstand all manner of conditions that, over time, do take their toll on the material. Rain will slowly erode the concrete, causing discolouration and weak points. Acid rain has an average PH value of between 4.2 and 4.4, which is slightly more acidic than a banana but less so than orange juice.
Although dry pouring of concrete might be fine for filling fence-post holes, it should be avoided as a placement method for concrete slabs if you want the concrete to look good and last for the long term.
Corrosion of reinforcing steel and other embedded metals is the leading cause of deterioration in concrete. When steel corrodes, the resulting rust occupies a greater volume than the steel. This expan- sion creates tensile stresses in the concrete, which can eventually cause cracking, delamination, and spalling (Figs.
Water containing bicarbonate ions and carbon dioxide causes a reaction known as carbonation in concrete. This often happens in the presence of salts and acid rain. As the acidic substances lower the concrete's pH, the calcium carbonate within the aggregates dissolves and reduces the concrete's strength.
However, concrete reaches its full strength after approximately 25-28 days. You should be able to walk and perform normal tasks on concrete one week after its application. However, the concrete will only be at around 70-70% of its full strength, so driving heavy machinery on it is not advised during this time.