The period of curing depends on the temperature because the rate of all chemical reactions is dependent on temperature. Therefore, in summer the rate of reaction (hydration) is faster so that a shorter curing time is required.
How does the temperature influence curing? A. The higher the temperature, the more rapidly the hydration and pozzolanic reactions proceed. Tests of specimens sealed against loss of moisture show higher early strengths but lower strengths at later ages as the temperature is increased above 5°C (40°F).
Warm temperatures cause cement to set faster, and the faster cement sets, the faster it begins to cure. At 80 degrees, concrete usually sets in about four hours. At 90 degrees, you can expect it to set in 2.5 hours, and at 100 degrees, your concrete will set in roughly an hour and a half.
High temperatures mean faster curing, but fast curing equates to weaker strength in the end. The following study by Paul Klieger in the Portland Cement Association Research Bulletin 103 illustrates this concept. At an age of 1 day the 120°F concrete was strongest and the 25°F concrete was weakest.
First things first, if it's hot enough where you don't want to leave the comfort of your air conditioning or cold enough that you need to put on a hat and gloves, you shouldn't lay concrete! It's advised that concrete be cured at a moderate temperature between 50 °F – 90 °F.
Cold weather can not only slow down the curing process but can also cause the water in concrete to freeze and expand, cracking and weakening the concrete.
As mentioned above, concrete prefers a mild temperature between around 50 and 60°F to set. Below this, the exothermic reactions that cause wet cement to transform into strong concrete will slow significantly.
The factors that affect curing are both this internally generated heat and the external temperature. Ideally, concrete should be poured and cured at an internal temperature of 50 to 90 degrees Fahrenheit. On a cold day, this may mean that your concrete contractor needs to heat or insulate the concrete.
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.
The heat produced by concrete during curing is called heat of hydration. This exothermic reaction occurs when water and cement react.
It also recommends that the curing duration should not be less than ten days for concrete exposed to dry and hot weather conditions and 14 days for concrete with mineral admixtures or blended cement in hot and dry weather.
The Australian Standard 1379: Specification and Supply of Concrete stipulates that concrete temperatures should be between 5°C and 35°C at the point of delivery.
On a hot day, freshly mixed concrete can start to set in as little as 30 minutes, so you have to work quickly to get the concrete poured and finished before it hardens. As well, concrete that dries out too quickly—a real issue in hot weather—isn't as resilient as concrete that dries more slowly.
Engineers use heat to speed up the adhesive curing process. “Most two-component adhesives will cure at room temperature, but many of these will have much faster cure times with the addition of heat,” notes Paul Brown, technical service engineer at Lord Corp.
Curing should be carried out at a temperature between 35°F and 40°F. The lower temperature is set for the purpose of ensuring cure penetration and the upper temperature is set to limit microbial growth (PHS/FDA 2001).
Since curing conditions have a great influence on the strength development of concrete, concrete specimens are often cured in a standard condition which is specified in standards or specifications. Normally, the standard curing condition is 20 ± 2°C, and relative humidity >95%.
At a minimum, concrete should be cured at temperatures above 7.2 degrees Celsius (45 degrees Fahrenheit). Below this temperature, concrete's chemical reaction completely stops – which can result in costly delays and rework.
Freshly placed concrete should be protected from rain for at least 12 hours from its placement. After that, the rainfall rarely influences concrete properties. How much strength does concrete gain after 24 hours from its placement?
Of course, pouring concrete mix in the rain is best avoided altogether, but sometimes it isn't possible to wait. If rain is forecast on the day you are pouring concrete, make sure the site is well covered with plastic sheets and tarpaulin to keep the ground as dry as possible.
Concrete curing, the hydration of the cement and the reaction between the cement and the water, is an exothermic reaction. Exothermic means it's a reaction that gives off heat. This is very advantageous to pouring concrete in the cold.
Concrete sets more slowly when it is cold—very slow below 50 degrees Fahrenheit and below 40 degrees Fahrenheit, the hydration reaction basically stops and the concrete doesn't gain strength. Anything below 40 degrees Fahrenheit will slow the curing process and may even stop it altogether.
Use cold mixing water, Substitute some water with ice, Cool down the cement – cement is stocked in silos, and often retains high temperatures from the factory, Pour concrete at night/outside of peak temperatures.
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.
Does concrete take 100 years to cure? No, this is a bit of a myth with the concrete industry. While concrete does continue to harden indefinitely, pore moisture has to drop below a certain level at some point and this isn't typically 100 years.
Water is mixed into concrete to activate the cement binding agent and as the mix dries, it hardens. The drying, or "curing," should be gradual, otherwise cracking may occur. To prevent cracks, plastic is placed over the curing concrete to trap the water inside and regulate its temperature, ensuring gradual curing.