What Temperature Is Too Hot to Pour Concrete

Hot Weather Concreting
Fourth dimension: 01:32
Tips for placing physical in hot weather condition including how to manage physical temperature and more.

Man, information technology'south hot outside! You may exist able to handle that estrus, simply can your concrete work? It can, if you take a few uncomplicated steps to help it along. There are many ways to lessen the effects of hot weather on physical. Once you understand the ability of heat and how to control it, your days of uncontrolable set up times, shrinkage and cracks will be over.

WHEN TO Use HOT Atmospheric condition CONCRETING METHODS

Get out information technology to the folks at the American Concrete Institute to provide a long detailed caption of when yous need to resort to hot weather concreting methods. Simply when you become to the end of that long detailed explanation, you probably nevertheless won't know the answer to the question of exactly what's hot. The Commission Report ACI 305R-99, Hot Conditions Concreting, says that hot is "whatsoever combination of the following weather that tends to impair the quality of freshly mixed or hardened concrete by accelerating the rate of moisture loss and rate of cement hydration, or otherwise causing detrimental results:

• High ambient temperature
• High concrete temperature
• Low relative humidity
• Wind speed
• Solar radiations

So basically Committee 305 says that nosotros should consider it hot whenever the heat might damage the concrete. Not very helpful. In nigh cases, effigy that you lot should offset thinking nearly hot weather techniques any time the air temperature is over about 85°, although even 80° with sun and a dry wind could be considered hot. For the physical temperature, anything higher up 80° requires some extra precautions.

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THE IMPORTANCE OF Concrete TEMPERATURE

Concrete sets as the cement hydrates. Hydration is an exothermic reaction, significant it generates estrus, and that reaction goes faster when the physical is hot. So the main concern with the physical'due south strength and fix fourth dimension isn't really the air temperature but the physical temperature.

When cement hydrates it sucks up water and grows crystals around the aggregate particles. When information technology's hot and that reaction is rapid, the crystals grow quickly but don't have time to abound potent. Early strength will be college but 28-24-hour interval strength suffers. If the concrete is near eighteen° hotter than normal (for example, 88° instead of seventy°), the ultimate compressive strength volition be about ten% lower.

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POTENTIAL CONCRETE Issues IN HOT WEATHER

Slump loss

In hot weather, equally the cement sets up, slump decreases rapidly and more mixing water is needed. This can also contribute to lower strengths (equally much as another ten% lower), and in integrally colored physical, can lead to variations in water content which can result in significant differences in physical color between side by side pours. A better solution is to modify your physical mix, learn how in Concrete Admixtures for Hot Weather.

Evaporation

Another potential trouble in hot weather condition is surface drying—although this 1 comes with a caveat. If the concrete is warm and the sun is shining and in that location is a hot dry wind beyond the concrete, yes, you are likely to go more drying and surface shrinkage. But let's become back to something every physical contractor should know about—beer.

In 1987, G.E. Munro who was managing director of technical services for Lafarge Cement, wrote an interesting commodity for the Lafarge newsletter. He started by posing a question: Does warm weather increase the probability of plastic shrinkage keen? Most people would say, yes. But he advises us to remember well-nigh a drinking glass of beer on a hot summer mean solar day. If the beer is colder than the air, what happens? Water condenses on the outside of the glass. Concrete works the same way. If it is cooler than the air, Munro says by virtually 18°F or more, the chances are that water volition exist condensing on the surface rather than the surface drying out. The real trouble with drying is when the air is libation than the concrete. So if we tin get cool concrete, we should be OK. This is NOT to say that hot conditions can't cause increased cracking and plastic shrinkage cracking, because it can if the concrete temperature is high and the humidity is depression.

Commencement at air temperature, draw a vertical line up to relative humidity, then a horizontal line to the right to concrete temperature, then go vertically downwardly to wind velocity, and horizontally to the left to determine the evaporation rate. If the evaporation charge per unit is greater than 0.1, plastic shrinkage bully is likely.

To decide if evaporation will be a problem, apply the nomograph from ACI 305. Knowing air temperature, relative humidity, physical temperature, and wind velocity, you make it at a charge per unit of evaporation. If the rate is greater than 0.1 pounds per foursquare foot per hour, shrinkage corking is possible.

Related: Curing Concrete in Hot Weather

Thermal differentials

Hot dry subgrades and formwork can too result in cracks by absorbing water from the mix. Some other trouble with oestrus and physical is thermal differentials. All that means is that one role of the physical mass is warmer than some other part. If the differential is greater than about xx°F then you are likely to get cracks. This tends to be a item problem in mass concrete (members thicker than about 18 inches).

Air content

Finally, maintaining air content tin be a trouble in warm concrete. Mixing is more likely to drive air out of the concrete making the level hard to control.

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Source: https://www.concretenetwork.com/hot-weather-concreting/problem.html

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