How Climate Affects Concrete – Hot Weather, Cold Weather, and Wind

Know what your concrete will likely do when the weather starts to get too hot, too cold, and/or too windy.

While working with concrete may come as second nature to many contractors, it is one of the trickiest substances to work with due to how quickly it can change when exposed to different temperatures, humidity, and wind rates. Ideal conditions for concrete are few and far between.

According to the ACI, concrete may be affected by, “…one or a combination of the following conditions 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; and high wind speed.” Under fair weather conditions, concrete can take anywhere from 8 to 48 hours to set properly. While concrete can reach its full strength in as little time as a week, it also takes nearly a month for it to cure properly.

However, anyone who has worked in construction before knows that weather conditions are seldom ideal.

While working with concrete may come as second nature to many contractors, it is one of the trickiest substances to work with due to how quickly it can change when exposed to different temperatures, humidity, and wind rates. The American Concrete Institute’s (ACI) technical publications are an excellent resource that provide insights regarding the plethora of effects of environmental factors on concrete. The ACI covers a variety of subtopics, ranging from extreme temperatures, humidity levels, wind velocity, natural disasters, saltwater, and freshwater’s effects on concrete in order to give contractors and concrete industry professionals accurate and up-to-date information.

Heat

The ACI’s (305.1 – 14 Hot Weather Concreting) specifications for setting and mixing concrete in hot weather suggests contractors should try to limit the maximum concrete temperature to 95º F. Contractors should ideally aim to work with, or pour, concrete when it is anywhere from 50-60º F. Under fair weather conditions, concrete can take anywhere from 8 to 48 hours to set properly. While concrete can reach its full strength in as little time as a week, it also takes nearly a month for it to cure properly.

However, anyone who has worked in construction before knows that weather conditions are seldom ideal, which is why contractors must have a firm understanding of the effects of hot weather on concrete structures and how to use weather to their advantage.

For example, concrete is known to set quicker in hot weather when compared to cold weather. This is because moisture found in freshly poured concrete evaporates at a quicker rate in hot weather and subsequently allows for a faster setting time.

Due to the rapid evaporation of moisture, concrete that is poured during warm weather conditions is also more likely to experience cracks. Concrete will also be prone to more cracks if it is poured in a location where the weather cools down quickly during the night. Because of these effects, concrete that is poured and cured in 75º F weather will likely outperform concrete that is poured and cured in 100º F weather. Simply put, timing and background knowledge are absolutely crucial when it comes to working with concrete in warm weather.

Cold

Cold weather, according to the ACI 306 – “Guide to Cold Weather Concreting”, is defined as three continuous days of low temperatures, specifically below 40º F. Additionally, the ACI also considers air temperatures below 50º F for more than 12 hours as “cold weather.”

Unlike working with concrete in hot weather, where certain warm temperatures can be used to a contractor’s advantage, colder temperatures can be detrimental to newly poured concrete.

When a concrete powder is mixed with water, an immediate chemical reaction will occur which results in an internal crystallization of the concrete. These crystals make it possible for concrete to withstand additional pressure that may be caused by frozen water molecules within the concrete.

Crystals will continue to grow for an extended period of time, even in cold weather. However, if temperatures drop below 15º they will no longer grow and the concrete will not cure at its full compressive strength.

Under ideal weather conditions, concrete can attain a minimum compressive strength of roughly 500 lbs. per square inch in as little as 24 hours. This is much harder to achieve in colder climates, so contractors have learned industry tricks to “fool” the concrete into thinking it’s in warmer conditions so it will ultimately cure faster.

The ultimate contractor rule when working with concrete in cold weather: Never pour concrete directly onto frozen or thawed ground space. The frozen ground will actually settle as it thaws. Because of this, concrete that is poured in very cold temperatures could also be susceptible to cracking, similar to working with concrete in warmer climates.

Wind

The ACI also states that wind velocity can affect freshly poured concrete by allowing too much water or moisture to evaporate from the concrete’s surface at a fast rate. In fact, the ACI technically classifies high wind velocity under hot weather due to the similar excessive loss of moisture concrete can experience when poured in warmer temperatures.

When concrete is poured during extremely windy weather, the rapid velocity of air will only contribute to excess moisture evaporating from the slab of concrete. Because of this, the abrasion resistance and curing condition of concrete will subsequently suffer.

Colder winds can produce what’s called a “wind chill,” which can strip excess heat from concrete. Additionally, plastic shrinkage cracking can occur when the surface of concrete dries before it has fully cured. To combat wind chill, it isn’t uncommon for contractors to turn to heaters to aid the curing process. Contractors can also use sealers to protect concrete from climates below 50º F.

Concrete is a delicate material. Unbeknownst to many people, it is not only affected by extreme temperatures, but also by humidity levels, as well as the velocity and intensity of the wind. Working with concrete demands skill and patience. It requires both the expertise of those working with concrete, as well as the cooperation of environmental factors in order to produce a smooth, strong, properly cured structure.


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Surging Multifamily Housing Starts Beat Forecasts

Demand for apartments near major employment centers has strengthened, reducing vacancy rates and driving rents higher.

Multifamily starts leaped 20.6% to a 539,000-unit annual rate. Demand for apartments has been surprisingly strong and rents have risen, giving developers confidence to move projects forward.

Single-family U.S. housing starts fell 2.8% in August, but the surging multifamily construction raised overall starts to beat expectations, rising 3.9%. Building permits jumped 6.0%. Total starts hit a 1.62-million-unit annualized rate after revisions raised the July totals, according to data from the Department of Commerce on Tuesday. The median estimate in a Bloomberg survey forecast a 1.55 million pace.

The drop in single-family starts has more to do with supply and labor shortages than weakening demand. “Builders are increasingly having to limit sales, as they are uncertain when they will be able to complete homes due to ongoing shortages of essential building materials,” says Mark Vitner, senior economist with Wells Fargo Securities.

The impact of supply shortages shows up in the rising number of single-family homes that have been permitted but not started, up 1.4% in August and 50% over the past year. Shortages are widespread. Similar to what is happening in the auto sector, a single part such as panel box or wedge anchors, can hold up construction.

Details in the Digits

Multifamily starts leaped 20.6% to a 539,000-unit annual rate. Demand for apartments has been surprisingly strong and rents have risen, giving developers confidence to move projects forward.

“The apartment market is seeing somewhat of a reversal of the pandemic exodus,” says Vitner. “Demand for apartments near major employment centers has strengthened, reducing vacancy rates and driving rents higher. Demand also remains strong in the suburbs, with many potential renters opting to renew their lease and wait for housing inventories to normalize.”

“The apartment market is seeing somewhat of a reversal of the pandemic exodus,” says Vitner. “Demand for apartments near major employment centers has strengthened, reducing vacancy rates and driving rents higher. Demand also remains strong in the suburbs, with many potential renters opting to renew their lease and wait for housing inventories to normalize.”

August’s 2.8% slide in single-family construction follows a 4.7% drop in July, but single-family construction remains at a robust 1.076-million-unit pace. Spot-market prices for lumber have plummeted, but those lower prices have not yet made their way to home builders.

Other essential building materials remain in short supply, including windows, cabinets, electric breaker boxes and wedge anchors. Builders are restricting sales due to the inability to let buyers know when homes will be completed.
Builder Confidence Rises in September

The September Housing Market Index (HMI) from the National Association of Home Builders and Wells Fargo points to where the single-family market is headed. The HMI rose one point in September to 76. While the index remains at a high level, it has been cooling since hitting an all-time high of 90 in November. The latest survey shows concerns about lumber prices have eased considerably, but builders are still dealing with widespread materials shortages, which is lengthening the time it takes to complete a home.

“The most encouraging aspect of the September HMI is the slight improvement in underlying demand,” says Vitner. “The present sales index rose one point to 82, following four months of decline.”

“The most encouraging aspect of the September HMI is the slight improvement in underlying demand,” says Vitner. “The present sales index rose one point to 82, following four months of decline.”

Prospective buyer traffic improved, although it remains well below levels seen earlier this year. Demand for homes remains strongest in the South and West, particularly the Mountain West. New home sales are increasingly being driven by the affordability migration from the West Coast and Northeast to more affordable markets in the Rocky Mountains, Southwest and Southeast. The influx of buyers from higher-priced housing markets has skewed new home sales more toward the upper-end of the price spectrum. Builders have focused their attention at this end of the market as well, contributing to the dearth of more affordable homes currently on the market.


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Concrete and cement industries brace for demand boom

$1 trillion infrastructure plan looks to create increased demand.

Concrete is the foundation of just about everything. It’s used to construct buildings, highways, bridges, roads and more.

During the Covid-19 pandemic, concrete fell victim to the same phenomena impacting other essential materials and goods: snarled supply chains and labor shortages. And demand for concrete — and its essential ingredient, cement — appears to have only increased, after the Senate passed the $1 trillion infrastructure package to upgrade America’s roads, bridges and tunnels.

“In the short-term, we continue to have the supply chain difficulties, particularly in certain markets, and so prices are rising,” Anirban Basu, chief economist for the national construction industry trade association Associated Builders and Contractors, told CNBC. “So right now, apparently, supply is not rising up to meet demand.”

The industry also faces labor shortages of skilled workers and truck drivers. And the recent housing boom means more demand for concrete and cement, putting more pressure on the industry to increase capacity.

On top of all of this, there’s also a push to reduce the amount of carbon emissions that come from the industry. A study published by the National Academy of Sciences in 2019 estimates that global cement production accounts for 8% of global carbon emissions, making it the largest single industrial emitter of carbon dioxide.

Watch the video

to learn more about the cement-concrete supply chain and whether the U.S. industry can handle the coming demand from the new $1 trillion infrastructure spending plan.

Here is a link to a video that does a great job explaining the current and forecast demand:


https://www.cnbc.com/video/2021/08/20/cement-industry-gets-ready-for-demand-boom-amid-us-infrastructure-push.html



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The U.S. multifamily construction market remains strong

2021 multifamily housing outlook: Dallas, Miami, D.C., will lead apartment completions

In its latest outlook report for the multifamily rental market, Yardi Matrix outlined several reasons for hope for a solid recovery for the multifamily housing sector in 2021, especially during the second half of the year.

While multifamily owners, developers, and property managers collectively braced for severe drops in rent growth, construction starts, project completions, and availability of capital amid the COVID-19 pandemic, the drastic declines never materialized.

Rent growth did take a step back in select markets, especially in “high-cost gateway” metros like San Jose (-13.7%) and San Francisco (-9.4%), as renters continued to leave pricey urban neighborhoods for less-dense, cheaper suburban areas.

But on the flip side, “many tertiary and tech hub markets have benefited from migration out of the gateways,” wrote the authors of the Yardi Matrix report. Secondary and tech markets like the Inland Empire, Sacramento, Tampa, and Las Vegas all saw solid rent growth in 2020.

Multifamily construction pipeline for 2021

Other than the temporary shutdowns of work sites during the pandemic, construction work on multifamily housing developments continued to hum along through 2020 and into 2021. In all, 285,000 multifamily units were delivered throughout U.S. markets in 2020, down about 7% from 2019, but not nearly as severe a drop as many had predicte

According to Yardi Matrix, the multifamily sector has a “robust pipeline” of new projects, with some 765,000 units in some stage of construction as of early 2021.

This “should keep deliveries above that 300,000 mark for the next few years.” The firm projects 327,718 units will be delivered in 2021.

Here are the top 25 multifamily markets for 2021 (total number of construction completions, % growth in completions YOY):

  1. Dallas: 22,909 completions (+12.1% YOY)
  2. Miami: 16,262 (+66.3%)
  3. Washington, D.C.: 14,541 (+50.5%)
  4. Houston: 11,500 (-3.1%)
  5. Los Angeles: 11,296 (+16.5%)
  6. Atlanta: 10,939 (+9.7%)
  7. Austin: 10,301 (-10.0%)
  8. Seattle: 9,816 (+29.9%)
  9. Phoenix: 9,334 (+13.6%)
  10. Denver: 8,653 (-29.7%)
  11. Boston: 8,449 (+20.8%)
  12. Chicago: 7,797 (+0.8%)
  13. New York City: 7,335 (+24.2%)
  14. San Francisco: 7,166 (+64.8%)
  15. Twin Cities: 6,760 (+4.9%)
  16. Charlotte: 6,692 (+55.3%)
  17. Orlando: 6,662 (+21.5%)
  18. Philadelphia: 6,071 (+27.7%)
  19. Nashville: 5,457 (+41.1%)
  20. Tampa–St. Petersburg: 5,103 (+20.1%)
  21. San Antonio: 4,960 (-6.5%)
  22. New Jersey–Northern: 4,955 (+29.9%)
  23. Salt Lake City: 4,633 (-0.6%)
  24. Louisville: 4,484 (+215.6%)
  25. White Plains: 4,464 (+199.6%)

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Gypsum an Important Source of Sulfur

Sulfur important in plant growth.

Long taken for granted as supplied by the soil and atmosphere, sulfur is slowly rising as a yield-limiting nutrient in crops across the US.

Ken Ihlenfeld is certainly finding this to be true. The West Bend, WI, producer farms 2,500 acres including 400 acres of alfalfa used for his 400-head dairy operation. When his standard soil test couldn’t explain the yellowing and unevenness in his alfalfa fields he dug deeper including tissue testing for secondary macronutrients and micronutrients. “We discovered sulfur levels were really low,” he says.

He spread one ton of gypsum — a source of sulfate sulfur and calcium — per acre after the first cutting on 150 acres of alfalfa and Ihlenfeld noticed a significant difference.

“There was a 6-inch height difference, the plants were greener and the crop was lush,” he says. “The treated acres yielded 0.6 tons more than the untreated acres on a dry matter basis.”

The success prompted him to apply gypsum on the rest of his alfalfa acres and to some corn and soybean ground.

“Already this spring our hay fields are greener and more even in color than our neighbors that haven’t applied gypsum and the check strips we left are very noticeable,” he says.

After hearing repeated farmer accounts of sulfur improving corn yields, Fabian Fernandez, researcher and assistant professor of soil fertility and plant nutrition at University of Illinois, decided to test response himself. His three years of research farm and on-farm trials seem to confirm the reports.

“We have seen an increase in the frequency and intensity of crop response to sulfur application compared to Illinois trials conducted in the late 1970s which showed little to no response,” he reports. “The responses are very variable, but we are identifying conditions where sulfur applications will be beneficial for farmers.”

Results from a 2006 Iowa State University study on corn yield response to sulfur application showed an average 38-bushel yield response to sulfur application for six sites across northeast Iowa. These sites were specifically chosen for their likelihood of being sulfur deficient.

In small research farm plots not specifically chosen for deficiency, Fernandez found a more moderate average 5-bushel corn yield response to sulfur applications over three years. One of his Illinois on-farm plots, though, yielded surprising results.

“It produced a one-year, 51-bushel corn increase over the check with an application of sulfur,” Fernandez says. “That’s not a normal response by a long shot, but it goes to show that if sulfur is truly deficient it can severely limit yields.”

Less sulfur in rain

Sulfur deposits on farm fields have decreased over the years, in part as a result of emission-reducing technologies used at coal-fired power plants. There is less sulfur in the atmosphere and in rain that hits farm fields.

There is no simple test for determining sulfur deficiency on individual farms, says Warren Dick, a researcher and former professor in Environmental and Natural Resources at The Ohio State University. Researchers have found, however, that certain factors can increase the likelihood of seeing a response to sulfur.

Soil type, cropping history and the crop planted can help determine on which acres farmers should try using sulfur. Soils with low organic matter are a good place to start as mineralization from organic materials is one of the leading sources of soil sulfur.

“Soils with low organic matter, such as coarse texture (sandy) soils or eroded soils likely found on sloping hills, are more likely to be low in sulfur and respond to sulfur applications,” Fernandez says.

Sulfur is an essential ingredient for creating proteins, so high-protein crops (alfalfa, canola, soybean, corn silage) require more sulfur than low-protein producing crops. A lack of sulfur can impact nitrogen utilization and yield.

There are several sulfur sources producers can use to meet crop demand including elemental sulfur one primary source is anhydrite and dihydrate gypsum.

Estimates vary, but roughly one pound of sulfur is needed to be applied to balance up to 16 pounds of applied nitrogen for a corn plant to produce proteins and grow. If there’s adequate nitrogen but deficient sulfur the plant won’t grow to its potential until it has the sulfur to balance that nitrogen. Deficiencies are particularly critical in early growth corn because that’s when yield potential is set. If the upper soil profile, where seedlings are growing, is deficient of sulfur there will be less yield potential.

Sulfur can be recycled back into the soil system through crop residue, Dick says, but in crops such as corn and alfalfa much of the protein — and sulfur — is removed with harvest.

“A 250-bushel corn crop removes quite a bit of sulfur every year without replacing it,” Dick says. “The same is true of hay fields. A lot of nutrients are removed when hay is cut and taken from the field, making alfalfa fields and mixed hay pastures good places to try sulfur applications.”

Sulfur Sources

There are several sulfur sources producers can use to meet crop demand including elemental sulfur one primary source is gypsum.

“Elemental sulfur is used, but it is very acid forming so it isn’t ideal for every situation,” Dick says.

At 16 percent sulfur by volume, gypsum is a budget-friendly option. The cost of a pound of sulfur in gypsum is significantly lower than sulfur in other forms. It also provides sulfur in a plant-available form and moves sulfur through the soil profile so it’s where it needs to be in the form it needs to be in for plants to use it. Gypsum provides the added benefit of 17-20 percent calcium and is often used in potato production and other calcium-loving specialty crops.

Extensive studies have shown all of the various gypsum sources are safe for land application, says Dick.

For Center Point, IN, producer Brad Brown, gypsum provides the double benefit of building soil structure and replenishing sulfur.

“We didn’t know about sulfur when we first started using gypsum in 1986 to loosen our soil for better drainage and rooting,” Brown says. “Getting sulfur with our gypsum was a win-win, it really helps our corn and it’s in the cheapest form we can get. Our yields are more even from acre to acre and year to year. The sulfur seems to excite the corn for good early season growth.”

Brown applies gypsum every other year. Initially he applied one ton per acre but has dropped to 1,400 pounds every other year applied in the fall ahead of corn.

“As the soil structure builds we’re able to cut back on the rate but we will keep applying it to maintain the sulfur supply for our corn. We shoot for 200-plus bushels per acre,” specifies Brown.

Wisconsin producer Ihlenfeld agrees gypsum is becoming a valued tool in his cropping operation. “We were attributing sulfur deficiency symptoms to disease, but now that we know what it is we’re able to correct the situation and our yields improved after only one application,” Ihlenfeld says. “Gypsum is a win-win for us because it boost yields by correcting the sulfur deficiency and the calcium helps loosen up our compacted soils.


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