Yes, concrete is poured in Chicago winters, but only with a plan. Fresh concrete freezes at about 25 F, and frozen concrete can lose more than half its potential strength. A prepared crew places warm concrete on a thawed, frost-free base, then protects it with insulated blankets or a heated enclosure until it reaches 500 psi, about two days. Accelerators can help, but they do not prevent freezing.
Pouring concrete in winter in Chicago is routine for a crew that plans for it and a bad idea for one that doesn't. The concrete is not the problem. The problem is the first two days, when water in the mix can freeze before the slab has any strength. Everything a good crew does in January is about getting through those two days.
This article covers how a winter pour is protected and what to ask. For the narrower question of how cold is too cold, see our guide on the coldest temperature to pour concrete in Chicago.
What actually goes wrong when concrete freezes
Fresh concrete freezes if its temperature falls below about 25 F. Frozen fresh concrete can lose more than 50 percent of its potential strength and will not be durable. The industry standard is to protect it from freezing until it reaches 500 psi, which takes about two days after placement (NRMCA).
That is the short version of the risk. A slab that froze early can look fine on day two. It shows up later as a surface that flakes, a slab that is weaker than the one next to it, or concrete that never seems to harden properly. You can't see the damage when it happens, which is why winter work depends on the process, not on inspection afterward.
Cold also slows things down. As a rule of thumb, every 20 F drop in concrete temperature roughly doubles setting time (NRMCA). A slab that would be ready to finish in a couple of hours in May can need much longer in January, and crews who rush the finish while bleed water is still rising weaken the surface.
When does a pour count as "cold weather"?
Cold weather practice starts well before the thermometer says 32. The NRMCA definition is more than three consecutive days with an average daily temperature under 40 F, with the air not above 50 F for more than half of any 24-hour period. Newer ACI wording applies the cold-weather provisions whenever air temperature is below, or expected to fall below, 40 F during the protection period (NRMCA). Which edition governs depends on the code adopted, so ask your contractor which standard the job follows.
In a Chicago year, that means cold-weather practice can apply well outside the deep-winter months.
How do crews get the base ready?
Before any concrete shows up, the ground has to be right.
- No frost, no ice, no snow. Snow, ice and frost must be removed before placing, and anything the concrete touches must be above freezing (NRMCA).
- No frozen subgrade. Concrete should never go on a frozen subgrade (NRMCA). A frozen base thaws and settles later, and the slab moves with it.
- Thawing the ground. Ask how the crew thaws the ground and how they check it before the truck is called.
This is also the step owners skip when they hire someone who is looking to fill a slow week. A crew that says it can just pour on the dirt "as long as it's above freezing" has told you what you need to know.
What temperature should the concrete be when it arrives?
The supplier can heat the mix water and sometimes the aggregate, so the concrete comes in warm. The NRMCA recommendations for concrete temperature as placed are 55 F for sections thinner than 12 inches, 50 F for 12 to 36 inches and 45 F for 36 to 72 inches, and the concrete should not exceed these by more than 20 F (NRMCA). A driveway, sidewalk or garage slab falls in the thinnest category.
Warm concrete is a head start, not a finish. Once it is placed, it begins to lose heat to the ground and the air, and that is where protection takes over.
How is a fresh slab protected: blankets, enclosures and heat?
This is the heart of the job. The slab has to stay warm long enough to reach 500 psi, and it should not cool faster than 5 F per hour for the first 24 hours (NRMCA).
- Insulated blankets. Thick insulating blankets go on as soon as the surface is finished. The idea is to hold in the heat the concrete is already giving off as it sets.
- Heated enclosures. For larger pours, or when it is very cold, a crew builds a temporary enclosure with plastic sheeting and frames and heats the inside. If heat is used, ask how the crew keeps hot air from drying the fresh surface, how they ventilate, and who monitors the temperature.
- Windbreaks and ground cover. Wind pulls heat out faster than most people expect. The ground under and around the slab matters as well.
- Cure with moisture retention, not wet curing. When freezing is expected, use a membrane curing compound, paper or plastic. Wet curing is not recommended when freezing is expected. Curing normally runs at least 3 to 7 days with concrete temperature kept above 50 F (NRMCA).
When the protection comes off matters too, because the slab shouldn't cool fast. Ask how the crew plans to remove it.
What do accelerators do, and what don't they do?
Accelerators speed setting, so the concrete gets through its vulnerable period sooner. Calcium chloride should not exceed 2 percent by weight of cement. Non-chloride accelerators are advised where reinforcing steel is a corrosion concern (NRMCA).
What they do not do is prevent freezing. NRMCA says so directly (NRMCA). An accelerator is one tool alongside warm concrete and insulation. If a contractor's whole winter plan is "we add something to the mix," get a better plan.
Does air entrainment matter more in winter?
Yes. Concrete exposed to freeze-thaw cycles while wet should be air-entrained, and new concrete should be protected from freeze-thaw cycling until it reaches at least 3,500 psi (NRMCA). For exterior slabs that face freezing and deicers, NRMCA recommends about 6 percent total air and a 4,000 psi specified strength, with no excess water at the site (NRMCA).
Skipping air entrainment is how a driveway ends up with a flaking face by its second spring. Our article on why concrete scales in Chicago covers the pattern in detail.
What to do the first winter after the pour
Even a good winter pour needs patience in its first season.
- Skip the salt if you can. NRMCA advises avoiding deicers on new concrete in its first winter and using clean sand for traction. After that, use moderate amounts. Never use ammonium sulfate, ammonium nitrate or magnesium-based products (NRMCA).
- Don't drive on it too soon. How long is the right wait depends on strength gain and weather. See how long to wait before using new concrete.
- Watch for scaling. Poor finishing and too much deicer on new concrete are both causes of surface scaling (NRMCA).
A common pattern is a late-season pour done to beat a deadline, where the slab was fine for a month and then started shedding its surface in March. The usual causes are no protection, a mix without enough air, or salt thrown on in the first winter. It's rarely one thing, and it isn't visible the day the crew leaves.
What to ask a contractor before a winter pour
- What temperature will the concrete be when it arrives?
- How will you thaw and check the base, and what do you do if it is frozen?
- What protection goes on, for how long, and who checks it?
- Is the mix air-entrained, and what is the specified strength?
- Are accelerators in the plan, and which type?
- When can I walk, drive and use salt on it?
If you can wait, a spring pour avoids all of this. If you can't, a prepared crew does it every winter. Our concrete crew can walk your site and tell you which one you are. For the bigger picture, start with the concrete and sidewalk guide, and keep our building maintenance calendar handy.
Common questions
Yes, with protection. The concrete has to be placed warm on a frost-free base and kept from freezing until it reaches about 500 psi, roughly two days. Insulated blankets or heated enclosures do the protecting. Skipping that step is what ruins winter pours.
Fresh concrete that freezes can lose more than half of its potential strength and will not be durable. The damage is not always visible at first. It tends to appear later as flaking, softness or a weak surface.
No. Accelerators speed up setting, but they do not prevent freezing. They are used alongside warm concrete and insulation, not instead of them.
Mild spring and fall days are easiest on the concrete and the crew, because less protection is needed. Winter pours work when they are planned. Ask your contractor what their plan is for the specific dates.
Avoid it if you can. Deicers on new concrete in its first winter make scaling more likely. Use clean sand for traction, and afterward use moderate amounts of an acceptable deicer. Never use ammonium or magnesium-based products.
Sources
- National Ready Mixed Concrete Association: Concrete in Practice 27: Cold Weather Concreting (PDF)
- National Ready Mixed Concrete Association: Concrete in Practice 11: Curing In-Place Concrete (PDF)
- National Ready Mixed Concrete Association: Concrete in Practice 2: Scaling Concrete Surfaces (PDF)
- National Ready Mixed Concrete Association: Concrete in Practice 4: Cracking Concrete Surfaces (PDF)
Facts last checked: October 7, 2026.
This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.