The "Cold Facts"
With the arrival of fall and cooler temperatures, the placement of exterior flatwork (driveways & sidewalks) can continue, provided that the principles of "Cold Weather Concreting" are followed. By definition (ACI 306), cold weather conditions exist when "…the air temperature has fallen to, or is expected to fall below, 40°F during the protection period."
Why Cold Weather Changes Everything
Concrete gains strength through hydration — a reaction between cement and water that generates its own heat and depends on temperature to keep going. Cold slows that reaction, and enough cold stops it:
- Below 50°F, hydration slows significantly. Set times stretch out and finishing windows move unpredictably.
- Below 40°F, hydration can stop almost entirely. Concrete held at these temperatures does not simply cure more slowly — it may gain almost no strength until it warms back up.
- Concrete that freezes before it reaches roughly 500 psi can be permanently damaged: water still held in the pore structure expands as it turns to ice and disrupts the paste before it has the strength to resist. At 50°F or above, concrete generally reaches 500 psi — enough to survive one freezing cycle — in about 48 hours.
Every guideline below serves one of those three facts: keep the concrete warm enough to react, and protect it long enough to outrun the first freeze.
Before You Pour
- Have protection materials on site before the first truck arrives. Protection that has to be found mid-pour arrives too late.
- The subgrade must be thawed and free of frost, snow and standing ice.
- Clear snow and ice out of the forms and off any reinforcement before concrete arrives.
- Check the forecast across the whole protection period, not just placement day. The ACI 306 trigger is the temperature expected during protection — a mild afternoon followed by a hard freeze is a cold weather pour.
Accelerated Early Strength Gain
To overcome delayed strength and initial set development associated with cold weather conditions, one or a combination of the following mix adjustments are recommended:
- Addition of non-chloride accelerating admixtures.
- Addition of calcium chloride admixtures. Because calcium chloride can promote corrosion of embedded reinforcement, use a non-chloride accelerator instead where the concrete contains reinforcing steel or will be exposed to deicing chemicals.
- Increasing the cement content by 100-200 lbs. This applies equally to portland cement (Type I) and to blended portland-limestone cement (Type IL).
Placement Guidelines
- Do not place concrete on a frozen subgrade; upon thawing, uneven settlement and cracking are likely to occur.
- The minimum concrete temperature, as placed and maintained, must exceed 55°F.
- However, caution should be exercised with concrete temperatures above 75°F.
- Appropriate curing and cold weather protection must be incorporated to prevent the concrete from freezing.
Curing and Cold Weather Protection
To develop the strength, durability, and permeability potential of the concrete, curing and protection during cold weather conditions are essential. The following guidelines are recommended upon placement:
- The curing period must extend a minimum of 7 days (maintaining the 55°F internal temperature of the concrete).
- Do not seal freshly placed concrete. Sealing retains water in the concrete thereby keeping it saturated during freeze/thaw conditions.
- Cold weather protection is best provided through insulating blankets or loose straw (minimum 12 inches deep) sandwiched between a waterproof cover e.g. polyethylene.
Curing Compounds Are Not Sealers
A membrane-forming curing compound (ASTM C309) holds moisture in so hydration can continue. A sealer is a separate, later decision — and sealing fresh concrete traps water where it will do damage. In cold weather the compounds themselves have temperature limits:
- Water-based (emulsion) C309 compounds generally require an application and surface temperature of at least 40°F.
- Solvent-based compounds tolerate roughly 35°F, but Michigan VOC limits may restrict their use — check the product data sheet before specifying one.
- Verify compatibility with any overlay or coating planned later. A curing compound that cannot be bonded over becomes the next contractor's problem.
Ending the Protection Period
Protection should not come off all at once. Concrete held warm under blankets while the air above it sits well below freezing will crack if its surface drops to ambient temperature suddenly — the warm interior and the chilled surface pull against each other. Remove protection gradually so the surface cools over hours rather than minutes, and plan removal for the warmest part of the day rather than the coldest.
Mix Design Recommendations
A minimum specified compressive strength of 4000 psi at 28 days is required for exterior flatwork exposed to cyclic freezing and thawing. The slump, as placed, should not exceed 5 inches with the exception of those mixes incorporating mid or high-range plasticizers. The recommended air content is 6.5 ±1.5%.
Owner Care — First Winter
New concrete is at its most vulnerable during its first winter, and much of the surface damage that shows up in spring was set in motion during those first months.
- Deicing salts must not be applied during the first winter. For traction, sand is recommended.
- Do not allow snow and ice to accumulate. Accumulated snow and ice maintain the concrete in a saturated condition during freeze-thaw conditions.
- New flatwork needs time to reach its design strength and dry out. Concrete that is still wet through its pore structure has no room to accommodate expanding ice, which is why the first winter is the most vulnerable one.
Cold Weather Concreting FAQs
What temperature is too cold to pour concrete?
There is no single cutoff — what matters is the temperature the concrete is held at, not the temperature outside. ACI 306 defines cold weather as air temperature at or expected below 40°F during the protection period. Concrete can be placed well below that, provided it is placed at a minimum of 55°F and protected so it stays there. Without protection, concrete placed into near-freezing conditions may never gain its designed strength.
Can you pour concrete in winter in Michigan?
Yes. Exterior flatwork is placed through Michigan winters routinely. It requires mix adjustments for early strength, a minimum 55°F placement temperature, and insulating protection maintained for at least 7 days. What you cannot do is place winter concrete the same way you place it in July.
When should you stop pouring concrete for the season in Michigan?
There is no calendar date. The question is not what month it is, but whether you can place at a minimum of 55°F and hold the concrete there, protected, for at least 7 days. A contractor equipped with blankets, an accelerating admixture and a mix designed for early strength can place well into a Michigan winter. One who cannot meet the placement and protection requirements should not be placing in October either.
What is ACI 306?
ACI 306 — currently published as ACI PRC-306-16, Guide to Cold Weather Concreting — is the American Concrete Institute's guidance document for placing and protecting concrete in cold conditions. It is what defines "cold weather" as air temperature at or expected below 40°F during the protection period, and it sets the minimum concrete temperatures and protection periods that specifications across Michigan reference. Curing itself is covered by a companion document, ACI 308R-16.
Does concrete stop curing in cold weather?
It can. Concrete gains strength through hydration, and that reaction depends on temperature: below 50°F it slows significantly, and below 40°F it can stop almost entirely. Concrete held near freezing is not curing slowly — it may be gaining almost no strength until it warms back up. This is why protection matters more than patience in winter.
What happens if concrete freezes before it cures?
If concrete freezes before reaching roughly 500 psi, the water in its pore structure expands as ice and disrupts the cement paste before it is strong enough to resist. The damage is permanent and cannot be cured out afterward — it shows up as reduced strength, scaling and a surface that deteriorates early. At 50°F or above, concrete typically reaches 500 psi in about 48 hours.
Can you pour concrete on frozen ground?
No. Concrete placed on a frozen subgrade sits on ground that will settle unevenly as it thaws underneath, and the slab cracks to follow it. The subgrade must be thawed and clear of frost, snow and standing ice before placement, and snow and ice should be cleared out of the forms and off any reinforcement as well.
What air content and strength does exterior concrete need in Michigan?
For exterior flatwork exposed to cyclic freezing and thawing, MCA specifies a minimum 4,000 psi compressive strength at 28 days and a recommended air content of 6.5 ±1.5%. Entrained air is what gives freezing water somewhere to go inside the paste; without it, Michigan freeze-thaw cycles will scale a slab regardless of how carefully it was placed. Slump as placed should not exceed 5 inches, except in mixes using mid- or high-range plasticizers.
Should I use calcium chloride to speed up concrete in cold weather?
Calcium chloride does accelerate early strength gain, but it can promote corrosion of embedded reinforcement. Where the concrete contains reinforcing steel or will see deicing chemicals, use a non-chloride accelerator instead. Increasing cement content by 100-200 lbs is another route to the same goal.
How do you protect fresh concrete from freezing?
Insulating blankets, or loose straw at least 12 inches deep sandwiched under a waterproof cover such as polyethylene. The goal is to hold the concrete's internal temperature at 55°F for a minimum of 7 days. In a Michigan cold season this protection is a requirement rather than an optional extra — and it needs to be on site before the first truck arrives, not sourced once the pour is underway.
How long does new concrete need to be protected in cold weather?
At minimum 7 days, with the concrete's internal temperature maintained at 55°F throughout. Insulating blankets, or loose straw at least 12 inches deep under a waterproof cover, are the usual methods. Remove protection gradually rather than all at once, so the surface is not dropped to ambient temperature suddenly.
What is the difference between a curing compound and a sealer?
A membrane-forming curing compound (ASTM C309) is applied to fresh concrete to hold moisture in so hydration can continue — it is part of curing. A sealer is applied much later, to finished and dried concrete, to resist water and staining. They are not interchangeable and they do not share a schedule. In cold weather, curing compounds carry their own temperature limits: water-based (emulsion) products generally need at least 40°F, and solvent-based products tolerate roughly 35°F, though Michigan VOC limits may restrict their use.
Should I seal new concrete before winter?
No. Sealing fresh concrete traps water inside it, and a slab that stays saturated going into freeze-thaw cycles is more vulnerable, not less. Keeping water out is the goal; sealing it in achieves the opposite. Sealing is a separate decision for later, once the concrete has reached strength and dried out.
When can I use salt on a new concrete driveway?
Not during the first winter. Use sand for traction instead. New concrete needs time to reach design strength and dry out, and a slab that is still saturated has no room to accommodate expanding ice. Keeping snow and ice cleared off matters as much as avoiding salt — standing snowmelt keeps the slab saturated through every freeze-thaw cycle.
Related MCA Resources
- Concrete Curing Methods and Best Practices — curing requirements year-round.
- Hot Weather Concreting — the other end of the season.
- Technical Support — talk to MCA about a specific placement.
- Certification & Training — ACI and MCA classes for crews placing in cold weather.
Download the following PDFs for additional resources on Cold Weather Care: