Can you pour concrete in winter in Bend?

Two separate problems: the first few days, and every winter after

Central Oregon is hard on concrete in two ways. The first is early: a slab poured on a cold day can freeze before it has gained enough strength, and ice crystals forming in the fresh concrete damage it permanently. The second is long term: years of freezing and thawing, wet snow and deicers can flake the surface of a driveway or walkway. Both are preventable, and both come down to planning.

What counts as cold weather

ACI 306R-16, the American Concrete Institute's guide to cold weather concreting, defines cold weather as when the air temperature has fallen to, or is expected to fall below, 40 degrees F (4 degrees C). Below 40 degrees F, the hydration reaction that hardens concrete slows, and the concrete stops gaining strength at a useful rate. In Bend that describes many nights well outside the calendar winter, so the rules apply in shoulder seasons too.

The temperature of the concrete itself, not just the air, governs the limits. ACI 306R-16 gives recommended placement temperatures in its tables.

The 500 psi rule

The key number is strength before the first freeze. According to the ACI guidance summarized in the NIH technical bulletin on cold weather concreting, concrete should be protected from freezing until it reaches a compressive strength of at least 500 psi. Until then, the water in it can freeze and expand, breaking the young concrete apart.

Getting there in the cold means holding heat in. The bulletin lists insulating blankets or heated enclosures to keep the concrete from freezing, non chloride accelerators to speed hydration, and insulating the subgrade with blankets a few days before the pour.

Never pour on ice or snow

Surfaces that touch the concrete matter as much as the air. The guidance is to keep forms, reinforcement and the ground free of ice and snow and above freezing at the time of placement. In practice that means clearing snow early, thawing the subgrade under blankets and scheduling the pour for the warmest part of the day.

Done right, cold weather is not a defect. The same bulletin notes that properly cured concrete placed in cold weather has the potential to develop higher ultimate strength and greater durability than concrete placed at higher temperatures.

Freeze and thaw: why air entrainment matters here

The long term problem is called scaling: local flaking or peeling of a finished surface. The Concrete in Practice sheet on scaling lists its causes: freezing and thawing with moisture or deicing salts, concrete with no or too little entrained air, finishing while bleed water is on the surface, insufficient curing, and heavy use of chloride deicers.

Air entrainment puts tiny bubbles in the concrete that give freezing water somewhere to go. The same sheet calls for 6 to 7 percent air in freshly mixed concrete for severe exposures, with 3,500 psi strength for freeze and thaw exposure and 4,000 psi where deicers are used. The Tennessee Concrete Association's summary of ACI 332 for driveways lists about 6 percent air and 4,500 psi.

Your first winter with new concrete

What you do after the pour matters too. The scaling sheet is blunt: do not use calcium or sodium chloride deicing salts in the first year after placing the concrete. Never use ammonium sulfate or ammonium nitrate as a deicer at all; they are chemically aggressive and attack concrete surfaces, and they show up in many fertilizers. A breathable silane or siloxane sealer can add protection.

Use sand for traction that first winter, and shovel or plow promptly. If you would rather not do it yourself, RCC offers snow removal in Bend.

What to ask before a cold weather pour

If your pour falls in a cold stretch, ask your contractor: What is the forecast low for the first few nights, and what protection is planned? Will the subgrade be thawed and covered before the pour? Is the mix air entrained, and is an accelerator being used? How long will blankets or heat stay in place? When can the slab take foot traffic and vehicles? Good contractors plan this before the truck is ordered, not the morning of.

Planning a winter pour with RCC

If your project has to happen between November and March, tell us when you call. We will plan the schedule, the mix and the protection around the forecast. For pricing, see what drives the cost of a driveway or slab, and for everything RCC pours, see concrete services.