{"id":16729,"date":"2022-06-12T09:26:18","date_gmt":"2022-06-12T16:26:18","guid":{"rendered":"https:\/\/essential.construction\/academy\/?p=16729"},"modified":"2026-11-04T07:13:41","modified_gmt":"2026-11-04T14:13:41","slug":"cold-weather-concrete","status":"publish","type":"post","link":"https:\/\/essential.construction\/academy\/tutorials\/cold-weather-concrete\/","title":{"rendered":"A Guide to Working With Concrete in Cold Weather"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><strong>Cold weather concrete is concrete that is mixed, placed and cured while the air temperature is at or below 40\u00b0F (4\u00b0C), or is forecast to drop that low before the concrete has been protected long enough.<\/strong> That threshold comes from ACI 306R-16, the American Concrete Institute&#8217;s Guide to Cold Weather Concreting. Below it, fresh concrete has to be delivered warm, kept above a minimum temperature and shielded from frost until it reaches roughly 500 psi (3.5 MPa). Let it freeze before that point and the damage is permanent.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Winter work does not have to mean poor concrete: ACI notes that cold-placed concrete that is kept from freezing and properly cured can end up stronger and more durable than the same mix placed in summer. This guide gives site supervisors and project managers the numbers that matter, a framework for the cold weather plan your specification will ask for, and practical advice on mixes, protection, strength monitoring and calcium chloride.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What Counts as Cold Weather for Concrete?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Two ACI documents define cold weather, and they do it in slightly different ways. It is worth knowing both, because your specification may cite either one.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>ACI 306R-16 (the guide)<\/strong> uses a forecast test: cold weather conditions exist when &#8220;the air temperature has fallen to, or is expected to fall below, 40\u00b0F (4\u00b0C) during the protection period.&#8221; The protection period is the time the concrete needs to be sheltered from the cold so it is not harmed.<\/li>\n\n\n\n<li><strong>ACI 306.1-90 (the standard specification, reapproved 2002)<\/strong> uses a trend test: more than three days in a row with an average daily temperature (the mean of the day&#8217;s high and low) below 40\u00b0F. The period stops counting as cold weather once the temperature stays above 50\u00b0F for more than half of a 24-hour day.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Plan around the guide&#8217;s version: one cold night after a mild afternoon pour can freeze an unprotected slab even when the three-day average looks fine.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Why Freezing Damages Fresh Concrete<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Concrete hardens because cement reacts with water (hydration). That reaction slows sharply as the concrete cools and almost stops near freezing. At the same time, the fresh mix is full of free water. Water grows by about 9% in volume when it turns to ice, so ice crystals forming in the young paste push it apart from the inside. Later curing cannot repair that damage.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The risk falls as hydration uses up the free water. ACI calls the danger point &#8220;critical saturation&#8221; and ties it to strength: once concrete reaches about 500 psi, and as long as no outside water is getting in, it can survive one freeze without lasting harm. Most well-proportioned mixes held at 50\u00b0F (10\u00b0C) reach that strength in about two days. Concrete that freezes in its first few hours, or before 500 psi, can lose as much as half of its potential strength and is left more porous.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">One freeze is not the only threat. Concrete that will face repeated freeze-thaw cycles or de-icing salts while still young should reach about 3,500 psi (24 MPa) before that exposure, and it needs to be air-entrained. Because the water in fresh concrete carries dissolved salts, it freezes a few degrees below 32\u00b0F (Concrete Foundations Association guidance puts it near 27\u00b0F), but that small margin is not something to rely on.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Cold Weather Concrete Temperatures at a Glance<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">ACI 306R-16 sets minimum concrete temperatures by the least dimension of the element. Thin members lose heat fastest, so they need to start warmer.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Least dimension of section<\/th><th>Minimum concrete temperature as placed and maintained<\/th><th>Max. gradual temperature drop in first 24 h after protection ends<\/th><\/tr><\/thead><tbody><tr><td>Less than 12 in. (300 mm)<\/td><td>55\u00b0F (13\u00b0C)<\/td><td>50\u00b0F (28\u00b0C)<\/td><\/tr><tr><td>12 to 36 in. (300 to 900 mm)<\/td><td>50\u00b0F (10\u00b0C)<\/td><td>40\u00b0F (22\u00b0C)<\/td><\/tr><tr><td>36 to 72 in. (900 to 1800 mm)<\/td><td>45\u00b0F (7\u00b0C)<\/td><td>See ACI 306R-16<\/td><\/tr><tr><td>Over 72 in. (1800 mm)<\/td><td>40\u00b0F (5\u00b0C)<\/td><td>See ACI 306R-16<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Warmer is not always better: ACI recommends staying within about 20\u00b0F (11\u00b0C) of these minimums, because overheated concrete needs more water and is more prone to cracking as it cools.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The guide also gives minimum protection periods, measured in days at the temperatures above. Accelerated-set concrete needs less time because it gains strength faster.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Service condition<\/th><th>Normal-set concrete<\/th><th>Accelerated-set concrete<\/th><\/tr><\/thead><tbody><tr><td>No load, not exposed to freezing in service<\/td><td>2 days<\/td><td>1 day<\/td><\/tr><tr><td>No load, exposed<\/td><td>3 days<\/td><td>2 days<\/td><\/tr><tr><td>Partial load, exposed<\/td><td>6 days<\/td><td>4 days<\/td><\/tr><tr><td>Full load<\/td><td>Determine from required in-place strength (ACI 306R-16 Chapter 8)<\/td><td>Determine from required in-place strength<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The service conditions describe what the element will do during the protection period and whether it will see frost once in use:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>No load, not exposed:<\/strong> no significant load during protection and no frost in service, such as an interior footing in a heated building.<\/li>\n\n\n\n<li><strong>No load, exposed:<\/strong> no significant load during protection but frost in service, such as a retaining wall.<\/li>\n\n\n\n<li><strong>Partial load, exposed:<\/strong> some load during protection, below its early-age capacity, and frost in service, such as pavement opened to light traffic.<\/li>\n\n\n\n<li><strong>Full load:<\/strong> must carry construction loads before reaching specified strength, typically shored or reshored elevated slabs and beams. Protection time comes from measured in-place strength, not the calendar.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Worked example: an 8-inch-thick site retaining wall cast with a normal-set mix carries no load during the protection period but will freeze every winter. Its least dimension is under 12 inches, so it should be placed and held at 55\u00b0F or warmer, and the condition is &#8220;no load, exposed&#8221;, so protection should last at least 3 days. Switch to an accelerated mix and the minimum becomes 2 days. Your project specification overrides these guide values, so always check it first.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How to Write a Cold Weather Concreting Plan<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Many specifications require the concrete contractor to submit a cold weather plan before winter work begins, and ACI 306.1 lets the engineer require that no cold weather concreting starts until the procedures have been reviewed and accepted. Once the engineer of record accepts it, the plan becomes the agreed record of what you will do, which heads off disputes later.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Three rules make the plan easier to approve and easier to live with:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Tie it to the specification.<\/strong> Open with a statement of which documents it responds to (the project specification and, where cited, ACI 306.1, ACI 301 or ACI 306R-16). Many specifications now point to ACI 301 or the ACI 306R-16 guide rather than ACI 306.1, so check which one yours names.<\/li>\n\n\n\n<li><strong>Describe means and methods, not textbook theory.<\/strong> Too little detail gets the plan rejected; too much can lock you into one way of working. Say what you will do and at what trigger temperatures.<\/li>\n\n\n\n<li><strong>Never promise what you will not do.<\/strong> If the plan says blankets go on within 30 minutes of finishing, the inspector will hold you to it.<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">ACI 306.1 lists what a detailed submittal should cover. Use it as the skeleton of your plan:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>How the subgrade, forms and reinforcement will be kept free of frost, ice and snow before the pour<\/li>\n\n\n\n<li>How concrete temperature will be kept up during delivery and placement<\/li>\n\n\n\n<li>The blankets, insulation, enclosures or heating to be used, by element and by temperature range<\/li>\n\n\n\n<li>Curing methods during and after the protection period<\/li>\n\n\n\n<li>Any accelerating admixtures<\/li>\n\n\n\n<li>How in-place strength will be verified<\/li>\n\n\n\n<li>How concrete temperatures will be measured and recorded<\/li>\n\n\n\n<li>How the concrete will be kept from drying out in cold, dry, windy weather<\/li>\n\n\n\n<li>What happens if the weather turns suddenly or equipment breaks down<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Production and Delivery<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Agree the cold weather mix and its delivery temperature with your ready-mix supplier, borrowing from their standard winter procedure where it fits. State how the minimum and maximum placement temperatures will be met, usually by heating the mixing water, and in hard cold the aggregates as well.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Note the strength-gain option you will use. ACI 306.1 allows a shorter protection period when early strength is boosted, for example by an accelerating admixture, Type III (high-early-strength) cement or extra cement (the specification quotes about 100 lb per cubic yard), and changes to the mix made to shorten protection should be submitted for acceptance. Price the options with the supplier. Where the specification permits calcium chloride it is usually the cheapest route; where only non-chloride accelerators are allowed, a cement change can work out cheaper.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Trucks rarely need insulated drums, because plants can batch warm enough. The real losses happen on site, when trucks queue or concrete sits in a crane bucket, a pump line or on a conveyor. Order deliveries to keep waiting time short, and write into the plan what you will do if a load arrives below the minimum temperature.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Placement and Subgrade<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Concrete must never go onto frozen ground. Say how the subgrade will be thawed (insulating blankets left down for a few days are often enough; otherwise use ground heaters or hydronic hoses) and how you will check that it has thawed to the depth the engineer requires. Clear snow and ice from forms and rebar, and identify any large metal embedments, such as heavy steel frames, rails or ducts, that need to be warmed above freezing before concrete is cast around them.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Protection<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">List the protection for each element type (slabs on ground, walls, columns, elevated slabs) and each temperature band, because one cold weather mix may not suit every element. Make sure enough material is on site before the first pour: blankets to give the R-value you need, plus poly sheeting, lumber, fasteners and vents for enclosures. If you plan to use combustion heaters, say how they will be vented. Wood forms on walls and columns give useful insulation if they can stay in place; if forms must be cycled quickly, you will need extra blankets for the stripped faces.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Curing<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Explain how the concrete will be kept from drying during the curing period. Avoid water curing in freezing weather: it leaves the concrete saturated just when protection comes off. Insulating blankets, forms left in place and curing compounds keep moisture in without that risk, and blankets also hold the heat.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Temperature Monitoring and Records<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Show where temperatures will be measured and how often. ACI 306.1 tells specifiers not to call for recording less than twice in each 24 hours, and many projects record far more often with data loggers. Include the checks that prove the concrete has reached the milestones that matter: about 500 psi for frost resistance, then the strengths needed to strip forms, remove shores or apply load. Finally, describe how protection will be removed gradually so the concrete surface does not cool faster than the limits in the table above.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Contingencies<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Name the weather service you will follow, the standby equipment on call, and how you will form an emergency construction joint if a pour has to stop.<\/p>\n\n\n\n<div style=\"height:32px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<figure class=\"wp-block-image alignfull size-large\"><picture><source srcset=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited.webp 2034w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited-300x169.webp 300w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited-1024x576.webp 1024w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited-768x432.webp 768w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited-1536x864.webp 1536w\" sizes=\"auto, (max-width: 2034px) 100vw, 2034px\" type=\"image\/webp\"><img loading=\"lazy\" decoding=\"async\" width=\"2034\" height=\"1144\" src=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited.jpg\" alt=\"Concrete sidewalk being poured in the cold\" class=\"wp-image-16743 sp-no-webp\" srcset=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited.jpg 2034w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited-300x169.jpg 300w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited-1024x576.jpg 1024w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited-768x432.jpg 768w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/concrete-mixer-truck-construction-industry-mixed-concrete-sidewalk-cement-concrete-pour-equipment_t20_G06gx3-edited-1536x864.jpg 1536w\" sizes=\"auto, (max-width: 2034px) 100vw, 2034px\"><\/picture><\/figure>\n\n\n\n<div style=\"height:32px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">Choosing a Cold Weather Concrete Mix<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The goal of a winter mix is to make heat and gain strength quickly, using as little water as practical. Talk to your ready-mix producer early, because the right answer depends on local materials, and test any new combination before the first cold pour.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Lever<\/th><th>What it does<\/th><th>Watch out for<\/th><\/tr><\/thead><tbody><tr><td>Lower water-cement ratio<\/td><td>Less free water to freeze and faster set; stronger, less bleed<\/td><td>Use a water reducer to keep the mix workable instead of adding water<\/td><\/tr><tr><td>Type III cement or more cement<\/td><td>Faster hydration and more internal heat<\/td><td>Higher shrinkage and cost; check the specification allows it<\/td><\/tr><tr><td>Fewer supplementary materials (fly ash, slag)<\/td><td>Mixes with high SCM content gain strength slowly in the cold<\/td><td>Reducing them may need engineer approval<\/td><\/tr><tr><td>Accelerating admixture<\/td><td>Shortens set time and speeds early strength<\/td><td>Chloride types are limited in reinforced concrete (see below)<\/td><\/tr><tr><td>Air entrainment<\/td><td>Protects against repeated freeze-thaw in service<\/td><td>Required for exterior concrete exposed to freezing<\/td><\/tr><tr><td>Heated water and aggregates<\/td><td>Raises the concrete temperature at the plant<\/td><td>Very hot water (roughly 140\u00b0F and above) should meet the aggregates before the cement to avoid flash set<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">ACI 306R-16 also covers proprietary cold weather admixture systems, sometimes called antifreeze admixtures, which are designed to let concrete gain strength at lower temperatures. These are engineered products used to a written procedure. They are not the same as the site myths: automotive antifreeze, windshield washer fluid and rock salt give concrete no useful frost protection and can harm its strength and durability. Never add them.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How to Protect Concrete During Cold Weather Pours<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Every protection method aims at the same three objectives, which ACI 306R-16 sets out:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Stop the concrete freezing while it is young.<\/li>\n\n\n\n<li>Keep it warm enough to gain the strength needed for stripping forms, removing shores and loading the structure.<\/li>\n\n\n\n<li>Let it cool slowly when protection ends, so the surface does not crack from thermal shock.<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">Temperature drives strength gain. By the maturity relationship ACI uses, concrete held at 40\u00b0F gains strength roughly a third as fast as the same mix at 70\u00b0F, so protection is also a schedule decision.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Insulation: The Cheapest Heat Source<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Cement makes its own heat as it hydrates. Insulating blankets and boards trap that heat, and on many pours they are all you need. The trapped heat speeds up hydration, which in turn produces more heat. Get blankets on as soon as finishing allows, overlap and weigh down the seams, and double up on corners, edges and wall tops, which freeze first. How much insulation you need depends on the element&#8217;s mass, cement content, air temperature and wind, and ACI 306R-16 includes tables for choosing it.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Supplementary Heat<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">When insulation alone cannot hold the temperature, add heat. Options include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Electric curing blankets<\/strong> laid directly on slabs or wrapped around columns<\/li>\n\n\n\n<li><strong>Hydronic heaters<\/strong>, which pump a heated glycol solution through hoses laid on the concrete, forms or frozen ground, with insulating blankets over the hoses to keep the heat in<\/li>\n\n\n\n<li><strong>Heated enclosures<\/strong> of poly sheeting on timber or scaffold frames, heated with indirect-fired or electric heaters<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Carbon dioxide reacts with the surface of concrete that is less than about a day old, leaving it soft and dusty, and carbon monoxide endangers workers. Use indirect-fired heaters or vent the exhaust outside the enclosure, and do not aim heaters at the concrete, which dries and cracks the surface.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Ending Protection Without Cracking<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">When the protection period is over, do not pull everything off at once. Remove heat first, then blankets in stages, so the surface cools gradually over the next 24 hours and stays within the temperature-drop limits in the table above. A sudden drop leaves a warm core inside a cold skin, and the stress between them can crack the surface. Leaving the insulation on until the concrete has cooled close to the average air temperature is often the simplest approach.<\/p>\n\n\n\n<figure class=\"wp-block-image alignfull size-large\"><picture><source srcset=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited.webp 1915w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited-300x169.webp 300w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited-1024x576.webp 1024w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited-768x432.webp 768w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited-1536x864.webp 1536w\" sizes=\"auto, (max-width: 1915px) 100vw, 1915px\" type=\"image\/webp\"><img loading=\"lazy\" decoding=\"async\" width=\"1915\" height=\"1077\" src=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited.jpg\" alt=\"Concrete pour\" class=\"wp-image-16745 sp-no-webp\" srcset=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited.jpg 1915w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited-300x169.jpg 300w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited-1024x576.jpg 1024w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited-768x432.jpg 768w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/construction-workers-making-concrete-foundation-for-a-house_t20_Wg2yAK-edited-1536x864.jpg 1536w\" sizes=\"auto, (max-width: 1915px) 100vw, 1915px\"><\/picture><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Monitoring Concrete Strength in Cold Weather<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">ACI 306R-16 recommends basing those decisions on in-place strength, and it specifically advises against relying on field-cured cylinders in cold weather, because cylinders sitting on a deck rarely match the temperature of the structure.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The most common tool is the maturity method (ASTM C1074). Temperature sensors or loggers are tied to the rebar at the critical locations, usually thin sections, corners and the most exposed faces, and record the concrete&#8217;s temperature history. That history is converted into an estimated strength using a strength-maturity curve developed in advance for that exact mix. Points to get right:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Build a separate curve for each mix. Changing the cement content, admixtures or water-cement ratio changes the relationship.<\/li>\n\n\n\n<li>Validate the estimate before removing forms or shores, for example with cylinders fitted with loggers or with in-place tests such as pullout (ASTM C900). ACI says a new curve is needed if the results differ by more than 10%.<\/li>\n\n\n\n<li>Put sensors where the engineer specifies, or at least where concrete will be coldest.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Acceptance cylinders need protecting too. ASTM C31 requires their initial curing environment to stay between 60 and 80\u00b0F (16 and 27\u00b0C) for up to 48 hours, so provide a heated curing box; cylinders left on a frozen deck break low and cast doubt on sound concrete.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Cold Weather Concrete Foundations<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Foundations are poured all winter across much of North America, and full-scale wall testing by the Concrete Foundations Association (CFA) backs up a few firm rules.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Protect the ground first.<\/strong> The excavation must be thawed and free of frost. A footing is sized for the bearing capacity of the soil beneath it, and frozen soil has swollen. Build on it and the foundation drops as the ground thaws, cracking the walls. Cover the footing area with insulating blankets or use ground heaters before the pour, and keep it covered until the concrete arrives.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Get the mix right.<\/strong> Keep the water-cement ratio low, because water is what freezes. A faster cement such as Type III, and a calcium chloride or non-chloride accelerator, both speed hydration and add heat. The CFA&#8217;s advice is to agree winter mixes with the local ready-mix producer and test them locally rather than copying a published mix.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Order the concrete warm.<\/strong> The warmer the concrete is when it arrives, the better its chance of reaching 500 psi before it can freeze. Balance delivery temperature and accelerator dose together: a cooler load needs more acceleration, and a well-heated load may need less.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Plan for the cold snaps.<\/strong> Have blankets ready for wall tops and exposed faces, and auxiliary heat for the worst nights.<\/p>\n\n\n\n<figure class=\"wp-block-image alignfull size-large\"><picture><source srcset=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited.webp 1915w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited-300x169.webp 300w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited-1024x576.webp 1024w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited-768x432.webp 768w,https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited-1536x864.webp 1536w\" sizes=\"auto, (max-width: 1915px) 100vw, 1915px\" type=\"image\/webp\"><img loading=\"lazy\" decoding=\"async\" width=\"1915\" height=\"1077\" src=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited.jpg\" alt=\"Troweling concrete to help finish\" class=\"wp-image-16744 sp-no-webp\" srcset=\"https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited.jpg 1915w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited-300x169.jpg 300w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited-1024x576.jpg 1024w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited-768x432.jpg 768w, https:\/\/essential.construction\/academy\/wp-content\/uploads\/sites\/22\/2022\/06\/finishing-concrete-foundation_t20_1nj2Yx-edited-1536x864.jpg 1536w\" sizes=\"auto, (max-width: 1915px) 100vw, 1915px\"><\/picture><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Small Pours and Bagged Concrete in Cold Weather<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Bagged mixes behave differently from truck-delivered concrete in winter. An 80 lb bag yields only about 0.6 cubic feet, so a fence post or small repair has very little mass to generate and hold heat, and the surrounding soil, forms and base stone soak up what heat there is. Expect set times to run longer than the chart on the bag suggests.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Before the pour:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Check the forecast for the day of the pour and the week after, including wind and humidity. If freezing temperatures are forecast within the next 48 hours, postpone.<\/li>\n\n\n\n<li>Prepare the subgrade or repair area and set forms the day before, then cover them with insulation overnight. Uncover just before placing.<\/li>\n\n\n\n<li>Store bags somewhere dry and warm instead of on the open site.<\/li>\n\n\n\n<li>Never place on frozen ground or a frozen substrate. A cheap infrared thermometer lets you spot-check the ground, the forms and the mix before you commit.<\/li>\n\n\n\n<li>Think about how the method will affect the finish. Blankets, enclosures and accelerators can all change the <a href=\"https:\/\/essential.construction\/academy\/tutorials\/concrete-slab-finishes-and-the-f-system-explained\/\" data-type=\"post\" data-id=\"16504\">concrete finish<\/a>.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">When mixing:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Choose a higher-cement or faster-setting winter product, and for setting posts, a fast-setting post mix mixed before it goes in the hole.<\/li>\n\n\n\n<li>Mix stiff. Using less water lowers the water-cement ratio, shortens set time and reduces bleed water. A flow-enhancing admixture can keep a low-water mix workable.<\/li>\n\n\n\n<li>Use warm water. Hot tap water (generally no more than about 120\u00b0F) is enough to start hydration. Never use boiling water, which can flash-set the mix, and follow the manufacturer&#8217;s temperature limits for repair products.<\/li>\n\n\n\n<li>If you use calcium chloride, a premixed liquid makes accurate dosing easier, and the reinforcement rules below still apply. Non-chloride accelerators are the safe choice around steel, but they are weaker, and some do not work with calcium sulfoaluminate (CSA) cement products, so mix a trial batch first.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Calcium Chloride in Cold Weather Concrete<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Calcium chloride is the most effective and lowest-cost accelerator available, and it lets finishers start work and get blankets on sooner. The catch is that chloride ions promote corrosion of embedded steel, so codes limit it and many specifications ban it outright. The American Society of Concrete Contractors (ASCC) argues that the code&#8217;s chloride limits, not blanket bans, should be the test.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Where It Is Not Allowed<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">ACI 318, the U.S. building code for structural concrete, does not allow calcium chloride or other chloride admixtures in:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Prestressed concrete, including post-tensioned slabs<\/li>\n\n\n\n<li>Concrete containing embedded aluminum, such as aluminum conduit<\/li>\n\n\n\n<li>Concrete cast against stay-in-place galvanized steel forms<\/li>\n\n\n\n<li>Concrete in severe or very severe sulfate exposure (classes S2 and S3), so check whether your mix has a sulfate requirement<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Chloride Limits by Exposure Class<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">For reinforced concrete, ACI 318 caps the water-soluble chloride ion content according to the corrosion exposure class. The value is tested to ASTM C1218 and includes chloride from every ingredient: cement, aggregates, water and admixtures.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Exposure class<\/th><th>Typical condition<\/th><th>Max. water-soluble chloride ion, reinforced concrete<\/th><\/tr><\/thead><tbody><tr><td>C0<\/td><td>Dry or protected from moisture, such as most interior slabs on ground<\/td><td>1.00%<\/td><\/tr><tr><td>C1<\/td><td>Exposed to moisture but not to outside chlorides, such as most exterior slabs<\/td><td>0.30%<\/td><\/tr><tr><td>C2<\/td><td>Exposed to moisture and chlorides from de-icing salt, seawater or brackish water<\/td><td>0.15%<\/td><\/tr><tr><td>Prestressed concrete (any class)<\/td><td><\/td><td>0.06%<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The limit is a percentage of the cement in the mix (later editions of ACI 318 express it against cementitious materials). Slabs on ground are often outside ACI 318&#8217;s structural scope, but the IBC applies the code&#8217;s durability requirements to them, so the limits still matter. If your submittal cites older editions such as ACI 318-11 or the 2012 IBC, note that the requirements have moved chapters in later codes (the current edition is ACI CODE-318-25), so check the edition your jurisdiction has adopted.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">How Much Can You Add?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The common dose is 2% flake calcium chloride by weight of cement, and that dose adds about 0.98% chloride ion. In a C0 mix with no other chloride sources, it just fits under the 1.00% limit. In C1 concrete the margin is far smaller, so only a fraction of that dose is possible, and in C2 concrete there is rarely room for any. Aggregates, especially some coastal sources, and water can contribute chloride of their own, so get the producer to state, in writing, the total chloride from all ingredients at the dose you want.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Is the Slab Actually Reinforced?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The chloride limits exist to protect reinforcement. A slab on ground with no steel in it is not covered by them, but the definition of reinforcement is not always clear-cut. Joint dowels, steel fibers, anchor bolts and other embedded items may or may not count. Ask the engineer of record.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Requesting Approval<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A request to use calcium chloride is far more likely to be approved if it is complete:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>State whether the slab is reinforced. If it is not, say that the code chloride limits do not apply.<\/li>\n\n\n\n<li>If it is reinforced, acknowledge that the IBC requires ACI 318 durability requirements to be met, and state the exposure class you believe applies (usually C0 or C1) and its chloride limit.<\/li>\n\n\n\n<li>Attach the producer&#8217;s written confirmation that, at the proposed dose, total chloride from all ingredients stays under that limit.<\/li>\n\n\n\n<li>Attach the <a href=\"https:\/\/ascconline.org\/Portals\/ASCC\/Files\/Position%20Statements\/PS-31_CalciumChlorideWebSC.pdf\" rel=\"noopener\">ASCC Position Statement #31 &#8220;Acceptable Use of Calcium Chloride in Concrete&#8221;<\/a>, which sets out the cost and schedule case for allowing it within the code limits.<\/li>\n<\/ol>\n\n\n\n<h2 class=\"wp-block-heading\">Cold Weather Concreting in the UK<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">UK work follows BS EN 206 (with BS 8500) and BS EN 13670 rather than ACI documents, but the principles are the same. NHBC Standards, following BS EN 206, set the minimum temperature of ready-mixed concrete on delivery at 5\u00b0C. For site-mixed concrete, NHBC says work should stop if the air temperature falls to 2\u00b0C, unless the ground is not frozen and the aggregates are above 2\u00b0C and free of frost and snow. The site rules in this guide (no frozen ground, insulate early, cure longer) apply just the same.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Common Cold Weather Concreting Mistakes<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Pouring onto a frozen subgrade, or onto forms and rebar covered with ice and snow.<\/li>\n\n\n\n<li>Leaving blankets in the truck until finishing is complete, or failing to weigh them down against the wind.<\/li>\n\n\n\n<li>Forgetting slab edges, corners and the tops of walls, which lose heat fastest.<\/li>\n\n\n\n<li>Running unvented fuel-burning heaters inside enclosures, which can carbonate the surface and endanger workers.<\/li>\n\n\n\n<li>Water curing just before a hard freeze instead of using blankets, forms or curing compounds.<\/li>\n\n\n\n<li>Pulling all protection off at once at the end of the protection period, causing thermal cracking.<\/li>\n\n\n\n<li>Adding antifreeze, salt or extra water to the mix on site.<\/li>\n\n\n\n<li>Leaving test cylinders unprotected, so they freeze and under-report strength.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Cold Weather Pour Checklist<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Use this as a quick pre-pour, pour-day and post-pour check alongside your <a href=\"https:\/\/essential.construction\/files\/construction\/quality\/concrete-pre-pour-checklist-template\/\">concrete pre-pour checklist<\/a>.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Before:<\/strong> cold weather plan accepted; mix, delivery temperature and accelerator agreed with the supplier; 7-day forecast checked; subgrade thawed and covered; forms and rebar clear of ice and snow; blankets, heaters, fuel and enclosure materials on site; sensors or loggers installed; heated cylinder curing box ready.<\/li>\n\n\n\n<li><strong>During:<\/strong> concrete temperature checked on arrival and before placing; truck waiting time kept short; blankets or enclosures in place as soon as finishing allows; edges and corners double-covered; heaters vented.<\/li>\n\n\n\n<li><strong>After:<\/strong> temperatures recorded at least as often as the plan requires; in-place strength confirmed before ending protection or stripping; protection removed gradually; records kept with the pour log.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Cold Weather Concrete FAQ<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">What temperature is too cold to pour concrete?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">There is no single cut-off. ACI treats any time the air is, or is expected to be, at or below 40\u00b0F (4\u00b0C) during the protection period as cold weather. In those conditions the concrete must be placed at, and kept above, minimum temperatures, typically 50 to 55\u00b0F for normal building elements. With heated materials, insulation and enclosures, concrete can be placed well below freezing.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Will concrete cure at 30 degrees?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Only if it is protected. What matters is the concrete&#8217;s own temperature, not the air&#8217;s. At 30\u00b0F air temperature, insulate or heat the concrete so it stays above the recommended minimum until it reaches about 500 psi; unprotected, it can freeze and be permanently damaged.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Is concrete ruined if it freezes?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">It depends when. Concrete that freezes before it reaches about 500 psi can lose up to half of its potential strength and may need to be removed; get it tested before you decide. Once it has passed 500 psi and is not saturated, it can usually survive a single freeze, but it should reach about 3,500 psi before facing repeated freeze-thaw cycles.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">How long does concrete take to cure in cold weather?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Much longer than in mild weather, because low temperatures slow hydration. ACI 306R-16 recommends protection periods of 1 to 6 days depending on the element and the mix, and structural elements may need longer before forms are stripped or loads applied. The maturity method (ASTM C1074) is the most reliable way to confirm in-place strength.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Can you pour concrete on frozen ground?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No. Frozen ground expands, and when it thaws the concrete will settle and crack. Thaw the subgrade first with insulated blankets or ground heaters, and keep it protected until the concrete is placed.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">What is the best concrete mix for cold weather?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A cold weather mix uses a low water-cement ratio, a higher cement content or Type III (high-early-strength) cement, and an accelerating admixture, plus air entrainment if the concrete will be exposed to freeze-thaw. Agree the mix with your ready-mix supplier and check whether chloride accelerators are allowed.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Does salt or antifreeze stop concrete from freezing?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No. Automotive antifreeze, windshield washer fluid and rock salt do not give concrete any useful frost protection and can damage its strength and durability. Use approved accelerating admixtures, heated materials and insulation instead.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Related Templates and Guides<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/essential.construction\/files\/information\/white-papers\/cold-weather-concreting\/\">Cold Weather Concreting Whitepaper<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/essential.construction\/academy\/tutorials\/10-important-items-to-include-in-your-winter-protection-plan\/\">Important Items to Include in Your Winter Protection Plan<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/essential.construction\/files\/construction\/quality\/concrete-pre-pour-checklist-template\/\">Concrete Pre-Pour Checklist Template<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/essential.construction\/files\/construction\/quality\/quality-assurance-checklist-pre-concreting\/\">Quality Assurance Checklist \u2013 Pre-Concreting<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/essential.construction\/files\/construction\/scheduling\/weather-tracking-log-template\/\">Weather Tracking Log Template<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/essential.construction\/academy\/tutorials\/a-best-guide-to-formwork\/\">Concrete Formwork: Types, Design and Stripping Times<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/essential.construction\/academy\/tutorials\/building-foundations\/\">Building Foundations 101<\/a><\/li>\n<\/ul>\n\n","protected":false},"excerpt":{"rendered":"<p>Understand the requirements and planning process for pouring concrete in cold weather.<\/p>\n","protected":false},"author":1,"featured_media":16739,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[94,3,31,19],"tags":[2298,93,2300,2299],"class_list":["post-16729","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-division-03-concrete","category-all-posts","category-featured-articles","category-general-construction-knowledge","tag-cold","tag-concrete","tag-pour","tag-weather","generate-columns","tablet-grid-50","mobile-grid-100","grid-parent","grid-33"],"_links":{"self":[{"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/posts\/16729","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/comments?post=16729"}],"version-history":[{"count":2,"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/posts\/16729\/revisions"}],"predecessor-version":[{"id":20449,"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/posts\/16729\/revisions\/20449"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/media\/16739"}],"wp:attachment":[{"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/media?parent=16729"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/categories?post=16729"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/essential.construction\/academy\/wp-json\/wp\/v2\/tags?post=16729"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}