ParsCo cold weather construction tips for concrete and masonry work

With the weather forecasting temperatures to drop below freezing this time of year (even in some Southern States) it is often wise to take precaution to make sure the materials you are working with will be done according to manufacturers recommendations for low weather temps. 

This might mean a higher cost than originally anticipated but it really is worth the extra cost and time planning when you consider the alternative - replacing the work you just completed!

Here are some standard and typical points to consider:

Concrete and Masonry install tips in Cold Weather 

Curing concrete in cold weather can be achieved using different materials depending on the amount of concrete being cured and the surface being protected. These materials when used properly will increase or produce a constant heat of hydration of the concrete. For example:

• Insulating sheets,
• Straw-plastic,
• Heating coils,
• Insulating blankets, and
• Windbreaks.

However, if the temperature is below 20 Degree F, simply skip the idea of placing concrete because it will lead you nowhere as hydration stops completely at such temperatures.

For this reason, ACI Committee 308 recommends the following minimum curing periods:

• ASTM C 150 Type I cement 7 days
• ASTM C 150 Type II cement 10 days
• ASTM C 150 Type III cement 3 days
• ASTM C 150 Type IV or V cement 14 days
• ASTM C 595, C 845, C 1157 cements variable

Curing Concrete in Cold Weather Tips

Try these recommended tips for curing concrete in cold weather:

• Maintain a proper water-cement ratio. The water to cement ratio should not be more than 0.40 under freezing conditions.
• If temperatures are too cold, a propane heater and polyethylene enclosure could be used to maintain temperatures hot enough, to avoid freezing point.
• Use Portland cement Type III, cement that helps in setting without reducing concrete's quality. It is important because high moisture content can induce corrosion problems in steel reinforcement.
• Control chloride ions by suing fly ash, silica fume and furnace slag.
• Leave forms in place as long as possible.  Corners and edges are most vulnerable.
• Removing the blankets suddenly in cold weather can cause a temperature differential to build up between the outside of the concrete and its middle. This can cause cracking from the thermal differential, but typically only in thicker members.
• Concrete under water curing for flatwork applications becomes easy with previous concrete. Pervious Concrete is all coarse aggregates and it contains a negligible percentage of fine aggregates, especially sand. Additives are mixed into it that do not allow water to penetrate inside the concrete surface. Pervious concrete is suitable for constructing pavement as it does not soak in water but allows gallons of water pass through it without damaging concrete pavement and strength.
• Wait until all bleed water has evaporated. Curing concrete in cold weather will produce a slower curing procedure, so the concrete is setting slowly, and bleeding will also start later than expected. Be prepared to handle more bleed water than regular concrete placement.
• While concrete is being cures, verify the concrete temperature using an infrared temperature gun.
• To determine how much insulating value you need to keep the concrete at 50°F, check out the tables in Chapter 7 of ACI 306. The insulation needed is based on concrete thickness, cement content, and the lowest air temperature anticipated for the protection period.
• Seal concrete by applying concrete sealant so water does not seep inside the concrete. Concrete sealants will extend concrete's life, and will reduce the concrete curing failure. In extremely cold regions, only a breathable concrete sealant must be used, as it will allow the evaporation of water and moisture, helping in fast setting of the concrete.

When working masonry under cold weather follow these material tips.

• It is recommended to use a speed hydration by using high-early cement or by using an accelerator. Caution: Type III cements could change mortar color varying the required appearance.
• Analyze how admixture could affect cold weather construction and reactions.
• Place materials on planks and cover them with tarps.
• All masonry materials should be completely covered to prevent wetting by rain or snow.
• Some masonry materials might need to be heated prior to use, so cement hydration can occur properly.
• Masonry units with high rates of absorption will accelerate stiffening.
• Calcium chloride (at a limit of 2% by weight of cement) is commonly used in concrete as an accelerator, but its use in mortar is prohibited by the Specification for Masonry Structures (ACI 530.1-95/ASCE 6-95/TMS 602-95).
• Place masonry on unfrozen surfaces because ice reduces bond and when it melts the masonry could move.

Mortar Temperatures

Working under cold or freezing temperatures can cause serious problems if not addressed properly. It is important to keep mortar above 40 degrees Fahrenheit. And you should be able to do it following these steps:

• Temperature above 32 degrees Fahrenheit- Cover walls with plastic to prevent water entering masonry.
• Temperature between 32 and 20 degrees- Cover walls with ½ inch insulation blanket to prevent or reduce rapid heat loss, or block water entering masonry.
• Temperature between 20 and 0 degrees- Cover wall with plastic insulation blanket, approximately one inch thick, or maintain a heated area to 40 degrees for two days following installation.

It is important to mix mortar in small amount, so it doesn't cool before it has been used. If temperatures are too low, mortar can be placed on heated surfaces such as metal mortar boards. Be sure to monitor closely mortar temperature to avoid mortar being dried due to excessive heat.

Masonry Cold Weather Tips

The following cold-weather procedures shall be implemented when either the ambient temperature or the temperature of masonry falls below 40ºF.

• Mortar shall be maintained above freezing until used.
• Sand or water shall be heated to produce mortar above 40 degrees Fahrenheit.
• Heat sources might be used on both sides of the masonry under construction.
• Wind breakers shall be installed if wind conditions are in excess of 15 miles per hour.
• Glass unit masonry shall not be laid during cold periods.
• Heated enclosures are recommended when the temperature drops below 20°F.
• Most commercially-available masonry 'antifreeze' admixtures are actually accelerators rather than freezing-point depressants. ASTM C1384 provides criteria for evaluating admixtures, including accelerators, for use in masonry mortars.
• It may be necessary to heat sand to thaw frozen lumps when temperatures fall below freezing.
• To avoid flash set, heated water should be combined with cold sand in the mixer before adding cement.
• Do not lay masonry units having either a temperature below 20°F or containing fro­zen moisture, visible ice, or snow on their surface.
• Masonry units should be kept dry, although very high absorption fired-clay brick may need to be wetted — but not saturated — prior to use.

If you have any questions or need further guidance feel free to contact ParsCo at info@pars-co.net.  

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