Cement, Mortar, and Curing During Cold Weather

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Cement can still be used as a building material in cold weather conditions for laying bricks and other applications; however, it is important to consider methods of ensuring effective curing during these construction procedures.

When operating under normal working temperatures, industry practices states that mortar use should remain in an ambient temperature range of 4.4 - 37.8° C. If the mix temperature drops to below 4.4°C within 24 hours for the mortar, and 24-48 hours for grout, the hydration of the cement will stop until the temperature returns to normal.

If incompletely hydration occurs prior to when the mortars and grouts dry out, the overall cured strength can be reduced, ultimately causing the mortar joints to fail and be squeezed out of the joints.

Furthermore, if temperatures are low enough for the mortar to freeze, it will expand to cause the formation of internal cracks and permanent damage to the mortar bed. These effects ultimately reduce the strength of the concrete or mortar, increase porosity, lead to a loss of durability and increase the possibility of spalling, which occurs when small pieces of concrete break off a surface.

There are many precautions that cement users can take to protect a job during the time in which the material hardens. Additionally, numerous quick-setting products are also available to ensure an even greater level of protection during these procedures. The three main objectives that construction workers are instructed to follow during cold weather concreting include:

• Protect newly placed cement from early-age freezing
• Protect the concrete to ensure it exhibits sufficient strength during development
• Protect the concrete against thermal shock and cracking

Mix Water Freezing

Freshly laid concrete or mortar can potentially be damaged in the event that cold water enters the mixture and freezes it. This occurs as a result of the ability of ice to expand up to 9% of its volume as it forms, thereby disrupting the crystal structure by introducing the formation of new ice crystals into the concrete and weakening the bond present between the aggregate particles and cement paste. This effect will ultimately reduce the strength by up to 50%of the concrete and/or mortar by increasing its porosity, reducing its durability, and possibly cause spalling to occur. Work should never be carried out when the temperature is lower than 5°C or when frost is expected within the following 24 hours.

Warm Water

Cement mixed with cold materials will have different properties as compared to those at a normal temperature. Lower temperatures often result in a mix that exhibits increased air content, lower water content, and reduced early strength. During these situations, the operator should consider using warm water of temperature around 25-30°C to increase the mix temperature. However, it is important to not allow the mortar to reach 49° C, as this increase in temperature can reduce the bond strength and compressive strength.

In addition to adjusting cement mixtures, numerous companies also strictly work with heated materials and tools during cold weather cementing as a further protective measure. For example, Consolidated Concrete utilizes a large heated water tank during cold weather concreting to provide its customers with concrete that maintains its warmest possible temperatures despite extremely cold weather conditions³.

Slab Protection

Freshly laid slabs of concrete can also be protected through the use of polythene sheeting and/or insulation; however, it is important to make sure that the slabs are clear in order to prevent the surface from being marked. To do this, hydronic heating tubes can be placed on top of the polythene sheets in addition to covering the entire system with insulated blankets.

Enclosures

Erecting windbreaks composed of wood, canvas tarpaulins or polyethene is also a useful way of adding protection from cold winds because even at moderate temperature strong winds can dramatically lower the temperature of unprotected concrete or mortar.

Large tents and temporary wooden structures with a plastic covering can be used to prevent the cold wind from entering the newly formed concrete structure. Windbreakers can also be coupled with forced air or torpedo heaters to circulate warm air and aid in the cement hydration.

If the ambient air temperature drops below 3° C, the construction work must be discontinued until a heated enclosure is constructed. While these options are extremely effective in preventing cold weather from entering concrete, these are often the most expensive options.

Heated Mortar Storage

After mixing, mortar can be stored onto heated surfaces, such as a metal mortarboard, to maintain a higher temperature. Note that additional care should be taken in order to avoid the excessive drying of the mortar as a result of exposure to excessive heat.

Three types of heaters that can be used with cold-weather construction include direct-fired, indirect-fired, and hydronic systems, all of which are used depending upon the specific nature of the construction project. For example, in the event that the concrete will not be directly exposed to the heater or exhaust, a direct-fired heater is suitable, whereas indirect-fired heaters are preferred when carbonation of fresh concrete surfaces must be avoided⁴.

Protection from Ice

During mixing and batching procedures, it is important to make sure that the mixing equipment, aggregate, and masonry are free from snow and ice. Note that applications that are shallow, or those that have a thin cross-section are at a greater risk of acquiring damage from freezing conditions as compared to thicker units; therefore, these types of structures often require a greater amount of protection.

If covered in ice or snow, the top course or surface that is laid down must be fully thawed and dried prior to proceeding with the procedures. Completing a job as early as possible in the day is also a good idea before the evening temperature drops.

Castle Products for Cold Weather Use

Products, such as the Castle Readybag High-Performance Post Mix, are formulated to produce high early strength concrete for setting in less than ten minutes. The quick setting and easy to use properties of Castle’s mix is attributed to the simple addition of water through a hole without requiring any additional mixing.

This, therefore, saves a tremendous amount of time spent on a job while also being an economical solution as it generates less waste as compared to other similar methods.

Castle Quickcem is a quick setting and hardening Portland-based cement that contains additives that are specially designed to provide quick setting and strength development properties to the cement. Depending upon the specific ambient temperature and mix being used, the Quickcem is capable of retaining the workability of applied cement structures between 10-20 minutes.

In addition to these benefits, the Quickcem can also be used for repair, maintenance, fixing, and cold weather applications where the increased speed of set and strength are required, thereby allowing normal service to be resumed after only a few hours.

The aforementioned products are still limited by the 4° C temperature limit; however, the time frame of setting is much lower when utilizing these products, and can, therefore, be used in a smaller warm weather window. Some common applications of these products include fixing manhole covers, fitting ridge tiles, repair of rendering and floor screeds, patch repairs, and concrete paths and steps.

Ground Heaters

For concreting in cold temperatures, ground heaters can be used to thaw the ground prior to pouring, while also maintaining warm temperatures for the concrete throughout curing procedures. A hose filled with warm fluid (similar to underfloor heating used in houses) is fed over the concrete between a poly-vapor barrier and a protective insulation sheet to prevent heat from escaping the structure.

This article was updated on the 14^th September, 2018.