Recommended Practices for
Cold-Weather Masonry Construction
Page
Section
Para.
Recommendation
7
General
2
It is acknowledged that As the ambient temperature falls
below freezing, more of the construction materials must be
are preconditioned in the effort to permit foster satisfactory
masonry strength development. To successfully ... is
essential.
3
The times, temperatures, moisture contents, and strengths
provided in this booklet do not apply to any one circum-
stance in the field. They do, however, suggest expected
trends. Good judgment is required to apply the guidance
herein to particular situations.
8
Mortar Performance at Temperatures Below Normal
General
1
As the ambient ... involved. The heat-liberating reaction
between portland cement and water is slowed or stopped
when the cement paste is subjected to temperatures cools
below 40F (5C). Hydration and strength development
proceed only at temperatures when the cement paste is
above freezing and only when sufficient water is available.
However, cold weather masonry construction may proceed
at air temperatures below freezing, ... construction.
9
Effects of Freezing
2
The water content ... characteristics. Mortars possessing
water contents in excess of 6 to 8% 8 to 10% expand on
freezing do not attain full potential strength on freezing.
Expansion Strength loss increases as the water content
increases, ... to some value below 6% 8% to avoid the
disruptive expansive forces frost-weakened mortar.
3
Through the combined effects of evaporation, hydration
and absorption, the moisture content of masonry mortar
will drop below 8% within 4 to 8 hours. By maintaining a
masonry assembly at or above 40F (5C) for at least 8
hours, the mortar will become immune to one cycle of
freezing and thawing. (It is unknown whether mortar in
this moisture condition can resist multiple freezethaw
cycles.)
9
4
In a situation where evaporation and absorption are held
to a minimum, such as when mortar is placed on glass
blocks and the masonry assembly is covered by plastic
sheets, the primary mechanism of moisture loss is that due
to cement hydration. In this situation, mortar that is
maintained at or above 40F (5C) for at least 6 hours
becomes immune to one cycle of freezing and thawing. (It is
unknown whether mortar at this maturity can resist
multiple freezethaw cycles.)
5
Therefore, based on both moisture content and maturity
considerations, it is necessary to maintain fresh mortar at
or above 40F (5C) for only 8 hours before it is allowed to
freeze. Beyond 8 hours, a single freezing will not have a
detrimental effect on the strength properties of masonry
mortar.
48
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