Page
Section
Para.
Recommendation
Loss of Water
1
The early freezing of mortars does not significantly reduce
either transverse or compressive strength. Mortar that is
frozen at a moisture content above 8% can lose nearly half
its potential compressive strength. The effect of ... un-
known. Masonry once frozen and dried may be expected to
suffer a strength reduction because it may not contain
water sufficient to complete cement hydration. Conse-
quently, ... development.
Note: Mortar develops maximum strength when it is cured
at a moisture content of 12%. Strength decreases if the
initial water content is changed in either direction. For
example, mortar mixed with only a 6% water content
(impractically dry) may produce only 20% of the strength
attained by the equivalent mortar with 12% water. Con-
versely, mortar mixed with 14% water (a typical field
mortar) attains only half the strength of its 14% counter-
part.
Summary
1
The performance characteristics of masonry mortars are
influenced by temperatures below normal. Early-age
freezing can lead to irreparable strength loss. The changes
... materials. Heated mortars, which prolong the period
before freezing, Mortars heated and maintained at 40F
(5C) possess hardened properties equal to or more desir-
able than their unfrozen highly heated or early-frozen
counterparts.
9
Performance of Masonry Units at Below-Normal Temperatures
Basis of Selection
1
The architect's ... construction. An absorptive ... freezing.
Conversely, a ... expansion. From maturity considerations,
auxiliary dry heat to promote mortar strength and drying
may be is not required for even very low absorptive units
such as glass blocks, provided the mortar can be maintained
at or above 40F (5C) by other means for at least 8 hours.
Performance of Masonry at Low Temperatures
10
General
3
When masonry freezes, two conditions are identifiable:
Masonry mortar becomes immune to one cycle of freezing
when either of two conditions is met:
(1) masonry frozen while the mortar is in the wet (greater
than 6% moisture) condition, and the moisture content of
the mortar is reduced by evaporation and/or absorption to
less than 8%, or
(2) masonry frozen while the mortar is in the dry (less than
6% moisture) condition the mortar has attained a maturity
equivalent to an 8-hour cure at 40F (5C) with no external
water to the mortar.
4
Masonry mortar frozen while the mortar is in the wet
condition (greater contains more than 6% 8% moisture)
contains has enough ... ice.
5
Masonry mortar frozen while the mortar is in the dry
condition ( contains less than 6% 8% moisture would ...
forces.
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