Table 1. Mortar mixture volumetric proportions.
The rate of absorption of water by masonry
units was also compared with their rate of ab-
Portland
sorption of free water (determined through par-
cement,
Hydrated
Masonry
Masonry
tial unit immersion in accordance with the initial
Type
type I
lime
cement
sand
rate of absorption procedures of ASTM C 67) as
PCL-M
1.00
0.25
--
3.75
well as with the total absorption potential of the
PCL-N
1.00
1.25
--
6.75
unit (determined through full unit immersion in
MC-M
--
--
1.00
3.00
accordance with the absorption procedures of
MC-N
--
--
1.00
3.00
ASTM C 140). If there is a correlation between ab-
sorption of water from mortar to either of these
Table 2. Specific gravity and density of
standardized procedures, the values of those
mortar ingredients.
standard procedures can be used to predict the
rate of mortar water loss.
Specific
Bulk density
gravity (kg/m3 [lb/ft3])
Ingredient
Full unit immersion tests
Portland cement
3.15
1507 (94)
The absorption procedures within ASTM C
Masonry cement, type M
2.97
1271 (80)
Masonry cement, type N
2.95
1122 (70)
140 involve the full immersion of units in water
Lime
2.34
641 (40)
maintained at approximately 20C (68F) for a
Masonry sand
2.67
1271 (80)
period of 24 hours. After 24 hours, the assump-
tion of the test method is that the unit has
absorbed as much water as it will ever absorb as a
result of the pressure created by the water in the
containing low amounts of portland cement.
tank. While immersed, the unit is weighed sus-
Thus, two of the four mortar types from the port-
pended so that its buoyancy force can be evaluat-
land cementlime (PCL-M and -N) and the
masonry cement (MC-M and -N) proportioning
ed to determine the volume of water it displaces.
methods were chosen for testing. The type M mor-
Once removed from the tank, the unit is weighed
tar contains more portland cement than does type
in air in a saturated, surface-dry condition and
N.
then placed into an oven maintained at approxi-
mately 107C (225F) for not less than 24 hours.
The mixture proportions of the four mortars
The oven dry weight of the unit is then recorded.
studied are given in Table 1 based on bulk vol-
The test method provides two methods of
umes as specified in ASTM C 270. Table 2 provides
expressing the total amount of water that the unit
the physical values used to determine batch
could absorb. The first is absorption expressed as
weights for each study.
the volume of water absorbed per net volume of
solid concrete material. The second method is
Experimental approach
absorption expressed as the weight of water
Lower water contents in mortar result in im-
absorbed per dry weight of material presented on
proved resistance to damage from freezing. Be-
a percentage basis. For concrete masonry units,
cause concrete masonry units are porous in nature
and have an affinity for drawing moisture from
the first method is preferred.
masonry mortar, the absorptive properties of the
The absorption values for a concrete masonry
unit are affected by a number of production vari-
masonry unit may play an important role in the
ables including gradation of the aggregates used,
performance of masonry assemblies in cold
mix water content, amount and types of cement,
weather.
Immediately after fresh mortar is placed in con-
admixtures and other materials used, production
tact with the masonry unit, the masonry begins to
machine type and settings, and even unit config-
draw free water from the mortar. Over time, water
uration. All of these variables affect how well a
loss in the mortar continues due to prolonged con-
unit can be compacted. However, the variable
tact with the masonry unit, evaporation to the air,
that has the most influence on the absorption of
and hydration of the cement within the mortar. We
the unit is the type of aggregate(s) used in its
manufacture. Lighter-weight aggregates tend to
evaluated the rate of water loss by the mortar as it
be more porous and therefore have more air
is affected by contact with the concrete masonry
unit. Several different unit types with a range of
voids that can be filled with water. The industry
unit properties, moisture contents, and tempera-
standards for concrete masonry units include
tures were used to document this effect.
maximum absorption limits as a means of ensur-
3
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