Table 3. Allowable absorption values for concrete
Partial unit immersion tests
masonry units.
A standard method of evaluating the water
uptake capabilities of a unit partially immersed
Light
Medium
Normal
in water is included in ASTM C 67. The method
Unit weight
weight
weight
weight
(kg/m3)
(kg/m3)
(kg/m3)
classification
involves placing a unit within a container of wa-
ter such that the immersion depth of the unit is
Unit oven-dry density
< 1680
1680 to 2000
>2000
3.2 mm (1/8 in.) for a period of 1 min. The amount
Max. allowable absorption
288
240
208
of water absorbed by the unit over the 1-min peri-
od is determined by the difference in unit weight
ing adequate compaction was achieved. The higher
before and after immersion.
absorptive properties of units made with lighter-
The primary force that pulls water up into the
weight aggregates is reflected in the sliding-scale
unit is capillary suction. The test method deter-
requirements for absorption based on unit density.
mines the effect of various parameters on water
ASTM C 90, "Standard Specification for Loadbear-
absorption including unit moisture, unit manu-
ing Concrete Masonry Units," includes the
facture, unit surface characteristics, and water
absorption requirements given in Table 3.
temperature (Table 5).
For this research, three sets of concrete masonry
The units described as having "dry" moisture
units, each having different absorption character-
content had been stored in the laboratory for sev-
istics resulting from production differences, and
eral months, and their moisture content at the
one set of concrete brick were used. Representa-
time of testing averaged 15% of their total absorp-
tive specimens from each set were tested in
tion, which is typically drier than most units used
accordance with the absorption procedures of
in winter construction. Those units referred to as
having "normal" moisture content are perhaps
ASTM C 140. The results of those tests are shown
nearer in water content to units typically used in
in Table 4 along with other tested parameters de-
winter construction. To obtain this moisture con-
termined in accordance with ASTM C 140.
Table 4. Unit properties.
Unit property
Concrete
CMU
CMU
CMU
(average)
brick
A
B
C
Width, mm (in.)
91.4
(3.60)
194.1
(7.64)
193.8
(7.63)
193.5
(7.62)
Height, mm (in.)
69.1
(2.72)
193.8
(7.63)
193.5
(7.62)
192.8
(7.59)
Length, mm (in.)
188.5
(7.42)
396.5
(15.61)
396.2
(15.60)
396.5
(15.61)
Net area, top, mm2 (in.2)
17,226.0
(26.7)
37,548.0
(58.2)
37,548.0
(58.2)
37,548.0
(58.2)
Net area, bottom, mm2 (in.2)
17,226.0
(26.7)
42,774.0
(66.3)
42,774.0
(66.3)
42,774.0
(66.3)
Absorption, kg/m3 (pcf)
157.0
(9.8)
155.0
(9.7)
229.0
(14.3)
230.0
(14.4)
Density, kg/m3 (pcf)
2,110.0
(131.9)
2,096.0
(131.0)
1,642.0
(102.6)
1,490.0
(93.1)
Net strength, MPa (psi)
--
21.9
(3,180)
16.1
(2,340)
21.2
(3,070)
Table 5. Matrix of partial unit immersion tests.
Unit
Water
Air
Test
Unit
Unit
temperature
Unit
temperature
temperature
(C) (F)
(C) (F)
(C)
(F)
no.
type
surface*
moisture
1t
CMU A
Top
20
68
Dry
20
68
20
68
1b
CMU A
Bottom
20
68
Dry
20
68
20
68
2t
CMU B
Top
20
68
Dry
20
68
20
68
2b
CMU B
Bottom
20
68
Dry
20
68
20
68
3t
CMU C
Top
20
68
Dry
20
68
20
68
3b
CMU C
Bottom
20
68
Dry
20
68
20
68
4
Brick
Side face
20
68
Dry
20
68
20
68
5
Brick
Side face
20
68
Normal
20
68
20
68
6
Brick
Side face
20
68
Wet
20
68
20
68
7
Brick
Side face
5
41
Dry
5
41
5
41
8
Brick
Side face
5
41
Dry
20
68
5
41
9
Brick
Side face
5
41
Dry
30
86
5
41
* Unit surface described based on orientation of unit as made.
4
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