Masonry Magazine February 1992 Page. 13
TABLE 3-Strength and Absorption Requirements, ASTM C90-90
Note - To prevent water penetration, protective coating should be applied to the exterior face of basement walls and when required, on the face of
exterior walls above grade.
Compressive Strength" min, psi (MPa)
Water Absorption, max, lb/ft (kg/m³)(Average of 3 Units)
Weight Classification--Oven-Dry Weight of Concrete, lb/ft³ (kg/m³)
Average Net Area
Average of 3 Units
1900 (13.1)
Individual Unit
1700 (11.7)
Light weight less than 105
(1682)
18 (288)
Medium weight 105 to less
than 125 (1682-2002)
15 (240)
Normal weight 125 (2002 of
more)
13 (208)
To prevent water penetration, proper detailing, construction, flashing, and drainage should be provided.
"Higher compressive strengths may be specified where required by design. Consult with local suppliers to determine availability of units of higher
compressive strength.
and S) were included, distinguished only by differences in
compressive strength and water absorption requirements. In
ASTM C90-90, the lower grade was discontinued and there
is now but one grade. Compressive strength based on net
cross-sectional area is required to average at least 1900 psi
(Table 3). Net area used for compressive strength determi-
nation is the "average" net area of the block, and is calculated
by determining net volume from water displacement tests
described in ASTM Test Method C140. For cored units
having tapered face shells and cross webs, "average" net area
is the net cross-sectional area at approximately mid-height of
the block.
Maximum permissible water absorption is shown in
Table 3. Absorption is a measure of the total water-fillable
void content of the concrete of which the block is made. It
is determined from the weight difference of the unit between
a saturated and an oven-dry condition and 's expressed in
terms of pounds of water per cubic foot of concrete. In Table
3 it can be noted that maximum permitted absorption values
range from 13 pcf to 18 pcf, depending upon the density of
the concrete of which the block is manufactured. Since ab-
sorption is a measure of the total water-fillable void content,
it is to be expected that an aggregate having pores, such as
lightweight aggregate, would have a greater absorption than
a dense, non-porous aggregate, given the same compaction.
As a result, lightweight units are permitted higher absorption
than medium weight or normal weight classifications.
Finish and Appearance
Provisions relating to finish and appearance pro-
hibit defects that would impair the strength or permanence of
the construction, but permit minor cracks incidental to the
usual methods of manufacturing.
For units to be used in exposed wall construction,
presence of objectional imperfections are based on viewing
the face or faces from a distance of 20 ft. under diffused
lighting. This provision is a new addition to C90, and reflects
the need to develop acceptance criteria for architectural
facing units. Similarly, the specification requires that color
and texture shall be specified by the purchaser, and that an
approved sample consisting of not less than four units,
representing the range of color and texture permitted, be used
to determine conformance.
Concrete Building Brick ASTM C55-85
ASTM C55 applies to solid, brick size units. The
requirements of this specification can also apply to solid
concrete veneer and facing units larger than brick size, such
as "split" block.
Two grades of concrete brick are covered by ASTM
CSS as follows:
Grade N-For use as architectural veneer and facing
units in exterior walls and for use where high strength and
resistance to moisture penetration and severe frost action are
desired.
Grade S - For general use where moderate strength
and resistance to frost action and moisture penetration are
required.
Compressive strength and absorption requirements
for the two grades of concrete brick are listed in Table 4.
Moisture content requirements for Type I concrete brick are
the same as ASTM C90-90 (Table 1).
Non-Load-Bearing Block, ASTM C129-85
ASTM C129 covers hollow and solid non-load-
bearing units. These units are intended for use in non-load-
bearing partitions. They are not suitable for exterior walls
subjected to freezing cycles unless effectively protected
from the weather. ASTM C129 requires that these units be
clearly marked to preclude their use as load-bearing units.
TABLE 4-Strength and Absorption Requirements for Concrete Brick, ASTM C55-85
Compressive Strength min, psi (MPa)
(Concrete Brick Tested Flatwise)
Average Gross Area
Water Absorption, max, (Average of 3 Brick) with Oven Dry
Weight of concrete, lb/ft (kg/m³)
Weight Classification
Grade
Average of 3 Concrete Brick
Individual Concrete Brick
Light weight
less than
105 (1680)
Medium weight
less than 125 to
105 (2000 to 1680)
Normal weight
125 (2000) or
more
N-I, N-II
S-1,S-II
3500 (24.1)
2500 (17.3)
3000 (20.7)
2000 (13.8)
15 (240)
18 (288)
13 (208)
15 (240)
10 (160)
13 (208)