Masonry Magazine August 1966 Page. 32
FIGURE 1-TESTS COMPARING THE COMPRESSIVE STRENGTH OF SCREEN BLOCK
WITH THEIR STRENGTH WITH HOLLOW CELLS VERTICAL
Units Tested in Position Shown With Load Applied Vertically
Relative Compressive Strength With Vertical Loading
on Units As Shown, Expressed As Percent Of Strength
With Cells Vertical.
No.
Percent
1
35%
2
32%
3
22%
4
42%
5
56%
6
42%
7
55%
8
47%
1
77%
2
82%
3
68%
4
53%
9
73%
10
57%
9
32%
10
40%
materials
Screen Units-Because the number of
shapes and sizes for concrete masonry
screen units is virtually unlimited, it is
advisable for the designer to check on
availability of any specific shape during
early planning. Some shapes are avail-
able only in certain localities and others
are restricted by patent or copyright. A
directory of leading manufacturers may
be obtained from the National Concrete
Masonry Association.
Screen units shown in Fig. I was from
22 to 82 percent of their strength with
cells vertical, depending on unit shape,
net area of concrete section supporting
load, and unit height-thickness ratio. As
a practical measure, the minimum thick
ness of the concrete section in screen
units should not be less than 4 inches.
Concrete masonry screen block desig-
nated as Q BLOCK® units by their manu-
facturer meet the requirements of high
quality described herein. In order to re-
ceive Q BLOCK certification, a manu-
facturer must demonstrate that his prod-
uct complies with rigid requirements by
means of periodic testing conducted by
an independent laboratory. Look for the
Screen units should be of high quality,
even though they seldom are employed
in load-bearing construction. When test-Q BLOCK "Certificate of Quality" as
ed with their hollow cells parallel to the
direction of the load, screen units should
have a compressive strength exceeding
1,000 psi of gross area; a quality of con-
crete unit comparable to "Specifications
for Hollow Load-Bearing Concrete Ma-
sonry Units" ASTM C 90-65T. When
loaded as in service, hollow cells normal
to load, the compressive strength of
your assurance of high-quality concrete
masonry screen block.
Mortar-Specify Type M or Type S
mortar, "Specifications for Mortars for
Unit Masonry," ASTM Designation:
C 270, for use in exterior screen walls
and for screen walls required to carry
any vertical load. For interior nonload-
bearing walls, specify Types M, S or N,
ASTM C 270.
Grout Grout for embedding steel rein-
forcement in horizontal or vertical cells
should comply with "Specifications for
Mortar and Grout for Reinforced
Masonry," ASTM Designation: C 476.
Pea-gravel grout should be used where
the clear dimensions of the screen unit
cells are 4 in. or more in both horizontal
directions.
Reinforcement-Steel wire reinforce-
ment should be of a prefabricated type
made with cold-drawn steel conform-
ing to "Specifications for Cold-Drawn
Steel Wire for Concrete Reinforcement,"
ASTM A 82. Steel bar reinforcement
should conform to "Specifications
for Billet-Steel Bars for Concrete Reinforce-
ment," ASTM A 15, or "Specifications
for Rail-Steel Bars for Concrete Rein-
forcement," ASTM A 16. Bars
in.
or larger in diameter should be deformed
in accordance with "Specifications for
Minimum Requirements for the Defor-
mations of Deformed Steel Bars for
Concrete Reinforcement," ASTM A 305.