Page 73 - Design of Reinforced Masonry Structures

2.26 CHAPTER TWO

2.6.5 Concrete Building Brick
Concrete building bricks conforming to ASTM C55 [2.43] are made from portland
cement, water and suitable mineral aggregates with or without the inclusion of other
materials. Their shapes are similar to those used for the clay bricks. Concrete brick has
two grades:
1. 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 is
required.
2. Grade S: For general use where moderate strength and resistance to frost are
desired.

2.6.6 Nonload-Bearing Concrete Masonry Units
These units may be solid or hollow, and are made from portland cement, water, mineral
aggregates with or without the inclusion of other ingredients. These units are generally
used for nonload-bearing partitions or nonload-bearing exterior walls above grade, which
are effectively protected from weather. All concrete masonry units are classified further
according to their unit weights. The weight classification for the nonload-bearing units is
same as shown in Table 2.7.

2.6.7 Shapes of Concrete Masonry Units and Their Applications
Concrete masonry units are produced in many different shapes to suit the many structural,
architectural and functional needs for a wide variety of applications (Fig. 2.18). A discus-
sion on shapes and sizes of concrete masonry units can be found in Refs. [2.1, 2.46], which
is summarized here. Some of these shapes are commonly used for most wall applications
(Fig. 2.19) while others are used for special applications. Of these the most commonly used
in masonry construction is the hollow concrete block conforming to ASTM C90 [2.42], a
two-cell hollow concrete masonry unit, which is specified as nominal 8 × 8 × 16 in. but actu-
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ally measures as 7 ⁄ 8 × 7 ⁄ 8 × 15 ⁄ 8 in. A more complete guide to masonry units is the Shapes
and Sizes Directory [2.47].
Typically, the face shells and webs are tapered on the concrete masonry units so that
their one end is slightly wider than the other. Depending on the type of molds used in the
manufacture of the units, the face shells and webs may be tapered with a flare at one end,
or may have a straight taper from top to bottom. The units are placed with the wider ends

facing up, which provide a wider surface for mortar, and afford easier handling.
Figure 2.20 shows several shapes of concrete masonry units that have been developed
to accommodate vertical and horizontal reinforcement required in structural masonry con-
struction. These include open-ended or “A” shaped units, double open-ended or “H” shaped
units, and pilaster units. All three are used where vertical reinforcement is to be provided
(e.g., in walls, columns and pilasters). The double open-ended unit is the biggest and has
the most voids. This unit should be specified when maximum grout flow is preferred. While
ungrouted open-ended cells are permitted by the code, it is preferable to grout them. This is
because an ungrouted open-ended cell is vulnerable to impact load on its face shell. Bond
beam units and lintel units are used where horizontal reinforcement is to be provided.
While the two cell units shown in Fig. 2.19 can also be used where vertical rein-
forcement is to be provided, the open-ended units shown in Fig. 2.20 are special in that