Masonry Magazine June 2008 Page. 38
AUTOCLAVED AERATED CONCRETE
tance due to reinforcement oriented parallel to the direc
tion of the shear. Because conventional bed-joint rein-
forcement produces local crushing of AAC under
cross-wires, the MSJC Code requires that only the shear
contribution of bond beams with grouted reinforcement
be considered. To prevent local crushing of the AAC, nom-
inal stresses in it are limited to specified compressive
strength. When floor or roof elements bear on AAC walls,
shear failure of the edge of the wall is also possible. This is
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handled by limiting the shear stress on potential inclined
failure surfaces.
Laying AAC masonry elements
AT DIAPHRAGM LEVELS, AAC masonry walls are
connected to the floor or roof using a grouted bond beam,
similar to clay or concrete masonry construction. After lay-
ing the AAC masonry units, the
plane of the wall can be
smoothed using a sanding
board made for this purpose.
Levelling bed and shims for first
course of AAC masonry units the
firstcourse of AAC masonry units is
laid on a levelling bed of ASTM C270
Type M or S mortar, using wedges f
desired to plush and level the units.
Electrical, plumbing installations in AAC
ELECTRICAL and plumbing
installations in AAC masonry are
placed in routed chases. Care
should be taken when laying out
chases to ensure that the structur-
al integrity of the AAC elements
is maintained. Do not cut rein-
forcing steel or reduce the struc-
tural thickness of the AAC
Laying AAC masonry units using this bed mortar and
toothed trowel-subsequent courses are laid using
a polymer-modified, thin bed mortar, applied with a
special toothed trowel.
it may be advantageous to provide
quantities of conduit or plumbing.
Exterior finishes for AAC
elements except where
permitted by the
designer. In vertically
spanning AAC ele-
ments, horizontal rout-
ing should be permitted
only in areas with low
flexural and compres-
sive stresses. In horizon-
tally spanning AAC
elements, vertical rout-
ing should be mini-
mized. When possible,
designated chases for large
UNPROTECTED EXTERIOR AAC deteriorates when
exposed to cycles of freezing and thawing while saturated. To
prevent such freeze-thaw deterioration, and to enhance the aes-
thetics and abrasion resistance of AAC, exterior finishes should
be used. They should be compatible with the underlying AAC
in terms of thermal expansion and modulus of elasticity, and
should be vapor permeable.
Many different types of exterior finishes are available.
Polymer-modified stuccos, paints or finish systems are the
most common exterior finish for AAC. They increase the
AAC's water-penetration resistance, while allowing the pas-
sage of water vapor. Heavy acrylic-based paints containing
aggregates are also used to increase abrasion resistance.
36 Masonry
June 2008
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