2.4
CONCRETE MASONRY UNITS (CMU)
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NOTE: Three weight classifications are included in
ASTM C 90. It is important that the weight
classification desired be designated. If structural
design requires an f'm greater than 10 MPa (1500
psi), or if the requirement in subpart d. of
paragraph entitled "Prism Tests," is specified
greater than 10 MPa (1500 psi) that must be
indicated here by adding an exception which states
the f'm.
Type I is moisture controlled, Type II is
non-moisture controlled. Specify nominal size
required. Check availability.
Low alkali cement should be specified for use in CMU
if efflorescence caused by the use of available
cement is a problem. If efflorescence is not a
problem edit last sentence.
A lightweight high performance CMU has been
developed by USACERL. This unit provides equivalent
performance to a standard normal weight CMU, yet
weighs only 8.5 kg (19 pounds). This CMU does not
meet a strict interpretation of the ASTM C 90
requirements and may require a variance from local
building officials. Contact USACERL for supporting
technical information.
Specify lightweight aggregate where required for
structural or "U" value purposes. Coordinate with
structural and mechanical designers. Specify only
normal weight aggregate for single-wythe, ungrouted,
exterior walls. For PACNAVFACENGCOM projects,
specify Brick Type II only. Otherwise, light or
normal weight aggregate should be optional with the
Contractor, including single wythe, grouted walls.
For single-wythe, concrete masonry unit exterior
walls, specify water-repellant admixture for both
the masonry units and the mortar. This is a
regional requirement which shall be used, when
applicable, for SOUTHNAVFACENGCOM projects; when
appropriate, the requirements may be used for
projects in other areas. Use only with ASTM C 744
masonry units.
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Cement shall have a low alkali content and be of one brand. Units shall be
of modular dimensions and air, water, or steam cured. [Surfaces of units
which are to be plastered or stuccoed shall be sufficiently rough to
provide bond]; [elsewhere,] [exposed surfaces of units shall be smooth and
of uniform texture]. [Exterior concrete masonry units shall have
water-repellant admixture added during manufacture.]
a.
Hollow Load-Bearing Units: ASTM C 90, Type I or II, made with
lightweight [or medium weight] [or normal weight] aggregate.
SECTION 04200
Page 19
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