2.2
MORTAR
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NOTE: In general, Type S mortar will be used. Type
S mortar will be used below grade and in locations
of high seismic activity when high flexural bond
strength is required. In all other cases, Type N
mortar could be used. The lower strength of Type N
mortar allows cracking in the masonry wythe at
relatively low load levels. Masonry cracking will
result in more uniformly distributed anchor forces.
Conversely, vertical beam action of the uncracked
masonry wythe causes nonuniform distribution of
loads to the wall anchors. Those wall anchors near
the top of the uncracked masonry wythe have much
higher loads than those in the lower half of the
wythe.
When specifying masonry cement the mix must be
compared to a portland cement-lime mix of the same
type. This test compares the compressive and bond
strengths of the two cements. The values for the
masonry cement must be equivalent to the portland
cement-lime mix.
Low alkali cement should be specified for use in
mortar if efflorescence caused by the use of
available cement is a problem.
The use of admixtures are not recommended in mortars
because they may cause efflorescence, may adversely
effect the strength of the mortar and may effect the
protection of embedded steel items.
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Mortar shall conform to ASTM C 270, Type [S] [_____]. Mortar mix shall be
based on proportion specifications. Laboratory testing of mortar shall be
in accordance with the preconstruction evaluation of mortar section of ASTM
C 780. Cement shall have a low alkali content and be of one brand.
Aggregates shall be from one source.
2.2.1
Masonry Cement
Masonry cement in conformance with ASTM C 91 may be used in the mortar.
When using a masonry cement a comparative test shall be performed between a
Portland cement-lime mortar and the masonry cement mortar proposed for the
project to evaluate the ASTM C 1072 bond and the ASTM C 780 compressive
strength of the two mixes. The test shall be conducted with the proposed
masonry units for the project. The masonry cement mortar will be
acceptable if the bond and compressive strength values are equal to or
higher than the portland cement-lime mix. The air-content of the masonry
cement shall be limited to 12 percent maximum.
2.2.2
Admixtures
In cold weather, a non-chloride based accelerating admixture may be used
subject to approval. Accelerating admixtures shall be non-corrosive,
contain less than 0.2 percent chlorides, and conform to ASTM C 494/C 494M,
SECTION 04810
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