When is Field Testing of Mortar Required?
Masonry Home > Designer and Specifier's Site > Field Tips: When is Field...
Field testing
of mortar is required whenever indicated by a project's contract
documents. Field testing of mortar has not been a mandatory requirement
of previous editions, nor does the 1999 edition of the MSJC Code
require field testing of mortar under any of the three levels of
quality assurance. As a "when required" provision of past
and current editions of the MSJC Specification, mortar testing is
an option left to the discretion of the specifier.
Perhaps a more
significant question is what criteria should the specifier consider
in deciding whether or not to require field testing of mortar and
what test(s) should be performed. The specifier should first establish
that the proposed testing meets the desired need. For example, if
it is necessary to establish conformance of mortar materials to
ASTM C 270 requirements, ASTM C 780 field testing of mortar is not
appropriate. Samples of the mortar materials need to be mixed and
tested in the laboratory in accordance with the procedures of ASTM
C 270. If the need is to verify structural performance, field testing
of mortar (particularly compressive strength) is not adequate. The
structural performance of a masonry wall cannot effectively be predicted
on the basis of field tests of mortars.
Field testing
of mortar according to ASTM C 780 can be used for quality control
of mortar production at the job site. ASTM C 780 defines procedures
for measuring properties of plastic mortar such as consistency,
board life, and air content. It also outlines procedures for determining
the aggregate ratio and water content of freshly mixed mortar, a
procedure that can be used to confirm accuracy of site proportioning
of mortars. Finally, it defines procedures for measuring properties
of the hardened mortar, such as compressive strength and splitting
tensile strength. If ASTM C 780 compressive strength tests are to
be conducted during construction, preconstruction tests need to
be performed to establish baseline values that can be expected during
construction when using the approved mortar mix design. Field test
results of mortar conducted according to ASTM C 780 are not required
to meet the minimum compressive strengths of the property specifications
of ASTM C 270 (See Section 1.4 of ASTM C780-96E1). MSJC Specification
Commentary Article 3.7D states: "Field sampling and testing
of mortar is conducted under ASTM C 780 and is used to verify consistency
of materials and procedures, not mortar strength." Field test
measurements of the compressive strength of mortar can be expected
to be lower and more variable than laboratory test results.
Since a significant
time interval is required between sampling of mortar and obtaining
results, compressive strength tests are not an effective means of
establishing control of mortar proportions. Observation or utilization
of the aggregate ratio test provides more timely information with
respect to proportioning. Thus the 1999 MSJC Code and Specification
Level 2 and Level 3 quality assurance provisions require inspection
to verify proportions of site-prepared mortar.
|