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RE: Masonry Cement

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"Prisms" are specially built for testing which makes me skeptical of how
well they reflect what is really going on in the field.  They have to be
transported from the field to the lab and although they are supposed to be
protected in transit I wonder how effective that is.  Another problem in
this area is that not much masonry testing of any kind is done and the
majority of the labs in some areas don't have equipment with big enough
openings to test prisms.

Roger C. Davis
SDS Architects, Inc.

-----Original Message-----
From:	Sherman, William [mailto:ShermanWC(--nospam--at)]
Sent:	Monday, July 02, 2001 8:58 AM
To:	'seaint(--nospam--at)'
Subject:	RE: Masonry Cement

Roger, why do you say "prism tests are certainly not good tests"?

Regarding mortar, ASTM C270 provides for compressive strength testing of
mortar (per ASTM C109) using a specific quantity of water. Since the amount
of water included in field mixed mortar is  not so well defined, compressive
test results of field mixed mortar cannot properly be compared with the lab
compressive tests. C270 even states that it "is not a specification to
determine mortar strengths through field testing". ASTM C780 can be used for
preconstruction testing and mortar testing during construction, including
compressive strength. However, C780 also states that "the test results
obtained under this test method are not required to meet the minimum
compressive values in accordance with the property specifications in
Specification C270" but such compressive strengths are to be considered
"approximate mortar strengths because lower water-cement ratios mortars are
more probable in the wall than can be measured for mortars from the mixer".
Thus it is inappropriate to require field mixed mortars to meet any specific
compressive strength requirement.

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