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Re: Mortar Testing

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Bill,



From ASTM C 270  (X1.6.3.2):



Perhaps because of the previously noted confusion regarding mortar and concrete, the importance of compressive strength of mortar is overemphasized. Compressive strength should not be the sole criterion for mortar selection. Bond strength is generally more important, as is good workability and water rententivity, both of which are required for maximum bond. Flexural strength is also important because it measures the ability of a mortar to resist cracking. Often overlooked is the size/shape of mortar joints in that the ultimate compressive load carrying capacity of a typical 3/8 in. (9.5 mm) bed joint will probably be well over twice the value obtained when the mortar is tested as a 2 in. (50.8 mm) cube. Mortars should typically be weaker than the masonry units, so that any cracks will occur in the mortar joints where they are more easily repaired.



Regards,

Dave Woodham

Atkinson-Noland & Assoc.





----- Original Message ----- From: "Bill Allen, S.E." <T.W.Allen(--nospam--at)cox.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, April 05, 2005 3:05 PM
Subject: RE: Mortar Testing


This thread reminds me of a question I've been meaning to ask.

With regards to grout, when should it be tested? The w/c ratio has to be
really high (producing an 8-9 in slump) so that the block has some water to
absorb when placing the grout and doesn't suck it all out. However, with a
w/c ratio so high, I doubt if a satisfactory sample can be cast. After all,
the in-situ condition of grout has a w/c ratio which is more normal range
once the excessive water is removed by the block. It would seem to me that
the sample should be cast before the water is added, but that sounds like a
complicated process.

Any enlightenment would be appreciated.

T. William (Bill) Allen, S.E. (CA #2607)
ALLEN DESIGNS
Consulting Structural Engineers
http://www.AllenDesigns.com
V (949) 248-8588 . F (949) 209-2509

-----Original Message-----
From: Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com]
Sent: Tuesday, April 05, 2005 1:38 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Mortar Testing

I just finished typing an email to a co-worker on this very subject.
Following is what I wrote:

I have deleted testing of mortar during construction from the project
specifications for the following reasons: Sections 3.1 and 3.3 of ASTM
C270-03 state that this standard is not to be used for field testing of
mortar or to determine compliance of field sampled mortar with the
specification; ASTM C780 provides methods for field testing of masonry
mortar but it also states that such testing should not be used to
determine compliance with compressive strength in ASTM C270. The reason
mortar is generally not field tested is that the mixed mortar has a
higher water content than the mortar in the constructed wall, due to
absorption of water by the CMU. Thus, compressive strengths of field
mixed mortar alone would be expected to be lower than laboratory tests
that use defined water contents.

Therefore, one should generally not specify field testing of mortar. UBC
does have a special test method using masonry units and mortar - but if
we are really concerned with strength of masonry, we should specify
prism testing. However, prism testing is not required by the code if the
specified compressive strength of masonry is within the permissible
requirements for the "Unit Strength Method".


William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com


-----Original Message-----
From: Kestner, James W. [mailto:jkestner(--nospam--at)somervilleinc.com]
Sent: Tuesday, April 05, 2005 2:30 PM
To: SEAINT
Subject: Mortar Testing

Why does the ACI 530, 3.7B, require only lab compressive
strength testing (ASTM C270) for acceptance of mortar? Field
testing (ASTM C780) is only to verify consistency of
materials and procedures, NOT FOR MORTAR STRENGTH. Yet, the
ASTM C780 tests for compressive strength.  This seems like
the mason and mortar suppliers have lobbied hard for this
provision to remove any checks and balance on their in place
work. Other than a prism test, what other basis do we have to
evaluate the strength of mortar that we are actually getting
in the field?

I realize that I'm really only interested in the strength of
the entire assembly, but if it is cost prohibitive to test
the prism assembly, then if I test each component
individually and it comes up to strength, than I would think
that the assembly is acceptable.


> Jim K.
>


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