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RE: Mortar Testing

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I am in agreement with everything that you said but it seems we are still giving a pass on field work without prism tests or mortar tests. 

Here is the issue. A testing firm, working for the Owner did mortar testing under ASTM C-780.
Some results were as low as 880 psi versus 1800 psi. This is still an indication of what we have in the field. They are using a batch mortar mix. What prevents the mason from adding too much water? This would be picked up by in field mortar tests, otherwise we are giving the mason a free pass to do whatever he wants. 

Jim K.

-----Original Message-----
From: Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com]
Sent: Tuesday, April 05, 2005 2:38 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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