Return to index: [Subject] [Thread] [Date] [Author]

RE: Mortar Testing

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Jim,

It is a tough thing.  Part of the problem is that mixing mortar and laying
masonry is to a large degree an "art".  Keep in mind that things like
temperature, humidity, wind conditions, etc can drastically effect how
well the mortar can/will bond with the masonry units as well as what the
workability will be.  The point is that the mortar strength has little
impact on the overall strength of the masonry.  The ability of the mortar
to bond with the masonry units is MUCH more important than just strength
of mortar.  You can have the strongest mortar in the world, but if does
not bond well with the masonry units (i.e. the brick or CMU sucks the
water to quickly form the mortar or doesn't suck enough water from the
mortar, etc) then it is all for naught...you will end up with a nice
"crack" (i.e. the surface where the mortar and masonry meet just won't
have a bond) before building is occupied.  It is extremely difficult to
replicate the field conditions when testing mortar.

So, the key thing to recall is that there is NO accepted FIELD testing
procedures to verify the required properties under the Property method of
ASTM C270.  ASTM C270 is _ALL_ lab testing and CANNOT be used to verify
values in the field.  In otherwords, the Property specs of the Property
method are MEANT to be laboratory properties...NOT field properties.
So, you just don't test field mortar to ASTM C270 values for the
Property method.  If you want to do field testing, then that is ASTM
C780...but those tests are really to just to be "quality control methods
based on preconstruction and construction testing".

The biggest thing to remember is that for mortar, stronger is not
necessarily better.  You should only be specifying the absolute minimum
strength mortar that you need.  So, the common structural engineering urge
of "strong (or bigger) is better" does not apply.  You generally want to
be using the weakest mortar that you can get away with.  The stronger the
mortar, the more difficult it is to work with and the better chance that
you will have bond issues.

Scott
Adrian, MI


On Tue, 5 Apr 2005, Kestner, James W. wrote:

> Scott:
>
> I am familiar with the reasoning that you have outlined.
>
> It seems that there is no checks in balances in the field after the mortar mix has been approved unless you want to go to the expense of Level 3 QA or prism tests.
>
> It sounds like the masons and the batched mortar manufacturers have successfully lobbied ACI 530 for little or no field oversight after approvals.
>
> Perhaps, it is more complicated than I am making it out to be.
>
> Jim K.
>
>
>
>
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> Sent: Tuesday, April 05, 2005 3:30 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Mortar Testing
>
>
> Jim,
>
> In addition to the reasoning that Bill gave (the fact that masonry units
> will absorb water, which will lower the w/c ratio and thus increase
> strength in the field and for prism tests...but not for mortar cube
> tests), keep in mind that a typical mortart joint is only 3/8" thick.
> This results in the mortar really being "confined" when loaded in the wall
> assembly (and prism test), while it will be unconfined when tested as just
> a mortar cube.  As a result, the actual infield strength of the mortar
> when used in actual masonry construction is not really even closely
> approximated by lab testing.
>
> In addition, if I recall correctly, research testing has shown that
> mortar strength has a relatively little impact on the overall masonry
> strength.  The more important factors for mortar are good bonding
> characteristics to the masonry units and workability for the masons (which
> will effect things like the bonding)...plus a few others (like water
> retentivity).
>
> Thus, there is no need to determine the stregth of the mortar...and thus
> there is no real testing procedure for field testing.  For ASTM C270, you
> either specify it by Proportion or Property.  In either case, there is no
> FIELD strength testing...the testing done per the Property specification
> if lab testing only.
>
> HTH,
>
> Scott
> Adrian, MI
>
> On Tue, 5 Apr 2005, Kestner, James W. wrote:
>
> > 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.
> > > >
> > >
> > >
> > > ******* ****** ******* ******** ******* ******* ******* ***
> > > *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> > > *
> > > *   This email was sent to you via Structural Engineers
> > > *   Association of Southern California (SEAOSC) server. To
> > > *   subscribe (no fee) or UnSubscribe, please go to:
> > > *
> > > *   http://www.seaint.org/sealist1.asp
> > > *
> > > *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> > > *   send to the list is public domain and may be re-posted
> > > *   without your permission. Make sure you visit our web
> > > *   site at: http://www.seaint.org
> > > ******* ****** ****** ****** ******* ****** ****** ********
> > >
> >
> > ******* ****** ******* ******** ******* ******* ******* ***
> > *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> > *
> > *   This email was sent to you via Structural Engineers
> > *   Association of Southern California (SEAOSC) server. To
> > *   subscribe (no fee) or UnSubscribe, please go to:
> > *
> > *   http://www.seaint.org/sealist1.asp
> > *
> > *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> > *   send to the list is public domain and may be re-posted
> > *   without your permission. Make sure you visit our web
> > *   site at: http://www.seaint.org
> > ******* ****** ****** ****** ******* ****** ****** ********
> >
> >
> > ******* ****** ******* ******** ******* ******* ******* ***
> > *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> > *
> > *   This email was sent to you via Structural Engineers
> > *   Association of Southern California (SEAOSC) server. To
> > *   subscribe (no fee) or UnSubscribe, please go to:
> > *
> > *   http://www.seaint.org/sealist1.asp
> > *
> > *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> > *   send to the list is public domain and may be re-posted
> > *   without your permission. Make sure you visit our web
> > *   site at: http://www.seaint.org
> > ******* ****** ****** ****** ******* ****** ****** ********
> >
> >
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********
>
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********
>
>

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********