[Ferro List] more Tom's crud testings

[tom rapenske]

TP and others,

To eliminate from the list of possible causes for Tom's crud I have recently set up and completed further crud tests (photos in link below) as follows:
--- I have further 'naturally'  passivated wire mesh used in the following tests to 16- 20 weeks in order to eliminate possibility that weather conditions during passivation time were not ideal for some unknown reason and subsequently caused insufficient passivation. This further passivation probably quells musings about  "unpassivated bare contact points" in unrolled mesh or in formwork as a cause.
--- purchased new Portland cement from another manufacturer (Georgia) to test the chances that the previous cement (Indiana) was contaminated, outdated, or its chemical makeup was somehow unusual.
--- I've left the cut ends of wire mesh unencapsulated to eliminate the chances that the crud was being caused by electrochemical galvanic reactions between bare steel and zinc both being in contact with fresh mortar. This test is therefore only relevant to 100% zinc surfaces being encapsulated.
--- purchased and used a new (and different manufacturer) sand source. Despite it being less fine (common 'masonry' sand), it is well graded, certified, and otherwise ok (according to my opinion) for test purposes.
--- I have encapsulated only one layer of mesh to eliminate remote possibilities of poor penetration/mortar segregation caused by multiple mesh layers.
--- I have eliminated all admixtures and pozzolans. The test's mortar mix is therefore only Type I/II Portland cement + sand + water.

See inverted test samples labeled #1 thru #4, and their closeups, at top of photo groupings at:  http://www.flickr.com/photos/14073523@N05/?saved=1. Enlargements are available by clicking on photo and then clicking on the magnifying icon.

Sample #1 = 2 parts new sand + 1 part new Port + .4 spring water
Sample #2 = 2 old sand + 1 new Port + .4 spring water
Sample #3 = 2 new sand + 1 previous Port + .4 spring water
Sample #4 = 2 old sand + 1 new Port + .4 distilled water

Once again, in these new tests it shows there is no cement paste bond with the wire mesh in all cases. The sand and the crud were 
easily removed from vicinity of wire with a wet toothbrush.
Also note (not easy to see)that in all samples I have easily (two fingers) been able to pull the left portion of mesh (two squares worth)up and out of its position, showing that it is 100% no bond on all sides of all wire strands. 
Note photo #3 for my error in not stapling securely
that resulted in too much mortar slipping beneath wire.
The checkerboard pattern of discoloration is not present
because a fraction of an inch of thin, normal-colored mortar is 
blocking immediate view of discolored crud. 

Are we approaching the validity of the following conclusion yet?:
1.) If you want to successfully passivate galv. mesh you 
must get serious about chromium. It can come into play from
4 possible sources: a.) chromate dips, where mesh is 
treated in the factory, b.) chromium in ordinary Portland
as a trace element, c.) chromium as a trace element in fly
ash and similar pozzolans, and d.)chromium trioxide admixes.
TP's success in achieving bond with New Delhi's cement needs
further investigation (his country's cement has tested out 
to have potentially 50 times more chromium than a U.S.
cement).

Tom
 

       
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