BACKGROUND :

The crud test started with Tom Rapenske's unfortunate Tank experience in his home state - Kentucky, USA. Having noticed an extra weak cement mortar matrix surrounding the GI wires it was suspected that the Galvanic reaction of the zinc with the cement alkali might have relased Hydrogen and caused a weak matrix. Tom then wanted a test to be conducted by others to see if a similar experience happened. He sent me two naturally passivated mesh samples - one from a US manufacturer, another from a chineese.








THE CRUD TEST
THE CRUD TEST
EXPERIMENT :

4 mesh samples were studied - US, CHINEESE and Two INDIAN
IND-1  : The zinc coating on the commercially available mesh here in India was too  thin.It was   electrogalvanized instead of hot dip ). So I bought a good hot- dip galvanized GI wire, cut pieces and placed them  loosely like a mesh.
IND-2  : This is a much thicker GI wire - again cut in pieces and loose   placed

3 Cement Mortar Mixes were Studied -
   M1 -  1 CEMENT, 2 COARSE SAND, WATER
   M2 -  1 CEMENT, 1 FLY ASH, 3 COARSE SAND, WATER
   M3 -  1 CEMENT, 2 COARSE SAND, WATER, 3 ppm Chromium Trioxide


OBSERVATIONS :

The  mortar managed to get underneath the mesh in most samples. In  the M3-China and a bit in M3-US the mortar did not fully encapsulate the mesh. This was perhaps due to operator error and  the mortar being  just a little  too dry.

In order to see the "crud" the mortar was chipped away with a small hammer and a 4" Nail used in place of a chisel. The GI wires were bared in small patches only to find - NO WEAK CRUD, but  A FAIRLY MATURE, HARD MORTAR JUST AS IN THE MIDDLE OF THE SQUARES.

Even in the indian - NON-PASSIVATED WIRES ( BOTH SAMPLES - IND-1, IND-2, AND WITH THE non-chromate MIX M1, there was NO WEAK CRUD. Just to make sure, the M1-IND-1 sample was broken and repeatedly bent over to study the regions in the immediate vicinity of the wires. Still NO WEAK CRUD.
PICTURES BELOW.
The imported samples were reportedly already passivated. They were dull grey. Although there   were negligible bright spots due to rubbing in transit, they were left in the open for a week before testing. The Indian GI wire samples were bought just 2 weeks before the test. They were quite bright and shiny at the time of the test.

The samples were arranged on a ply covered with a mylar sheet ( a thick smooth transparent plastic sheet - the kind they used as transparencies with OH projectors. Three nos.samples of each type for the 3 mixes  as shown in the PICTURE. These were then filled manually with respective mortars - 1/2 inch thick  and left indoors. The only vibration for proper placement was the trowel being tamped on the samples during application. After 12 hrs. the samples were covered with a wet hessian cloth and kept moist for a week.


After a week the samples were brought out in the sun  and let dry for a few days.They were then demoulded, and inverted. Some of these were then chipped to bare the GI wires.
        
                            
US              CHINA           IND-1            IND-2


      M1           
PIC            PIC                PIC             PIC
                      
CL                CL

     
       M2         
PIC


      M3                                 
PIC

    
PIC = Picture       CL = Close-up

Conclusion :  Go on to
CRUD TEST-2
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     sing.tp@gmail.com 
       
10th DEC. 2007
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