Chris:
 
The material that separates sidewalk concrete from buildings, light  pole 
footings, etc.,  should not be tubular.  It should be the  thickness of the slab, 
1/2" thick, and composed of something like  asphalt-impregnated fiber, cork, 
plastic, or neoprene rubber.  These  materials are resistant to weathering and 
rot, along with being  compressible. The joint between the sidewalk and a 
building, etc., is  called an expansion joint.  Depending upon specifications, it 
often is not  placed between adjacent sidewalk placements to lessen the 
potential tipping  hazard or the development of lippage if the two slabs settle  
differentially.  My guess is that the "tubular stuff" that you mention is  
backing rod (often called backer rod".  Backer rod just will not function  properly 
in this application.
 
In addition to the expansion joints, concrete flatwork must have control  
joints to deal with the cracks that form from shrinkage.  The cracks that  form 
from shrinkage should be relatively straight and in a designed location  both 
for appearance and performance.  If the locations of the shrinkage  cracks are 
not controlled, they tend to snake back and forth, often with small,  easily 
displaced fragments of concrete in the cracked zones.  Control  joints may be 
scored with a grooving tool into the concrete after the initial  set .  The 
groove should be 1/4 of the slab thickness. For  a normal 4" thick sidewalk the 
cut needs to be 1" deep.  Making a 1"  cut is hard work.  Only walking groovers 
tend to make a 1"deep cut.   Most hand groovers make a 3/4" or 1/2" cut when 
new.  In practice,  the control joints are almost never cut deep enough.  But, 
 realistically, this never results in a problem for the contractor because 
there  is no quality control.  And, as a practical matter, just about any  
relatively deep groove does the job, except those cut with the worn out tools  used 
by the worn-out masons who achieve high production.  
 
Control joints can also be sawn into sidewalk and other concrete  flatwork.  
I won't go into that unless you insist, and maybe not even  then.
 
Concrete often cracks for reasons other than shrinkage.  It may crack  
because the concrete stuck to a building, which then moved, but not as  dramatically 
as one sees on the Saturday morning cartoons.  But, the  primary reason 
sidewalk concrete cracks is because of structural failure.   It is overloaded, 
causing compaction of the underlying soil, which even if  compacted according to 
specifications, is not compacted sufficiently to support  truck or car traffic. 
 Sidewalk concrete cracks extensively when it is  driven on by cars and 
trucks, instead of the designed light pedestrian  loads.  
 
So, whenever you see a delivery truck, a moving truck, or even the  careening 
taxi cab on the sidewalk, just remember that they are cracking and  
destroying the sidewalk.  Feel free scream at them.  Let us know  what you accomplish.
 
Let me compliment you on using the term concrete instead of cement.   But, 
remember that concrete is placed, not poured.  Milk is  poured.   So is 
slopcrete.  Whenever I have a finisher talk to me  about "pouring the cement" I 
immediately suspect the  worst. 
 
In parting, let me say that laying hunks of sidewalk can't be all it's  
cracked up to be.  
 
S. J.  Stokowski, Jr.
Stone Products Consultants
1058 Sodom Rd., Bldg.  2
Westport, MA  02790
508-881-6364
www.members.aol.com/crushstone/

 
In a message dated 5/23/2007 5:41:17 P.M. Eastern Daylight Time,  
[log in to unmask] writes:

In New York, sidewalks are typically laid in  large hunks, say 20 x 30 all at 
one pour, each section separated from the  other by that tubular stuff, I 
guess for expansion and contraction.  

But, within each larger pour, the concrete  is invariably scored to produce 
imitation "flags" of about 5' x 5'.   I dimly recall that the 5' x 5' scoring 
is a city requirement, but what is the  ultimate thinking behind it?   Cracks 
seem to ignore the score  lines, frequently passing through them without 
deviation. The scoring is too  shallow to concentrate run-off. 



 



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