This project
|mainly involves building box culverts, runoff slabs and road beds.
|According to my buddy, these structures are built to interstate highway
|specifications, even though a 5/4 ton pickup is the heaviest vehicle
|these roads will probably ever see.

|Further, he swore that the joints could not be welded, as the welding
|process weakens the steel.

One reference I have at hand, "Placing Reinforcing Bars", Concrete
Reinforcing Steel Institute, Chicago IL, 1970, states in part," The
field welding of crossing bars should be avoided.... Tests have shown
that this can reduce the strength of a bar to 35 to 40 percent of its
capacity."

Only an engineer can authorize the use of weldable rebar and the weld
specifications.
It is very common to weld this type of rebar. Welding any other kind can
weaken the bar ajacent to the welds, but even non-weldable rebar can be
welded in certian circumstances.


Here's a quick reference from a PE:

http://www.k1ttt.net/technote/welding.html

From above link.
The ACI 318-99 Building Code Requirements for Structural
Concrete (which is referenced by all building codes in
the US) states:

"7.5.4 -- Welding of crossing bars shall not be
permitted for assembly of reinforcement unless
authorized by the engineer."
"R 7.5.4 -- 'Tack' welding (welding crossing bars) can
seriously weaken a bar at the point welded by creating a
metallurgical notch effect. This operation can be
performed safely only when the material welded and
welding operations are under continuous competent
control, as in the manufacture of welded wire fabric."

Dave