huangyhg

welding to old rebar
i have a retrofit project that requieres removal and replacement of existing corroded rebar with substantial section loss. i anticipate welding new bars to old once sound material in the existing is encountered. however, i am concerned with the weldablity of a305 billet steel rebar from the early 1960's. is anyone aware weldablity issues to steel of this type from this time period.

i'm not sure i'd weld rebar to old rebar that exists in a corrsion environment. despite removing old, loose concrete, there is still the potential for oxidation via electrical currents to occur, especially if the concrete is chloride impregnated. many times patches are performed and at the juncture of the old concrete to the patch a huge increase in oxidation kicks in - this would be right smack dab at your welds.
usually, we extend the new bar alongside the old, spliced along good quality lengths of the old bar. or a mechanical splice would possibly be appropriate....but welding - i wouldn't do it.
add new bars to replace the existing ones with the appropriate lap (you may find drilling and adhesive anchoring helpful in some locations providing you can lap the existing rebar sufficiently), or use bar couplers, see the following for typical barcouplers -

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