bars cut by acetylene torth
bars cut by acetylene torth
(OP)
The worker use acetylene to cut excess rebars protruding from a footing. When a rebar is heated by acetylene until it is cut. How much is the thermal expansion of the bars inside the concrete? What is the strain usually? Would it be more than the strain the concrete can handle and would the concrete crack from the inside from the thermal expansion of the bars?






RE: bars cut by acetylene torth
RE: bars cut by acetylene torth
If you hold a rebar and acetylene torch the front of it a foot away. Are you saying the heat of the torch won't even travel 1 foot? Isn't it iron a great heat conductor?
RE: bars cut by acetylene torth
As to the other points, yes, the steel conducts heat fairly well, but the concrete is a pretty good heat sink, and effectively limits the temperature excursion.
Should you elect to conduct an experiment, do be careful; concrete spalls violently when heated directly by oxyacetylene.
Mike Halloran
Pembroke Pines, FL, USA
RE: bars cut by acetylene torth
RE: bars cut by acetylene torth
RE: bars cut by acetylene torth
RE: bars cut by acetylene torth
Sure, it will be a little bit slower deep inside the concrete because air flow is limited down there, but it will never stop corroding. Completely covered rebar will NOT corrode.
Cut off rebar (by definition!) will be left with the ends exposed, and is likely to be further exposed by the concrete spalling from incidental heating at the concrete surface.
To the original question. This is a bad idea, but not because of the thermal expansion of the rebar. The distance between "cold" rebar and the very hot tip is very, very short once the rebar goes into the concrete and doesn't get hit with the flames. thus, there very very little linear thermal expansion. Right at the surface, the rebar is constrained against movement INTO the concrete, and has no restraint against expanding into the air outside the concrete, so it will tend to expand away from the surface, not axially nor radially into the concrete. Spalling is a danger.
RE: bars cut by acetylene torth
BA
RE: bars cut by acetylene torth
Cutting it off at the surface will not lead to corrosion deep within the footing unless the footing is in a very corrosive environment. The alkalinity of the concrete protects the reinforcing. There is always oxygen within concrete, as it is a porous material, but corrosion does not occur as long as the pH is high.
RE: bars cut by acetylene torth
RE: bars cut by acetylene torth
RE: bars cut by acetylene torth
[To the original question. This is a bad idea, but not because of the thermal expansion of the rebar. The distance between "cold" rebar and the very hot tip is very, very short once the rebar goes into the concrete and doesn't get hit with the flames. thus, there very very little linear thermal expansion. Right at the surface, the rebar is constrained against movement INTO the concrete, and has no restraint against expanding into the air outside the concrete, so it will tend to expand away from the surface, not axially nor radially into the concrete. Spalling is a danger. ]
Were you describing about concrete or bars spalling (breaking away into pieces)?
What is the evidence concrete can act as heat sink of the bars inside it.. concrete are not metal and doesn't conduct heat so easily. It is said concrete conducts heat only about 1/500 the rate of silver.
Not that I'd do it again. The workers did it without my knowledge. I won't let them do it again, but want to know the principles. Ty
RE: bars cut by acetylene torth
Mike Halloran
Pembroke Pines, FL, USA