Heat curing: tendons cut 1

[ione]

When heat curing prestressed concrete products (slabs, panels etc), have the tendons to be cut immediately after the heat application or is it necessary to delay the cutting procedure until the concrete is cooled down?

 

[Ron]

Fundamentally it makes little or no difference. You can argue either side of the thermal issues that can result. You are less likely to spall the concrete at the cut (assuming flame cutting)if the concrete is dry (flame cutting will superheat the moisture in concrete and blow out if heat is directly applied to the concrete face).

 

[ione]

Thanks Ron.
My concern was about shrinkage and possible residual tension rising during the cooling period, so I presumed it was better to cut tendons immediately after the heat application and leave concrete (and tendons) to shrink without any constraints applied.

 

[Prestressed Guy]

The coefficient of linear expansion for concrete and steel are essentially the same so change in temperature will not create any loss or gain to the prestressing force. This is one of the reasons that reinforced concrete works so well. The main consideration for when the strand is cut is the required initial concrete strength required for the bonding of the strand.

Shrinkage is not an issue. There will be no residual tension because this is a “prestressed” member. The worst you could get if the coefficients were different would be a very slight loss in perstressing force. The elongation to stress the strand is magnitudes greater than the thermal contraction due to a change of 100 degrees max.