Removal of Falsework Supporting Wide Culvert Slab

[BigH]

Just wondering what the structural engineering group sees as the criterion (criteria) for removing falsework supporting a thick wide (10 m) culvert slab (one way steel). For instance, the Alberta Ministry of Transportation states:

Portion of Work Age or Minimum Strength
Arches and girders - 14 days (or 80% of 28-day strength)
Pier caps and beams - 5 days (or 50% of 28-day strength)
Columns - 1 to 3 days
Decks & Slabs - 5 days (or 50% of 28-day strength)
Vertical faces of supported elements - 12 to 24 hours
Walls over 3 m high - 2 days

I would think that these strengths are based on using OPC (ordinary Portland cement) concrete whereas today, in many cases the use of fly ash up to 50% are being used in concrete mixes which will delay the initial hydration potential of the concrete. Too, some specifications that use fly ash constituents in the 30 to 50% range will actually specify 90-day characteristic strength values rather than the more traditional 28-day values.

Your comments would be appreciated.

 

[MikeHalloran]

Right; leave it until it rots and falls down of its own accord.

Is there some pressing need for the falsework material elsewhere?



Mike Halloran
Pembroke Pines, FL, USA

 

[hokie66]

Those numbers seem appropriate to me, fly ash or otherwise. For your culvert slab, 5 days or 50%, whichever comes latest, is reasonable for formwork removal, but not for applied loading.

 

[BigH]

Mike - monsoon and needing to open channel for river diversion . . . so yes, there is some urgency but not of the material - don't personally care if, after the slab can support itself, the river takes the falsework for a ride (I care, but . . .)