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Pre-Cast Concrete Fire Training Facility

Pre-Cast Concrete Fire Training Facility

(OP)
Hello - I am looking at determining the continued usage of the cited facility. I came across this thread and response from Eng-Tips user Ron:
In general, no. You can get some localized spalling if the temperature gets very high. To lose strength in concrete due to heat, it has to be held at temperatures above 600 to 800C for 3 to 4 hours.The most common effect of heat on concrete is spalling due to moisture expanding in the pores, and carbonation of the surface, usually to a depth less than 1/8". http://www.eng-tips.com/viewthread.cfm?qid=259795

My questions are:
1. Anyone know the resource(s) for Ron's response?
2. We had a structural evaluation from a structural firm that recommended epoxy injection in the vertical walls cracks. Removal of spalled or delaminated concrete to sound concrete, sandblast of corrosion and prepare the substrate for bonding. Reinstalling fire panels at the burn stations. The spec. for the fire panels and the set is uploaded. Due to budget restraints, the fixes are limited to fire panel replacements and some remove and replace of spalled concrete. I would like input from the community on their confidence of the continued usage of the building with the limited repairs. We could also direct the fire department to control the burns for the training to max temperature. If we pursue that route anyone has experience on how to implement such a control?
Thanks on Advance for your help.

RE: Pre-Cast Concrete Fire Training Facility

Hi civilstr11,
I don't have any resources at hand (maybe Ron will chime in). But the structures for fire training buildings I've worked on in the past have been detailed to do two primary things:
1. Drain the water away from the building as fast as possible and minimize concrete exposure to water via sloped floors, well ventilated spaces, and sometimes specialized mixes (to create low permeability concrete).
2. Use steel plate shields, mounted in strategic locations, to minimize heat exposure to concrete and avoid spalling (per Ron's description you stated).

The steel sheets were panelized to allow thermal expansion, with slip covers at the gapped joints and mounted off the walls about 6" to allow air movement behind the plates.

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RE: Pre-Cast Concrete Fire Training Facility

Here is a somewhat dated but knowledgeable 3 part series from Concrete Construction in 1972.
Part 1 Link
Part 2 Link
Part 3 Link

Most epoxies lose their structural load capacity within 18F of their Heat Deflection Temperature. ASTM C-881 requires an HDT of 120F. The exposed epoxy will char starting at about 385F. It would be better to route the cracks after the epoxy has cured and patch the chase with a cement mortar. Even the best high temperature service/room temperature cure epoxy injection materials only have an HDT of 165F and are fairly thick, so difficult to inject unless the technician is experienced & patience. Lack of patience to sit on a crack is usually the failing of the majority of epoxy injection repair techs. I noticed you have slab cracks both vertical & horizontal. If the slab concrete is sound, you will want to ring the the concrete to make sure there isn't decontamination taking place and corrosion of the rebar. Determinations should be pinned before attempting injection. It takes surprising little back-pressure to propagate delams, once they start. Areas to receive concrete patching, spalls and those that will have concrete removed, should be tested with an indicator solution to be be sure all carbonated concrete has been removed. Phenolphthalein is the most common one in use. You can obtain small bottles from chemical supply houses that service K-12 science educators. Once the surface turns pink or darker, the pH of the concrete can be assured as greater than 9.5
Link
and
Link

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