Field Manutention of Concrete Slabs

[capliard]

Hi everyone,

I designed a slab for a mine closure application.

To prevent workers from working above an open raise, Slabs are to be poured on the ground, then lifted and placed on a fill raise.

The operations proposed a modification. The idea is to install styrofoam prior to pour. Upon cure, we will push forks through foam for manipulating the slabs.

The issue is long term stability here. I know crack will form eventually and reach the steel.

Any thoughts on the issue.

I also Added a sketch. See attached pdf.

Charles, mine engineer



Ingenieur Minier. QuTbec, Canada.

 

[JStephen]

Can you make the slab thicker to hold the same concrete cover in that area?
Make sure the styrofoam can't float up.
"Manutention" = "handling" per the online translators, I had to look that up.
Possibly just put lifting lugs in the top surface and handle with slings?

 

[dik]

I'd be casting lifting lugs in the top... no cover to rebar and corrosion... generally lots of water at mine sites... maybe HDG? but, cost...

Dik

 

[SlideRuleEra]

To cure the concrete keep it as wet as possible (24 hours per day) for a week, starting a couple of hours after the concrete is placed in the forms.

Don't pick up the slab until the concrete is at, or very near, design strength (usually specified as strength at 28 days after placement). With a proper concrete mix, this could be less than 28 days, but more than 7 days (the wet curing time).

Keep the 50 mm rebar cover above the styrofoam. This will mean 100 mm cover in other places... if the slab is designed with this in mind, 100 mm is ok.

Depending on the dimensions shown in red on your marked up sketch, a top rebar mat (shown in orange) may be needed to keep the slab from cracking, or even breaking, when picked up by the forklift.

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[capliard]

Thank you all for the great input.

SlideRule, finaly I do not need the upper rebar Mat. But i had not realized i might need it.

Ingenieur Minier. QuTbec, Canada.

 

[Ron]

Agree with dik's lifting lug or embedded cable idea. Will also negate the need for top mat, assuming it is placed at about the quarter points of the slab length. Otherwise, I agree with SRE...top mat needed.

You don't give slab dimensions, but if the overhang on either side of the forks is more than about 25% of the slab length, and you are picking up from the bottom, you will need a top mat.

I don't see the need for the Styrofoam. Forks can easily penetrate the ground at the surface and pick up the slab.

 

[SlideRuleEra]

capliard - Will a crane be available at the project site? Or, are you having to design the slab considering the capabilities or a fork lift that is available?

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[miningman]

Is there even the slightest possibility that the water level in the closed flooded mine ever reaching the surface elevation of the raise?? If so , this design will not be accepted by the regulators.