Steel fibre reinforced concrete - truck slab 2

[Motorspirit]

Hi

We have been asked to design a truck wheel wash facility.As part of this the client has requested that a SFRC slab be used.I have experience is in designing conventional RC slabs on grade but not SFRC. The design procedures I can find seem reasonably complex and it appears that these are normally designed by the companies that supply the fibres or who specialise in industrial flooring/roading systems.

Is the design of SFRC slabs a specialist area or is it something that is normally done by a structural Eng with RC design experience?

What would be the advantages/ disadvantages of using SFRC slab for a truck was slab versus a conventional design?

Appreciate any feedback.

Thanks

 

[ooox]

I would leave it to the manufacturer's. Some like Adfil wil carry out a design as long as you supply the design parameters, like concrete finish, wheel loads, bearing capacities/CBR%.

 

[Ron]

If you understand that steel (and other) fibers only enhance the properties of the concrete and do not provide true "reinforcement" you're ahead of the game.

Steel fiber enhances the durability of the concrete and helps to mitigate drying shrinkage cracks. Polypropylene fiber does similar, but in my opinion, not as well.

You will get a nominal increase in compressive strength, a fairly large increase in the modulus of rupture, and the corresponding shear strength is increased. Outside of that, the only enhancement you get is a tougher surface (that's good for your application).

I would design the slab based on the modulus of rupture increase and keep control joint spacing the same as a conventional slab. You'll probably save 1 to 2 inches of concrete thickness with an appropriate fiber mix.

 

[dik]

I think that steel fibres increase the flexural strength of concrete, but they have to be in significant proportions. I do know that they increase the toughness. Polypropylene fibres only help by modifying the rate of bleedwater and provide better hydration of the mix; they do not provide strength.

The critical issues are the modulus of subgrade reaction for the soil, the flexural tensile strength of concrete and the wheel load and pattern. You also have to include for flexural tensile 'fatigue' and look at jointing.

 

[Teguci]

Did the client tell you to not reinforce the slab with coventional reinforcement? or can you just add some fibers for belt and suspenders?

 

[Motorspirit]

Thanks guys

I must admit I had approached it on the basis that the SFR would be the only reinforcement. Makes sense to reinforce conventionally and simply use the SFR for toughness etc.

Cheers

 

[CTW]

Rusting of the steel fibers will be an issue in a wash area.

Did the owner site any particular reasons for requiring steel fibers?

 

[kellnerp]

You might look at this Tuf-Strand. It is used in this area for hydraulic structures like sewage plants, white-topping, etc.

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[csd72]

normally pavements are designed based on the concrete capacity alone and ignoring any effects of reinforcement as far as strength is concerned.

This is the same whether it is fibres or welded fabric.

If it is just there to prevent cracking then it would be highly conservative to provide both fibres and reinforcement. It would also be a good way to lose a client.

If rust is an issue you may consider using synthetic fibres.

If reinforcement is required for the strength of the pavement then I would normally specify it as reinforcement due to the reliance of random mixing of fibres.

 

[hokie66]

While it is true that steel fibres at the surface will rust, this does not affect the slab performance. The appearance will change to a mottled brown surface, but in an industrial application, that should not be an issue. The rusting does not lead to spalling. As others have said, the main advantage of steel fibres is improvement in toughness including impact and abrasion resistance.

 

[concretemasonry]

Could this possibly be a "wash-out" area for a ready-mix plant?

If you get into the quality controls and mixing times he could be the man that decides on what type of fibers he is comfortable with based on testing.

If the structural design is good, he probably knows what he wants to use and what he is comfortable and doesn't want a failure since it may be a demonstration project in the future.

Dick