Alternate re-enforcement for slab

[cannuck]

New guy here, can be a **** disturber but since I am deep into building my final "dream shop" (and have been waiting 72 years to do so) I feel a bit of urgency to reach "final solutions" before spending the bux one time.

Let me start out by saying I am a mechanical guy, not a civil type (in more ways than one). Since my build (to be followed by house and greenhouse(s)) will involve a lot of concrete, I have been trying to understand the material. When I see someone putting steel rebar down, the first thoughts I have is that the slab will shrink constantly but the steel won't. So who would put in a material that will ultimately fail the concrete, first providing a conduit (through micro-cracks) for corrosive media to enter then allowing it to expand the steel (from oxide exfoliation) failing the surrounding concrete in tension ???

I have done a few slabs with fiber re-enforcement and they have worked out reasonably well, but the materials used seem not great for bond strength (even in shear) and I assume would permanently deform plasticly when stained axially - in other words not strong enough to contribute anything to tensile strength of the concrete.

I found "Helix" some time ago (haven't had opportunity to use it yet) and it seems to provide a LOT more benefit to a pad than steel rebar could ever provide. Having been developed into blast-resistant structures, my purely mechanical mind would have to ask why we don't see more of it (or do "we"??). I understand that in the US it now has approval to completely replace re-bar. For those who haven't encountered it, Helix is very small flat sections of twisted wire either in galvanized steel or stainless.

The next thing I encountered was basalt fiber rebar. about 8x the strength/weight ratio to steel, can't corrode (already a stable oxide), very similar co-efficient of thermal expansion to concrete. Was all from Russia/Ukraine, then Europe, Asia and finally one supplier opened up in TX make US sizes with approvals done by treating it as "fiber" similar to "glass fiber". Second supplier now in FL. Other than need to order bent shapes from manufacturer (can not be formed once resin sets) and limited performance at elevated temps (for the resin, exactly the opposite for basalt fiber that makes fantastic heat shields), why would I (and everyone else doing slab-on-grade) not use this????? You can get it in coils from Asian suppliers (not sure how that works for approvals in US market) making placement a much simpler thing of cut-to-length.

There are of course a fair number of fiber re-enforcements now (my first two were polypropylene IIRC). Glass can be formulated to be more tolerant of the high pH of concrete, the shot crete guys seem to use steel wire (not sure you could spary Helix), basalt with epoxy sizing seems promising and of course the dreamers all think carbon nanotubes are the be all and end all (I should mention, I will probably spend much of this winter in a lab playing with CNC in PFCC). What are the materials that the concrete people around this site have used and to what effect??

As I said: this will be my ultimate facility to work and play with, teach my grandkids, build some dreams and I really want to get it right and leave behind something with a long future. Just a bear of a thing to get my head around when my whole thought process is dedicated to structures in steel and aluminum, not concrete.

 

[formula388]

I have been trying to understand the material.

If you really want to understand concrete, find Tyler Ley on YouTube. http://www.tylerley.com/
Worth the read/ watch time.

 

[ConCretin]

Welcome to the GJ cunnuck. I admire your desire to think outside the box but with all due respect, you are overthinking this. If cost is no object and you want to experiment with a more exotic type of reinforcing, by all means do so. But if you really want a quality slab, I'd focus my attention on the construction details, the concrete itself and the methods used to finish it. These factors are far more likely to affect the appearance, serviceability and durability of your slab than the type of reinforcing you use.

Most of the reinforcing types you mention perform the same function. They hold cracks together after they occur. Plain old rebar or wire mesh are affordable, simple to install and proven to work. I'd be more concerned with minimizing and controlling cracks rather than what's holding them together.

The bearing capacity of your slab primarily depends on the soils underneath and to a lesser degree the thickness of the concrete. I say this because increasing the thickness of the concrete makes a slab stronger but it takes a lot of inches to make up for an poor base. Reinforcing doesn't really enter into the equation.

Take a look at my Guide to Floor Slabs in the link below for some practical ways to construct a quality slab and good luck with your project.

 

[cannuck]

Thanks, LL. I read your (excellent) slab post(s) and thread, but did not want to divert from your topic by posting about re-enforcement in that thread. I am relatively aware of base preparation issues and will probably go with compacted subsoil (will have an acquaintance who is an engineering prof and well known soils guy in private practice give me direction) to a spec probably what we used building a tank farm 2 miles East of here. I have a shallow layer of boulders (glacial) embedded between very thin topsoil (all unbroken land) and subsoil (alluvial till, 15' thick) over 90' of clay. All site work starts with blading off the topsoil with D5 then picking little rocks by hand, big ones with track hoe so once the subsoil is flat it is probably 6-8" below grade. Plan on compacting as directed then placing at least 6" of PFCC instead of gravel as an insulating area and base for slab, with pockets for pads for columns holding roof and cranes as well as pad for 12k 2 post lift. Heat will be radiant (as in overhead gas fired IR, not in floor).

I can do everything on site but don't have the experience to place and finish a large pad, so will bring in some pros to do that. We are seeing about 30% improvement in strength using sulfate resistant cement and cellulose nano-crystals (friend is able to produce near-commercial quantities) so should be able to make 35 MPa (= 5,000 psi) at reasonable cost. Probably do 5", but since I have some heavy equipment might go to 6" - but at 5k with a very stable base not sure I need to.

I assume you would place the hydro membrane between subsoil and PFCC base? The till layer on top of the clay layer has been extremely dry last few years, but some times ( 1in yr in 50) that surface water table gets right up to the surface, so we pretty much want to keep everything on grade and go up.

 

[mcbane]

What is PFCC?

 

[cannuck]

What is PFCC?

Preformed Foam Cellular Concrete ("foamcrete in slang"). Essentially a neat cement mix using air/blowing gas instead of aggregate. Makes a great geofill and insulation layer. I will eventually try to make wall panels then structural panels from this material.

 

[billconner]

I'm with LL on most of this but on the moisture barrier - reading here one poster spoke of using Stego wrap directly under slab. The one for sure is concrete will shrink, and the concept that if it's unrestrained - either at edges, columns, thickened areas, or even by the base - thus the Stego wrap - it can shrink and not crack. The other poster was good with glass fiber mesh.

But well prepared base, basic mix, and curing has to be fundamentals.

I like the look of the helix but not sure plants and contractors in this area would.

And have you looked at Glavel, perhaps in place of foam or PFCC? Interesting product.

 

[cannuck]

I like the look of the helix but not sure plants and contractors in this area would.

And have you looked at Glavel, perhaps in place of foam or PFCC? Interesting product.

The problem with Helix is that being steel it will ultimately still corrode and fail (unless of course you use stainless alloy$$). I like basalt fiber a bit better for that reason.

I think the closest I could find glavel would be a few thousand kms away, and it can't come anywhere near the low thermal conductivity of PFCC (can get down to 0.1 W/mK

 

[billconner]

Just said the helix was interesting. I still believe the reinforcing is of less importance than other items.

Glavel made is 200 or so miles from me, so changes to that. Plus it replaces gravel at same time providing frost protection. Looks promising for me.

Not really familiar with the PFCC, but seems more beneficial over poor soils.

 

[cannuck]

Just said the helix was interesting. I still believe the reinforcing is of less importance than other items.

Glavel made is 200 or so miles from me, so changes to that. Plus it replaces gravel at same time providing frost protection. Looks promising for me.

Not really familiar with the PFCC, but seems more beneficial over poor soils.

PFCC used often as geofill material as you can dial up the density so easily. In some places (Europe) it is used to allow an excavation under an urban roadway (i.e. where directional drilling can't be done) that can be filled and put back in service in very short time. If the concrete was made light enough, you can dig it up with excavator like well compacted soil. Have even heard of it being used (in NJ IIRC) to float and entire shopping mall on poor soil (a literal "floating slab...but HUGE).

I am starting to lean towards post tensioning as it is about the only thing that can significantly increase the strength of the slab (I have some heavy equipment) other than making it very thick.

 

[billconner]

I think of a slab on ground as a floor covering - like tile or carpet - and the base under it as the subfloor and flooring structure. There may be situations requiring a structural slab on ground but for budget seems like a last resort.

 

[ConCretin]

I am starting to lean towards post tensioning as it is about the only thing that can significantly increase the strength of the slab (I have some heavy equipment) other than making it very thick.

Unless post tensioning is common in your area, good luck finding someone to do it. In addition, it's not really a great application for it. It's fine for expansive soils and extending suspended spans but you'll still have thick concrete and pay a premium for it.

Regardless of what you are driving onto your slab, the bar just isn't as high as you seem to think it is. Hire an engineer to do some basic geotechnical work and design a base and slab using conventional materials. I doubt you'll end up with more than 6" of concrete and spend a whole lot less.

We've placed dozens and dozens of industrial slabs for about every load imaginable. It's just not that complicated.