19-11-2012, 02:53 PM
Basalt rock rebar
Basalt rebar.docx (Size: 105.1 KB / Downloads: 43)
Materials - Rebar
Why not use regular steel rebar?
The biggest factor with rebar is avoiding corrosion. A particular concern is rebar that spans a cold joint in the concrete. There will be a cold joint between the footing slab and the bottom of the ICF wall and in the wall between stories. Cold joints let in water as fresh concrete does not stick to hardened concrete. Something like NitoBond or Ronofix can be used between pours and is worth doing, but even so it is worth assuming that water can get in the joint.
When steel rebar rusts it expands and this splits open the concrete letting yet more water in that causes even more rusting. This fairly common concrete failure mode is called spalling. Using steel rebar is not compatible with a house designed to last 500 years.
Other possibilities
Galvanizing
If using steel rebar then certainly I believe it should be galvanized to stop it rusting. It is best to have it galvanized after you have cut it and bent it. Galvanizing companies exist in most areas so you should find a local one. They seem to charge by weight (even though it would seem more logical to charge by surface area). Overall, galvanizing is an expensive choice.
Fiberglass rebar
Fiberglass rebar is a much better choice that steel rebar. It is available from two American manufacturers but they charge three times the price of steel rebar. A better bet is to buy it from one of the many manufacturers in China. Even with shipping, it is only about the same price as regular steel rebar.
There is some question about whether fiberglass rebar is stable in the alkaline environment of concrete. A Canadian study on bridges had some doubts. The Rock Rebar guys say: "Rock rebar does not need a special coating to resist the high ph from exposure to concrete like fiberglass rod requires".
Vinyl ester resin is used to bind all the glass fibers together. Vinyl ester resin also provides protection from alkalines.
Typical fiberglass rebar of 12mm diameter has this spec:
Weight: 0.22±0.05kg/m
Tensile strength: ≥500MPa
Shear strength: ≥100MPa
E-modulus: 35-45GPa
Elongation: 1.5%~2.5%
Rock Rebar
My conclusion is that rock rebar is the best choice for all the reasons described below.
Rock Rebar
Rock rebar was specifically developed for harsh environments such as sea walls and road bridges. It is made from volcanic rock called basalt. Magma in the earth's core is basalt. It does not corrode. Basalt rebar is manufactured from continuous basalt filaments and epoxy polymers. Adhesion to the concrete is primarily done using a sand surface but there is also a wound spiral "thread". Basalt filaments are made by melting crushed volcanic basalt rock of a specific mineral mixture to 1,700 degrees Celsius for 6 hours. The white hot material is drawn through special platinum bushings and then cooled into fibers. The fibers cool into hexagonal chains resulting in a resilient structure substantially stronger than steel or fiberglass. Rock rebar consists of 80% fibers and 20% resin. Basalt is non-toxic and inert. The production process creates no environmental waste and it is non-toxic in use or recycling. It does not loose strength in a house fire situation (it can stand 600 degrees C quite happily). It is also naturally resistant to UV exposure.