[Ferro List] Basalt Fiber

[Keith Britton]

 From the data at www.sudaglass.com:

OPC based ferrocement won't benefit much thermally, if at all, and might 
actually suffer. The matrix will give up well before the basalt, i.e. 
same as before, and the basalt is noted as highly thermally conductive 
(though that doesn't show in the comparative data...IR transparent?) - 
true for steel fibers but notably not for PVA.  Refractory cement 
doesn't make much use of glass, if any, and silica suffers an annoying 
phase change plus chemical sensitivity. 

Using PVA fibers for burnout is an interesting thought, though not for 
OPC.  There's no free water in dry OPC unless it's being already 
destroyed to produce it (and I suspect the temperature to carbonize and 
oxidize PVA is higher than to destroy OPC anyway).  Burnout fibers in 
clay for ceramics have previously been paper/cloth, comparatively 
coarse, anything but straight, and relatively low firing.  Notably, such 
swell/shrink strongly with water content, affecting handling and 
behavior during drying prior to firing and necessarily leaving 
relatively coarse holes.  PVA would behave differently in all domains, 
wet, drying, greenware and fire.

Much more to the point for our fc issues are limited mass and cost, 
variety of forms, high modulus, no rust, probable intrinsic chemical 
inertness and OPC compatibility...   Of concern is the downside of high 
modulus, unforgiving failure mode, no data on fatigue behavior or long 
term aging in cured OPC etc.  I do note that even fibers seem to need 
coating for OPC use, and the very attractive bars, meshes and geofabric 
may need coatings/bonders specific to the service duty.  Lots of things 
to think through...  How, for instance, do you design for rebar which 
comes straight and won't bend?  Bar stock with thermoplastic or one shot 
thermosettable bonding?

On balance, this certainly seems the brightest new thing in a long 
time.  If the price is right, it probably offers unprecedented 
durability with high tensile strength for skinning lightweight fc 
items.  Furniture, roof and siding panels, doors and shutters come to 
mind, as do boats.  PVA offers but limited tensile strength short of 
incipient or gross matrix failure.  If basalt proves cheap enough to 
provide the tensile component of a high performance composite, then it's 
probably more likely to increase the market for PVA.  Reduced mass and 
reliably distributed short fiber reinforcement should lead to thinner 
sections and more critical design criteria.  A PVA/basalt mix then looks 
very desirable to better control flaws during set and cure - and to 
provide graceful degradation in the event of failure, at least for 
anything man rated...

kb

Christopher Glasspool wrote:
>  Ferrocement made with this material should be expected to have a much larger temperature range. .... Maybe PVA fibers added for a release of moisture from the portland cement. 
>
>