I am looking for possible (non-expensive) treatment that prevent bio-degradation of pig hair (a food industry by-product) as well increases the roughness of the pig hair to impact the flexural toughness of fiber-reinforced concrete.
Generally, there are 3 methods to treat reinforcing materials in concrete (based on my experience in nanomaterials).
1) Mechanical methods
2) Physical surface modification using the aid of surfactants
3) Chemical functionalization
In the context of natural fibers, I would recommend option 2 since bio-degradation needs to be taken into consideration.
Paradoxically, increasing the roughness of the pig hair is likely to decrease, not increase the composite toughness, as for microfibre frc toughness is derived via the energy expended through friction during fibre pull-out mechanisms, rather than fibre fracture. Increasing the bond between the fibre and the matrix will lead to fracture of fibres, which expends less energy than friction. So, unless you are using a fibre volume fraction above the critical value (probably well over 5% for pig hair and very, very difficult to achieve) I would not try to roughen the fibre. However, the detail of the mechanical behaviour will depend on the modulus of the pig hair; not a parameter I have to hand, regrettably. The mechanics of brittle matrix composite theory pertinent to this is summarised in my chapter in either the 4th of 5th Edition of "Construction Materials: Their nature and behaviour" (CRC Press).
With regard to the bio-degradation; I'm not sure what you mean. The fibres will not degrade via biological processes in concrete; the high pH renders the environment effectively sterile. However, the same high pH (>13) will also degrade the proteins in the fibre, weakening them; this is the fate of all biological fibres in concrete. It is difficult to avoid this, although some investigators have tried pre-treating the fibres with siliceous suspensions (e.g. microsilica/silica fume) which then act pozzolanically with the cement to reduce the pH in the vicinity of the fibres.
Thanks a lot to everyone and specially to Dr.
Purnell.
Dear Dr. Purnell, thanks a lot for your answer. Regarding the degradation that I mentioned, you are right, I meant degradation of this bio-material in an alkaline environment such as concrete. Would it be possible that you recommend some good papers addressing the treatments with silica fume and/or addressing an accelerated process that might correlate the degradation of natural fibers in a short time (e.g., months) to the degradation of natural fibers embedded in concrete for years?
With regard to the correlation, I've published quite a bit on this, see for example [DOI: 10.1016/j.compscitech.2008.08.026] Article Service life modelling of fibre composites: A unified approach
but whether the correlation is valid for pig hair I don't know, as I don't know the activation energy for degradation of keratin (?) in alkali environments. With regard to the treatments, the references are very old now (1987) -Article Direct incorporation of silica fume into glass fibre strands...
- but might be useful. You should also read the literature on how changing the matrix chemistry to reduce alkalinity and/or remove calcium hydroxide can help (some starting points are in the first paper I suggested).
Dear Dr. Purnell, thanks a lot again. Your articles are very useful to this issue.
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