The replacement of asbestos fibres with cellulose fibres in producing
corrugated fibre reinforced cement sheets by the Hatschek process resulted
in edge cracking for stacked sheets. This was due to the hydrophilic nature of
cellulose, which increases its tendency for exchanging water with the
surroundings. The drying process of corrugated sheets, in a stack, resulted in
shrinkage hence edge cracking along the sheet. To reduce the magnitude of
drying shrinkage and edge cracking potential, several mitigation strategies
were proposed including the surface treatment of cellulose fibres,
incorporation of wollastonite microfibres, addition of admixtures and
superplasticizers, kaolin inclusion as partial replacement of cement and
different exposure conditions. A fundamental understanding in mechanisms
behind volume changes and how cracks form was crucial for optimization of
the mitigation strategies.
This thesis initially used a review approach to understand the mechanisms
involved in different types of shrinkage and the role of different mitigation
techniques. The ultimate goal was to achieve lower drying shrinkage and
cracking risks in corrugated sheets along with reducing its economic impact.
As a result, surface treatment of cellulose fibres, based on transforming the
hydrophilic nature of cellulose to hydrophobic state, was investigated.
Furthermore, inclusion of wollastonite/ kaolin as partial replacement of
cement, were evaluated. Also, the potential of adding admixtures/
superplasticizers was explored. Finally, investigation on development of edge
cracks in stacked corrugated fibrecement sheets was conducted under
different exposure conditions.
The results and findings of this research showed no significant improvement
in permeability with cellulose surface treatment. Wollastonite microfibres
promoted pore discontinuity hence significant reduction in permeability thus lower drying shrinkage. However, the resultant sheets were brittle. By
reducing water content with addition of superplasticizers, density was
enhanced thus reducing volume change from drying and wetting. Kaolin
acted as internal restraint for shrinkage, refining the microstructure at the
interfacial transition zone thus increasing density and its pozzolanic reaction
enhanced mechanical properties. The inclusion of kaolin in the fibrecement
mix in conjunction with controlling exposure conditions managed to eliminate
edge cracking.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/14890 |
| Date | 07 July 2014 |
| Creators | Mtsweni, Ntombikayise Beauty |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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