Fibre-Cement Paste Transition Zone
- PDF / 3,105,203 Bytes
- 8 Pages / 414.72 x 648 pts Page_size
- 110 Downloads / 217 Views
ABSTRACT The characteristics of fibres and paste of ordinary Portland cement transition zone are analysed and correlated to the mechanical properties of the produced composites. The water-cement ratio of the matrix varies from 0.30 to 0.46 and the age of the specimens varies from 7 to 180 days. Composites of vegetable fibres (coir, sisal and malva) are compared with those of chrysotile asbestos and polypropylene fibres. The analysis is made by backscattered electron image (BSEI) and energy dispersive spectroscopy (EDS). Mechanical tests evaluate the composite tensile strength and ductility. Mainly for vegetable fibre composites the transition zone is porous, cracked and rich in calcium hydroxide macrocrystals. These results are directly associated with the fibre-matrix bonding and with the composite mechanical performance. Further studies considering the impact performance of the composites compare the porosity of the transition zone with the toughness of the composites.
INTRODUCTION Studies of hydrophobic fibres [1], aggregates [2] and steel re-bar [3] in cement matrix showed that the transition zone of these materials is approximately 40 micrometers thick and that it has moderate portlandite (calcium hydroxide crystals) accumulation. Observations were made with scanning electron microscopy (SEM) and with X-ray microanalysis and with these techniques the evolution of porosity and of hydrated products on the interfacial surface was registered for a period of time. However with water absorbent fibres, such as the vegetable fibres, the transition zones in cementitious matrices have different porosity and concentration of the hydrated products [4]. This research analyses the basic characteristics of the portland cement paste and vegetable fibres of malva (Urena lobata Linn.), sisal (Agave sisalana Perrine) and coir (Cocos nucifera Linn.) composites and compare them with those composites of fibres of chrysotile asbestos and of polypropylene. The vegetable fibres present some singular characteristics: (i) high water absorption (near 100% or even more); (ii) impurities, such as powder and husk; and (iii) heterogeneous mechanical properties [5]. These singularities affect the composites mechanical properties as well as their microstructure.
479 Mat. Res. Soc. Symp. Proc. Vol. 370 0 1995 Materials Research Society
The importance of vegetable fibres is due to its great availability in Brazil and in other developing countries. Building components reinforced with vegetable fibres can be technically feasible, with cost reduction as high as 15% [6].
EXPERIMENTAL WORK The matrix consisted of portland cement paste only so that there is no interference of aggregates in the transition zone between fibres and matrix. The water-cement ratios are 0.30, 0.38 and 0.46 and the study ages of the specimens are 7, 28, 90 and 180 days. The selected fibres for this study are: chrysotile asbestos type 4Z (QUEBEC SCREEN TEST classification), polypropylene (filament), coir, malva and sisal. All the fibres do not have any type of treatment.
Data Loading...
