Concrete Composites Transition zone studies of vegetable fibre-cement paste composites

The transition zone of short filament fibres randomly dispersed in a paste of ordinary Portland cement was analysed. Composites with vegetable fibres (malva, sisal and coir) were compared with those with chrysotile asbestos and polypropylene fibres. The composites were prepared for testing at the ages of 7, 28, 90 and 180 days. The water-cement ratio was 0.38; at the age of 28 days specimens with w/c = 0.30 and a w/c = 0.46 were also tested. Mechanical tests evaluated the composite tensile strength and ductility. Backscattered electron imaging (BSEI) and energy dispersive spectroscopy (EDS) were used to identify the major properties of the fibre-matrix interface. Mainly for vegetable fibre composites the transition zone is porous, cracked and rich in calcium hydroxide macrocrystals. These characteristics are directly related to the fibre-matrix bonding and to th