Lightweight autoclaved cement based composites reinforced with wollastonite fibers
Waldemar Pichór, Agnieszka Różycka Akademia Górniczo-Hutnicza, Wydział Inżynierii Materiałowej i Ceramiki, al. Mickiewicza 30, 30-059 Kraków, Poland
Quarterly No. 4, 2008 pages 344-348
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abstract The results of investigation the lightweight cement composite with cenospheres from coal ash reinforced with wollastonite fibres are presented in this paper. Cenospheres are lightweight, thin-walled amorphous hollow spheres consisting mainly of silica and alumina filled with air and gasses and are by-products of the combustion of pulverized coal at the thermal power plants. The properties of cenospheres make possible to use them either in dry or in wet slurry form. They are potentially interesting filler due to their properties and may be used to lightweight cement based composites production. In this study the volume of cenospheres added to all series of samples were constant and was 65%. Cement matrix of composites were modified by adding different amount of wollastonite fibers (from 0 to 10% vol. respectively). Two kinds of wollastonite were used: natural fibres with different shape and size of crystals and synthetic one. Synthetic wollastonite were obtained from thermal dehydration of xonotlite (calcium silicate hydrate) at 1000°C. Precursor of wollastonite was made by hydrothermal synthesis of SiO2 and CaO reagents at 240°C for 24 h. The thermal treatment led to phase change of xonotlite to wollastonite fibres with needle-like shape similar to the xonotlite fibres. Samples were formed form cement paste without pressing and after 24 h of hydration at 20°C and 100% RH the composites were autoclaved during hydrothermal process at 180°C for 12 h. The bulk density, flexural strength and stress intensity factor KIc of fiber reinforced cement composites with cenospheres vs. fibers volume were investigated. The stress intensity factor were calculated from results obtained during three-point bending test of notched samples. The influence of fibres content on the bulk density of composites are insignificant. Mechanical results show that the major effect of strengthening of composites were about 2% vol. for samples reinforced with synthetic wollastonite and 6% vol. for natural wollastonite fibres. The stress intensity factor increased due to synthetic fibres volume up to 6% vol. The results show that synthetic wollastonite are promising reinforcement for lightweight cement composites but in case of large volume of fibres the main problem is homogenous distribution of fibres. Keywords: fiber-reinforced cement composites, wollastonite, fibers, cenospheres, mechanical properties