Properties of fiber reinforced cement composites with cenospheres from coal ash
Waldemar Pichór, Marek Petri Akademia Górniczo-Hutnicza, Wydział Inżynierii Materiałowej i Ceramiki, al. Mickiewicza 30, 30-059 Kraków
Annals 4 No. 11, 2004 pages 319-325
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abstract The results of investigation the fibers reinforced cement composites with cenospheres as fillers are presented in this paper. Cenospheres are lightweight, thin-walled 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. Some properties of used cenospheres are shown in Table 3. Usually, cenospheres are polluted by ash particles and before application they should be cleaned. Figure 1 shows the difference between cenospheres before and after wet dust separation. They are potentially interesting filler due to their properties and may be used to lightweight cement based composites production. Several series of composites with different amount of fibers and different volume of cenospheres have been prepared in this experiment. But in each case the fibers’ volume has been set as proportion to cement matrix content. Mix proportions and properties of fiber used have been presented in Tables 1 and 2, respectively. The influence of cenospheres content on the relative density of composites and the influence on the total open porosity are shown in Figure 2. Relative density of composites linearly drops due to increase of cenospheres volume. Open porosity of such composites may be connected only with cement paste. The effect of cenospheres content on this property may be explained closely by decreasing of cement paste volume in composites. Load-deflection curve for two different series of composites subjected to third-point bending and the method of calculation the toughness indexes I5 and I10 are shown in Figure 3. Figure 4 shows result of mechanical properties investigation of composites. The flexural strength mainly depends on cenospheres content but influence of fiber volume is rather small. However, in the modulus of rupture case his level depends on the cenospheres volume (similar to effect on the flexural strength) and on the fibers content. The role of fibers in fracture process is significant when the brittle cement matrix is broken. According to results obtained in bending test the toughness indexes are calculated, too. A value of each of them mainly depends on fiber type and volume and on properties of matrix. In this case the level of toughness indexes are quite high. The SEM observations of interfacial zone between cenosphere-cement matrix and fibercement matrix are presented, too. Figure 6 presents specimen’s surface after cracking where broken fibers are visible. Those pictures and SEM observation presented in Figure 7 show the good bonding between fiber and cement matrix and cenospheres and cement matrix, too. The interfacial region between components with porous structure and crystals of portlandite didn’t observed. The results show that use of the cenospheres as lightweight filler may be a way to obtain the low or moderate density fiber reinforced cement composites with good mechanical properties. Key words: fiber reinforced cement composite, cenosphere, mechanical properties, modulus of rupture, fibers