Issue 38

U. Haider et alii, Frattura ed Integrità Strutturale, 38 (2016) 305-318; DOI: 10.3221/IGF-ESIS.38.41 309 Upper limit diameter, d 97 , listed in Tab. 1, is a useful measure to determine the upper limit of particle size distribution and is used by industries dealing with powdery materials [41]. The table shows that d 97 of second layer is lesser than that of raw fly ash and third layer, but larger than that of cement, which is an indication that second layer particles are finer for even the upper limit of particle sizes. Comparison of densities for cement, raw fly ash, second layer, and third layer is also presented in Tab. 1, which shows that cement has the highest density followed by third layer, raw fly ash, and second layer. Density of raw fly ash is more than second layer and lower then third layer, but closer to the second layer, which indicates that second layer particles are present in larger quantity in raw fly ash, nearly 55-60% against the 35-40% of the third layer particles. Specific surface areas of raw fly ash, second layer, and third layer presented in Tab. 1, showing that second layer particles have 100% larger specific surface area compared to that of raw fly ash particles, and 73% larger specific surface area compared to cement particles. Therefore, second layer particles have lesser particle size, lesser density, and more specific surface area as compared to raw fly ash and third layer particles. Table 1 : Physical properties of particles. (a) Raw fly ash (b) First layer (c) Second layer (d) Third layer Figure 3 : Optical images of: raw fly ash (a), first layer (b), second layer (c), and third layer particles (d) at 10 X magnification. Particle type Median diameter, d 50 (µm) Upper limit diameter, d 97 (µm) Density (g/cm 3 ) Specific surface area (cm 2 /g) Cement 14.6 47.0 3.1 22000 Raw fly Ash 60.1 230.7 2.2 19000 Second layer 32.2 110.3 1.9 38000 Third Layer 146.7 413.3 2.7 9000