Figure 3: Fly Ash at 25 000X Magnification Figure 4: Fly Ash at 50 000X Magnification An Energy Dispersive Spectroscopy (EDS) comparison was done on an angular particle and a spherical one (shown in Figure 2) in order to observe any compositional variations which could explain the differences in shape. Table 1 shows the EDS findings from the analysis done on particles 1 to 4 in Figure 2. : Elemental weight composition from EDS The particles are primarily composed of Carbon and Oxygen, fewer amounts of Aluminium and Silicon and trace amounts of Magnesium, Potassium, Calcium and Iron. Deo (2014) attributes the strength development in concrete containing fly ash to the silica and alumina in the fly ash. The high Carbon readings in the sample is most likely unburnt Carbon from the coal burning process and the high Oxygen content can be attributed to the fact that the other elements exist as oxides in the fly ash (See Table 2). Table 2 is the composition of the ash as received from the manufacturer. : Composition of fly ash product (Mgangira, 2015) Parameter Range of Composition (%) SiO2 51.0 65.0 – Al2O3 25.0 35.0 – Fe2O3 3.0 5.0 – CaO 1.0 6.0 – MgO 0.5 2.0 – Loss On Ignition (LOI) 0.8 2.5 – Particle 2 does not contain Calcium and Iron compared to the other particles while Particle 1 does not contain Potassium. The low calcium content is indicative of a Class F fly ash which is low in lime (Cao). Particle 2, which is the most angular in shape, has a lower weight composition of Silicon and Aluminium than the other particles and higher Carbon content by weight which may be attributed to its shape. Kutchko & Kim (2006) showed that unburned Carbon particles tended to be irregularly shaped and on the upper end of the size distribution. According to Sun et al (2001) angular particles can belong to the dense particle” sub-group of “irregular
Figure 3: Fly Ash at 25 000X Magnification Figure 4: Fly Ash at 50 000X Magnification An Energy Dispersive Spectroscopy (EDS) comparison was done on an angular particle and a spherical one (shown in Figure 2) in order to observe any compositional variations which could explain the differences in shape. Table 1 shows the EDS findings from the analysis done on particles 1 to 4 in Figure 2. : Elemental weight composition from EDS The particles are primarily composed of Carbon and Oxygen, fewer amounts of Aluminium and Silicon and trace amounts of Magnesium, Potassium, Calcium and Iron. Deo (2014) attributes the strength development in concrete containing fly ash to the silica and alumina in the fly ash. The high Carbon readings in the sample is most likely unburnt Carbon from the coal burning process and the high Oxygen content can be attributed to the fact that the other elements exist as oxides in the fly ash (See Table 2). Table 2 is the composition of the ash as received from the manufacturer. : Composition of fly ash product (Mgangira, 2015) Parameter Range of Composition (%) SiO2 51.0 – 65.0 Al2O3 25.0 – 35.0 Fe2O3 3.0 – 5.0 CaO 1.0 – 6.0 MgO 0.5 – 2.0 Loss On Ignition (LOI) 0.8 – 2.5 Particle 2 does not contain Calcium and Iron compared to the other particles while Particle 1 does not contain Potassium. The low calcium content is indicative of a Class F fly ash which is low in lime (Cao). Particle 2, which is the most angular in shape, has a lower weight composition of Silicon and Aluminium than the other particles and higher Carbon content by weight which may be attributed to its shape. Kutchko & Kim (2006) showed that unburned Carbon particles tended to be irregularly shaped and on the upper end of the size distribution. According to Sun et al (2001) angular particles can belong to the “irregular dense particle” sub-group of
1a_mgangira_compressive-strength-of-a-concrete-mix-for-pavement-blocks.docx