Issue 38

U. Haider et alii, Frattura ed Integrità Strutturale, 38 (2016) 305-318; DOI: 10.3221/IGF-ESIS.38.41 308 0 10 20 30 40 50 60 70 80 90 100 0,10 1,00 10,00 100,00 1.000,00 Accumulated fraction, Volume (%) Diameter of particles (µm) Cement Raw fly ash Second layer particles Third layer particles Small area and point analysis were carried out by using point and irregular area selection tools in EDX software AZtecEnergy to determine chemical composition of thirty elements both in the individual raw fly ash and separated fly ash particles. Regarding the X-ray Diffraction (XRD) analysis used to determine the mineralogical composition; X-ray powder diffraction data were collected at room temperature with a Bruker AXS D8 θ-θ powder diffractometer with parafocusing Bragg-Brentano geometry using CoK α radiation (λ = 1.79021 Å, U = 34kV, I = 30 mA). Tests to determine mechanical properties Specimens of size 40 x 40 x 160 were prepared for flexural strength testing in accordance with ČSN ISO 4013 [35], by employing a cement replacement of 60% by weight of raw fly ash, or second layer particles, or third layer particles at water to cement ratio of 0.4. For compression, half-broken specimens from flexure test were used in accordance with ČSN ISO 1920 [36]. Mixture was prepared in accordance with ČSN EN 480-1 [37] and, after preparation, specimens were cured in an environmental chamber at a constant temperature of 22 o C, with relative humidity of 50% up to 90 days. During flexural testing, load and deflection of the specimens were measured. Vicat apparatus was used to carry out measurements of compliance by means of setting time measurements in accordance with ČSN EN 196-3 [38]. Tests to determine the mixture behaviour under harsh environments Non-standardized rapid chloride penetration tests were carried out to determine the mixture behaviour under harsh environments which is slightly different from that of ASTM C1202 [39]. The apparatus of this test consisted of electro- migration chamber with two compartments filled with a 3% NaCl solution on the negative end and with 0.3 M NaOH solution on the positive end. R ESULTS AND DISCUSSION Physical properties s is well known, particle size indicates performance and quality of powders, suspensions, emulsions, and aerosols and has strong influence on mechanical properties of concrete [40]. Therefore particle size distribution (Fig. 2) was carried out to determine the measures of central tendency. Median diameter, d 50 , is regarded as a useful measure in comparing particle sizes of distributions. Tab. 1 shows that particles of second layer are finer than raw fly ash and third layer, but coarser than cement particles, whereas third layer particles are the coarsest. Figure 2 : Cumulative particle size distribution comparison: cement, raw fly ash, second layer particles, and third layer particles. A