Issue 38

U. Haider et alii, Frattura ed Integrità Strutturale, 38 (2016) 305-318; DOI: 10.3221/IGF-ESIS.38.41 314 0 1 2 3 0 30 60 90 Flexural Strength (MPa) Time (days) 60% Raw Fly ash 60% Second layer 60% Third layer 0 10 20 30 40 0 30 60 90 Compressive Strength (MPa) Time (days) 60% Raw Fly ash 60% Second layer 60% Third layer 0 300 600 900 0,0 0,1 0,2 0,3 0,4 Load (N) Deflection (mm) 60% Raw fly ash 60% Second layer 60% Third layer 0 10 20 30 40 0 200 400 600 Vicat needle penetration (mm) Setting time (mins) Pure cement 60% Raw fly ash 60% Second layer 60% Third layer Mechanical properties Specimens were prepared with 60% cement replaced with raw fly ash, 60% cement replaced with second layer, and 60% cement replaced with third layer. Specimens prepared with pure cement developed cracks due to high heat of hydration and gave inappropriate results: therefore their results are not included in this paper. Flexural and compressive strengths were tested at 7, 14, 28, and 90 days as shown in Fig. 7(a) and (b). Load-deflection relationships were developed for specimens at 90 days only as shown in Fig. 7(c). Fig. 7(a) shows that as the age of specimens increase, flexural strength of all three types of samples increase. However the flexural strength increase for third layer particles is 20% more than that of raw fly ash, and second layer particles. The reason for 20% more flexural strength of third layer particles can be attributed to the compact angular fibre type morphology of third layer particles which resist flexural load more than spherical particles [45-46]. The reason of trend of strength curve of second layer is due to its glassy particles rich in active silica and amorphous content which produces more hydration products as compared to raw fly ash and third layer particles. (a) (b) (c) (d) Figure 7 : Flexural strength (a) , compressive strength (b) , load deflection curve (c) for cementitious: raw fly ash, second layer particles, and third layer particles; and setting time determination by vicat apparatus for cement, raw fly ash, second layer, and third layer particles (d) .