Fig. 1. X-ray diffraction pattern of fly ash B for quantitative Rietveld analysis of crystalline and amorphous phases.
Fig. 2. 28 days compressive strength of fly ash B-based geopolymer cylinders. Higher strength was developed by geopolymers having 1.0 Na/Al ratio cured a elevated temperature for an extended period (B-1, B- 2 and B-3). Less than 1.0 Na/Al ratio weakened the mechanical strength of geopolymers (B-4 and B-5).
Fig. 3. SEM micrographs of the fresh fractured surfaces for B-1 (a), B-2 (b), B-3 (c) and B-4 (d). Samples having Na/Al ratio of 1.0 show better connectivity between geopolymer particles than those having Na/Al ratio of 0.8. Unreacted spherical particles are present in all samples.
Fig. 4. Photographs of fly ash B-based geopolymer specimens tested for efflorescence at the end of the test period. At 3 weeks, efflorescence was observed on the surface of all samples. The weakest efflorescence was observed in B-2 and B-3 specimens, the widest efflorescence was observed in B-5 specimen.
Fig. 5. The white surface deposit of fly ash B-based geopolymers is determined to sodium carbonate monohydrate (Na2CO3·H2O) by X-ray diffraction.
Fig. 6. X-ray diffraction patterns of geopolymers having different Na/Al ratios and curing conditions. The peaks caused by crystal phases present in fly ash B.
Table 2. Bulk chemical composition of fly ash B (wt%). Fly ash B is categorized as ASTM Class F for its rich (SiO2 + Al2O3 + Fe2O3) content
Table 1. Formulation of solid geopolymers using fly ash B and curing scheme
Table 3. Amorphous composition of fly ash B used in this study. The reactive Si/Al ratio in this fly ash is determined as 2.6
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