| Summary: | 博士 === 國立臺灣科技大學 === 營建工程系 === 102 === In this study, the sodium hydroxide and sodium silicate were used as the alkali activator to activate the blended powder of slag and fly ash. Under the condition of fixed liquid-solid ratio, experimental parameters including different dosages of activator, moduli of sodium silicate and proportions of slag-fly ash mixtures were used to investigate the effects of various combinations of parameters on the fresh and hardened properties of alkali activated paste. The second is to investigate the effects of exposure to various elevated temperatures for 1.5 hour on the properties of alkali-activated paste. Finally, the variations of chemical compositions and microstructures of alkali-activated paste were examined by the microstructural analyses.
The research results show that: (1) For the fresh properties, the flowabilities of alkali-activated slag-fiy ash paste were in the range from 145 to 248 mm, the initial and finial setting times of paste were from 4 to 46 and 15 to 54 min, respectively. Increase of dosages of activator could decrease the flowability and setting times. (2) The increase of dosages of activator could enhance the material strength, and the compressive strngths of all mixture at 28 days were in the range from 28.4 to 82.05 MPa. However, when the slag powder mixed with fly ash had lower strength with the amount of fly ash replacement by 50%, the compressive strength at 28 days were decreased by 34.1 to 38%. (3) The thermal conductivity of all mixture were in range from 0.701 to 0.793 w/m•k, and the results were lower than that of normal concrete by 20 to 53%, which showed that alkali-activated slag-fiy ash paste has excellent insulation properties. In addition, the properties of thermal conductivity were controlled by composition of powder material. (4) The results of drying shrinkage test indicated that the increase of activator dosages could increase the drying shrinkage and the increase of drying shrinkage by 1.25 to 2.41 times from ages of 3 to 28 days, but specimens added with fly ash significantly decreased the drying shrinkage. (5) The compressive strength of slag-based alkali-activated material after exposoure to elevated temperature were lower than these of ambient temperature, but the compressive strengths of slag-fly ash alkali-activated material were higher. The optimum powder ratio of slag to fly ash with the highest compressive strrnghts afte exposure to 100 oC was 9:1, while those for exposure to 200 oC, 400 oC and 600 oC was 7:3. It shows that the slag-fly ash alkali-activated material has good properties to resist the elevated temperatures. (6) The results of SEM photos indicated that, in ambient condition, the alkali-activated slag-fly ash paste had many undissolved particles of fly ash, which reduced its mechanical properties. However, the filling effect of fly ash particle and its characteristic of hollow spheres help increase the volume stability and thermal insulation properties of material.
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