| Summary: | 碩士 === 中原大學 === 土木工程研究所 === 105 === The findings of this study show that it is feasible to manufacture eco-cement by using water washing dechlorinated pasty tailings to replace partial cement iron slag material. Because the pasty tailings contain ferrous carbonate and a little silicon oxide which can be used to manufacture cement.
Method to control sintering of eco-cement, the raw material is designed by cement factor as: Hydraulic modulus =2.10, Silica modulus =3.02 and Iron modulus =1.42, when the replaced proportion of iron slag is determined, the required contents of limestone, silica sand, clay, tailings and the rest of iron slag are calculated and mixed well. The sintering specimen (Φ50mm × 15mm) is made by hydraulic press with force of 20 tonnes for 3 minutes. The test ingot is placed on the crucible upright and burnt. The specineus are placed in a saggerfor sintering. The cement firing temperature rises from room temperature to 850℃ at heating rate of 10℃/min. The temperature is kept at 850℃ for 30 minutes, it rises from 850℃ to 1210℃ at heating rate of 6℃/min, and from 1210℃ to 1450℃ at heating rate of 4℃/min, the temperature is kept at 1450℃ for 30 minutes to complete the sintering. The cooling curve is not controlled externally. The furnace door is closed until it is cooled to 500℃. The sagger with the specimen is taken out quickly when it reaches 500℃. Then the door of the furnace is closed to protect itself. The specimen is cooled quickly in the ambient.
The eco-cement is made by specific raw material blending, it is found that the excessive addition of tailings will not lead to severe liquid phase to stick specimen with sagger during high temperature. Even the replaced iron slag is high, the cement factor can match the target value. The specific gravity test shows that there is no obvious relation between the setting time and the replacement of iron slag by tailings, theu are compliant with the CNS standard. But the autoclave expansion test showed it is out of the specification. The soundness test will be required in the future. The f-CaO content shall be the a measurement of eco-cement quality.
The analysis and property testing of eco-cement. It is found that in the eco-cement paste compression test, when the water-cement ratio is controlled at 0.35, the compressive strengths at the ages of 7 and 28 days are good. When the water-cement ratio is controlled at 0.485, and the replacement of iron ore by tailings is 30 %, the compressive strengths at the ages of 7 and 28 days still conform to CNS 61. The dry shrinkage of the eco-cement with tailings is better than control group. The XRD analysis shows that the main hydration products in the eco-cement are CH, C-S-H gel and AFm. The TGA result shows that the eco-cement contains CH, C-S-H gel colloid and CC(CaCO3). The CH content in eco-cement at the age of 7 days is higher than control group. The NMR analysis result of 29Si shows that the Q0 transfers to Q1 and Q2 peaks gradually with age, it can be inferred that the C-S-H gel in the cement grows continuously. When the replacement of iron ore by tailings is higher than 50 %, the degree of hydration at the age of 7 days is lower than control group, but there is no significant difference in the degree of hydration at the age of 28 days. The SEM observations show that there is no significant difference in the hydration products of eco-cement. To sum up the aforesaid results, the potential of tailings in replacing iron ore to make eco-cement is validated, but the tailings replacement shall be less than 30 % of total content of iron ore. If the replacement exceeds 30 %, it can develop towards the objective of manufacturing special cement.
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