| Red mud is a kind of solid by product raised from the alumina refining plant. It is reported that at least more than 3,000,000 ton red mud is discharged annually in China, and the accumulated amount of red mud discarded has reached 41,000,000 ton. Among those only little part was reutilized in some different ways, the rate of reutilization being said to be fewer than 15%, and large amount of red mud was exposured to atmosphere, which not only occupy land and caused pollution on environment but also resulted in the waste of natural resource. Therefore how to eliminate the problem of pollution and at the same time to transfer the waste residue into useful raw material consequently became a social focus meanwhile an interesting research subject for many investigators. On other hand, many disadvantages such as vast energy demanding and large natural resource consumption during the manufacture process of Portland cement and the deterioration of properties during its long term service attracted a severe challenge from the principal of persist development of modern society. As a result, the investigation of red mud to be used as a property modifying mineral admixture for high performance cement became one of the important subjects of a National Basic Research Priorities Programme, i.e. 973 programme, titled as "a basic research on the preparation and application of high performance cement".Based on the fact described above and aimed at the goal of the utilization of red mud in high performance, the following research activities were carried out in this study, such as the analysis of chemical and physical properties of red mud, and the attempt of activation method of red mud, and tests of strength development on red mud – clinker systems with different mix proportions and different dosage of chemical additives, finally the analysis of hydration process of red mud – clinker systems and the microstructure of hardened cement pastes.Results of TG-DTA, XRD, and IR analysis showed that the main crystalline substances existed in aged red mud which was exposed in atmosphere for long time are calcium carbonate, mostly calcite and little aragonite, and perovskite. Electronic microscope observation and analysis showed that the red mud agglomerate was actually composed of very fine first particles which were in irregular outline and variable chemical composition, and most of them being amorphous alumino-silicates. Furthermore, it was proved that the absorbed water and crystalline water in red mud was found to be driven out before 600℃ during heating from ambient to 900℃, the decomposition of calcium carbonate took place between 620℃ and 760℃, the formation of (-C2S was detected to begin at 700℃ and continually to form thereafter, whereas perovskite remained unchanged during heating.Test results on the strength development of red mud – clinker systems with different proportion of red mud and clinker and different kinds of red mud thermally treated at different elevated temperatures and with different dosage of chemical additives showed an obvious drop in 28d compressive strength when raw red mud was used in replacement of cement, especially when the addition of red mud is more than 20%, however, the degree of the 28d compressive strength drop was effectively controlled when the thermally treated red mud was used or some chemical additives was introduced.Tracking of the hydration process of red mud – clinker systems by means of chemical analysis such as the dissolution of Ca2+ ions in liquid phase, the amount of combined water and Ca(OH)2 in hardened cement pastes along with curing age revealed that pozzolanic reaction occurs between the components of red mud and Ca(OH)2 released from the hydration of Portland cement clinker during the hydration process of red mud – clinker systems, especially the red mud was thermally treated at 600℃.SEM observation and MIP determination on hardened cement paste proved that parts of the large capillary pores in hardened cement paste of red mud – clinker systems were effect...
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