| The cement production and the cement concrete application has brought the huge change for the infrastructure construction, and established the abundant foundation for the universe social economy development. In 2004 cement annual output has surpassed 900 million tons in our country, approximately 50% of the world cement output. With the swift development of our country's economics and high advance of infrastructure construction, further growth is expected for the cement demand. However, the cement production needs to consume the massive natural resource and the energy. For example 1.3 t limestone and 0.3 t other materials are needed to produces only 1 t cement clinker. The energy consumption for cement clinker production is 4000 kJ/kg and the comprehensive electricity consumption 120 kW? h/t. In addition, 1t carbon dioxide would be released with the production of 1t cement clinker. Cement and cement concrete has the un-substituted position in this society, but the shortage of resources and the environmental pollution, which puzzle the whole world, are also directly related with the cement production. For long time people diligently take the many kinds of measures to make cement production to be sustainable. To improve the performance of cement and to use the least cement content to satisfy the requirement of high performance cement concrete is the mutual recognition, which the domestic and foreign experts, the government department, the production and the construction enterprise have achieved. Cement is a general designation of cementitious materials, which are used in the construction, including Portland cement (silicate cement) series, aluminate cement series, sulphoaluminate cement series. The silicate cement series is widely applied as they are economical building materials, whereas the sulphoaluminate cement series have our country's independent intellectual property rights and are special engineering materials with high performance. The two series have the different unique mineral composition and the performance characteristics, and fine performance combination may improve their properties. This also raises a new method for improvement of cements. This project studied the performance and properties of the silicate -sulphoaluminate compound system and the hydration as well as hardening mechanism, in compare with silicate cement series. The research conducted the investigation on various aspects of the system, which has the important instruction significance regarding the silicate -sulphoaluminate compound cement system and its application. The research results can be highly referred for the hydration theory research in compound system. The present paper utilized the concept of "the even design" and designed experimental plan in comparatively wide range conformed to the restraint condition, which guaranteed the scientific nature and the representation of the composition experiment in the compound system. Through the conventional physics and mechanics performance test of specimens in the experimental plan, which have different proportions, the relationships between the compositions and properties of the materials in the three compound system of Portland cement -sulphoaluminate cement -gypsum composes have been investigated in detail. It is illustrated that the proportions near the P area of silicate with Portland cement: sulphoaluminate cement: Gypsum =86.4%: 4.5%: 9.1% P3 shows the best comprehensive performance. Besides, specimens of P2, P15, P16 have the rapid setting characteristic and may satisfy the requirement of quick hardening for some special projects. Among them P2 is most economical. In C area near sulphoaluminate, the material composition may be regulated so as to adjust the setting and strength in comparatively wide range and meet the needs of different projects. The results also indicated when 10% of sulphoaluminate cement clinker and 15% of gypsum were added, compound cement material with early high strength can be obtained, the later strength of which may continues to develop obviously. When added with 10 -20% Portland cement and 5 -15% gypsum, sulphoaluminate cement clinker may turn to a compound cement exhibiting a rapid setting, early high strength and later continuous strength development. Based on the understanding of the relationship between the composition and the performance, the present paper has also studied the influence of the raw material's characteristic and the particle size distribution to the performance of the compound system, and has analyzed the mechanism of the influence of raw material's characteristic on the compound system. The findings showed that there exists a close relationship between the absolute value of the performance of compound system and the raw material characteristic, especially Portland cement characteristic, but change rule is consistent along with the composition. When the composition and the raw material are the same, the particle size distribution of the system has a more influence on its performance. After the research on the macroscopic performance of the compound system, modern analyses with X-ray diffraction, thermal analysis and scanning electron microscope were conducted on the cement hydrates and microscopic structure in the compound system. At the same time, exothermic behavior during hydration, electronic receptivity change of hydrates as well as other thermoelectricity characteristics have been tested in reference to some related cement chemistry theory. The abnormal setting behavior of the compound system has been explained and the mechanism of hydration and hardening of the compound system have been thoroughly discussed. Finally the issue of compatibility of the compound system with fly ash, which is unavoidable in practical application, and the workability, the durability as well as the mechanics'properties have been studied. The results proved that, the compound system has a good promoting action to the hydration of fly ash. Compared with the Portland cement concrete, concrete made of the compound system cement has a better workability and better mechanics'performance, and the majority of durable indexes also surpass that of the Portland cement concrete. The research characteristic of the present paper lies in the utilization of the concept of "the even design" for experimental plan design, comprehensive and systematical study of the brand-new silicate -sulphoaluminate compound system as well as their properties, and comparison of the influences of the raw materials with different properties on the compound system in comparatively wide range. The present paper thoroughly discussed the cement hydrated and hardening mechanism in the silicate -sulphoaluminate compound system for the first time; the paper also...
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