Research On Hydrating Characteristics And Hydrates Of Multi-component Cement-based Materials

With the concept of HPC being put forward, the manufacturing technology of concrete has developed greatly. Compared with that of 10 years before, material designation has changed much and that mineral mixtures as main components are applied in concrete has also become more common. But research on hydrating characteristics, hydrates and microstructure of hardened cement-based materials, especially mixing with all sorts of mineral mixtures, has not attracted much attention. This paper discusses hydrating characteristics, hydrates and microstructure of hardened cement mixing with slag, fly ash and silica fume by modern testing method.The hydrating characteristics of multi-elemental cement-based materials are discussed. It is indicated that the hydration process of cement-based materials with slag, fly ash and silica fume is different in some degree from that of neat cement because of the difference in mineral structure and hydration mechanism. The periods of accelerating, decelerating and terminating are prolonged and hydration reaction decelerates. The second peak of rate curve of the heat evolution could be divided into two small peaks, which are contributed to the hydration of clinkers and mineral mixtures at the temperature of 30℃ But when temperature comes to 50℃, the two small peaks combine into one and the reaction accelerates. The type and amount of mineral mixtures incorporated also have much influence on the hydration process. The kinetic equation of hydration is set up and the hydration mechanism is discussed by analyzing the kinetic parameters. The content of hydrates in hardened cement is calculated. From the studies on the hydrates structure, it is reduced that the connection between the irons and phases change, which causes to change structural stability of hydrates, with the changes of the amount incorporated. And the transition disciplinarian of hydrates with changes of the types and amount of mineral mixtures incorporated are also discussed. The microstructure of hardened cement-based materials and its development are also studied. The result indicates that the fibrous and needle-like hydrates become flocculent hydrates individually with the proportion of mineral mixtures incorporated and the geometric shapes of crystals would also change. The gel C-S-H has the trend to crystallizing and transforming into low crystallized hydrates, which were similar to tobermorite. The incorporation of mineral mixtures improves greatly the orientation of CH either in interface zone or matrix zone and thecrystal sizes also become small.Equal-transition ratio method is applied for the calculation of apparent activation energy (E) from the heat of hydration. The results from the calculation indicate that this method could be applied well for the E of cement-based materials. The values of E vary between 40 kJ/mol-70kJ/mol. From the research results, it can be concluded that the formation of early hydrates achieves through the recycle process of dissolution-deposition and the late through the reaction similar to the sinter of solid particles.