Study On The Material Based Geopolymer Cement

The geopolymer cement making use of the meta-kaolin that was produced by calcining the kaolin from Baoding was studied. The properties of the cement were tested and the production technique of the cement on the concept was designed. DTA, XRD, SEM and chemical analysis methods have been taken to study the hydration and hardening mechanism of the cement. For the practical application, the high-calcium geopolymer cement was prepared and the mechanisms of hydration and hardening have also been discussed. On the basis of these studies, a new standpoint about the structure and properties of the materials based on the cement has been brought out.The results indicate that the geopolymer cement has many characters such as quick setting, rapid hardening, high early strength, good thermostability, excellent corrosion resistance and so on. The hydration process of the geopolymer cement may also be divided into the initial stage, the induce stage, the accelerate stage, the decelerate stage and the stable stage. Finally, the silicon-aluminum tetrahedron network structure is formed in the harden paste. But the hydration mechanism of the geopolymer cement is different from the traditional cement. For the cement, the surface hydration is the primary process at the initial stage, the kaolin disorganizes and gets into the solution in the form of the silicate tetrahedron and aluminate tetrahedron at the induce stage; the silicon-aluminum tetrahedron network structure is formed at the accelerate stage; the unti-network structure is formed and the rate of heat evolution falls at the decelerate stage; the reaction finished ultimately at the stable stage. The alkali ions that can balance the electrovalence exist in the network structure at this time. The amount of the alkali is important to the strength developing and other properties of the geopolymer cement. When the amount of alkali is low, the velocity of the disorganization and dissolve of meta-kaolin is slow. When it is high, the polymorization degree of the network is low. All of this can reduce the strength of the geopolymer cement.Using the clinker, the granulated blast furnace slag, the meta-kaolin and 9 percent additives, a kind of high-calcium geopolymer cement that is called as Pyrament in foreign has been produced. The early strength of the cement is higher than that of the slag cement about 11 percent. The study indicates that the amounts of C-S-H gel, CH etc. are tiny in the early hydration products of the high-calcium geopolymer cement, which are different from the materials based on the traditional cement, and their distribution is not uniform. As dominating product a kind of network structure where the content of calcium is very low is made up of in the paste. But along with the hydration, the network structure disorganizes and the final product is the same as the slag cement. In the condition that a lot of active admixtures are mixed, the high-calcium geopolymer cement also possesses more superior properties than slag cement. This kind of cement has a good applied foreground. The materials based on the traditional cement are made up of crystals and gels. The proportioning of crystals and gels is important for the properties of the material. However the geopolymer cement forms the silicate-aluminum network. The new-style structure offers a new field for the development of the materials based on the cement and the study on the structure theory of non-metallic inorganic materials.