The Research Of Preparation, Microstructure And Properties Evaluation Of Geopolymer

Geopolymer is a new alkali activated cement. It is similar to zeolite in chemical composition and shows a three-dimensional network in physical framework acting as a structural foundation of geopolymer. It combines some characteristics of organic high polymers, cements and ceramics. Geopolymer has become one of the active investigated field in cemetitiou materials for its unique properties,such as abundant raw materials resources, easy preparation, energy saving, no CO₂ emission, high strength, fast strength development, excellent durability and resource saving superiority and so on.In order to establish the simple method of evaluate the properties of geopolymer from chemical analysis in this paper, First, zeolite products which are similar to geopolymer in structure and composition were investigated. Zeolite 4A and its precursors with different crystallization time were synthesized from kaolin and chemical materials ( sodium silicate,sodium hydroxide and aluminum hydroxide) .The series of 4A zeolites samples were characterized and analyzed the similarities and differences of crystallization process with different materials by the X-ray diffraction,scanning electronic micrograph and FT-IR. Zeolite X and its precursors with different crystallization time were synthesized from sodium silicate,sodium hydroxide and aluminum hydroxide. Zeolite products' structural units have been formed in the early crystallization process, whether they were synthesized from kaolin or chemical materials.NH₄⁺ ion exchange experiment were carried out on the samples. Test results showed that the capacity of NH₄⁺ ion exchange increased with the crystallization time increasing and arrived max value until crystallization completed. The amorphous precursors of zeolite have some certain ability of NH₄⁺ ion exchange. Especially, the capacity of NH₄⁺ ion exchange of 4A zeolite from kaolin has great difference with crystallization or not. And it is worth to note that the 4A zeolites synthesized from kaolin and chemical materials have different forming mechanism.NH₄⁺ ion exchange experiments were carried out on the three types of geopolymer from the kaolin which corresponding SiO₂/Al₂O₃ of zeolite. Test results show that the NH₄⁺ ion exchange capability of geopolymer is similar to that of the precursors of zeolite 4A from kaolin, and the combination of XRD verified that geopolymer has three-dimensional framework structure similar to the precursors of zeolite. Accordingly, the method of ion exchange experiment can evaluate the capability of geopolymer primarily.The modification methods of main raw materials kaolin of geopolymer were studied in the paper. NH₄⁺ ion exchange experiment and compressive strength tests were used to study the effect of origin, calcined time and calcined temperature of caolin on the properties of geopolymer. A fast method to determine the reactivity of metakaoline in synthesizing geopolymer was put forward. The experimental results show that the reactivity of calcined kaolines from the same origin was different after they were calcined at different temperatures, their reactivity reach the biggest value after the kaoline was calcined at 800℃with 6h; the reactivity of calcined kaolines from different origins were much different after they were calcined at different temperatures; the total level of the elution Al₂O₃ and SiO₂ content in the metakaolines determined using this method was related to the compressive strengths and NH₄⁺ ion exchange capacity of metakaoline-based geopolymer.Investigation on properties of geopolymer with blast furnace slag were carried out, NH₄⁺ ion exchange experiment and compressive strength tests were used to study the dosage of slag setting time and the structure of the product. The results show that setting time of alkali-metakaolin-slag system decreases with increase of dosage of slag, while compressive strength changes reversely. And the product content with analogous zeolite structure decreases with increase of dosage of slag.