| Geopolymer is a new type of inorganic nonmetal aluminosilicate cementing material developed in recent years. This kind of material belongs to one of chemically bonded ceramics with a special three-dimensional network structure which is hardening at20～150℃under the action of the alkali activator and appropriate preparation process. The raw material was mainly industrial solid waste including aluminosilicate phase, such as natural aluminosilicate minerals, fly ash, metakaolin, etc. Due to the special structure, geopolymer not only has the characteristics of organic polymer materials, ceramics and cement, but also has its unique and excellent function of good mechanical properties, high temperature resistance, corrosion resistance, aging resistance, good stability, good heat insulation effect and uninflammability.In this paper, fly ash-based geopolymer gel material was prepared using fly ash as the main raw material and casting dust and used foundry sand as admixture, under the trigger action of alkaline solution. Based on the test and analysis of the raw materials performance, the feasibility of geopolymer prepared by casting dust and dust in reclamation of used foundry sand was discussed.In this experiment, the effect of admixtures dosage, the alkali activator solution species and dosage, ratio of liquid to solid and curing conditions on the mechanical properties of geopolymer was studied. The preparation process of casting dust and fly ash-based geopolymer was optimized and the suitable technological parameters were obtained.The results showed that sand preparation dust and fly ash-based geopolymer was prepared in the case of30%of sand preparation dust dosage,70%of fly ash dosage,0.4of ratio of liquid to solid,1.2of the modulus of soluble sodium silicate and natural conservation (23±5℃, room temperature), whose28d compressive strength and tensile strength respectively reached25.74MPa and1.67Mpa. While the dosage of hot-reclamation dust was40%, fly ash dosage was60%, ratio of liquid to solid was0.45, the modulus of soluble sodium silicate was1.2curing in natural situation(23±5℃, room temperature), hot-reclamation dust and fly ash-based geopolymer was prepared and its28d compressive strength and tensile strength respectively reached65.99MPa and3.20Mpa. In addition, sand preparation dust and fly ash-based geopolymer and hot-reclamation dust and fly ash-based geopolymer had the characteristic of high acid resistance and their acid erosion rates respectively reached2.42%and2.14%.The phase composition, microstructure and morphology characteristics of casting dust and fly ash-based geopolymer were analyzed respectively using XRD, IR and SEM. The results showed that the phase of geopolymer was mainly composed of amorphous phase and crystal phase. The production had the structure of-O-Si-O-Si-,-O-Al-O-Si-, Al-OH and Si-OH. The section morphology of specimen revealed that geopolymer microstructure mainly consisted of flocculent gel and powder spherical particles, which was a dense structure.According to the synthetic mechanism of geopolymer, the polymerization reaction mechanism of casting dust and fly ash-based geopolymer was analyzed and discussed based on the experimental study. There was a point of view that the active aluminosilicate phase of mixed powder was dissolved into the low polymers, which was composed of sand preparation dust or hot-reclamation dust and fly ash. The low polymers were condensed into positively aluminosilicate polymers by dehydroxylation reaction. Then the positively aluminosilicate polymers formed the geolopolymer gel matrix with three-dimensional network structure by condensation polymerization, which was connected-O-Si-O-Si-to-O-Al-O-Si-. Geopolymer exhibited remarkable mechanical properties resulting from the compact structure, which was formed by flocculent matrix and spherical particles or quartz crystal of the powders not participating in the reaction. |
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