The Research On Fly Ash Based Geopolymer And The Preparation Of Geopolymer Porous Materials

Geopolymers are environmentally-friendly materials involved in the silicate and aluminates reaction to form 3-D networks and undergoing the process of geopolymerization. Because of the special three-dimensional structures and chemical bonds, they have excellent properties incorporating the comprehensive properties of ceramic, cement and polymer with good mechanical properties and stability, high temperature resistance, corrosion resistance and other characteristics. Fly ash is a solid waste material containing silicon and aluminum which has pozzolanic activities. So using fly ash to prepare geopolymer through alkali activation is an environmentally-friendly and promising study with economic value.In this paper, F-class fly ash based geopolymer(FFAG) and C-class fly ash based geopolymer(CFAG) were prepared by using F-class fly ash(FFA) and C-class fly ash(CFA) as raw materials respectively. The comparative studies on mechanical properties, volume stabilities, morphology differences and corrosion resistances were done to find that CFAG can be hard in the early age and have good compressive strengths and volume stability, and also have good corrosion resistance to different salt solution; while FFAG can be solid only in the late age with high compressive strength in later time, have obvious volume shrinkage, and have no corrosion resistance.The metakaolin was added into fly ash to improve the properties of two different fly ash based geopolymers. The results showed that metakaolin made fly ash geopolymer hard in the early time, but it could not enhance the compressive strength of fly ash based geopolymer in the later age. In addition, calcium compounds were added to investigate the effects on improving the properties of FFAG, it proved that the addition of calcium compounds not only improved the early compressive strength and made them hard in the early age, but also reduced the volume shrinkage and improved the resistance to the corrosion of the seawater of FFAG.By means of SEM, XRD and IR analysis, it indicated that the main structures of fly ash geopolymer were the 3-D networks with gels encircling crystal unreacted fly ash which was generated from amorphous fly ash. There were no obvious changes in crystal phases but decreases of the peaks intensities and the shift of steamed bun shaped peak position proving that the amorphous fly ash and part of crystalline fly ash were dissolved and reacted to form new network. In the IR, Al-O bonds and Si-O bonds changed and adjusted continually demonstrating that silica and alumina were dissolved and dissociated to polymerize and harden in Al-O-Si forms ending with amorphous network geopolymer.Finally, fly ash geopolymer porous materials were prepared using CFAG as matrix by two methods, one is adding hollow spheres and the other is generating foam through aluminum powder. The two methods of preparing geopolymer porous materials were evaluated.