Investigation into the influence of calcium compounds on the properties of micropore-foamed geopolymer

Abstract

Zeolite Socony Mobil-5 (ZSM-5) waste is formed by deactivation after many cycles. A new type of geopolymer composite was fabricated from fly ash, ZSM-5 waste and calcium hydroxide. The resulting products were characterized by compressive strength tests, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and mercury intrusion porosimetry to ascertain the influences of calcium on the mechanical property, microstructure and geopolymerization products. The air in the cavity of ZSM-5 waste can be expanded under high temperature, and it has a strong foaming ability. A homogeneous and porous structure can be fabricated by adding ZSM-5 waste. The higher content of calcium hydroxide results in an increase in compressive strength ranging from 4.8 to 9.2 MPa, as well as bulk density increasing from 0.73 g/cm3 to 1.38 g/cm3, which is attributed to the increase in viscosity caused by the formation of C-(A)-S-H in which the free water shifts to bound water. In addition, the addition of calcium hydroxide can accelerate the reaction process, which also influences the pore structure. The compositional analysis demonstrated that the final products are composed of two kinds of gels, including N-A-S-H and C-(A)-S-H, with crystalline phases as unreacted fillers derived from materials. Overall, calcium hydroxide has a positive effect on the specimens. The results may shed light on references for the application of foamed geopolymers with calcium components.