Preparation of metakaolin-fly ash cenosphere based geopolymer matrices for passive fire protection

Abstract

In this paper, fly ash cenosphere (FAC) with spherical and hollow structure has been adopted as a pore-forming agent to prepare low density and high strength geopolymer foams. Serial analyses of physical properties, mineral characterization, and thermostability have been employed to investigate the feasibility of metakaolin (MK)-FAC based geopolymer for passive fire protection. FAC addition not only significantly decreases the dry bulk density and thermal conductivity of geopolymer blocks, but also helps to achieve acceptable compressive strength. Meanwhile, FAC addition into geopolymer matrices has brought obviously negative effects on heat transfer and led to the reaction enthalpy rise under high temperature. Owing to the conversion of the amorphous geopolymer gel at the surface to ceramics and excellent thermal insulation performance, the reverse-side temperatures of the geopolymer specimens with FAC addition from 30 to 90 wt% always maintain at about 260 °C until the end of the fire resistance tests. Although weak reactions between alkali activator and FAC have happened and enhanced the bonding between FAC and geopolymer gels, the improvement in physical properties of the MK-FAC based geopolymers would mainly be attributed to the physical characteristics of the FAC. This study could open opportunities to employ MK-FAC geopolymers as alternatives in the application of thermal insulation and fire protection.