Experimental Evaluation of Geopolymer and ‘Lunamer’ Binders as Radioactive Shielding Materials for Space Applications

Geopolymers are inorganic cementitious binders produced by polymeric reaction between an aluminosilica rich material and an alkali metal hydroxide/silicate liquid, forming a binding gel, which can be used to encapsulate fine and coarse aggregates to produce concrete. While earth-based applications utilize commonly available materials, such as metakaolin, fly ash, or even rice husk, researchers have reproduced lunar regolith to make geopolymer concrete specimens ('Lunamer') by activating the regolith with alkali liquid. Geopolymer binder technology presents superior mechanical and thermal performance, and has been shown to be compatible with an abundantly available lunar resource (lunar regolith).  The highly conductive geopolymer has been enhanced further for use  in electromagnetic (EMI) shielding and electrostatic discharge (ESD) applications. Conductive filler materials (carbon fibers and/or carbon black) were added to the geopolymer matrix. Impedance measurements were performed to determine the conductivity value of different conductive composite formulations. Results indicated that conductive geopolymer matrices are very effective in blocking electromagnetic waves of frequencies greater than 1 GHz. Therefore, to understand space-based applications, next steps should include characterizing radiation shielding effectiveness of geopolymer and 'Lunamer' concrete.

The purpose of this project is to develop lunar regolith based geopolymer concrete and perform differential shielding studies on various geopolymer formulations to determine if sufficient protection from radiation in space environments can be enabled. For the initial testing of these concrete matrices, a variety of locally-available radiation sources will be used. As part of the proposed work, geopolymer and 'Lunamer' concrete matrices will be constructed and their ability to shield radiation will be evaluated. The geopolymer matrices will be prepared using fly ash as the pre-curser, barite (BaSO4) and hematite (Fe2O3) as the aggregate and metallic chips, representing the state-of-the-art in Earth-based construction practices. The 'Lunamer' concrete matrices will be made using geopolymerized lunar regolith with entrained carbon fibers and carbon black for EMI shielding and metallic chips. These will include radiation energies within this range of biological interest, but will also include those of lower energies. While such low energy sources cannot be used to correlate the biological impact of high energy radiation, they do provide a useful tool to quantify the relative shielding behavior of different materials.