Measurement of radon exhalation and emanation in synthesized coal fly ash-based geopolymer paste for building applications

Abstract

This study examines the radon exhalation potential of CFA and CFA-based GPP products, focusing on their elemental composition, structural properties, and radon containment capabilities. The particle size analysis result revealed that a substantial portion of CFA particles are fine, contributing to a greater surface area, which increased the potential for radon emanation. SEM analysis highlighted microstructural differences, with denser structures in the geopolymer products. XRF result revealed reductions in potassium (⁴⁰K), uranium (²³⁵U, ²³⁸U), and thorium (²²⁶Ra) progenitors in CFA-based GPP products compared to CFA, and resulted in lower radioactivity due to the dilution effect of fillers and additives. XRD analysis showed the presence of crystalline phases such as quartz, mullite and amorphous phases in CFA and in the CFA-based GPP. The amorphous glassy phase in CFA, being rich in SiO₂ and Al₂O₃ precursors was critical for forming the aluminosilicate geopolymer network, that reduced porosity and trapped radon progenitors. Variations in CaO content and the formation of Ca containing mineral phases enhanced radon retention in CFA-base GPP products. Density measurements indicated that higher-density products exhibited lower permeability, reducing radon exhalation. Radioactivity measurements showed that CFA emitted 684 Bq/kg, above the world average of 420 Bq/kg and CFA-based GPP emitted between 408 and 459 Bq/kg. These findings underscored the need for controlling formulations and curing conditions to mitigate radon emanations of CFA-based products such as geopolymers.