Microstructural Evolution and Radon Emission Dynamics in Class F Fly Ash-Blended Cement Pastes

Year 2025, Volume: 8 Issue: 4, 1195 - 1203, 15.07.2025

Ahmad Hosseinpour Sheikhrajab , Ahmet Erdal Osmanlioglu

https://doi.org/10.34248/bsengineering.1695365

Abstract

Radon release from cementitious building materials is a major indoor air quality concern due to the presence of naturally occurring radionuclides in raw materials. This study investigates the influence of partially replacing Portland cement with Class F coal fly ash (0–50% by weight) on the pore structure and radon emission of hardened cement pastes. Cement paste specimens with varying fly ash content were analyzed using mercury intrusion porosimetry (MIP) to quantify porosity and pore size distribution, and an open-loop radon concentration setup (using a DURRIDGE RAD7 detector) to measure radon exhalation. The results reveal that increasing fly ash content leads to a pronounced increase in total porosity (from 14.23% at 0% fly ash to 20.22% at 50% replacement) and a corresponding rise in radon concentration (steady-state radon concentrations increasing from 20.8 Bq/m³ to 32.1 Bq/m³ for the same range). Microstructural analysis indicates that high fly ash substitution coarsens the pore network – the volume-based median pore diameter expanded from ~102 nm to ~381 nm – while also nearly doubling the internal surface area, reflecting the development of both larger capillary voids and fine pores. These changes suggest enhanced radon transport pathways at higher fly ash levels. The findings underscore a mechanistic link between fly ash-induced pore structure modifications and radon diffusion behavior. High-volume fly ash use, while beneficial for sustainability and reduced clinker usage, can thus inadvertently increase radon release. Therefore, optimizing the replacement ratio is essential to balance sustainability goals with indoor air quality considerations and to minimize potential health risks associated with indoor radon exposure.

Keywords

Radon emission, Fly ash, Cement paste, Microstructure, Porosity, Sustainability

Thanks

This study is derived from the author’s doctoral dissertation and forms part of the PhD research conducted within the Department of Mining Engineering, Faculty of Engineering, Istanbul University–Cerrahpaşa. The author sincerely thanks his thesis advisor, Prof. Dr. Ahmet Erdal Osmanlıoğlu, for his scientific contributions, guidance, and unwavering support.

References

• Blissett RS. 2012. A review of the multi-component utilization of coal fly ash. Fuel, 97: 1-23.
• Diamond S. 2000. Mercury porosimetry: Porosity or artifact? Cem Concr Res, 30: 1517-1525.
• EPA. 2023. Health risks of radon. United States Environmental Protection Agency. URL: https://www.epa.gov/radon/health-risk-radon (accessed date: April 8, 2025)
• Field RW, Krewski D, Lubin JH, Zielinski JM, Alavanja M, Catalan VS, Klotz JB. 2007. An overview of the North American residential radon and lung cancer case–control studies. J Toxicol Environ Health A, 70: 1882-1889.
• Hosseinpour Sheikhrajab A, Osmanlıoğlu AE. 2024. Comparison of radioactivity concentration levels of coal and lignite used in major thermal power plants in Turkey. In: Proceedings of the 10th International Artemis Scientific Research Congress, April, Romania, pp:59-96.
• Hosseinpour Sheikhrajab A, Osmanlıoğlu AE. 2024a. The effect of Tunçbilek Thermal Power Plant waste fly ash on mechanical properties of Portland cement. Nat Appl Sci J, 7: 40.
• Hosseinpour Sheikhrajab A. 2025. Determination of radon emission in cements made with coal fly ash. PhD thesis, Istanbul-Cerrahpaşa University, Institute of Engineering, Istanbul, Türkiye, pp: 115-175.
• Kumar A, Chauhan RP, Dahiya N. 2010. Radon exhalation rate in fly ash and fly ash blended cement. Radiat Meas, 45: 223–226.
• Mehta PK, Monteiro PJM. 2014. Concrete: Microstructure, properties, and materials. McGraw-Hill Education, New York, USA, pp: 646.
• Osmanlıoğlu AE. 2019. Natural radioactivity in Turkish coal-fired power plant ashes. J Environ Radioact, 208-209: 106021.
• Osmanlıoğlu AE. 2021. Evaluation of radiological risks from coal combustion residues used in building materials. Constr Build Mater, 270: 121473.
• Papastefanou C. 2009. Radon in ambient air and soil gas in the vicinity of uranium mining and milling facilities. J Environ Radioact, 100: 385-392.
• Righi S, Bruzzi L. 2006. Natural radioactivity and radon exhalation in building materials used in Italian dwellings. J Environ Radioact, 88: 158-170.
• Scrivener KL, Nonat A. 2011. The chemistry of cement hydration. Cem Concr Res, 41: 651-665.
• Taylor-Lange SC, Stegemann JA, Weiss WJ. 2014. Assessing the transport properties and radon emanation of concrete containing fly ash for radioactive waste encapsulation. Cem Concr Compos, 53: 103-113.
• World Health Organization. 2010. WHO handbook on indoor radon: A public health perspective. WHO Press. URL: https://apps.who.int/iris/handle/10665/77945 (accessed date: March 10, 2025)
• Yüksel İ, Göncüoğlu MC. 2011. Utilization of high volumes of Turkish fly ashes to produce sustainable construction materials. Constr Build Mater, 25: 1610-1618.
• Zhang MH, Malhotra VM. 1996. High-performance concrete incorporating rice husk ash as a supplementary cementing material. ACI Mater J, 93: 629-636.