Determination of radon emission in cements made with coal fly ash

This thesis presents a comprehensive study on the engineering properties of hardened cement paste in which Portland cement is replaced by fly ash at 0%, 5%, 10%, 15%, 30% and 50% by weight. In particular, the unit weight, compressive and tensile strength, ultrasonic properties, microstructural properties and radon emission of hardened cement pastes were investigated. Previous studies on this thesis topic were conducted in a case study format and did not examine the fly ash content in a way that would be expected. The research findings are aimed to guide research that will produce solutions to radon gas emissions affecting public health. First of all, the radioactivity levels of coals from domestic coal fields used in large-scale power plants in Turkey were investigated and the Tunçbilek coal field, which reflects the average radioactivity levels in Turkey, was selected and fly ash sample was supplied from the Tunçbilek power plant using the coal of this field. 36 hardened cement paste samples in accordance with the TS EN 196-1 standard and 3 powder samples of aggregate, cement and fly ash were prepared. Then, the chemical and physical properties of aggregate, cement and fly ash, engineering properties and microstructure of hardened cement paste were investigated. Finally, radon gas emissions and concentrations were measured from all these variables. The results showed that, compared to the control sample containing 0% fly ash, unit weight, ultrasonic properties and 2, 7 and 28-day compressive and flexural strength decreased with increasing fly ash content, while porosity increased. According to the obtained results and EN 197-1, the compressive strengths of the samples containing 5%, 10% and 15% fly ash remained within the standards. In the open-loop radon measurement, the radon concentration of the control sample was 20.8 Bq/m³, while the incorporation of a 50% fly ash mixture elevated this value to 32.1 Bq/m³. A similar trend was observed in the closed-loop radon measurement, where the radon concentration of the control sample increased from 318 Bq/m³ to 524.5 Bq/m³ with the 50% fly ash sample. These results indicate that cement mortars with high fly ash content act as significant radon emitters, leading to a notable increase in radon concentrations. The findings of this research are expected to provide the most valid metrics within the borders of Turkey.