Optimization of fly ash content in cement and assessment of radiological risk

摘要

As for all materials of mineral origin, fly ash contains natural radionuclides such as Ra-226, Th-232 and K-40 which contribute to radiation exposure. The present study is aimed to investigate variation of natural radionuclides (Ra-226, Th-232 and K-40) in Ordinary Portland Cement due to variation in the concentration of fly ash. For this purpose, seven cement-fly ash mixtures were experimentally tested for radiological content with NaI(Tl) gamma spectrometer. From the measured gamma-ray spectra, radium equivalent, hazard indices, gamma index, annual effective and gonadal dose were determined. Radium equivalent for samples ranged from 209.53 Bq kg(-1) to 336.06 Bq kg(-1) with a mean of 265.41 Bq kg(-1). The external and internal hazard indices varied from 0.57 to 0.91 Bq kg(-1) and 0.64 to 1.13 Bq kg(-1), respectively. The gamma index exceeded unity for samples with fly ash concentration greater than or equal to 20% by mass. The average annual effective and gonadal dose from different cement-fly ash mixtures was 0.92 mSv y(-1) and 0.95 mSv y(-1), respectively. The study demonstrated that as concentration of fly ash increased in the cement, the concentration of Ra-226 and Th-232 also increased, whereas K-40 content remained the same for all practical purposes.