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

Abstract

As for all materials of mineral origin, fly ash contains natural radionuclides such as 226Ra, 232Th and 40K which contribute to radiation exposure. The present study is aimed to investigate variation of natural radionuclides (226Ra, 232Th and 40K) 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 226Ra and 232Th also increased, whereas 40K content remained the same for all practical purposes.