Roughly annual production of slag in Qatar is 350ktp/a. For the purpose of exposure evaluation about 2 million tons slag considered. For radioactivity estimation of produced slag, samples taken from steel slag pile randomly, the slag samples prepared for measurements by low background Gamma ray spectroscopy system equipped with high-purity germanium (HPGe). The presence of isotopes 40 K, 232Th (228Ra), 226Ra and 238U were determined and effective dose for public and workers have been estimated according to exposure scenario. The presence of natural isotopes seem to be in normal concentration and comparable with the published data. The main concentration of Th-232 and Ra-226 are 135.176 and 273.176 Bq/Kg respectively. For the purpose of compression,the radioactivity in normal gabbro have been analyzed. The results of gabbro analyses for 40 K, 232Th (228Ra), 226Ra are 25, 0.7 and 10 Bq/kg respectively. Radiation risk estimation were done for two sets of asphalt samples including the loose asphalt and asphalt cores from the Qatar Steel trials with different ratio (20%,40, and 50%) of slag ,the same ratios used for making concrete block samples. Radioactivity’s, radiation exposure and hazard index were measured and calculated for each case. The calculated absorbed dose value for the 20% slag asphalt is 26.13 μSv/y, and 78.12 μSv/y for the 40% slag asphalt, For extreme conditions at full occupancy factor (indoor with direct contact with human), the dose values are 134.68 and 396.6 μSv/y for the 20% and 40% slag asphalt, respectively. Two case studies were considered for the dose estimation to the public when steel slag aggregate used to replace 40% of total aggregate weight in asphalt applications. In the case studies, the Uranium (U-238) decay chain was considered in the analysis which takes into account all radionuclides in the chain including Radium (Ra-226), Radon (Rn-222) and Lead (Pb-210). The first case study was made for a car park constructed of asphalt pavement. Steel slag aggregate was used to fully replace the coarse aggregate, i.e. replacing 40% of the total normal gabbro, The dose to an adult from external exposure from the ground is 0.08 μSv/y. The second case study considered a children’s playing area made with 40% slag asphalt pavement. Similar to the car park, The doses to 10-year old children from playing on the 40% slag asphalt. The total dose from external irradiation from the play area is 2 μSv/y. It is recommended that loose steel slag aggregate may not use internally in direct contact with humans. However, it could be used in external construction applications below the ground surface. Asphalt made with up to 40% steel slag aggregate could be safely used in road applications in cities. However, concrete made with up to 50% slag aggregate could be safely used in construction applications.
Read full abstract