Light weight concrete: 226Ra, 232Th, 40K contents and dose reduction assessment

Four types of light weight concrete (LWC) commonly used in Hong Kong, namely, autoclave aerated concrete (plus lime), autoclave aerated concrete (plus Pulverized Fuel Ash or PFA), concrete with synthetic aggregate 'Leca' and concrete with polystyrene bean as aggregate were measured for their 226Ra, 232Th and 40K contents using high-resolution gamma spectrometry. All the radionuclide contents except those for the PFA autoclave aerated concrete were below the world averages of building materials. The Ra-equivalents for these four LWC were 49.6, 249, 122 and 44.2 Bq kg-1, respectively, and were much smaller than a recommended limit of 370 Bq kg-1 for construction materials for dwellings. The gamma-dose rate for an indoor environment with partition walls built with LWC was estimated to be about 20 x 10-8 Gy h-1, which corresponded to a reduction in the effective dose of about 0.25 mSv y-1 when compared to that obtained for an indoor environment built with normal concrete (NC) only. The Rn exhalation rates from the three lowest Ra-equivalent LWC were calculated as 0.509, 1.28, and 0.335 mBq m-2 s-1, respectively, which corresponded to a reduction in the indoor Rn concentration of around 14 Bq m-3 and reduction in the tracheobronchial dose reaching 1 mSv y-1 by using the James lung-dosimetry model, when compared to the case of NC