The present paper reports the results of experiments to develop environmentally and economically friendly structural lightweight concretes utilizing coal ashes and other waste materials. The product complies with national and international regulations setting limits on the activity concentration of natural radioisotopes in building products. The utilization of coal ashes in the building industry carries (in addition to its economic advantages) a fringe environmental benefit. This utilization reduces the potential damage to the environment caused by the radioactivity in the combustion by-products (the ashes) stored in piles and ponds near the power stations prior to their disposal. The study deals with the radiological characteristics of coal ashes and lightweight concretes based on these ashes. The ashes are generated at Israel's power stations from coal supplied from different sources in South Africa, Columbia and Indonesia. (C) 2007 Elsevier Ltd. All rights reserved.