The content of unburned carbon is an important characteristic of bottom ash which could make it unsuitable for incorporation as aggregate for road construction. In this work, the effect of the content of unburned carbon in the bottom ash from the Serbian power plant "Nicola Tesla" on its applicability for road construction was examined. Four samples with different contents of unburned carbon, i.e., raw bottom ash, two size fractions obtained from it (2-5 and <2 mm) and bottom ash treated by the "float-sink" method, were investigated. When these materials were used as a component in the mixture: fly ash-Portland cement-bottom ash-water for road construction, it was found that only mixtures containing bottom ash with a lower carbon content (size fraction <2 mm and treated) were employable. The content of unburned carbon in the mentioned materials was determined by simultaneous DTA/TGA. This method was also used to investigate the composition of the hardened mixtures. (C) 2009 Elsevier B.V. All rights reserved.