The largest coal company in Kalimantan operating is PT Adaro Energy Tbk located in Tabalong Regency. This coal processing produces waste in the form of fly ash and bottom ash. The more coal production is produced, the more waste resuIts from the combustion process which has an impact on environmental polIution. UtiIization of coal waste as a mixed material to increase subgrade stabiIity in road construction.

TheApurpose of this study was toAdetermine the characteristic value of each combination of fly ash, sand and cement as a mixture of subgrade Iayers with a composition ofa1 fly ash 50%, sand 40%, cement 10%, a mixture of 2afly ash 55%, sand 40%, 5% cement, mixture of 3afly ash 60%, sand 35%, cement 5%, mixture of 4a fly ash 65%, sand 30%, cement 5%, mixture of 5afly ash 70%, sand 25%, cement 5 %, a mixture of 6afly ash 75%, sand 20%, cement 5%, a mixture of 7afly ash 80%, sand 35%, cement 5%, a mixture of 8afly ash 85%, sand 10%, cement 5%, a mixture of 9afly ash 90%, sand 5%, cement 5%, a mixture of 3 fly ash 95%, sand 5%, cement 0%. The tests carried out were testing atterberg Iimit, specific gravity, filter analysis, compaction and Laboratory CBR.

From all theseacombinations, we get resuIts that meet thexcharacteristic vaIues ??that are Iarge enough to be used as a mixture of subgrade Iayers with a minimum CBR specification of 6%, and azmaximum PI of 6%, an economicaI combination for the composition of fly ash, sand, and cement which is recommended forrembankment soil is a combination of 6 with the composition of fly ash 75%, sand 20%, cement 5%.

Keywords: fly ash, cement, CBR