As part of the research, concrete mixes containing the addition of bottom ash as well as bottom and fly ash mixtures from the combustion of biomass only were made. The ashes were obtained from the combustion of 80% of wood and 20% of sunflower in a fluidized bed boiler. In the study, the elemental composition of ashes was determined by testing with an XRF X-ray spectrometer. Ashes in the amount of 10, 20 and 30% of the cement mass were used as a substitute for sand for testing concrete samples. During the preparation of concrete mixes, tests of consistency and air content in the mixes were carried out. Concrete samples were tested in terms of e.g. compressive strength, water absorption or frost resistance. The compressive strength of the samples with the addition of bottom ash was lower than the strength of the control samples. The use of a mixture of ashes allowed to improve this property and each of the samples obtained a higher compressive strength than samples without the addition of ash. The addition of ashes significantly improves the frost resistance of concrete, i.e. reduces the decrease in the compressive strength of concrete after frost resistance tests. The absorbability of the samples, regardless of the amount and type of added ash, changed slightly in relation to the control samples.