Acta Scientiarum Polonorum

Nowadays, the concrete is the most widely used composite material among those made by human and the
second (after water) among all materials used by people. It is an ecological material, being made of local raw
materials – aggregate, cement, water, admixtures and mineral additives − characterized by the lowest carbon
trace. The paper presents results of investigations of the concretes of C20/25 class based on the cement
CEM I 42.5R, pebble aggregate as well as fly ashes from thermal conversion of sewage sludge replacing 5,
10, 15 and 20% of the cement mass. In the course of experimental work, compressive strength measurements
were made at two stages of curing and frost resistance F150. The collected research results made it possible
to compare the properties of concretes produced with the ash from two treatment plants. The obtained results
confirm possibility of manufacturing of the concretes modified by fly ash from combustion of municipal
sewage sludge. The average compressive strength for the concrete containing 20% of ash from Kraków has
been established at the level of 50.1 and 50.6 MPa after 28 and 56 days of curing, respectively and for ash
from Warsaw at 42.6 and 45.7 MPa.