Concrete is currently the most widely used man-made composite material and second only to water in the entire
range of materials used. It is a material with a high potential to adapt to specific operating conditions and can
be made from local raw materials (aggregate, cement, water, and mineral additives), which can be selected to
minimize the carbon footprint. The use of fly ash from the thermal conversion of sewage sludge in concrete is in
accord with the advice on waste management proposed in the European Union. This paper presents the results
of research on the effect of the partial replacement of Portland cement with this material on the strength parameters, frost resistance, and carbonation of concrete compared to reference concrete and to concrete containing
a conventional additive – siliceous fly ash. In addition, the potential environmental impact of the use of sewage
sludge ash was investigated by determining the leachability of heavy metals. Concrete mixtures of C20/25 ordinary concrete, based on CEM I 42.5R Portland cement, with varying ash contents comprising 0–20% of the
cement mass, were produced for the experimental work. The obtained test results confirmed the possibility of
producing plain concrete modified with fly ash from the thermal treatment of sewage sludge and the concrete’s
compliance with the environmental requirements relating to the leaching of heavy metals.