Fly ash from sewage sludge as an additive to concrete in terms of current standards

The introduced limits of carbon dioxide emissions by the European Union encourage experimental work on new generation materials containing smaller amounts of clinker. Currently, silica fly ash from hard coal combustion is widely used in cement and concrete technology in Europe and Poland. Their wide application is determined mainly by the chemical and phase composition, and in particular the activity of pozzolanic, their high fineness, similar to cement. The aim of the research was to assess the chemical composition and properties of fly ash from the thermal treatment of sewage sludge for use in concrete technology in relation to PN-EN 450-1, ASTM-C618-03 and ASTM C379-65T. The obtained test results confirm that the tested material is characterized by a different physicochemical composition and does not meet the requirements related to the use of ash for the production of concrete. In addition, the research showed the possibility of producing ordinary concrete, modified with fly ash from the thermal treatment of sewage sludge. The average compressive strength for concrete containing 15% ash from Krakow was set at 47,1MPa and 48,2MPa after 28 and 56 days of ripening, for ash from Warsaw at 41,1MPa and 44,9MPa and for ash from Łódź at 40,1MPa and 43,3MPa. The concentrations of heavy metals are determined below the maximum values to be met for discharge of waste water into the ground or into water, the leaching limits required for the release of inert waste for landfilling and for substances particularly harmful to the aquatic environment. On this basis, it was concluded that the migration of heavy metals from concrete with the addition of ashes to the aquatic environment is negligible and should not pose a significant problem.