This paper reports on the results of a research about utilization of inorganic sludge (IS) produced by paper industry as cement and fine sand substitute secondary raw material in concrete. The inorganic sludge IS valorization   as cement partial substitute into concrete has been supported by experimental data concerning the  pozzolanic potential evaluated  by Al and Si content of IS waste compounds solubility into leachant of pH=12 and by the compressive strengths time evolution. The concrete samples with the addition of inorganic sludge from paper industry have been characterized by overtime variation of the following characteristics: water absorption, dimensional changes, compressive and flexural strengths. There have also been determined leaching properties by monolithic leaching test. The evolution of the physical and mechanical characteristics suggest the inorganic sludge can be used as a substitute for fine sand in concrete in an amount up 50%, and / or substitution of up to 20% cement. The heavy metal leaching properties measured by the concrete monolithic samples leaching test with the highest content of IS, showed  a heavy metal  Pb, Cr and Cu release trend diminishing during time, after a logarithmic plot.