Possibility of Using Waste Materials as Substitutes for Gravel or Water in Concrete Mix

Analyzing the global waste management sector, we can see that some waste, due to its specificity, is a major challenge when it comes to its management. This group includes rubber waste and sewage sludge. Both items pose a major threat to the environment and human health. The remedy for this problem may be the solidification process, in which the presented wastes are used as substrates in the production of concrete. The aim of this work was to determine the effect of waste addition to cement in the form of an active additive (sewage sludge) and a passive additive (rubber granulate). An unusual approach to sewage sludge was used, which was introduced as a substitute for water, and not, as in most works, sewage sludge ash. In the case of the second waste, commonly used tire granules were replaced with rubber particles resulting from the fragmentation of conveyor belts. A wide range of the share of additives in the cement mortar was analyzed. The results for the rubber granulate were consistent with numerous publications. For the addition in the form of hydrated sewage sludge, the deterioration of the mechanical properties of concrete was demonstrated. It was found that the flexural strength of the concrete in which water was replaced with hydrated sewage sludge was lower than that of the sample without the addition of sludge. The compressive strength of concrete with the addition of rubber granules was higher than the control sample and did not significantly depend on the amount of granulate used.