Cement Mortars Based on Polyamide Waste Modified with Fly Ash from Biomass Combustion—A New Material for Sustainable Construction

The article presents an analysis of the possibility of using the waste of polyamide 6 modified with fly ash (in the amount of 5, 10 and 15%) from the burning of wood–palm kernel shells biomass as an addition to cement mortar. Fly ash from the burning of biomass in a circulating fluidized bed boiler (which currently has no practical use) was first used to produce polyamide 6, and then post-production polymer waste (added at 20, 40 and 60%) was used to produce ecological mortar. The use of this type of waste is both economically profitable and desirable due to the need to implement waste material management processes in a closed circuit. The addition of polyamide 6 waste containing 5% fly ash in amounts of 20 and 40% and waste containing 10% ash in 20% to cement mortars improves their mechanical properties. The compressive strength of cement mortars (after 28 days of maturation) containing 20 and 40% of polyamide waste containing 5% fly ash increases by 6.6 and 4.6%, respectively, and the flexural strength by 4.9 and 3.4% compared to the control mortars. However, the compressive strength of mortars with the addition of 20% polyamide waste containing 10% fly ash increases by 4.2% and the flexural strength by 3.7%. Cement mortars modified with waste are characterized by slightly lower water absorption and mechanical strength after the freezing–thawing process (frost resistance) compared to control mortars and do not have an adverse effect on the environment in terms of leaching metal ions.