The extensive use of cement in contemporary construction raises severe concerns about its impact on the environment and human health. Besides, trash like used paper adds to landfill overflow and environmental damage. Waste Paper Sludge Ash (WPSA) is investigated in this study as a potential solution to mitigate these issues and enhance the resilience of ultra-high performance concrete (UHPC). WPSA was mixed into UHPC in amounts that varied from 5% to 15% of the total weight of cement. Prisms with dimensions of 100 mm × 100 mm × 500 mm were prepared with different percentages of WPSA. It was then subjected to flexural and non-destructive tests (NDT), which included ultrasonic pulse velocity (UPV) and rebound impact tests, to evaluate the mechanical properties and flexural strength. The flexural strength of UHPC was significantly reduced when WPSA was added, with the control mix showing the highest strength. These results were supported by the rebound hammer test, which revealed reduced compressive strengths in comparison to the control. The compressive strength gradually declined as WPSA concentrations of 5%, 10%, and 15% were added. The findings show that adding WPSA to UHPC reduces its flexural strength, thus, more adjustment and research are needed to improve the efficiency of UHPC with WPSA.