This study explores the use of waste plastic aggregate (WPA) as a sustainable replacement for natural fine aggregates in cement asphalt mortar (CAM), with a focus on comparing the performance of anionic and cationic asphalt emulsions. WPA content was varied from 0% to 50% in the CAM mix, and its effects on workability, mechanical strength, durability, and microstructure were evaluated. Materials used included ordinary Portland cement (OPC), normal sand, WPA, and both types of asphalt emulsions. Key tests included the flow cone table test for workability, unconfined compressive strength (UCS) test, durability tests under environmental stress, and scanning electron microscope (SEM) analysis. The results showed that CAM mixes with anionic emulsion consistently outperformed those with cationic emulsion. For example, a mix with 20% WPA achieved a compressive strength of 11.3 MPa with anionic emulsion, compared to 10.2 MPa with cationic emulsion. Durability tests also revealed higher strength losses in CAM mixes with cationic emulsion, particularly at higher WPA levels. The study concludes that anionic emulsion is more effective in maintaining workability, strength, and durability in CAM mixes with WPA, making it the preferred choice for sustainable construction applications.