<p>Egypt's rapidly expanding highway network requires balancing accelerated construction schedules with rigorous quality control (QC). While highways are vital for economic growth, speed of delivery often compromises QC in asphalt production. This study examines how variations in aggregate gradation—a common QC issue—affect the performance of Egypt’s widely used 4B and 4C asphalt mixtures. Gradations 4B and 4C are standardized blends for asphalt concrete wearing courses—the top pavement layer exposed to traffic. They are designed to provide durable, skid-resistant surfaces, typically with a nominal maximum aggregate size of 19 mm (¾ inch). Slight differences in their gradation curves influence workability and performance. Laboratory experiments simulated real-world QC variability, with mixes prepared at design, specification-limit, and tolerance-limit gradations. Performance was evaluated through Marshall stability, rutting resistance, and moisture susceptibility, with statistical validation. The results show clear differences between mix types. The 4B formulation demonstrated higher resilience, with its lower-limit gradation M2 increasing load-bearing capacity by 9% (p = 0.012) and moisture resistance by 8.5% (p = 0.001). In contrast, upper-limit gradations M1 reduced strength by up to 21% (p &lt; 0.001) and increased rutting susceptibility. The 4C mix was more sensitive to such deviations, underscoring the need for stricter fines control. Composite Performance Index analysis further confirmed 4B-M2 as the most balanced and robust gradation. These findings establish tolerance thresholds for 4B and 4C mixes and provide practical QC guidance. By prioritizing 4B-M2 in critical applications and applying real-time monitoring, agencies can mitigate premature failures and align construction efficiency with long-term durability.</p>