Investigation of the Impact of Zeolite on the Detrimental Effect of Changes in the Water Acidity Level on the Intermediate Properties of HMA Using Rheological, Mechanical, and Thermodynamical Tests

Moisture is an essential factor that can alter an asphalt mixture’s performance against fatigue cracking of hot-mix asphalt (HMA). Accordingly, this study investigated the impact of runoffs with various degrees of acidity (pH) on the performance of HMA at a medium temperature. Twelve types of HMA samples were made using two types of aggregates (siliceous and limestone aggregates), two types of performance grade (PG) bitumens, and zeolite (a water pollution adsorbent additive) at 1% and 2% of the bitumen mass. The HMA samples were subjected to environmental conditions with pH levels of 5, 6, 7, 8, and 9. The bitumen was tested using a dynamic shear rheometer (DSR), and the HMA samples were subjected to semicircular bending beam (SCB) tests. Thermodynamic tests to determine the surface free energy (SFE) components of the bitumens and aggregates were also performed using the Wilhelmy plate (WP) method and the universal sorption device (USD), respectively. The application of environmental conditions reduced the bitumen–aggregate adhesion and increased the probability of fatigue cracking. Acidic and basic environmental conditions raised the stiffness of the bitumen after drying and increased the phase angle, which raised the fatigue parameter and fatigue cracking probability. Applying acidic and basic conditions elevated the fracture energy and fracture toughness, indicating a marked decline in the asphalt mixture’s ability to absorb stress and resistance to crack growth, especially in acidic environments. The addition of zeolite as a bitumen additive increased the basic SFE component and decreased the acidic SFE component of the bitumen, thereby improving tensile strength, especially in samples containing siliceous aggregates which were sensitive to bitumen-aggregate debonding. However, zeolite improved the nonpolar SFE component, which positively affected both cohesion and adhesion strength parameters. The statistical analysis revealed that using 1% and 2% zeolite significantly changed the modified bitumen’s fatigue parameter and the modified HMA samples’ fracture energy and fracture toughness parameters. As such, this additive can be recommended as a suitable modifier for the environmental conditions of acidic and basic runoffs.