مهدي زال نژاد

Colored asphalt mixtures have gained increasing application in recent years due to their safety, environmental, aesthetic, and landscaping advantages in urban areas. The development of durable colored asphalt production techniques and the use of protective technologies such as slurry seal and microsurfacing are among the important methods in this field. To achieve high-quality mixtures, proper design and mechanical performance are crucial, and analyzing the color durability of these mixtures is essential for color development and stability. In this regard, two types of protective mixtures were considered for producing colored surface treatment mixtures: surface treatment containing natural aggregates and pigments, and colored surface treatment mixtures containing steel slag. This study examined the performance of colored asphalt samples in three distinct sections. In the first section, the microstructural properties of materials and pigments were investigated using XRF, XRD, BET, FESEM, FTIR tests, and moisture absorption analysis. In the second section, sample performance was eva‎luated using wet cohesion test, wet track abrasion test, loaded wheel-displacement test, and loaded wheel-bleeding according to ASTM D6372 and ASTM D3910 standards. Subsequently, within the optimal bitumen content range for each composition, SFE tests were conducted on colored mastics, and fracture tests were performed on ENDB samples at low temperatures under three pure loading modes: I, II, and III. In the third section, mixtures were prepared for color analysis tests based on CIELCH colorimetric coordinates and surface temperature analysis. The FESEM microscopic study results showed that steel slag has a rough surface, while colored powders exhibit angular shapes. BET analysis revealed that red powder has the highest specific surface area, leading to maximum absorption and contact with bitumen. XRF, XRD, and FTIR analyses indicated that fillers have varying compositions and phases, affecting the properties of the final bitumen and mastic. Additionally, the addition of SBR latex significantly altered the bitumen structure, improving its elastic properties and viscosity. Among the asphalt samples, the mixture containing red pigment demonstrated optimal performance, showing an increase in adhesion by 1.8% and 6.7% after 30 and 60 minutes respectively, reducing moisture sensitivity by 27.6%, and decreasing vertical displacement under traffic loading by 11.7% compared to the control sample. In determining color characteristics, it was found that using TiO2 in quantities of 1-3% for blue and red compositions and 1% for yellow compositions is appropriate. Furthermore, among samples containing steel slag, the mixture with 33% steel slag showed the best performance, demonstrating an increase in adhesion by 37.3% after 60 minutes, reducing moisture sensitivity by 47.7%, and decreasing vertical displacement under traffic loading by 50.8% compared to the control sample. The fracture test revealed that the fracture resistance of colored mixtures in all pure loading modes increases with decreasing test temperature. Moreover, KIc has the maximum stress intensity factor, while KIIIc shows the lowest fracture resistance. This indicates that crack potential in pure mode I is lower than in pure modes II and III. SFE results showed that microsurfacing mastics have lower contact angles compared to slurry seal samples, indicating better wettability and adhesion. Additionally, red samples and natural filler exhibited the highest surface free energy and cohesion work, confirming improved elastic properties and bitumen adhesion. Thermal performance analysis revealed that colored asphalts have higher solar reflectance compared to conventional black asphalt (yellow powder 44%, blue 39%, and red 35%). Moreover, the surface temperature of colored asphalts is on average 20-39% lower than black asphalt, demonstrating the positive effect of higher solar reflectance on reducing the surface temperature of colored asphalts.

آسفالت حفاظتي رنگي , رنگدانه‌هاي طبيعي , حساسيت رطوبتي , خصوصيات رنگ‌سنجي , عملكردي حرارتي و طيف بازتاب

Colored surface treatments , Natural pigments , Moisture sensitivity , Colorimetric properties , Thermal performance and reflectance spectrum

Mahdi Zalnezhad

Hassan Ziari