Tehran University Researchers Enhance Cold Recycled Asphalt Performance via Polymer-Modified Emulsified Bitumen

According to the University of Tehran's Public Relations Office, researchers from the College of Engineering, in collaboration with the Iran University of Science and Technology, have investigated the simultaneous effects of using Reclaimed Asphalt Pavement (RAP) and emulsified bitumen modified with Styrene-Butadiene Rubber (SBR) latex on the performance of cold asphalt mixtures.

Dr. Mohammad Zia Alavi, a faculty member of the School of Civil Engineering, stated: "In this study, mixtures were produced with nominal RAP contents of 0, 25, 50, 75, and 100 percent, utilizing both modified and unmodified emulsified bitumen. The binder properties and overall mixture performance were evaluated through a comprehensive series of physical, chemical, mechanical, and moisture susceptibility tests."

He further added: "The results demonstrated that the addition of SBR increased the softening point of the bitumen from 54 to 64 degrees Celsius and elevated the penetration index from 0.41 to 2.28, indicating a marked reduction in temperature susceptibility. Moreover, the adhesion energy of the modified mastic increased by approximately 16.2 percent."

Dr. Alavi noted: "Increasing the RAP content up to the nominal level of 100 percent reduced Marshall stability by 24.2 percent; however, modifying the bitumen with SBR compensated for a portion of this decline. Conversely, the indirect tensile strength increased by up to 15.2 percent with higher RAP content, while moisture resistance indicators also demonstrated notable improvement through the application of both RAP and SBR."

Nevertheless, a substantial increase in RAP content led to a significant reduction in flow value and resistance to permanent deformation. While the addition of SBR improved this specific index, it was unable to restore the performance of the mixture to that of the control sample at the highest RAP percentages.

According to Dr. Alavi, these findings highlight the potential of utilizing SBR and reclaimed materials to produce more sustainable cold asphalt mixtures. However, he emphasized that mix design optimization, alongside pilot project implementation and field performance monitoring, remains essential prior to widespread application.

This research was conducted in collaboration with Dr. Mohammad Ali Ziari, Dr. Masoud Palasi, and Dr. Mehdi Zalnezhad. The findings have been published in 2026 in the journal Case Studies in Construction Materials.

https://www.sciencedirect.com/science/article/pii/S2214509526004973