Low-Temperature Characterization of Foamed Warm-Mix Asphalt Produced by Water Injection

• Published in: Transportation research record 2014-01, Vol.2445 (1), p.1-11
• Main Authors: Alhasan, Ahmad A., Abbas, Ala R., Nazzal, Munir, Dessouky, Samer, Ali, Ayman, Kim, Sang-Soo, Powers, David
• Format: Article
• Language: English
• Subjects: Aggregates; Asphalt; Binders; Cracking (fracturing); Foams; Fracture mechanics; Rheometers; Water injection
• ISSN: 0361-1981; 2169-4052
• DOI: 10.3141/2445-01

This study evaluated the low-temperature performance of foamed warmmix asphalt (WMA) produced by water injection and compared it with that of hot-mix asphalt (HMA). Two asphalt binders (PG 70–22 and PG 64–28), two aggregate types (limestone and crushed gravel), and two aggregate gradations [nominal maximum aggregate size (NMAS)] (12.5-mm NMAS and 19.0-mm NMAS) were used in this study. The low-temperature properties of the asphalt binders were measured with the bending beam rheometer, and the low-temperature behavior of the asphalt mixtures was evaluated with the thermal stress restrained specimen test after being subjected to short-term and long-term aging. As expected, the fracture temperatures obtained for the short-term aged specimens were lower than those obtained for the long-term aged specimens. This was the case for both foamed WMA and HMA mixtures. The HMA mixtures exhibited colder fracture temperatures than did the foamed WMA mixtures for the short-term aged specimens, but fracture temperatures comparable to those for the long-term aged specimens. This comparison suggests that the traditional HMA mixtures may have better resistance to low-temperature cracking than foamed WMA does during the initial service life of the asphalt layer, but may have similar resistance to low-temperature cracking at later stages. This study also showed that the low-temperature binder grade had the most significant effect on fracture temperature, whereas the aggregate type had the most significant effect on fracture stress.