PURPOSES : It is well known that low temperature cracking is one of the most serious distresses on asphalt pavement, especially for northern U.S. (including Alaska), Canada and the northern part of south Korea. The risk of thermal cracking can be numerically measured by estimating thermal stress of a given asphalt mixture. This thermal stress can be computed by low temperature creep testing. Currently, in-direct tensile (IDT) mixture creep test mentioned in AASHTO specification is used for measuring low temperature creep properties of a given asphalt mixture. However, IDT requires the use of expensive testing equipment for performing the sophisticated analysis process, however, very few laboratories utilize this equipment. In this paper, a new and simple performance test (SPT) method: bending beam rheometer (BBR) mixture creep testing equipment is introduced, and the estimated experimental results were compared with those of conventional IDT tests.
METHODS: Three different asphalt mixtures containing reclaimed asphalt pavement (RAP) and roofing shingles were prepared in the Korea Expressway Corporation (KEC) research laboratory. Using the BBR and IDT, the low temperature creep stiffness data were measured and subsequently computed. Using a simple power-law function, the creep stiffness data were converted into relaxation modulus, and subsequently compared. Finally, thermal stress results were computed from relaxation modulus master curve using Gaussian quadrature approach with condierations of 24 Gauss number.
RESULTS: In the case of the conventional asphalt mixture, similar trends were observed when the relaxation modulus and thermal stress results were compared. In the case of RAP and Shingle added mixtures, relatively different computation results were obtained. It can be estimated that different experimental surroundings and specimen sizes affected the results.
CONCLUSIONS: It can be said that the BBR mixture creep test can be a more viable approach for measuring low temperature properties of asphalt mixture compared to expensive and complex IDT testing methods. However, more extensive research and analysis are required to further verify the feasibility of the BBR mixture creep test.

ABSTRACT
1. Intorduction
2. Materials and testing
    2.1. Prepared asphalt mixtures
    2.2 Bending Beam Rheometer (BBR) mixturecreep testing
    2.3. In-Direct Tensile (IDT) mixture creep testing
3. Basic theory back grounds for materialproperty computation
    3.1. Relaxation modulus: E(t) computation
    3.2. Thermal stress computation
4. Data analysis
    4.1. Relaxation modulus comparison (BBR versusIDT)
    4.2. Thermal stress comparison (BBR versus IDT)
5. Summary and conclusion
REFERENCES

• Park Hae Won(Inha univeristy) | 박해원
• Moon Ki Hoon(Korea Expressway Corporation Pavement Research Division·Seinor researcher) | 문기훈 Corresponding Author
• Seo Jin Seok(Inha university) | 서진석
• Lee Chan Hee(Inha university) | 이찬희
• Jeong Jin Hoon(Inha university) | 정진훈