Abstract
The cooling test or Thermal Stress Restrained Specimen Test (TSRST) simulates fully restrained pavements, as they occur in field for laboratory assessment of the thermal cracking resistance of asphalt mixtures. In the TSRST, cryogenic stress builds up due to cooling and prevented shrinkage until the tensile strength of the specimen is exceeded and the specimen fails by cracking. By carrying out TSRST various viscoelastic parameters, e.g. relaxation, evolution of tensile stresses, and tensile strength can be analyzed. Thus, a comprehensive view on the low temperature performance is possible. Standard TSRST is controlled by setting the cooling rate of the air within the chamber at a fixed value, e.g. -10°C/h. In thermodynamics, the actual cooling rate of objects is not only influenced by the cooling but also by external conditions like humidity, air velocity, radiation condition, etc. A current study investigates the impact of additional cooling parameters rather than just the air cooling rate. Two test machines of the same manufacturer that differ in the year of production and the setup of the climate chamber are compared. An initial wide scatter of test results from the two devices could be explained by taking thermodynamics into account and the reproducibility could be significantly enhanced.
Highlights
Asphalt mixtures are the dominant construction material for today’s road pavements, e.g. about 90% of the paved US road network is made of asphalt pavements [1], and by far more than 90% of the European road network
When the temperature falls below a certain value, the stress relaxation capability of the binder is not sufficient and once the tensile strength is reached, the asphalt pavement will fail by thermal cracking
The dummy is placed in the thermal chamber close to the actual test specimen at the same height to make sure that both, the dummy and test specimen are subject to the same temperature profile in the chamber
Summary
Asphalt mixtures are the dominant construction material for today’s road pavements, e.g. about 90% of the paved US road network is made of asphalt pavements [1], and by far more than 90% of the European road network. [2] Asphalt mixtures are a composite of asphalt binder and mineral aggregates with a predefined mix design. When the temperature falls below a certain value, the stress relaxation capability of the binder is not sufficient and once the tensile strength is reached, the asphalt pavement will fail by thermal cracking. These cracks allow for water to penetrate the pavement, leading to further frost‐thaw damage and eventually complete disintegration of a pavement structure. To ensure durable pavement structures, it is important to assess the thermal cracking resistance at the stage of mix design For this reason, various test methods have been developed in the last decades. Studies on the impact of warm mix asphalt (WMA) [16], rubberized binders [17] and the correlation to field performance [18] have been carried out
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