The NCHRP rpt 513 says that the range of stress for unconfined test on asphalt concrete (both static and repeated load test) is 69 - 207 kPa and for confined test it is 483 - 933 kPa. The typical confinement range is 35 - 207 kPa.
What is the reason for stress range? (Whether the material will behave as linear viscoelastic?)
How to choose the a specific stress for loading?
Most researchers recommended the 207 kPa stress level for Dynamic Creep Test. However, selection of stress level is depended on flow number or flow time. That is, level of stress should be selected so that flow number can be seen. Also, a high stress level which results in rapid specimen failure should not be selected. So, the selection of stress level is quite material dependent and experimental.
For example, our lab experiences indicate that 207 kPa stress level is convenient for most asphalt mixtures including WMA mixtures. But, a higher stress level is needed for SBS modified asphalt mixtures to achieve flow number.
Dear Nithin,
In static creep tests, whether confined test or unconfined test, the applied pressure is usually cannot exceed 206.9 kPa (30 psi) and the test temperature usually cannot exceed 40°C (104°F) or the sample may fail prematurely.
Dear Nithin, What test method you are following? Are you following AASTHO T322? If so, what we did we came up with the stress (load) by trial and error method. This method allowed us to have an idea of loading until it met strain limit given in the Standard.
Dear Nithin..it depend into large extent on testing temperature due to the rheological properties of asphalt..anywhy..you can consider low limit of stress when testing on high temperature say over 40 degree Celsius otherwise when testing at low temperature you can pickup high stress level,,but you should remember that the testing loading cycles better to be more than 1000 repetitions to get good statistical relationship..regards
Dr. Abbas you remember our last research work how much we suffer from this specific point..i hope after publication of our research we can share it to help the researcher in this regards..regards
Of course Dr Amjad. I think our research may be helpful and can other researchers benefit from our conclusions or readjusted. Thanks.....
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