In Asphalt Rheology, to study the behavior of material(Bitumen) Stress relaxation tests can be conducted. On what basis the input shear strain(%) can be fixed.
We have done a lot of stress relaxation tests in the DSR in the low temperature range already and this kind of test is currently discussed for standardization in Germany.
The decision of a suitable strain depends upon your objective. Do you want to characterize the low temperature behaviour? In that case, I tried to identify a universal strain level which can be applied to all bitumen types, without leading to a brittle fracture of the specimen. At the moment, I am using 1 % of strain (with 4mm geometry at low temperatures, -15 °C, -20 °C). I also systematically varied the strain to be 0.01, 0.1 % and it seems the general behaviour is very similar (percentual stress relaxation is identical).
Thank you for your reply, sir
I am testing Hydrated Lime treated mastic at high temperatures 30-80°C.In this do, we have to take the higher strain.
I agree with Johannes' recommendation. It is also important to apply this target shear strain within a shortest possible time interval. The interval of 0.1 s is a good standard.
Good morning! The easiest way is to perform a linearity test in monotonic or cyclic mode. The relaxation test is a small strain test, therefore, the chosen strain must be inside the linear viscoelastic domain. It is also necessary that the time of the load application to be very short to approach the theory which consists in applying an instantaneous load.
Generally the Linear Viscoelastic Region is higher for higher temperatures, but the test results should be technically the same as long as you are within the LVE region. A higher strain, that is outside the LVE would be an issue. As Johannes mentioned that he tested at 0.01, 0.1 and 1%, he got the same results and they all fall within the LVE region. You of course have to consider the limitation of your device as well. You can find the LVE for your particular material by running a simple amplitude sweep and the point where your shear modulus reduces to 95% of its peak modulus value (so 5% lower) would be the highest strain you could arrive at. So for testing, reduce this limit by 15-20% to ensure LVE region. Generally from experience, at 30°C, unaged bitumen would have a limit of around 2-3% while at 80°C around 6-7%
- Badges
- Science topic
- Similar topics
- Instrumentation Engineering
- Instruments