Addressing the Low-Temperature Behavior of Bitumen with the DSR
Investigation of the frequency-dependent behavior of five road construction bitumen at low service temperatures with the solid state clamping and the PP04
Purpose of the Investigation
The determination of the low-temperature properties of bitumen and bituminous binders represents an interesting field of application for road construction. At low temperatures, the stiffness of the binder increases and the viscous properties are reduced. The formation of a crack is favored by the predominating elastic behavior and the binder’s high rigidity. Depending on the traffic load and the temperature as well as the weather conditions, the cracks can lead to so-called "potholes". Consequently, it is of significant importance to be able to test and evaluate the reaction of the visco-elastic building material bitumen upon different mechanical and cryogenic loads.
For this purpose, two standardized procedures are nationally available in Germany. The older method generates the Fraaß breaking point, which represents the lower limit of the plasticity span. With the General Circular 11/2012 of the Federal Ministry of Transport, Building and Urban Developmenti, the bending beam rheometer (BBR) from the "AASHTO T315" of the "American Association of State Highway and Transportation Officials" established itself in Europe. In the USA, the method is used to determine the lower limit of "performance grade", which is ten Kelvin below the prevailing examination temperature
The latter method showed similar weaknesses in the test precision (standard deviation of the BBR = 1.8 K 2) in recent ring investigations as the breaking point according to Fraaß.
In the USA, this circumstance led to a drafting of a standard, which was intended to represent an alternative method for the investigation of low - temperature behavior using the Dynamic Shear Rheometer (DSR) and a 4 mm parallel-plate measuring system (PP04).
Reasons for the insufficient precision of previous test methods are on the one hand the almost ideally elastic specimen behavior and suspected irreversible structural changes of the specimen on the other hand. These events can be considered with a Solid Rectangular Fixture (SRF) in the Dynamic Shear Rheometer.
Experiments with the dynamic shear rheometer and the solid state clamping, as well as the PP04 should lead to a development of a measuring concept, which allows a more precise approach of the cryogenic behavior with equivalent evaluation as the BBR. Secondarily, an attempt should be made to derive a repeatability of the measurement methods with the DSR.
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