Bitumen, a product of a crude oil refining process, is a mixture of various hydrocarbons that occur naturally. Bitumen is used in roofing, sealing, and insulation; the most common application is in road pavement. Bitumen serves as a binder for the mineral components (rocks) in the upper asphalt (concrete) layers of roads, parking lots, runways, etc. Roads are exposed to heavy traffic and a wide range of weather conditions, leading to undesired effects such as the formation of grooves or cracks. New asphalt concrete formulations that are more durable and withstand increasing traffic loads as well as extreme weather conditions are needed.
The rheological properties of bitumen binder play an important role in the development of new formulations. A set of rheological testing protocols have been defined over the past several decades to guarantee consistent quality control of bitumen binder materials. The most common rheological testing methods are described below.
Used for asphalt binder specification according to AASHTO M320/ AASHTO T315 or ASTM D7175/ ASTM D6373
Measuring geometry: 8 or 25 mm parallel plates
Temperature range: between 4 °C and 88 °C
Measuring mode: oscillation test within linear-viscoelastic range at a frequency of 10 rad/s (1.59 Hz)
Performed on original and RTFOT / PAV aged asphalt binder
IG*I/sinδ as a measure to estimate rutting at high temperatures (high temperature stiffness)
IG*I · sinδ as a measure to estimate fatigue cracking at intermediate temperatures (intermediate temperature stiffness)
Multiple stress creep recovery test
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According to AASHTO T350, ASTM D7405, DIN EN 16659 or FGSV AL 723
Measuring geometry: 25 mm parallel plates
Temperature range: between 50 °C and 80 °C
Measuring mode: multiple creep and recovery tests at two different stress values (0.1 and 3.2 kPa)
Performed on original and RTFOT / PAV aged asphalt binder (RTFOT aged sample for performance grading)
Results can be used for performance grading according to AASHTO M332
Determination of the average percent recovery, non-recoverable creep compliance and percent difference between non-recoverable creep compliance at two stress levels
Results can be correlated with the ability to resist rutting and identify the influence of modifier
Viscosity determination of asphalt binder at elevated temperatures
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According to AASHTO T316, ASTM D4402, DIN EN 13702
Measuring geometry: coaxial cylinder
Temperature range: up to 200 °C*
Measuring mode: shear viscosity determination at constant rotational speed
Testing is performed with unaged original binder
Viscosity provides information about behavior during mixing, pumping, and application of asphalt binder
*Higher temperature possible with electrical temperature control module
Other standard compliant testing methods
AASHTO TP 123 (Measuring asphalt binder yield energy and elastic recovery) Two types of tests with either monotonic shear for an extended period or a shorter period of monotonic shear followed by an extended relaxation process.
DIN EN 14770 (Determination of complex shear modulus and phase angle) Oscillatory tests over a wider range of frequencies and temperatures.
FGSV AL 720 (Binder fast characterization test) Measurement of the complex shear modulus and the phase angle in a temperature range from 20°C to 90°C.
FGSV AL 722 (Testing with constant shear rate) Rotational test at constant shear rate in a temperature range from 150 °C to 70°C.
FGSV AL 724 – Temperature Sweep Determination of the complex shear modulus and phase angle at different temperatures 30 °C and 90 °C.
Rheology beyond the standards
Understand the rheological behavior of bitumen at the molecular level:
Simultaneous rheological and FTIR spectra measurements
ATR (attenuated total reflection) principle
Analysis of structural changes on the molecular level under shear/deformation and temperature
All standard-compliant bitumen measurement routines are also available