Eurobitume’s mission is to promote the efficient, economic, effective and safe use of bitumen. Harmonised standards are the basis for defining the consistent and effective specifications for supply of bitumen across Europe. Eurobitume contributes to the development of standards and test methods by participation in CEN working groups to ensure that bitumen specifications are fit for purpose. Various fundamental test methods are used for the technical classification and assessment of the different bitumen types which, in the first instance, determine the consistency of the bitumen in different temperature ranges.
The main characteristics of Bituminous binders are tested using traditional test methods, which have been used for many years. These test methods were developed and validated for non-modified bitumen. For practical reasons, these test methods have also been adopted for polymer modified binders. However, new, fundamental test methods might be useful to better describe the properties of modified binders. These new test methods have been reviewed by Eurobitume and are recommended for incorporation into specifications when they are revised. Unmodified binders can be described reliably and their use behaviour assessed using traditional test methods.
INDIVIDUAL TEST METHODS
Softening point – Ring and Ball method (EN 1427)
This method, under European standard EN 1427, serves to test the behaviour of bitumen at elevated service temperatures. The temperature is determined at which a layer of bitumen, in a brass ring, experiences a certain deformation under the weight of a steel ball as the temperature rises. This test method has been used for more than one hundred years.
A test method that has been used for decades, which is now described in EN 1426. Needle penetration is determined by the depth, measured in 1/10 mm, to which a 100 g needle penetrates in 5 seconds into the bitumen at a temperature of 25 °C. It serves to test the behaviour of bitumen at intermediate service temperatures. This test method is suitable for all types of bitumen.
Penetration Index is not a test method as such, but obtained by calculation from the Ring and Ball Softening Point and Needle Penetration. The calculation formula is based on the assumption that the penetration of the binder is 800 0,1 mm at its softening point. This is correct for most conventional binders but not for Polymer Modified and special binders. The original calculation was based upon determination of the needle penetration at different temperatures.
Fraass breaking point
The determination of the Fraass breaking point is described in the test standard EN 12593. It describes the transition of the binder from a flexible to a brittle condition and provides the temperature at which a thin bitumen layer on a steel sheet cracks during uniform cooling when it is bent under defined conditions. The test indicates the behaviour of the bitumen at low service temperatures.
The test for elastic recovery is applicable to binders modified with elastomers, and serves to demonstrate the modification of the binder. The sample is stretched at a fixed temperature and speed to a maximum of 20 cm and then severed. After a prescribed period of time, the degree of elastic recovery is determined relative to the original length.
The further development of the well-known ductility test serves to determine the cohesive characteristics of a binder, the test is used in the standard for polymer-modified bitumen. A sample is stretched at a fixed temperature and speed and the necessary tensile force is measured and recorded continuously. The data are used, among other things, to calculate the deformation energy, the maximum tensile force or the stretch length of the sample until breakage. Further options for interpretation of the data are currently being researched and discussed.
Complex shear modulus and phase angle - Dynamic Shear Rheometer (DSR) (EN 14770)
The Dynamic Shear Rheometer (DSR) is an instrument which is used to test bitumen properties under a variety of loading conditions and temperatures. The DSR can apply a controlled stress to the sample and measures the response, from which it can calculate properties such as the complex shear modulus G* and phase angle. Testing using the DSR is described in the test method standard EN 14770. Typically, DSR testing is conducted over a range of test temperatures and/or loading frequencies, called temperature and frequency sweep respectively. From the recorded data complex shear modulus G* and its phase angle (δ) at given temperatures/frequencies are calculated.
Multiple Stress Creep and Recovery Test (MSCRT) (EN 16659)
The Dynamic Shear Rheometer (DSR) testing device is also used to perform the Multiple Stress Creep and Recovery Test. This test method is described in the test standard EN 16659 and addresses elastic response and sensitivity to permanent deformation of bituminous binders as well as stress dependence. A sample of binder is placed between two parallel plates and loaded with constant stress for exactly 1,0 s, followed by 9,0 s without any load. Ten creep and recovery cycles are conducted, from which the percent recovery and non-recoverable compliance of the binder are calculated. The test uses different stress levels, hence the name; ‘Multiple-Stress Creep and Recovery Test’.
Bending Beam Rheometer
The Bending Beam Rheometer (BBR) is a device to address the behaviour of bitumen at low service temperatures and is described in the test standard EN 14771. The sample is placed under a constant load in a liquid bath at low temperature for a fixed duration. The creep stiffness of the sample is calculated from the applied stress and resultant strain over time. The test provides information on the stiffness of the binder at low temperatures and its ability to dissipate, or relax, the stress.
Short Term Ageing:
RTFOT-Method (EN 12607-1)
The Rolling Thin Film Oven Test (RTFOT ) is a conditioning process, rather than a test method and is described in EN 12607-1. RTFOT simulates the combined effects of heat and air on a thin film of bituminous binder. The procedure is intended to simulate the ageing that takes place during the mixing and transportation process for hot mixtures. For paving grade binders a reasonable correlation with the bitumen ageing during asphalt mix production is reported. However, the standard conditioning parameters are not necessarily applicable to modified binders, for which the viscosity may be too high to provide a moving film.
Long Term Ageing: Pressure Ageing Vessel (PAV) Method
As with the RTFOT, the PAV ageing is a conditioning process intended to give information about long-term ageing susceptibility. It is usually carried out after RTFOT-conditioning. Although there are still questions about the applicability of this ageing procedure, due to the prolonged high-temperature experienced by the binder, PAV is the current reference long-term ageing procedure used in Europe & the US and is described in EN 14679. The sample is subjected to high air pressure (2,1MPa), applied to a thin film of bituminous binder under elevated temperature for a given time. PAV ageing is intended to simulate the degree of age hardening that the binder will experience over several years in service.