Testing Asphalt

The introduction of EU standard EN 12697 -24/ -25/ -26 established a uniform basis for tests on asphalt. This standard defines test methods for determining deformation, stiffness and fatigue properties of asphalt. The tests are carried out using servo-hydraulic testing machines, with a test load of 10 - 25 kN and at temperatures between -25 and 40°C; the temperature must be maintained at a constant level to within 1 K during the test, making a temperature chamber with accurate control a necessity.

Fatigue Testing on Asphalt

Road asphalt is subject to changing stresses caused by environmental influences and loads imposed by goods vehicles, leading to constantly increasing demands on the materials used in road construction. Intensive development work is taking place on new formulations and additives for asphalt mixes. These must be tested for suitability. The main area of interest is the change in properties due to dynamic loads. Dynamic test methods are also used for continuous quality control. European asphalt mixture producers are required to test their various mixture types in accordance with uniform standard EN 12697 in order to obtain the mandatory CE mark. Parts 24, 25 and 26 of this standard define different dynamic test methods. These are implemented in national test standards such as the Technical Testing Standards of the German Research Association for Highway and Traffic Engineering (FSGV). Different European countries favor different test methods, resulting in a variety of test devices being required. Zwick’s response to this situation was to develop a flexible servo-hydraulic testing system equipped with the necessary test fixtures and appropriate testing and evaluation software.

Testing at Defined Temperatures  

The asphalt testing system is based on a specific adapted load frame from the HB range. Mounted on the upper fixed crosshead is a testing actuator with hydrostatic bearings, servo valve and hydraulic accumulator unit. A load cell with accelerometer is installed on the piston rod of the testing actuator. The testing system is available for test loads up to 10 kN, 25 kN and 50 kN. Since all tests must be performed at defined temperatures, a temperature chamber with cooling unit is also available. The temperature chamber is mounted on guide rails and can simply be pushed back out of the way to facilitate installation of test fixtures.

Triaxial cyclic compression tests

The triaxial cyclic compression test according to EN 12697-25 (Test Method B) is used to determine permanent deformation and creep properties under constrained transverse strain. The test fixture consists of the compression test fixture for uniaxial cyclic compression tests and a triaxial cell operated by compressed air. Static lateral pressure is adjusted via a control valve.
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Indirect Tensile Tests

Indirect tensile tests according to EN 12697-24, Annex E, EN 12697-26, Annex C and cyclic indirect tensile tests to AL-SP-Asphalt 09 are used to determine stiffness and fatigue properties. The cyclic indirect tensile test is the standard test method in Germany. The test fixture is designed for specimen diameters of 100 mm and 150 mm and is equipped with integrated insertion and centering aids for the specimen and the clamping frame attached to it. Horizontal deformation is measured via two inductive displacement transducers in the clamping frame. 

2-Point Alternating Flexure Tests

The 2-point alternating flexure test according to EN 12697-24, Annex A and EN 12697-26, Annex A is used to determine fatigue resistance and dynamic stiffness. It is the standard test method in France. The test fixture has frictionless, wear-free flexure pivots, which translate the vertical piston travel into horizontal motion. Two specimens can be tested simultaneously at the same amplitude, with separate measurement of force and horizontal displacement for each specimen. A reference specimen with strain gages attached is available for calibration purposes.
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4-Point Alternating Flexure Tests

The 4-point alternating flexure test to EN 12697-24, Annex D and EN 12697-26, Annex B is used to determine fatigue resistance and dynamic stiffness. It is the standard test method in the Netherlands. The test fixture has frictionless, wear-free flexure pivots which adjust to the movement of the specimen, while the clamps feature motorized compensation adjustment and possess the necessary freedom of movement. An inductive displacement transducer measures deflection on the underside of the specimen. The fixture is designed for test loads up to 5 kN and deflections up to a maximum of ±0.5 mm. Specimen dimensions are 450 mm x 50 mm x 50 mm or 450 mm x 70 mm x 70 mm. Special versions are available on request. Dynamic calibration with reference specimens ensures high accuracy, even at high testing frequencies.