BS/EN 12697-24-2018 pdf download.Bituminous mixtures – Test methods Part 24 : Resistance to fatigue.
The conventional failure criterion for the type of test undertaken, as defined in 3.1.2, shall be used to determine the failure life of a material unless otherwise prescribed. In such cases, the criterion used shall be included the test report.
6 Selection test conditions
For fatigue tests according to Annexes A to D, the test loads, deformations and frequencies shall be selected so that the E6-value Is calculated by interpolation and not by extrapolation. At least 20 % of the measurements shall be at either side of the calculated result.
For tests according to Annexes E and F, the procedure for finding suitable test conditions is described in the individual annexes.
7 Summary of the procedures
7.1 Two-point bending test on trapezoidal shaped specimens (2PB-TR)
This method characterizes the behaviour of bituminous mixtures under fatigue loading with controlled displacement by two-point bending using trapezoidal shaped specimens. The method can be used for bituminous mixtures with a maximum aggregate size of up to 20 mm on specimens prepared in a laboratory or obtained from road layers with a thickness of at least 40 mm. For mixtures with an upper size D between 20 mm and 40 mm, the test can be performed using the same principle but with adapted specimen sizes. For a given frequency of sinusoidal displacement, the method shall be carried out on several elements tested in a ventilated atmosphere at a controlled temperature.
7.2 Two-point bending test on prismatic shaped specimens (2 PB-PR)
This method characterizes the behaviour of bituminous mixtures under fatigue loading by 2-point- bending using square-prismatic shaped specimens. The method can he used for bituminous mixtures with a maximum aggregate size of up to 20 mm and on specimens prepared in a laboratory or obtained from road layers with a thickness of at least 40 mm.
7.3 Three-point bending test on prismatic shaped specimens (3PB-PR)
This method characterizes the behaviour of bituminous mixes under fatigue loading, with controlled displacement by three-point bending using prismatic beam shaped specimens. The behaviour is characterized through the determination of the fatigue law in terms of strain (relation between strain and number of load cycles at failure) and the associated energy law. The method can be used for bituminous mixture specimens with a maximum aggregate size of 22 mm or for samples from road layers with a thickness of at least 50 mm. For a given frequency of sinusoidal displacement, the method shall be carried out on several elements tested at a controlled temperature.
7.4 Four-point bending test on prismatic shaped specimens (4PB-PR)
This method characterizes the behaviour of bituminous mixtures under fatigue loading in four-point bending test equipment in which the inner and outer clamps are symmetrically placed and slender rectangular shaped specimens (prismatic beams) are used. The prismatic beams shall be subjected to four-point periodic bending with free rotation and translation at all load and reaction points. The bending shall be realized by loading the two inner load points (inner clamps) in the vertical direction, perpendicular to the longitudinal axis of the beam. The vertical position of the end-bearings (outer clamps) shall be fixed. This load configuration shall create a constant moment, and hence a constant strain, between the two inner clamps. The applied load shall be sinusoidal. During the test, the load needed for the bending of the specimen, the deflection and the phase lag between these two signals shall be measured as a function of time, The fatigue characteristics of the material tested shall be determined from these measurements.
7.5 Indirect tensile test on cylindrical shaped specimens (IT-CY)
This method characterizes the behaviour of bituminous mixtures under repeated load fatigue testing with a constant load mode using an indirect tensile load. A cylindrical specimen manufactured in a laboratory or cored from a road layer can be used in this test. A cylinder-shaped test specimen shall be exposed to repeated compressive loads with a (ha)versine load signal with rest periods through the vertical diametrical plane. This loading develops a relatively uniform tensile stress perpendicular to the direction of the applied load and along the vertical diametrical plane, which causes the specimen to fail by splitting along the central part of the vertical diameter. The resulting horizontal deformation of the specimen shall be measured and an assumed Poisson’s ratio used to calculate the tensile strain at the centre of the specimen.
An alternative failure criterion is that the fracture life can be determined as the total number of load cycles before fracture of the specimen occurs. Further alternative failure criterions can be based on energy ratio. The use of this criterion should be stated in the test report.
7.6 Cyclic Indirect tensile test on cylindrical shaped specimens (CIT-CY)
This method characterizes the behaviour of bituminous mixtures under cyclic load fatigue testing in a force-controlled loading mode using an indirect tensile load. A cylindrical specimen manufactured in a laboratory or cored from a road layer can be used in this test. A cylinder-shaped test specimen shall be exposed to vertical cyclic compressive load impulses without rest periods through the vertical diametrical plane. This loading develops a sinusoidal tensile stress perpendicular to the direction of the applied load and along the vertical diametrical plane, which causes the specimen to fail by splitting along the central part of the vertical diameter. The resulting horizontal deformation of the specimen shall be measured and an assumed Poisson’s ratio used to calculate the tensile strain at the centre of the specimen. As alternative failure criterion, the number of load cycles until macro crack initiation shall be applied.BS/EN 12697-24-2018 pdf download.