BS EN 12697-44:2010 pdf download.Bituminous mixtures – Test methods for hot mix asphalt Part 44: Crack propagation by semi-circular bending test.
BS EN 12697-44 specifies the Semi-Circular Bending (SCB) test method to determine the tensile strength or fracture toughness of an asphalt mixture for the assessment of the potential for crack propagation. The results of the test can be used to calculate:
— the maximum load that the material containing a notch (crack) can resist before failure; when the presence of a notch is critical.
It should be noted that the test only describes a method to determine the resistance to crack propagation of an asphalt mixture. The crack propagation phase describes the second part of failure mechanism during dynamic loading. The first phase, which is the crack initiation phase, is mainly covered by the fatigue test
(EN 12697-24).
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated referenced, only the edition cited applies, For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 12697-27, Bituminous mixtures — Test methods for hot mix asphalt — Part 27: Sampling
EN 12697-31, Bituminous mixtures — Test methods for hot mix asphalt — Part 31: Specimen preparation by gyrator,’ compactor
EN 12697-33, Bituminous mixtures — Test methods for hot mix asphalt — Part 33: Specimen prepared by roller compactor
EN 12697-35, Bituminous mixtures — Test methods for hot mix asphalt — Part 35: Laboratory mixing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 test piece
sample obtained by sawing an asphalt cylinder through a diameter
3.2 strain
relative deformation of the test piece
3.3 stress
force per unit area
3.4 horizontal stress
tensile stress prevailing at the base of the test piece
3.5 tensile strength
strength of the material under tensile loading
3.6 fracture toughness
resistance to failure of the test piece by breaking
4 Symbols
Notch depth in millimetres (mm)
Diameter in milimetres (mm)
f(a/W) Geometric factor
Force in newtons (N)
Maximum force in newtons (N)
Fracture toughness in newtons per millimetre to the power of 1,5 (N/mm’ “)
Thickness in millimnetres (mm)
Vertical displacement at maximum force in millimnetres (mm)
Strain at maximum force in percent (%)
Stress in newtons per square millimetre (N/mm2)
Horizontal stress in newtons per square millimetre (N/mm2)
Maximum stress at failure in newtons per square millimetre (N/mm2)
5 Principle
A half cylinder test piece with a centre crack is loaded in three-point bending in such a way that the middle of the base of the test piece is subjected to a tensile stress. During the test, the deformation increases at a constant rate of 5 mm/min. The corresponding load increases to a maximum value, Fmax that is directly related to the fracture toughness of the test sample. In Figure 1 an example of the test frame and specimen is given.
6 Apparatus
6.1 Test Machine
The machine should have a range of at least 50 kN and have a drive with which a constant deformation rate of (5,0土0,2) mm/min is maintained during the test.
6.2 Load cell or other force-measuring gauge
Capable of measuring the load with an accuracy of士0,2 kN.
6.3 Deformation gauge
Capable of measuring the deformation to an accuracy of土0,01 mm.
6.4 Roller bearings
Capable of rotating on its axis with a support length (centre to centre) of (120,0士0,5) mm and a diameter of (35,0土0,5) mm, as shown in Figure 2.
6.5 Specimen bearing strips
Between specimen and roller bearing, a metal specimen bearing strip (two per specimen) of dimensions (52土1) mm by (20土1)mm by (1,0土0,2)mm (Lx W x H) shall be placed. The centre of each bearing strip shall be directly above the centre of the each roller bearing.
6.6 Metal loading strip L
With a length of at least the thickness of the specimen, a width of (10,0 土0,2) mm and a height of (20,0士土0,5) mm, as shown in Figure 1.
6.7 Monitoring equipment
Capable of continuously logging the loading and the vertical deformation of the test piece.
6.8 Sliding callipers
Capable of measuring the dimensions of the specimens with an accuracy of t 0,1 mm.
6.9 Climatic chamber
Capable to maintain the test temperature in the vicinity of the specimen to土1 °C.
6.10 Cutting machine
Capable to cut a notch in the specimen with a width of (0,35土0,10) mm and a depth of (10,0土1,0) mm. BS EN 12697-44 pdf download.