DIN EN 12697-46-2012 Bituminous mixtures - Test methods for hot mix asphalt - Part 46 Low temperature cracking and properties by uniaxial tension tests German version EN 12697-46 2.pdf

1、-XO7UDQVODWLRQE,16SUDFKHQGLHQVW(QJOLVKSULFHJURXS1RSDUWRIWKLVWUDQVODWLRQPDEHUHSURGXFHGZLWKRXWSULRUSHUPLVVLRQRI,1HXWVFKHV,QVWLWXWIU1RUPXQJH9%HUOLQ%HXWK9HUODJ*PE+%HUOLQ*HUPDQKDVWKHHFOXVLYHULJKWRIVDOHIRU*HUPDQ6WDQGDUGV ,11RUPHQ , minimum temperature that the asphalt can resist before failure, using the

2、thermal stress restrained specimen test (TSRST); tensile strength reserve at a specified temperature (using a combination of TSRST and UTST); relaxation time, using the relaxation test (RT); creep curve to back calculate rheological parameters, using the tensile creep tests (TCT); fatigue resistance

3、 at low temperatures due to the combination of cryogenic and mechanical loads, using the uniaxial cyclic tension stress tests (UCTST). 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated

4、 references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 12697-6:2012, Bituminous mixtures Test methods for hot mix asphalt Part 6: Determination of bulk density of bituminous specimens EN 12697-27, Bitu

5、minous mixtures Test methods for hot mix asphalt Part 27: Sampling EN 12697-33, Bituminous mixtures Test methods for hot mix asphalt Part 33: Specimen prepared by roller compactor 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 tensile streng

6、th tmaximum tensile stress measured in a tensile stress test 3.2 tensile failure strain failuretensile strain that is measured when the tensile strength has been reached 3.3 cryogenic stress cry(T) tension stress, induced by prohibited thermal shrinkage, at the temperature T 3.4 failure stress cry,

7、failurecryogenic stress that causes a failure of the specimen in the thermal stress restrained specimen test (TSRST) DIN EN 12697-46:2012-07 EN 12697-46:2012 (E) 7 3.5 failure temperature Tfailuretemperature at which the cryogenic stress causes a failure of the specimen in the thermal stress restrai

8、ned specimen test (TSRST) 3.6 tensile strength reserve tdifference between the tensile strength and the cryogenic stress at the same temperature T where )()()(cryttTTT = 3.7 time of relaxation treltime until the stress decreases to 36,8 % (1/e) of its initial value 3.8 remaining tension stress rem(t

9、) remaining stress after the time t in the relaxation test 3.9 initial complex modulus E*0complex modulus after 100 load cycles, calculated according to EN 12697-26 3.10 conventional failure criterion Nf/50number of load cycles reducing the complex modulus E* to half of its initial value E*0(fatigue

10、 criterion) 3.11 additional failure criterion Nfailurenumber of load cycles leading to the development of a visible and recognisable crack in the asphalt specimen (fracture criterion) 4 Principle The low-temperature performance of asphalt specimens can be tested using different test methods: In the

11、uniaxial tension stress test (UTST), a specimen is pulled with a constant strain rate at a constant temperature until failure. Results of the UTST are the maximum stress (tensile strength) t(T) and the corresponding tensile failure strain failure(T) at the test temperature T (see Figure 1). In the t

12、hermal stress restrained specimen test (TSRST), a specimen, whose length is held constant, is subjected to a temperature decrease with a constant temperature rate. Due to the prohibited thermal shrinkage, cryogenic stress is built up in the specimen. The results are the progression of the cryogenic

13、stress over the temperature cry(T) and the failure stress cry, failureat the failure temperature Tfailure(see Figure 2). In the the tensile creep test (TCT), the specimen is subjected to a constant tension stress at a constant temperature T. The progression of the strain is measured. After a given t

14、ime, the stress is withdrawn. Rheological parameters describing the elastic and viscous properties of the asphalt can be determined by interpreting the strain measurements (see Figure 4). In the relaxation test (RT), the specimen is subjected to a spontaneous strain , which is held on a constant lev

15、el. The decrease of tension stress by relaxation over the testing time is monitored. The results are the time of relaxation treland the remaining tension stress remafter the test has ended (see Figure 3). DIN EN 12697-46:2012-07 EN 12697-46:2012 (E) 8 In the uniaxial cyclic tension stress test (UCTS

16、T), a specimen is subjected to a cyclic tensile stress which is characterised by a sinusoidal stress to simulate the dynamic loading condition by traffic in combination with a constant stress, which symbolises the cryogenic stress. During the test, the strain response is monitored and the course of

17、the stiffness is recorded until fatigue failure. Results of the tests are the num-ber of applied load cycles until failure Nfailureand the number of load cycles until the conventional fatigue criterion is reached Nf/50 (see Figure 5). Figure 1 Test principle of UTST Figure 2 Test principle of TSRST

18、Figure 3 Test principle of RT Figure 4 Test principle of TCT Figure 5 Test principle of UCTST Key for Figures 1 to 5 Y1 strain X time Y2 temperature Y3 stress DIN EN 12697-46:2012-07 EN 12697-46:2012 (E) 9 5 Apparatus 5.1 Testing device for conducting UTST, TSRST, RT and TCT 5.1.1 General Figures 6

19、and 7 show suitable testing devices for conducting uniaxial tension stress, thermal stress restrained specimen, relaxation and tensile creep tests, at low temperatures. 5.1.2 Load device The load device shall be able to generate movements with an accuracy of 0,1 m. In order to avoid radial and/or tr

20、ansversal forces as well as moments in the test specimen, the specimen is connected to the loading device by two gimbal suspensions. Key 1 load cell 2 displacement transducer 3 thermal indifferent measurement base 4 crossbeam 5 gimbal suspension 6 adapter 7 specimen 8 gear box with stepping motor Fi

21、gure 6 Example of a test device for uniaxial tension tests at low temperatures DIN EN 12697-46:2012-07 EN 12697-46:2012 (E) 10 Key 1 load cell 2 load frame 3 swivel jig 4 clamp 5 specimen 6 end plate 7 loading rod 8 temperature sensor 9 invar rod 10 environmental chamber 11 dummy with temperature se

22、nsor 12 fan 13 displacement transducer 14 step motor Figure 7 Example 2 for a test device for uniaxial tension tests at low temperatures 5.1.3 Deformation measurement system The deformation of the specimen shall be measured in a range of 2,5 mm and 0,5 m. Because the test equipment is exposed to the

23、 same thermal changes as the examined specimens with thermal shrinkage and expansion, accurate measuring of the actual strain in the specimen requires a basis with constant length at various temperatures (e.g. special carbon fibre reinforced plastic or invar steel). Several single measurements may b

24、e averaged into one mean value, which shall fulfil the accuracy requirement. This mean value shall be used for the closed-loop circuit for controlling the tests. 5.1.4 Load measurement system Load measurement system, capable of monitoring the axial load up to (20 20) N. 5.1.5 Recording equipment Rec

25、ording equipment, comprising a digital interface unit connected to a computer, which shall be capable of monitoring and recording the electrical signals from the load and deformation transducers. NOTE The displacement should be measured and controlled with a resolution of 0,5 m. DIN EN 12697-46:2012

26、-07 EN 12697-46:2012 (E) 11 5.1.6 Thermostatic chamber Thermostatic chamber, consisting of a cabinet or a suitable room with forced air circulation, in which the specimen can be conditioned and in which the test can be performed. The temperature inside the enclosure shall be maintained at a constant

27、 temperature between (40 and +30) C with an accuracy of 0,5 K. The thermostatic chamber shall be capable of enabling a temperature rate in the core of the specimen of 10 K/h. 5.2 Testing device for conducting UCTST 5.2.1 Dynamic testing device The dynamic testing device consists of a bending-resista

28、nt load frame with at least two supports, a temperature chamber, a hydraulic system and a control unit controlling force or displacement (see Figure 8). The test device shall be capable of applying a dynamic load of at least the applied test frequency with an accuracy of 0,1 Hz along the longitudina

29、l axis of a test specimen. The load shall be sinusoidal with or without a rest period. The test specimen is glued to adapters connected to the loading rod. Key 1 specimen 2 temperature chamber 3 load frame 4 load cell 5 measuring unit 6 clamp 7 displacement transducer 8 dummy with temperature sensor

30、 Figure 8 Example for a servo-hydraulic test device for UCTST at low temperatures 5.2.2 Monitoring system The test system shall be equipped with a system monitoring the load acting on the test specimen with a load cell that shall have a minimum measuring range of 15 kN with an accuracy of 10 N. The

31、displacement transducers shall have a minimum measuring range of 2,5 mm with an accuracy of 5 m. 5.2.3 Electronic signal amplifier The electronic signal emitted by the displacement and force transducer shall be amplified by means of a low-noise amplifier and recorded by analogue or digital devices w

32、ith an accuracy of 1 N for the force measured and of 1 m for the displacement measured. DIN EN 12697-46:2012-07 EN 12697-46:2012 (E) 12 5.2.4 Thermostatic chamber Thermostatic chamber, consisting of a cabinet with forced air circulation, in which the specimen can be condi-tioned and in which the tes

33、t can be performed. The temperature inside the enclosure shall be maintained at a constant temperature between 40 C and +40 C with an accuracy of 1 K. Suitable measures shall be taken to ensure that the specimen and chamber remain at the test temperature throughout the test. 5.2.5 Recording equipmen

34、t Recording equipment capable of continuously recording throughout a test the testing time, the force acting on the test specimen as measured by load cell, the displacement of the loading piston, the displacements of the two displacement transducers, the temperature of the test specimen, and the tem

35、perature of the thermostatic chamber. The rate at which data can be recorded shall be able to be selected in order to give comprehensive coverage. 6 Calibration 6.1 Testing device for conducting UTST, TSRST, relaxation test and tensile creep test 6.1.1 If the load frame or parts of the load frame as

36、 well as the measurement systems are subjected to temperature changes, the whole system shall be calibrated to ensure reproducibility and repeatability in addi-tion to the calibration of the load and deformation measurement systems. 6.1.2 The system shall be tested by conducting tests on a calibrati

37、on material of known material specifica-tions. Suitable materials are steel or aluminium. In order to load the equipment with comparable loads to those that occur during tests on asphalt, calibration beams with a smaller cross-section may be used. 6.2 Testing device for conducting UCTST 6.2.1 The se

38、rvo-hydraulic test device shall be calibrated at least once a year using a calibration block of known stiffness and thermal expansion coefficient. The stiffness calculated from the measured data shall not exceed a deviation of 3 %. 6.2.2 The calibration block is glued in and clamped in by the same m

39、ethod as a bituminous mixture speci-men. NOTE A suitable material for a calibration block is, for example, aluminium with an elastic modulus of about 72 GPa. 7 Specimen preparation 7.1 Number of samples At least three specimens shall be tested for each asphalt material and test condition (temperatur

40、e and level of stress) combination. 7.2 Dimensions 7.2.1 The specimen shall have the shape of a prismatic beam or of a cylinder with nominal dimensions according Table 1, depending on the nominal aggregate size of the asphalt mixture D. DIN EN 12697-46:2012-07 EN 12697-46:2012 (E) 13 Table 1 Dimensi

41、ons for prismatic and cylindrical specimens (mm) Specimen type Dimension Maximum aggregate size D (mm) D 11,2 11,2 D 22,4 D 22,4 Prismatic specimens with square cross-section Width and height, mm 40 2 50 2 60 2 Cylindrical specimens Diameter, mm 50 2 50 2 60 2 All specimens Minimum specimen length,

42、mm 160 160 160If the specimens are taken from courses whose thicknesses do not reach the required height, rectangular specimens with reduced height can be used for conducting the test. The specimen sizes shall be recorded in the test report. If the test device allows for specimens longer than 160 mm

43、, their length shall be four times the width/height or diameter. 7.2.2 The ends of the specimen shall be perpendicular to the axis of the specimen within 1. 7.3 Preparation 7.3.1 The specimens shall be obtained by sawing from slabs made in a laboratory according to EN 12697-33, or taken from road la

44、yers according to EN 12697-27. 7.3.2 The slabs made in the laboratory shall have at least a thickness of the required height (see Table 1). The specimens shall be sawn from the middle of the slab. The distance of the specimen to the border of the slab shall be at least 20 mm. 7.3.3 The longitudinal

45、axis of the asphalt specimen shall be orthogonal with the axis of loading during com-paction. 7.4 Bulk density The bulk density of each specimen shall be determined in accordance with EN 12697-6. NOTE The bulk density of asphalt mixtures with a required void content 7 % Vmax 10 % should be determine

46、d using Procedure B (SSD) or Procedure D (dimensions) according EN 12697-6:2012. 7.5 Drying After sawing, the test specimen shall be dried to a constant mass in air at a relative air humidity of less than 80 % and at a temperature between 15 C and 25 C. A specimen shall be considered dry when two we

47、ightings performed at intervals of 24 h differ by less than 0,25 %. 7.6 Storage The specimen shall be stored fully supported. The support on which the specimen rests shall be flat and clean. Specimens shall not be stacked on top of each other. Specimens shall be stored in a dry room at a temperature

48、 between 15 C and 25 C. NOTE The relative humidity in the storage room should not exceed 80 %. DIN EN 12697-46:2012-07 EN 12697-46:2012 (E) 14 7.7 Mounting The specimen shall be glued to two adapters with the specimen being adjusted centrally to the adapters with a mounting bench. NOTE The mounting bench is used to create a centric positive connection between the test specimen and the two connec