BS EN 12697-46:2012 BSI Standards Publication Bituminous mixtures — Test methods for hot mix asphalt Part 46: Low temperature cracking and properties by uniaxial tension tests BS EN 12697-46:2012 BRITISH STANDARD National foreword This British Standard is the UK implementation of EN 12697-46:2012 The UK participation in its preparation was entrusted to Technical Committee B/510/1, Asphalt products A list of organizations represented on this committee can be obtained on request to its secretary This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application © The British Standards Institution 2012 Published by BSI Standards Limited 2012 ISBN 978 580 75916 ICS 93.080.20 Compliance with a British Standard cannot confer immunity from legal obligations This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 May 2012 Amendments issued since publication Date Text affected BS EN 12697-46:2012 EN 12697-46 EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM May 2012 ICS 93.080.20 English Version Bituminous mixtures - Test methods for hot mix asphalt - Part 46: Low temperature cracking and properties by uniaxial tension tests Mélanges bitumineux - Essais pour mélange hydrocarboné chaud - Partie 46: Fissuration et propriétés basse température par des essais de traction uniaxiale Asphalt - Prüfverfahren für Heißasphalt - Teil 46: Widerstand gegen Kälterisse und Tieftemperaturverhalten bei einachsigen Zugversuchen This European Standard was approved by CEN on 23 March 2012 CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels © 2012 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members Ref No EN 12697-46:2012: E BS EN 12697-46:2012 EN 12697-46:2012 (E) Contents Page Foreword 1 Scope 2 Normative references 3 Terms and definitions 4 Principle 5 5.1 5.2 Apparatus .9 Testing device for conducting UTST, TSRST, RT and TCT .9 Testing device for conducting UCTST 11 6 6.1 6.2 Calibration 12 Testing device for conducting UTST, TSRST, relaxation test and tensile creep test 12 Testing device for conducting UCTST 12 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Specimen preparation 12 Number of samples 12 Dimensions 12 Preparation 13 Bulk density 13 Drying 13 Storage 13 Mounting 14 Installation and conditioning 14 8 8.1 8.2 8.3 8.4 8.5 Procedure 15 Uniaxial tension stress test (UTST) 15 Thermal stress restrained specimen test (TSRST) 15 Relaxation test (RT) 15 Tensile creep test (TCT) 16 Uniaxial cyclic tensile stress test (UCTST) 16 9 9.1 9.2 Evaluation 17 Tension strength reserve 17 Uniaxial cyclic tensile stress test (UCTST) 18 10 10.1 10.2 10.3 10.4 Test report 19 General 19 Information on specimen 20 Information on test method 20 Information on the test and results 20 11 Precision 21 Bibliography 23 BS EN 12697-46:2012 EN 12697-46:2012 (E) Foreword This document (EN 12697-46:2012) has been prepared by Technical Committee CEN/TC 227 “Road materials”, the secretariat of which is held by DIN This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by November 2012, and conflicting national standards shall be withdrawn at the latest by November 2012 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights This document is one of a series of standards for bituminous mixtures which includes the following: EN 12697-1, Bituminous mixtures — Test methods for hot mix asphalt — Part 1: Soluble binder content EN 12697-2, Bituminous mixtures — Test methods for hot mix asphalt — Part 2: Determination of particle size distribution EN 12697-3, Bituminous mixtures — Test methods for hot mix asphalt — Part 3: Binder recovery: Rotary evaporator EN 12697-4, Bituminous mixtures — Test methods for hot mix asphalt — Part 4: Binder recovery: Fractionating column EN 12697-5, Bituminous mixtures — Test methods for hot mix asphalt — Part 5: Determination of the maximum density EN 12697-6, Bituminous mixtures — Test methods for hot mix asphalt — Part 6: Determination of bulk density of bituminous specimens EN 12697-7, Bituminous mixtures — Test methods for hot mix asphalt — Part 7: Determination of bulk density of bituminous specimens by gamma rays EN 12697-8, Bituminous mixtures — Test methods for hot mix asphalt — Part 8: Determination of void characteristics of bituminous specimens EN 12697-9, Bituminous mixtures — Test methods for hot mix asphalt — Part 9: Determination of the reference density EN 12697-10, Bituminous mixtures — Test methods for hot mix asphalt — Part 10: Compactibility EN 12697-11, Bituminous mixtures — Test methods for hot mix asphalt — Part 11: Determination of the affinity between aggregates and binders EN 12697-12, Bituminous mixtures — Test methods for hot mix asphalt — Part 12: Determination of the water sensitivity of specimen EN 12697-13, Bituminous mixtures — Test methods for hot mix asphalt — Part 13: Temperature measurement EN 12697-14, Bituminous mixtures — Test methods for hot mix asphalt — Part 14: Water content BS EN 12697-46:2012 EN 12697-46:2012 (E) EN 12697-15, Bituminous mixtures — Test methods for hot mix asphalt — Part 15: Determination of the segregation sensitivity EN 12697-16, Bituminous mixtures — Test methods for hot mix asphalt — Part 16: Abrasion by studded tyres EN 12697-17, Bituminous mixtures — Test methods for hot mix asphalt — Part 17: Particle loss of porous asphalt specimen EN 12697-18, Bituminous mixtures — Test methods for hot mix asphalt — Part 18: Binder drainage EN 12697-19, Bituminous mixtures — Test methods for hot mix asphalt — Part 19: Permeability of specimen EN 12697-20, Bituminous mixtures — Test methods for hot mix asphalt — Part 20: Indentation using cube or Marshall specimen EN 12697-21, Bituminous mixtures — Test methods for hot mix asphalt — Part 21: Indentation using plate specimen EN 12697-22, Bituminous mixtures — Test methods for hot mix asphalt — Part 22: Wheel tracking test EN 12697-23, Bituminous mixtures — Test methods for hot mix asphalt — Part 23: Indirect tensile test EN 12697-24, Bituminous mixtures — Test methods for hot mix asphalt — Part 24: Resistance to fatigue EN 12697-25, Bituminous mixtures — Test methods for hot mix asphalt — Part 25: Cyclic compression test EN 12697-26, Bituminous mixtures — Test methods for hot mix asphalt — Part 26: Stiffness EN 12697-27, Bituminous mixtures — Test methods for hot mix asphalt — Part 27: Sampling EN 12697-28, Bituminous mixtures — Test methods for hot mix asphalt — Part 28: Preparation of samples for determining binder content, water content and grading EN 12697-29, Bituminous mixtures — Test methods for hot mix asphalt — Part 29: Determination of the dimensions of bituminous specimen EN 12697-30, Bituminous mixtures — Test methods for hot mix asphalt — Part 30: Preparation of specimen by impact compactor EN 12697-31, Bituminous mixtures — Test methods for hot mix asphalt — Part 31: Specimen preparation, gyratory compactor EN 12697-32, Bituminous mixtures — Test methods for hot mix asphalt — Part 32: Laboratory compaction of bituminous mixtures by a vibratory compactor EN 12697-33, Bituminous mixtures — Test methods for hot mix asphalt — Part 33: Specimen prepared by roller compactor EN 12697-34, Bituminous mixtures — Test methods for hot mix asphalt — Part 34: Marshall test EN 12697-35, Bituminous mixtures — Test methods for hot mix asphalt — Part 35: Laboratory mixing EN 12697-36, Bituminous mixtures — Test methods for hot mix asphalt — Part 36: Method for the determination of the thickness of a bituminous pavement EN 12697-37, Bituminous mixtures — Test methods for hot mix asphalt — Part 37: Hot sand test for the adhesivity of binder on precoated chippings for HRA BS EN 12697-46:2012 EN 12697-46:2012 (E) EN 12697-38, Bituminous mixtures — Test methods for hot mix asphalt — Part 38: Common equipment and calibration EN 12697-39, Bituminous mixtures — Test methods for hot mix asphalt — Part 39: Binder content by ignition EN 12697-40, Bituminous mixtures — Test methods for hot mix asphalt — Part 40: In-situ drainability EN 12697-41, Bituminous mixtures — Test methods for hot mix asphalt — Part 41: Resistance to de-icing fluids EN 12697-42, Bituminous mixtures — Test methods for hot mix asphalt — Part 42: Amount of coarse foreign matters in reclaimed asphalt EN 12697-43, Bituminous mixtures — Test methods for hot mix asphalt — Part 43: Resistance to fuel EN 12697-44, Bituminous mixtures — Test methods for hot mix asphalt — Part 44: Crack propagation by semi-circular bending test EN 12697-45, Bituminous mixtures — Test methods for hot mix asphalt — Part 45: Saturation Ageing Tensile Stiffness (SATS) conditioning test EN 12697-46, Bituminous mixtures — Test methods for hot mix asphalt — Part 46: Low temperature cracking and properties by uniaxial tension tests EN 12697-47, Bituminous mixtures — Test methods for hot mix asphalt — Part 47: Determination of the ash content of natural asphalts prEN 12697-48 ), Bituminous mixtures — Test methods for hot mix asphalt — Part 48: Inter-layer bond strength prEN 12697-49, Bituminous mixtures — Test methods for hot mix asphalt — Part 49: Skid resistance of asphalt in the laboratory 1) prEN 12697-50 , Bituminous mixtures — Test methods for hot mix asphalt — Part 50: Scuffing resistance of surface course asphalt According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom 1) In preparation BS EN 12697-46:2012 EN 12697-46:2012 (E) Scope This European Standard specifies uniaxial tension tests for characterising the resistance of an asphalt mixture against low temperature cracking The results of the uniaxial tension tests can be used to evaluate the following: tensile strength at a specified temperature, using the uniaxial tension stress test (UTST); minimum temperature that the asphalt can resist before failure, using the 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 at low temperatures due to the combination of cryogenic and mechanical loads, using the uniaxial cyclic tension stress tests (UCTST) Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application For dated 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, Bituminous 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 Terms and definitions For the purposes of this document, the following terms and definitions apply 3.1 tensile strength βt maximum tensile stress measured in a tensile stress test 3.2 tensile failure strain εfailure tensile strain that is measured when the tensile strength has been reached 3.3 cryogenic stress σcry(T) tension stress, induced by prohibited thermal shrinkage, at the temperature T 3.4 failure stress σcry, failure cryogenic stress that causes a failure of the specimen in the thermal stress restrained specimen test (TSRST) BS EN 12697-46:2012 EN 12697-46:2012 (E) 3.5 failure temperature Tfailure temperature at which the cryogenic stress causes a failure of the specimen in the thermal stress restrained specimen test (TSRST) 3.6 tensile strength reserve ∆βt difference between the tensile strength and the cryogenic stress at the same temperature T where ∆β t (T ) = β t (T ) − σ cry (T ) 3.7 time of relaxation trel time until the stress decreases to 36,8 % (1/e) of its initial value 3.8 remaining tension stress σrem(t) remaining stress after the time t in the relaxation test 3.9 initial complex modulus E*0 complex modulus after 100 load cycles, calculated according to EN 12697-26 3.10 conventional failure criterion Nf/50 number of load cycles reducing the complex modulus E* to half of its initial value E*0 (fatigue criterion) 3.11 additional failure criterion Nfailure number of load cycles leading to the development of a visible and recognisable crack in the asphalt specimen (fracture criterion) Principle The low-temperature performance of asphalt specimens can be tested using different test methods: In the 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) β t(T) and the corresponding tensile failure strain ε failure(T) at the test temperature T (see Figure 1) In the thermal 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 stress over the temperature σcry(T) and the failure stress σcry, failure at the failure temperature Tfailure (see Figure 2) In the the tensile creep test (TCT), the specimen is subjected to a constant tension stress σ at a constant temperature T The progression of the strain ε is measured After a given time, 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 ε, which is held on a constant level The decrease of tension stress by relaxation over the testing time is monitored The results are the time of relaxation trel and the remaining tension stress σrem after the test has ended (see Figure 3) BS EN 12697-46:2012 EN 12697-46:2012 (E) In the uniaxial cyclic tension stress test (UCTST), 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 the stiffness is recorded until fatigue failure Results of the tests are the number of applied load cycles until failure Nfailure and the number of load cycles until the conventional fatigue criterion is reached Nf/50 (see Figure 5) Figure — Test principle of UTST Figure — Test principle of TSRST Figure — Test principle of RT Figure — Test principle of TCT Figure — Test principle of UCTST Key for Figures to Y1 X Y2 Y3 strain time temperature stress BS EN 12697-46:2012 EN 12697-46:2012 (E) 5.2.4 Thermostatic chamber Thermostatic chamber, consisting of a cabinet 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 temperature between −40 °C and +40 °C with an accuracy of ± 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 equipment 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 temperature of the thermostatic chamber The rate at which data can be recorded shall be able to be selected in order to give comprehensive coverage 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 well as the measurement systems are subjected to temperature changes, the whole system shall be calibrated to ensure reproducibility and repeatability in addition to the calibration of the load and deformation measurement systems 6.1.2 The system shall be tested by conducting tests on a calibration material of known material specifications 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 servo-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 ± % 6.2.2 men NOTE 7.1 The calibration block is glued in and clamped in by the same method as a bituminous mixture speciA suitable material for a calibration block is, for example, aluminium with an elastic modulus of about 72 GPa Specimen preparation Number of samples At least three specimens shall be tested for each asphalt material and test condition (temperature 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 12 BS EN 12697-46:2012 EN 12697-46:2012 (E) Table — Dimensions 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 crosssection Width and height, mm 40 ± 50 ± 60 ± Cylindrical specimens Diameter, mm 50 ± 50 ± 60 ± All specimens Minimum specimen length, mm 160 160 160 If the specimens are taken from courses whose thicknesses 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, their length shall be four times the width/height or diameter 7.2.2 7.3 The ends of the specimen shall be perpendicular to the axis of the specimen within ± 1º Preparation 7.3.1 The specimens shall be obtained by sawing from slabs made in a laboratory according to EN 1269733, or taken from road layers 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 axis of the asphalt specimen shall be orthogonal with the axis of loading during compaction 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 % < Vmax < 10 % should be determined 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 weightings 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 between 15 °C and 25 °C NOTE The relative humidity in the storage room should not exceed 80 % 13 BS EN 12697-46:2012 EN 12697-46:2012 (E) 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 connectors (adapters) used to clamp the test specimen into the testing device (as shown in Figures and 10) Key adapter specimen height adjustable support spindle bottom part Figure — Example for a mounting bench for specimen preparation Key adapter specimen height adjustable support spindle bottom part Figure 10 — Example for a mounting bench for the preparation of cylindrical specimens 7.8 Installation and conditioning 7.8.1 The specimen shall be installed into the test device by joining the adapters with the load device Before the test starts, the specimen shall be stabilised to the test temperature T (or, in case of the TSRST, the start temperature T0) for an adequate duration without applying any load During the conditioning phase, the closed-loop control of the test device shall ensure that the specimen is not subjected to any loads The thermal strain shall be balanced 14 BS EN 12697-46:2012 EN 12697-46:2012 (E) 7.8.2 The duration of conditioning phase shall depend on the specimen size and the material tested The temperature in the specimen shall be constant within ± °C of the test temperature for not less than 10 NOTE 8.1 The temperature in the specimen can be measured using a dummy specimen placed close to the specimen Procedure Uniaxial tension stress test (UTST) 8.1.1 At the constant test temperature, the specimen shall be subjected to a time-dependent strain based on the initial length The constant strain rate shall be dε = (0,625 ± 0,025) %/min NOTE The temperatures of + 20 °C, + °C, − 10 °C and − 25 °C are recommended NOTE The strain rate for test specimens with a length of 160 mm corresponds to a tension rate of mm/min 8.1.2 Results of the UTST shall be the tensile strength and the failure strain at the test temperature The tensile strength βt (MPa) is calculated by dividing the measured tension force at failure by the initial crosssection area of the specimen The failure strain εfailure is calculated by the measured strain at the failure time divided by the initial length of the specimen 8.2 Thermal stress restrained specimen test (TSRST) 8.2.1 In the TSRST, the specimen shall be held at a constant length while its temperature is decreased with time Because of the prohibited thermal shrinkage, the specimen is subjected to a (cryogenic) tension stress NOTE It is recommended to start the test at a temperature of T0 = + 20 °C and to change the temperature at a rate of dT = − 10 K/h NOTE The core temperature of the specimen shows a time lag with the air temperature in the test chamber In order to register the correct specimen temperature, it is necessary to measure the temperature in an additional specimen during the test or determine the temperature lag between air temperature and specimen temperature in advance 8.2.2 The temperature-dependent cryogenic stress σcry(T), the failure stress σcry, failure and the failure temperature Tfailure shall be recorded 8.3 Relaxation test (RT) 8.3.1 The specimen shall be subjected spontaneously to a strain, which is held on a constant level for the test The induced tension stress shall be recorded during the test NOTE The relaxation property depends on the temperature and the initial stress Thus, in order to compare tests, it is recommended to always use the same proportion of the tensile strength for introducing the test strain Higher initial stresses will reduce the relaxation times The initial stress should not be greater than 75 % of the tensile strength βt Recommended test temperatures are + 20 °C, + °C, − 10 °C and − 25 °C 8.3.2 Record the relaxation time and the remaining stress at the end of the test The relaxation time is the time when the stress is reduced to (36,8 ± 0,1) % (1 / e = / 2,718 = 0,368) of its initial value NOTE Because the relaxation test can take a long time, especially at low temperatures, it is recommended to stop the test after a suitable duration, e.g 48 h In such cases, the remaining tensile stress at the end of the test should be recorded 15 BS EN 12697-46:2012 EN 12697-46:2012 (E) 8.4 Tensile creep test (TCT) 8.4.1 The specimen shall be loaded spontaneously by a constant stress at a constant temperature The progression of the strain shall be monitored After a given period of time, the specimen shall be unloaded and the regression of the strain shall be measured NOTE It is recommended to hold the constant load for duration of h and record the regression after unloading for additional h NOTE βt(T) Table gives the suggested test temperatures and suitable stress levels as a proportion of the tensile strength Table — Recommended test conditions for the tensile creep test Temperature T °C Proportion of βt(T) % + 20 +5 10 − 10 30 − 25 50 8.4.2 The strain shall be plotted with the time The measured valued shall then be fitted with a rheological model to obtain the rheological material parameters (e.g for the Burgers-Model: elastic, viscous, visco-elastic and visco-plastic parameters) 8.5 8.5.1 Uniaxial cyclic tensile stress test (UCTST) Test temperature and test frequency The UCTST shall be carried out at one or more test temperatures T and testing frequencies fr NOTE 8.5.2 It is recommended to use a testing frequency of fr = 15 Hz and a test temperature of T = - 15 °C Base stress The base stress at test temperature T shall be derived from the TSRST, where the base stress corresponds to the cryogenic tensile stress σcry(T) at test temperature T The base stress shall be set with an accuracy of ± 0,01 MPa 8.5.3 Peak stress 8.5.3.1 The maximum stress σtot shall be the sum of the base stress σcry(T) and the stress caused by the traffic load ∆σ NOTE The traffic load stress is defined as a factor of the expected traffic load (axle load), taking the maximum tensile stress fmax at test temperature Tf,max derived from the UTST into account It is recommended to derive the traffic load stress ∆σ analytically, using a linear elastic model as a factor of traffic load as well as of the stiffness and thermal material properties of the pavement layers and their composition For comparing surface course asphalts, a traffic stress of ∆σ = 1,6 MPa has been found to be appropriate 8.5.3.2 The maximum stress shall be set with an accuracy of ± 0,01 MPa The peak stress at test temperature T shall be obtained from Formula (1) The resulting value for the peak stress shall be given with an accuracy of ± 0,01 MPa 16 BS EN 12697-46:2012 EN 12697-46:2012 (E) σ tot = σ cry (T ) + ∆σ (1) where σtot is the peak stress; σcry(T) is the base stress; ∆σ is the traffic load stress 8.5.3.3 After the test specimen has been installed, it shall be cooled to the test temperature of ± 0,5 °C without inducing any vertical load (± 20 N) The test specimen shall then be subjected to a tensile load increasing at a rate of (2 000 ± 50) N/s up to the level of base stress σcry(T), as illustrated in Figure 11 8.5.3.4 The duration of the conditioning phase shall depend on the specimen size and the material tested The temperature in the specimen shall be constant within ± °C of the test temperature for not less than 10 8.5.3.5 As soon as the base stress has been reached, the test specimen shall be exposed to a constant cyclic tensile load at the test frequency fr, the amplitude of which shall be defined by the base stress σcry(T) and the peak stress σtot, until failure occurs (see Figure 11) 8.5.3.6 During the test, the load and the displacements shall be recorded for at least 15 measurements per load cycle in order to enable the signal to be interpreted 8.5.3.7 The test shall be carried out on a minimum of three test specimens for each material and condition to be tested Key σ ∆σ stress due to traffic load in MPa σkry (T) lower stress level in MPa tensile stress in MPa time in s σtot upper stress level in MPa t Figure 11 — Sinusoidal loading for the UCTST 9.1 Evaluation Tension strength reserve 9.1.1 The presence of thermal tensile stresses reduces the capacity for mechanical induced tensile stresses In order to calculate and visualize the tension strength reserve, the results of UTST at not less than four test temperatures shall be plotted in a temperature/tensile strength diagram A cubic spline function shall be used to link the measured tensile strength values 17 BS EN 12697-46:2012 EN 12697-46:2012 (E) NOTE If the recommended test temperatures + 20 °C, + °C, − 10 °C and − 25 °C are used, the values below − 25 °C and above + 20 °C can be drawn by calculating further tensile strengths: βt(T = − 40 °C) = 0,9 x βt(T = − 25 °C); βt(T = + 30 °C) = 0,5 x βt(T = + 20 °C) 9.1.2 The course of cryogenic stress measured in the TSRST shall be plotted on the same temperature/stress diagram 9.1.3 The tensile strength reserve, ∆βt(T), shall be calculated as the difference between the tensile strength, βt(T), and the cryogenic stress, σcry(T), at the same temperature T using Formula (2) Figure 12 gives an example for evaluating the tensile strength reserve from the results of the UTST and the TSRST ∆β t (T ) = β t (T ) − σ cry (T ) (2) Key σ T tensile stress in MPa temperature in °C tensile strength βt, (T) tensile strength reserve ∆βt, (T) cryogenic stress σcry (T) Figure 12 — Principle of evaluating the tensile strength reserve from the test graphs of the UTST and the TSRST in the temperature-stress diagram 9.2 Uniaxial cyclic tensile stress test (UCTST) The complex modulus E* shall be calculated at constant intervals of load applications as follows: 9.2.1 Smix = E * = (3) F E1 = ì × cos(φ ) + × ω z 10 (4) F E2 = γ × × sin(φ ) z (5) where 18 E12 + E22 BS EN 12697-46:2012 EN 12697-46:2012 (E) F is the force amplitude (N); z is the displacement amplitude (mm); ω is the angular frequency (rad/s), where ω = x π x fr at frequency fr; γ is the form factor, where γ = H/A with specimen height H and cross-sectional area of specimen A; µ is the mass factor, where µ = M/2 + m with mass of specimen M (g) and mass m (g) of movable parts having an impact on the resulting force on account of their inertia effects 9.2.2 The cumulated strains and the change in the stiffness modulus shall be plotted in a diagram as a function against the loads applied (see Figure 13) Key stiffness modulus cumulated strain Figure 13 — Example of graphic representation of UCTST result 9.2.3 The initial complex stiffness modulus E*0 after N = 100 load applications shall be indicated 9.2.4 The result of the test shall be the number of load applications at the onset of the conventional or additional failure criterion (i.e Nf/50 and Nfailure) 10 Test report With reference to this European Standard, the test report shall include the following information: 10.1 General a) Name and address of the testing laboratory; b) a unique serial number for the test report; c) name of client; d) the number and date of this European Standard; 19 BS EN 12697-46:2012 EN 12697-46:2012 (E) e) signature of person accepting technical responsibility for the test report; f) date of issue 10.2 Information on specimen a) Type and origin of bituminous mixture; b) method of manufacture of the bituminous mixture; c) method of compaction; d) specimen identification; e) bulk density of the specimen prior to testing, and the method used for its determination; f) dimensions of the specimen 10.3 Information on test method a) Test method; b) testing equipment 10.4 Information on the test and results 10.4.1 Uniaxial tension stress test (UTST) a) Temperature at which the test was carried out T (°C); b) applied deformation rate dε (%/min); c) tensile strength βt (MPa); d) failure strain εfailure (‰) 10.4.2 Thermal stress restrained specimen test (TSRST) a) Start temperature T0 (°C); b) temperature rate dT (K/h); c) failure stress σcry, failure (MPa); d) failure temperature Tfailure (°C); e) plot of the cryogenic stress against temperature T 10.4.3 Tension strength reserve a) Temperature of the maximum tensile strength reserve T∆β, max; b) maximum value of the tensile strength reserve ∆βt, max 20 BS EN 12697-46:2012 EN 12697-46:2012 (E) 10.4.4 Relaxation test (RT) a) Test temperature T (°C); b) initial stress (MPa or % of the tensile strength at the test temperature); c) relaxation time (s); d) time at which the test is stopped (s); e) remaining stress at the end of the test (MPa); f) plot of the stress over the time (optional) 10.4.5 Tensile creep test (TCT) a) Test temperature T (°C); b) duration of loading and unloading (h); c) stress (MPa or % of the tensile strength at the test temperature); d) plot of the strain over the time; e) rheological model and fitting parameters (optional) 10.4.6 Uniaxial cyclic tensile stress test (UCTST) a) Test temperature T (°C); b) test frequency fr (Hz); c) type of periodic loading (e.g sinusoidal); d) base stress σcry (T) (MPa); e) peak stress σtot (MPa); f) initial complex stiffness modulus and phase angle; g) type of failure criterion (fatigue or fracture); h) number of load applications to failure criterion (Nf/50 or Nfailure); i) stiffness modulus as a function of number of load cycles; j) cumulative strain as a function of number of load cycles 11 Precision No repeatability or reproducibility has been evaluated to date However, based on the experiences of German laboratories, the following repeatability limits can be estimated until an international round-robin of tests have been conducted: a) Results of the tensile strength derived from UTST on three duplicates by the same operator shall be considered suspect if they differ by more than: 21 BS EN 12697-46:2012 EN 12697-46:2012 (E) 1) − 25 °C: 0,7 MPa; 2) − 10 °C: 0,7 MPa; 3) + °C: 0,3 MPa; 4) + 20 °C: 0,1 MPa b) Results of the failure temperature derived from TSRST on three duplicates by the same operator shall be considered suspect if they differ by more than °C c) Results of the failure stress derived from TSRST on three duplicates by the same operator shall be considered suspect if they differ by more than 0,5 MPa NOTE 22 The precision highly depends on the range of void contents of the samples of the analysed mixture BS EN 12697-46:2012 EN 12697-46:2012 (E) Bibliography [1] EN 12697-26, Bituminous mixtures — Test methods for hot mix asphalt — Part 26: Stiffness 23 This page deliberately 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