1、Standard Method of Test for Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT) AASHTO Designation: T 314-121American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001TS-2b T 314-1 AASHTO Standard Method
2、 of Test for Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT) AASHTO Designation: T 314-1211. SCOPE 1.1. This test method covers the determination of the failure strain and failure stress of asphalt binders by means of a direct tension test. It can be used with unaged or
3、aged material using T 240 (RTFOT) or R 28 (PAV), or both. The test apparatus is designed for testing within the temperature range from +6 to 36C. 1.2. This test method is limited to asphalt binders containing particulate material having dimensions less than 250 m. 1.3. This test method is not valid
4、for specimens exhibiting a failure strain of greater than 10 percent considered outside the brittle-ductile range. 1.4. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the re
5、sponsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 320, Performance-Graded Asphalt Binder R 28, Accelerated Aging of Asphalt Binder
6、 Using a Pressurized Aging Vessel (PAV) R 49, Determination of Low-Temperature Performance Grade (PG) of Asphalt Binders R 66, Sampling Asphalt Materials T 240, Effect of Heat and Air on a Moving Film of Asphalt Binder (Rolling Thin-Film Oven Test) 2.2. ASTM Standards: C670, Standard Practice for Pr
7、eparing Precision and Bias Statements for Test Methods for Construction Materials E1, Standard Specification for ASTM Liquid-in-Glass Thermometers E4, Standard Practices for Force Verification of Testing Machines E77, Standard Test Method for Inspection and Verification of Thermometers E83, Standard
8、 Practice for Verification and Classification of Extensometer Systems 2.3. ISO Standard: ISO 10012, Measurement Management SystemsRequirements for Measurement Processes and Measuring Equipment 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplica
9、tion is a violation of applicable law.TS-2b T 314-2 AASHTO 3. TERMINOLOGY 3.1. Definitions: 3.1.1. asphalt binderan asphalt-based cement that is produced from petroleum residue either with or without the addition of particulate organic modifiers of size less than 250 m. 3.2. Description of Terms Spe
10、cific to This Standard: 3.2.1. brittletype of failure in a direct tension test where the stressstrain curve is essentially linear up to the point of failure and the failure is by sudden rupture of the test specimen without appreciable reduction in cross section of the specimen. 3.2.2. brittle-ductil
11、etype of failure in a direct tension test where the stress-strain curve is curvilinear and the failure is by sudden rupture of the test specimen. Limited reduction in cross-section of the specimen occurs before rupture. 3.2.3. ductiletype of failure in a direct tension test where the specimen does n
12、ot rupture but fails by flow at large strains. 3.2.4. tensile strainaxial strain resulting from the application of a tensile load and calculated as the change in length of the effective gauge length caused by the application of the tensile load divided by the original unloaded effective gauge length
13、. 3.2.5. tensile stressaxial stress resulting from the application of a tensile load and calculated as the tensile load divided by the original area of cross-section of the specimen. 3.2.6. failurepoint at which the tensile load reaches a maximum value as the test specimen is pulled at a constant ra
14、te of elongation. 3.2.7. failure stressthe tensile stress on the test specimen when the load reaches a maximum value during the test method specified in this standard. 3.2.8. failure strainthe tensile strain corresponding to the failure stress. 3.2.9. gauge sectionthe central portion of the specimen
15、 where the cross-section does not change with length. For this geometry, the gauge section is 18 mm in length (see Figure 1). 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b T 314-3 AASHTO Figure 1
16、Superpave Direct Tension Specimen Geometry 3.2.10. effective gauge lengthfor specimens used in this test, the effective gauge length, Le, has been determined to be 33.8 mm. This is an effective gauge length that represents the portion of the specimen that contributes to the majority of the strain. 4
17、. SUMMARY OF TEST METHOD 4.1. This method describes the procedure used to measure the stress at failure and strain at failure in an asphalt binder test specimen pulled at a constant rate of elongation. Test specimens are prepared by pouring hot asphalt binder into a suitable mold. Two G10 phenolic e
18、nd tabs are used to bond the asphalt binder during the test and to transfer the tensile load from the test machine to the asphalt binder. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b T 314-4 AAS
19、HTO 4.2. This test method was developed for asphalt binders at temperatures where they exhibit brittle or brittle-ductile failure. A brittle or brittle-ductile failure will result in a fracture of the test specimen as opposed to a ductile failure in which the specimen simply stretches without fractu
20、ring. The test is not applicable at temperatures where failure is by ductile flow. 4.3. A displacement transducer is used to measure the elongation of the test specimen as it is pulled in tension at a constant rate of 1 mm/min. The load developed during the test is monitored and the tensile strain a
21、nd stress in the test specimen when the load reaches a maximum are reported as the failure strain and failure stress, respectively. 5. SIGNIFICANCE AND USE 5.1. Stress at failure is used in a mechanistic pavement cracking model to compute critical cracking temperature. The procedure to compute criti
22、cal cracking temperature is described in AASHTO R 49. The critical cracking temperature is then used in specifying the low-temperature grade of asphalt binder in accordance with M 320. 5.2. The test is designed to measure the strength of the asphalt binder at the critical cracking temperature. The a
23、sphalt binder has limited ability to resist stress without cracking. In the asphalt binder specification failure, stress is used to determine the critical cracking temperature. 5.3. For evaluating an asphalt binder for conformance to M 320, the elongation rate of the gauge section is 1.0 mm/min and
24、the test temperature is selected from Table 1 of M 320 according to the grade of asphalt binder. Other rates of elongation and test temperatures may be used to test asphalt binders. 6. APPARATUS 6.1. Direct Tension Test SystemA direct tension test system consisting of (1) a closed feedback loop disp
25、lacement-controlled tensile loading machine; (2) a specimen gripping system; (3) either a fluid bath or an insulated chamber for reliable, accurate, and uniform temperature control during testing and conditioning of specimen; (4) real-time load measuring and recording devices; (5) real-time elongati
26、on measuring and recording devices; (6) a real-time temperature detection and recording device; and (7) real-time data acquisition and display devices. The system shall have an electromechanical or a servohydraulic loading unit capable of applying and measuring tension and compression forces of at l
27、east 500 N and actuator travel of 20 mm (0.78 in.). The system stiffness shall be at least 3 mN/m including the load cell and the loading pins. The unit shall have a transducer to measure and control grip separation and provide a feedback for strain control with a displacement resolution of 1.0 m. T
28、he system shall be capable of closed-loop elongation rate control accurate to at least 1 percent of the commanded specimen elongation rate using feedback from a displacement transducer mounted between the loading pins or a noncontact extensometer measuring the elongation of the specimen. 6.1.1. Tens
29、ile Loading Machine Equipped with Temperature ControlA tensile loading machine with a controlled-displacement loading frame capable of producing at least a 500-N load is required. The loading frame shall be table mounted. The gripping system (loading pins and platens) shall be completely submerged u
30、nder the cooling fluid if a fluid-based system is used. The gripping system shall be a minimum of 25 mm (1 in.) under the cooling fluid surface. Loading shall be accomplished by pulling directly in tension in the plane of the specimen. The distance between the load frames loading points (between loa
31、ding pins) shall accommodate specimens with total length (including the end tabs) of at least 100 mm (see Figure 1). If an air-cooled system is used, the testing frame shall be equipped with two standards (columns) with sufficient clear space between the standards so that an insulated temperature co
32、ntrol chamber can be placed between the standards. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b T 314-5 AASHTO 6.1.2. Specimen Gripping SystemThe gripping system must produce a self-aligning uni
33、axial test load and accept the end tabs described in Section 6.1.2.1 and be designed so that test specimens can be easily mounted in the machine. The system shall include two grips. Each grip shall include a specially shaped pin that is mounted rigidly to the loading platens of the testing machine.
34、Figure 2 shows a typical grip and loading pin assembly. One grip shall be fixed and remain stationary during the test while the other grip is displaced at the desired elongation rate. Figure 2Loading Pin and Grip Assembly for the Superpave Direct Tension Test 6.1.2.1. Specimen End TabsEnd tabs made
35、from G10 phenolic sheets having the dimensions specified in Figures 3, 4, and 5 shall be bonded to both ends of the test specimen to transfer the tensile load to the asphalt binder. The end tabs shall be machined from a standard G10 phenolic sheet. Each end tab shall contain a precisely machined hol
36、e lined with a 304 stainless steel ring. The diameter of the lined hole shall be 10 0.05 mm. Gripping of the specimen is accomplished through the bond (adhesion) between the asphalt binder test specimen and the end tab. Each end tab shall be mounted on a specially shaped pin that is part of the grip
37、ping system. The specimen shall be mounted on the grips by positioning the end tabs in the test machine such that the end tabs fit onto the pins and are indexed against the face of the grips. Matching the coefficient of thermal expansion of the asphalt binder and the end tabs is necessary to reduce
38、thermal shrinkage stresses at the interface that otherwise cause bond failures. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b T 314-6 AASHTO Figure 3Superpave End Insert for Direct Tension Test (
39、See Figure 4 for the Metal Ring Dimensions to Be Press Fitted into This End Insert.) Notes: 1. All dimensions are in millimeters.2. Tolerances are as follows: Fractions 1.6X.X 0.6X.XX 0.25X.XXX 0.12Angles 303. Remove all sharp edges.4. Surface finish for machined surfaces: unless otherwise specified
40、.5. Material: G10 phenolic.6. Also see Metal Ring and Assembly Drawings.12530.010.010.020.0N7 Typ.12.67512.6256.0 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b T 314-7 AASHTO Figure 4Superpave En
41、d Insert Metal Ring for Direct Tension Test (See Figure 3 for Dimensions of the Insert to Be Press Fitted with This Ring.) Figure 5Superpave End Insert for Direct Tension Test (See Figures 3 and 4.) Notes: 1. All dimensions are in millimeters.2. Tolerances are as follows: Fractions 1.6X.X 0.8X.XX 0.
42、25X.XXX 0.12Angles 303. Remove all sharp edges.4. Surface finish for machined surfaces: unless otherwise specified.5. Material: Stainless Steel Type 316 or 304.May be made from 0.25 in. schedule 40 seamless pipe.125N7N512.70012.72510.059.95Press Fit Ring into hole such that ring is flush or slightly
43、 below surfaceon either side.21 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b T 314-8 AASHTO 6.1.3. Test Chamber for Temperature Control and TestingThe temperature control chamber shall have suff
44、icient space for storing at least 12 specimens. The temperature control range for the cooling chamber, without asphalt binder specimens, at all points within the bath, shall be from +6 to 36C with temperature stability as a minimum of 0.1C. Placing a room temperature specimen in the cold chamber is
45、allowed to cause the chamber temperature between the grips to fluctuate 0.2C from the target test temperature during testing and isothermal conditioning of the specimen. However, during testing the temperature gradient between the grips shall not exceed 0.1C. The temperature measurement shall be acc
46、omplished with a calibrated Platinum Resistance Temperature Detector (PRTD) located in the chamber in proximity of test area (NIST Traceable, calibrated at eight temperatures in the range of +6 to 36C). If an air-based cooling system is used, mechanical cooling or liquid nitrogen may be used to cool
47、 the chamber. It shall have a dehumidifying system with a capacity such that the formation of frost on the interior of the chamber, the test specimen, or any of the test fixtures is eliminated. The chamber shall be capable of storing a minimum of 12 test specimens on a rack that is thermally isolate
48、d from the walls and floors of the chamber such that heat conducted from the walls and floors of the chamber does not affect the temperature of the stored specimens. If an air-based cooling system is used, the chamber shall be fitted with a front-opening door for maintenance and standardization purp
49、oses and an access port that allows for insertion of the operators hand and forearm to position test specimens on the storage shelf for conditioning and to position test specimens on the grips for testing. The access port shall be designed so that changes in chamber temperature are 0.2C during an operation in which the operators hand or forearm is inserted into or removed from the chamber. Visual access to the interior of the test chamber shall be provided to permit prope
