SH/T 0776-2005 Determination of Fracture Properties of Asphalt (DT Method)

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Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: SH/T 0776—2005
• Chinese full name: Determination of Fracture Properties of Asphalt (DT Method)
• English name: Standard test method for determining the fracture properties of asphalt binder in direct tension (DT)
• Replacement relationship: This standard is first published (not provided in the available source regarding replacement of other standards)
• Adoption relationship: Modified adoption of ASTM D 6723-02 "Standard Test Method for Determining Fracture Properties of Asphalt by Direct Tension (DT)" (English version), redrafted according to ASTM D 6723-02
• Publication/implementation: published on 2005-11-28, implemented on 2006-06-01
• Issuing authority: National Development and Reform Commission of the People's Republic of China
• Technical custodian: Technical custodian by the Heavy Oil Research Institute of China University of Petroleum (East China)
• Drafting organization: Heavy Oil Research Institute of China University of Petroleum (East China)
• Main drafters: Zhang Yonghe, Zhang Xiaoying, Kong Xianming, Zhang Yuzhen

2. Scope of application and non-applicability

• 1.1 specifies the method for determining the failure strain and failure stress of asphalt by direct tension test. It can be used for unaged asphalt materials, or for asphalt materials after the Rolling Thin Film Oven Test (RTFOT) or the Pressure Aging Vessel accelerated aging test (PAV).
• Applicable test temperature range: +6 ℃ to -36 ℃ (the source text writes "6C~-36°C", requires confirmation against the source standard (source-text extraction)).
• If 1.2 is used for asphalt materials containing particles, it is only applicable to asphalt with particle size less than 250 μm (source text "250ym", requires confirmation against the source standard (source-text extraction)).
• 4.2 This test method measures the stress and strain at brittle failure or ductile-brittle failure of asphalt at a certain temperature; it is not suitable for measuring ductile flow failure under simple tension.
• 1.3 This standard does not address safety regulations for use; users of the standard are responsible for establishing appropriate safety application procedures before use.

3. Method principle

• 4.1 After heating, the asphalt is poured into a specified mold; two phenolic plastic end molds are placed at both ends of the mold to bond the asphalt and transmit load. The specimen composed of the end molds and asphalt is pulled at a constant tensile rate, and the stress and strain at failure are measured.
• 4.2 The stress and strain at brittle failure or ductile-brittle failure of asphalt at a certain temperature are measured; these two types of failure are characterized by sudden fracture of the specimen.
• 4.3 A displacement sensor measures the elongation of the specimen when pulled at a constant rate of 1.00 mm/min, monitors the load change during the test, records the tensile strain and stress when the load reaches its maximum value, and reports them respectively as the failure strain and failure stress of the specimen.

4. Reagents and materials (purity / preparation)

• 7.1 Cooling bath medium: a mixture of potassium acetate powder and deionized water or distilled water in a mass ratio of 42% to 58%; alcohol is not allowed (alcohol will degrade asphalt performance). The prepared liquid has a relative density value of 25 ℃ between 1.235 and 1.240 (see 6.1.4).
• 7.2 Release agent: a paste of appropriate consistency made by mixing glycerin and talc powder in a mass ratio of 1:1.
• 7.3 Release paper: release paper coated on both sides with at least 0.3 μm of fluorocarbon or silicone coating (source text "0.3ym", requires confirmation against the source standard (source-text extraction)).
• 7.4 Solvent: for cleaning the test mold, end molds, and plates, use petroleum ether, heptane, or other solvents that have no dissolving or corrosive effect on plastic end molds.
• 7.5 Cleaning cloth: cotton cloth used for wiping the mold, end molds, and plates.
• 6.2 Test mold release agent: fluorocarbon compound or silicone release paper.

5. Apparatus and equipment

• 6.1 Direct tension testing machine; the complete system should include: (1) a displacement and loading system with closed-loop coupled feedback control; (2) a specimen gripping system; (3) a low-temperature liquid cooling bath and insulated environmental chamber with precise and uniform temperature control provided according to test conditions; (4) load measurement and recording equipment; (5) elongation measurement and recording equipment; (6) temperature detection and recording equipment; (7) data acquisition and display equipment. It should have a mechanical or electro-hydraulic servo loading unit with at least 500 N of tensile and compressive force, an actuator connected to the grips with a stroke of 20 mm, and a system composed of a load cell and force-transmitting pins with a stiffness of at least 3 MN/m. The loading unit can control grip clamping and separation and provide a feedback signal with a displacement resolution of 1.0 μm (source text "1.0m", requires confirmation against the source standard (source-text extraction)).
• 6.1.1 Loading equipment equipped with a temperature control system: the loading frame generates at least 500 N of tensile force. If a liquid cooling bath is used, the gripping system should be immersed in the coolant; the grips should be at least 25 mm below the liquid surface (source text "25hm", requires confirmation against the source standard (source-text extraction)). The distance between pins on the loading bracket should be at least 100.0 mm to accommodate the total length of the specimen including the end molds (see Figure 1). If an air-cooled environmental chamber is used, the space between the two columns of the loading bracket device should be able to accommodate the environmental chamber.
• 6.1.2 Specimen gripping system: must be able to generate axial tensile force and have self-aligning capability, allowing the plastic end molds described in 6.1.2.1 to be easily hung; each grip should have a specially designed force-transmitting pin and be firmly fixed to the loading plate. Figure 2 shows a typical grip and force-transmitting pin assembly. One grip remains fixed during the test, and the other grip moves at the required tensile rate.
• 6.1.2.1 Specimen end molds: the end molds are made of phenolic plastic, as shown in Figure 3; each end mold should have a dedicated hole lined with a stainless steel liner ring with a diameter of 10.0 mm (Figure 4). During the test, each end mold fixing body is closely attached to the grip as part of the gripping system. To reduce interfacial thermal stress, the thermal expansion coefficient of the end mold should be compatible with (the source text is incomplete here, requires confirmation against the source standard (source-text extraction)).
• 6.1.3 Temperature-controlled environmental chamber: should have sufficient space to store at least 8 specimens. The temperature control range of the cooling bath is adjustable between +6 ℃ and -36 ℃, and can be stabilized at least at 0.1 ℃ (source text "0.16", requires confirmation against the source standard (source-text extraction)). Placing specimens into the cooled environmental chamber at room temperature is allowed to cause a temperature gradient fluctuation of ±0.2 ℃ between the two ends of the grips; however, during the test the temperature gradient between the grips should not exceed ±0.1 ℃. Temperature is measured with a calibrated platinum resistance thermometer placed near the test area (calibrated at 8 temperatures in the range +6 ℃ to -36 ℃). If an air-cooled environmental chamber is used, it should have a dehumidification system so that specimens and grips inside do not frost; the environmental chamber should be able to store at least 8 specimens on the specimen rack, and the specimen rack is insulated from the chamber walls and door. If an air refrigeration system is used, the front door of the environmental chamber should have a hand hole large enough for the operator to reach in to install specimens; during the period of reaching in and withdrawing the arm, the temperature fluctuation of the environmental chamber should not exceed 0.2 ℃. The environmental chamber should have an observation port. If laser measurement is used, optical glass windows are required on both sides of the chamber.
• 6.1.4 When liquid is used as the cooling medium, the more suitable liquid is a mixture of potassium acetate powder and deionized water or distilled water in a mass ratio of 42% to 58%; the prepared liquid has a relative density value of 25 ℃ between 1.235 and 1.240. Alcohol should not be used as the coolant for asphalt specimens.
• 6.1.5 Load measurement and recording equipment: load is measured by a sensor with a force measuring capacity of at least 500 N and a sensitivity of 0.1 N; the sensor should be calibrated once a year as required. The data acquisition system can analyze data according to the failure load and tensile amount at 1%; the point where the load signal is equivalent to 2 N±0.3 N serves as the mark for zeroing the displacement sensor; it can promptly record the peak load and calculate the failure stress and strain. Typical peak loads range from 10 N to 250 N. The stress calculated according to 13.1 and 13.2 should be accurate to at least 0.1 MPa, and the strain should be accurate to at least 0.1.
• 6.1.6 Elongation measurement and recording system: a displacement sensor on the grips measures the elongation of the specimen, and the elongation rate is controlled to an accuracy of 1 μm.
• 6.1.6.1 The data acquisition system should have at least data acquisition channels for load, elongation, and temperature respectively.
• 6.1.6.2 Stress-strain curve display: the data acquisition and display system should be able to display a stress-strain curve expressed as stress (MPa) and strain percentage, displayed on a computer monitor or a X-Y recorder.
• 6.2 Test mold: made of aluminum alloy, with dimensions as shown in Figure 5. The release agent is fluorocarbon compound or silicone release paper.
• 6.3 Specimen support plate: made of polytetrafluoroethylene or polyacrylate or other suitable plastic plate, used for transferring and storing specimens in an air environmental chamber. These plates are not required when using a liquid cooling bath.
• 6.4 Calibrated standard thermometer: a calibrated liquid-in-glass thermometer suitable for this standard, with a graduation value of 0.1 ℃, used for comparative verification of temperature sensors. Temperature sensors should be calibrated according to the method in Appendix A, ASTM E77, and the thermometer model specified in ASTM E1, ASTM 133C. Alternatively, calibration may be performed with a standard thermometer with an accuracy greater than or equal to 0.033 ℃, traceable to the National Institute of Standards and Technology (NIST) standard equipment RTD digital thermometer.
• 6.5 Freezer: only when using air-cooled testing is a freezer capable of maintaining a temperature of -15 ℃±5 ℃ required.
• 6.6 Oven: a forced-convection oven capable of maintaining a temperature of 160 ℃±5 ℃, used for heating asphalt.

6. Recommended operating conditions

• Tensile rate: 1.00 mm/min (i.e., tensile strain rate of 3%/min) (see 5.3, 12.4).
• Test temperature: applicable test temperature range +6 ℃～-36 ℃; the test temperature may be determined according to the provisions of the asphalt grade requirements (see 9.1).
• Temperature equilibration: place the specimen in a cold bath or environmental chamber set to the temperature, and let it stand at the test temperature for 60 min±5 min (see 11).
• In general, select a tensile rate of 1.00 mm/min, and determine the test temperature; the direct tensile tester should also be capable of testing at other rates and temperatures (see 5.3).

7. Sampling and specimen preparation

• 9.1 Unaged specimens shall be sampled in accordance with GB/T 11147 (original text “GRB/T J1147”, requires confirmation against the source standard (source-text extraction)). Set the cold bath to the required test temperature and (the original text is incomplete here, requires confirmation against the source standard (source-text extraction)). The test temperature may be determined according to the provisions of the asphalt grade requirements.
• 9.1.1 Heat the asphalt uniformly until it flows and can be poured easily; however, avoid heating above 165 ℃. For modified asphalt or aged asphalt, to ensure fluidity during pouring, it may be heated to 180 ℃. The heating time should be as short as possible; stirring occasionally is allowed to ensure uniformity, and care should be taken not to entrain air bubbles into the asphalt.
• 9.2 Coat the two inner side plates of the test mold completely with release agent, so that a thin layer of release agent is evenly distributed on the metal surfaces, with no exposed parts of the metal surfaces. Place a pre-cut release paper on the base plate of the test mold, place the side plates on the release paper, and place the end molds at both ends of the test mold (the original text here has severe source-text extraction noise, requires confirmation against the source standard (source-text extraction)). Place this assembly on a flat (not provided in the available source) and put it into the oven used for heating the asphalt, and let it stand at the same temperature as the heated asphalt for 3 min±1 min, then remove.
• 9.3 Remove the ceramic tile and test mold from the oven, place them horizontally on a flat table, and pour the hot asphalt from one end of the mold frame to the other in a single pour; the pouring process should be continuous, avoiding air bubbles and interruptions; the pouring operation should be completed as quickly as possible to avoid excessive temperature drop of the asphalt. The liquid level of the hot asphalt should slightly exceed the surface of the test mold to facilitate trimming after cooling. It is best to pour only two specimens per heating.
• 9.4 After pouring the specimens, the test mold and ceramic tile should be placed on the table to cool for 30 min～60 min to room temperature; it should not cool below room temperature (25 ℃ or lower) (original wording doubtful, requires confirmation against the source standard (source-text extraction)).
• 9.5 For specimens cooled to room temperature, use a hard and flat scraper of about 165 ℃ to scrape the asphalt on top of the test mold flat; the surface of the trimmed asphalt specimen should be flat and smooth. Be careful not to trim it into a concave surface and not to damage the plastic end molds. The trimming operation should be continuously pushed out along the long axis of the sample; after trimming, remove excess asphalt from the end holes or mold grooves, and leave the specimen at room temperature for 10 min～15 min.
• 9.6 Demolding method:
  • 9.6.1 Before demolding, the two unused metal side plates (Figure 5①) should be placed in a cold bath or air environmental chamber to cool; these side plates will be used to clamp the specimen and transfer it to the cold bath or air environmental chamber.
  • 9.6.2 Take the base plate of an unused test mold (Figure 5②), place it face up on the workbench as a transfer support plate, and place two sheets of release paper overlapping along the length direction to cover the surface of the plate.
  • 9.6.3 Carefully slide the specimen cooled to room temperature to the side until half of the side plate is beyond the edge of the base plate, press down gently, and remove the side plate.
  • 9.6.4 Put the just-removed side plate back in place, push the specimen to slide toward the other edge, and repeat the 9.6.3 demolding step to remove the other side plate.
  • 9.6.5 Gently attach the cold side plate taken from the cold bath or environmental chamber to the specimen, replacing the side plate just removed.
  • 9.6.6 Repeat steps 9.6.4 and 9.6.5 to remove the other side plate of the test mold, and replace the other side plate with a cold side plate taken from the cold bath or environmental chamber. At this point, both side molds have been replaced with cooled unused side molds.
  • 9.6.7 Carefully hold the middle of the test mold assembly with two fingers of each hand, and place it horizontally with its trimmed face down on the support plate covered with release paper (note to operate vertically).
  • 9.6.8 Gently slide the specimen with its face down and the base plate, carefully hold the two side plates to protect the specimen, and remove the release paper exposed on the bottom surface of the specimen.
  • 9.6.9 Holding the support plate by hand, place the specimen with its face down together with the two side plates onto a tray in the cold bath or environmental chamber; the support plate with release paper should not be placed into the cold bath or environmental chamber.
  • 9.6.10 After placing for 2 min, remove the two side molds (the original text is incomplete here, requires confirmation against the source standard (source-text extraction)). For some softer grades of asphalt, it may be necessary to exceed (the original text is incomplete here, requires confirmation against the source standard (source-text extraction)).
  • 9.6.11 In the cold bath or environmental chamber, carefully turn over the specimen with the side molds removed so that the trimmed face is up (the original text is incomplete here, requires confirmation against the source standard (source-text extraction)). Note that during demolding, twisting or bending of the specimen should be avoided, otherwise the test results will be affected.

8. Analysis procedure

• 12.1 Prepare 6 specimens as described in 9.
• 12.2 Clamp the specimen with a special clamp, align the hole of each end mold with the force-transmitting pin on the loading frame; first align the hole at one end, then turn the handwheel on the control box so that the hole at the other end falls onto the pin.
• 12.3 After the specimen is in place, gently clamp both ends of the specimen with the special clamp to check the alignment of the specimen, then zero the instrument.
  • 12.3.1 For equipment with automatic zeroing function, the initial point of tension may be automatically adjusted according to its program; with an initial load value of 2 N±0.3 N, zero the strain and start the test; at this time there is no need to press the start button.
  • 12.3.2 For equipment with manual zeroing, or when using a vertically installed air-cooled environmental chamber, adjust by turning the handwheel on the chamber; turn the handwheel so that the display shows an initial tensile force of 2 N±0.3 N.
  • 12.3.2.1 Use the special clamp to check again the seating and loading of the specimen. Repeat the above manual loading method, turning the handwheel for fine adjustment so that the display again shows an initial tensile force of 2 N±0.3 N.
• 12.4 Set the tensile rate to 1 mm/min (i.e., tensile strain rate of 3%/min).
• 12.5 If the specimen breaks or its elongation has reached 10%, whichever occurs first, stop the test and remove the specimen and asphalt fragments.
• 12.6 When the specimen suddenly breaks when the load reaches the peak, record it as brittle failure; at this time the maximum strain is obtained under the maximum stress state; if the specimen does not break when reaching the maximum stress but continues to deform, the failure strain shall be recorded as the strain corresponding to the maximum stress; when the strain exceeds 10%, it is not necessary to continue the test, and record the failure strain as “greater than 10%”.
• 12.7 Record the failure load and failure elongation: if the specimen fails in the reduced section of the neck, record the failure data and note that failure occurred in the reduced section; if it is a non-fracture failure mode with 10% elongation, record the load at 10% elongation and note that the specimen did not break. Normal fracture of the specimen should occur within the gauge length interval 18 mm described in 3.2.8 (ideally failure should occur in the middle of each specimen). If it is not within this interval, it indicates non-uniform specimen preparation and errors in the specimen placement process, and the specimen shall be discarded.
• 12.8 Repeat steps 12.2～12.7 to test the remaining 5 specimens.
• 12.9 After the test is completed, clean up the waste asphalt, soak the plastic end molds in solvent and then wipe them clean with a soft cloth; after wiping clean, use a clean soap solution to remove the oil film left by the mineral solvent, because the oil film on the bonding surface will weaken the bond between the asphalt and the plastic end mold, causing the specimen to be discarded.

9. Qualitative and quantitative and calculation formulas

• 13.1 Calculation of failure stress: σf = Pf / A ………………（1） Where: σf— failure stress, MPa; Pf— failure load, N; A— original cross-sectional area of the specimen (6 mm×6 mm); for this standard: A=36×10⁻⁶ m² (original text “36x 10-9m²”, requires confirmation against the source standard (source-text extraction)).
• 13.2 Calculation of failure strain: εf = δ / L₀ ………………（2） Where: εf— failure strain, mm/mm; δ— elongation value at failure, mm; L₀—effective tensile length of the specimen, mm; for this standard: L₀=33.8 mm.
• 13.3 In the test results, remove the two specimens with the lowest failure stress; if two or more specimens have the same failure stress but different strains, remove the two specimens with the lower failure strain values (research suggests: asphalt failure stress values follow a Weibull distribution, while in a Weibull distribution high strength values are expected; removing the two lowest values makes the failure stress more consistent with a Weibull distribution).
• 13.4 Use the remaining 4 test results to calculate the average and standard deviation of failure stress and failure strain.
• Failure type terms (3.2): brittle failure, ductile-brittle failure, ductile failure, effective tensile length (initial value 33.8 mm), failure load, failure strain, failure stress, measurement interval (initial measurement interval length 18 mm), tensile strain, tensile stress.

10. Precision

• 15.1 The precision of the test is not specified. Based on data from multiple laboratory operators, it is recommended to estimate the error interval according to the following precision:

• 15.2 Bias: this test method has no established reference value, so bias cannot be determined.

11. Report

The test report records the following information:

• 14.1 Sample number.
• 14.2 Date and time.
• 14.3 Test temperature, accurate to 0.1 ℃.
• 14.4 Tensile rate, accurate to 0.01 mm/min.
• 14.5 Average failure strain, accurate to 0.01%.
• 14.6 Average failure stress, accurate to 0.01 MPa.
• 14.7 Peak load, accurate to N.
• 14.8 Record the failure type (fracture or no fracture, or reduced section).

12. Referenced documents

• GB/T 11147 Petroleum bitumen sampling method (original text "CB/T 11147", requires confirmation against the source standard (source-text extraction))
• GB/T 16839.1—1997 Thermocouples — Part 1: Reference tables (original text "CB/T 16839.1—1997", requires confirmation against the source standard (source-text extraction))
• SH/T 0652 Petroleum bitumen terminology (original cited as SH/T 0652—1998, see foreword)
• SH/T 0736 Asphalt rotating thin film oven test method
• SH/T 0774—2005 Asphalt accelerated aging test method (PAV method)
• Annex A (informative annex) Reference standards related to sensor calibration:
  • ASTM E 1 ASTM Thermometer specification
  • ASTM E 4 Calibration method for mechanical testing machines
  • ASTM E 77 Thermometer inspection and calibration method
  • ASTM E 83 Classification and calibration method for extensometer systems
  • ASTM E 220 Comparative calibration test method for thermocouples
  • ASTM C 670 Specification for determining precision and bias in building materials testing methods
  • ASTM E 69 Method for determining precision and bias of research data between laboratories
  • ASTM E 1137 Specification for industrial platinum resistance thermometers
  • DIN 43760 Thermocouple calibration standard

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Q&A reference