1、Standard Method of Test for Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR) AASHTO Designation: T 313-121American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS 2b T 313-1
2、AASHTO Standard Method of Test for Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR) AASHTO Designation: T 313-1211. SCOPE 1.1. This test method covers the determination of the flexural creep stiffness or compliance of asphalt binders by means of a ben
3、ding beam rheometer. It is applicable to material having a flexural stiffness value from 20 MPa to 1 GPa (creep compliance values in the range of 50 nPa1 to 1 nPa1) and can be used with unaged material or with material aged using T 240 (RTFOT) or R 28 (PAV), or both. The test apparatus is designed f
4、or testing within the temperature range from 36 to 0C. 1.2. Test results are not valid for beams of asphalt binder that deflect more than 4 mm, or less than 0.08 mm, when tested in accordance with this method. 1.3. This standard may involve hazardous materials, operations, and equipment. This standa
5、rd does not purport to address all of the safety concerns associated with its use. It is the responsibility 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. AASHT
6、O Standards: M 320, Performance-Graded Asphalt Binder R 28, Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV) R 66, Sampling Asphalt Materials T 240, Effect of Heat and Air on a Moving Film of Asphalt Binder (Rolling Thin-Film Oven Test) T 314, Determining the Fracture Prope
7、rties of Asphalt Binder in Direct Tension (DT) 2.2. ASTM Standards: C670, Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials C802, Standard Practice for Conducting an Interlaboratory Test Program to Determine the Precision of Test Methods for Co
8、nstruction Materials E77, Standard Test Method for Inspection and Verification of Thermometers E220, Standard Test Method for Calibration of Thermocouples By Comparison Techniques 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a vio
9、lation of applicable law.TS 2b T 313-2 AASHTO 2.3. Deutsche Industrie Norm (DIN) Standard: 43760, Industrial Platinum Resistance Thermometers and Platinum Temperature Sensors 2.4. NCHRP Document: NCHRP Web-Only Document 71 (Project 09-26), Precision Estimates for AASHTO Test Method T 308 and the Tes
10、t Methods for Performance-Graded Asphalt Binder in AASHTO Specification M 320 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 nonparticulate organic modifiers. 3.1.2. physical hardeninga time
11、-dependent stiffening of asphalt binder that results from the time-delayed increase in stiffness when the asphalt binder is stored at low temperatures. The increase in stiffness due to physical hardening is reversible when the temperature is raised. 3.2. Descriptions of Terms Specific to This Standa
12、rd: 3.2.1. flexural creepa test in which a simply supported asphalt binder prismatic beam is loaded with a constant load at its midpoint and the deflection of the beam is measured with respect to loading time. 3.2.2. measured flexural creep stiffness, Sm(t)ratio obtained by dividing the maximum bend
13、ing stress in the beam by the maximum bending strain. 3.2.3. estimated creep stiffness, S(t)the creep stiffness obtained by fitting a second-order polynomial to the logarithm of the measured stiffness at 8.0, 15.0, 30.0, 60.0, 120.0, and 240.0 s and the logarithm of time. 3.2.4. flexural creep compl
14、iance, D(t)ratio obtained by dividing the maximum bending strain in the beam by maximum bending stress. D(t) is the inverse of S(t). S(t) has been used historically in asphalt technology, while D(t) is commonly used in studies of viscoelasticity. 3.2.5. m-valueabsolute value of the slope of the loga
15、rithm of the stiffness curves versus the logarithm of the time. 3.2.6. contact loadload required to maintain positive contact between the beam and the loading shaft; 35 10 mN. 3.2.7. seating loadload of 1-s duration required to seat the beam; 980 50 mN. 3.2.8. test loadload of 240-s duration require
16、d to determine the stiffness of material being tested; 980 50 mN. 3.2.9. testing zero time, stime at which the signal is sent to the solenoid valve to switch from zero load regulator (contact load) to the testing load regulator (test load). 2015 by the American Association of State Highway and Trans
17、portation Officials.All rights reserved. Duplication is a violation of applicable law.TS 2b T 313-3 AASHTO 4. SUMMARY OF TEST METHOD 4.1. The bending beam rheometer measures the midpoint deflection of a simply supported beam of asphalt binder subjected to a constant load applied to the midpoint of t
18、he beam. The device operates only in the loading mode; recovery measurements are not obtained. 4.2. A test beam is placed in the controlled temperature fluid bath and loaded with a constant load for 240 s. The test load (980 50 mN) and the midpoint of deflection of the beam are monitored versus time
19、 using a computerized data acquisition system. 4.3. The maximum bending stress at the midpoint of the beam is calculated from the dimensions of the beam, the span length, and the load applied to the beam for loading times of 8, 15, 30, 60, 120, and 240 s. The maximum bending strain in the beam is ca
20、lculated for the same loading times from the dimensions of the beam and the deflection of the beam. The stiffness of the beam for the loading times specified above is calculated by dividing the maximum stress by the maximum strain. 4.4. The load and deflection at 0.0 and 0.5 s are reported to verify
21、 that the full-testing load (980 50 mN) during the test is applied within the first 0.5 s. They are not used in the calculation of stiffness and m-value and should not be considered to represent material properties. The rise time of the load (time to apply full load) can be affected by improper oper
22、ation of the pressure regulators, improper air bearing pressure, malfunctioning air bearing (friction), and other factors. By reporting the 0.0- and 0.5-s signals, the user of the test results can determine the conditions of the loading. 5. SIGNIFICANCE AND USE 5.1. The test temperature for this tes
23、t is related to the temperature experienced by the pavement in the geographical area for which the asphalt binder is intended. 5.2. The flexural creep stiffness or flexural creep compliance, determined from this test, describes the low-temperature, stressstraintime response of asphalt binder at the
24、test temperature within the linear viscoelastic response range. 5.3. The low-temperature thermal cracking performance of paving mixtures is related to the creep stiffness and the slope of the logarithm of the creep stiffness versus the logarithm of the time curve of the asphalt binder contained in t
25、he mix. 5.4. The creep stiffness and the slope of the logarithm of the stiffness versus the logarithm of the time curve are used as performance-based specification criteria for asphalt binders in accordance with M 320. 6. APPARATUS 6.1. Bending Beam Rheometer (BBR) Test SystemA bending beam rheomete
26、r (BBR) test system consisting of (1) a loading frame that permits the test beam, supports, and the lower part of the test frame to be submerged in a constant temperature fluid bath; (2) a controlled-temperature liquid bath that maintains the test beam at the test temperature and provides a buoyant
27、force to counterbalance the force resulting from the mass of the beam; (3) a computer-controlled automated data acquisition component; (4) specimen molds; and (5) items needed to calibrate and/or verify the BBR. 6.1.1. Loading FrameA frame consisting of a set of sample supports, a blunt-nosed shaft
28、that applies the load to the midpoint of the test specimen, a load cell mounted on the loading shaft, a means for 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS 2b T 313-4 AASHTO zeroing the load on
29、the test specimen, a means for applying a constant load to the loading shaft, and a deflection measuring transducer attached to the loading shaft. A schematic of the device is shown in Figure 1. Figure 1Schematic of the Bending Beam Rheometer 6.1.1.1. Loading SystemA loading system that is capable o
30、f applying a contact load of 35 10 mN to the test specimen and maintaining a test load of 980 50 mN. 6.1.1.2. Loading System RequirementsThe rise time for the test load shall be less than 0.5 s. The rise time is the time required for the load to rise from the 35 10 mN contact load to the 980 50 mN t
31、est load. During the rise time, the system shall dampen the test load to 980 50 mN. Between 0.5 and 5.0 s, the test load shall be within 50 mN of the average test load, and thereafter shall be within 10 mN of the average test load. 6.1.1.3. Sample SupportsSample supports with specimen support strips
32、 3.0 0.30 mm in top radius and inclined at an angle of 45 degrees with the horizontal (see Figure 1). The supports, made of stainless steel (or other corrosion-resistant metal), are spaced 102.0 1.0 mm apart. The width of 2015 by the American Association of State Highway and Transportation Officials
33、.All rights reserved. Duplication is a violation of applicable law.TS 2b T 313-5 AASHTO the supporting area of the supporting strips shall be 9.5 0.25 mm. This is required to ensure that the edges of the specimen, resulting from the molding procedure, do not interfere with the mid-span deflection of
34、 the specimen measured during testing. The supports shall also include vertical alignment pins 2 to 4 mm in diameter placed at the back of each sample supports at 6.75 0.25 mm from the center of the supports. These pins should be placed on the back side of the support to align the specimen on the ce
35、nter of the supports. See Figure 1 for details. 6.1.1.4. Loading ShaftA blunt-nosed loading shaft (with a spherical contact point 6.25 (0.30) mm in radius) continuous with a load cell and a deflection measuring transducer that is capable of applying a contact load of 35 10 mN and maintaining a test
36、load of 980 50 mN. The rise time for the test load shall be less than 0.5 s where the rise time is the time required for the load to rise from the 35 10 mN preload to the 980 50 mN test load. During the rise time, the system shall dampen the test load after the first 5 s to a constant 10-mN value. 6
37、.1.1.5. Load CellA load cell with a minimum capacity of 2000 mN, having a minimum resolution of 2.5 mN mounted in-line with the loading shaft and above the fluid to measure the contact load and the test load. 6.1.1.6. Linear Variable Differential Transducer (LVDT)A linear variable differential trans
38、ducer or other suitable mounted device mounted axially above the loading shaft capable of resolving a linear movement 2.5 m with a range of at least 6 mm to measure the deflection of the test beam. 6.1.2. Controlled-Temperature Fluid BathA controlled-temperature liquid bath capable of maintaining th
39、e temperature at all points within the bath between 36 and 0C within 0.1C. Placing a cold specimen in the bath may cause the bath temperature to fluctuate 0.2C from the target test temperature; consequently, bath fluctuations of 0.2C during isothermal conditioning shall be allowed. 6.1.2.1. Bath Agi
40、tatorA bath agitator for maintaining the required temperature homogeneity with agitator intensity such that the fluid current does not disturb the testing process, and mechanical noise caused by vibrations is less than the resolution specified in Sections 6.1.3 and 6.1.3.1. 6.1.2.2. Circulating Bath
41、 (Optional)A circulating bath unit separate from the test frame that pumps the bath fluid through the test bath. If used, vibrations from the circulating system shall be isolated from the bath test chamber so that mechanical noise is less than the resolution specified in Sections 6.1.3 and 6.1.3.1.
42、6.1.3. Data Acquisition SystemA data acquisition system that resolves loads to the nearest 2.5 mN, beam deflection to the nearest 2.5 m, and bath fluid temperature to the nearest 0.1C. The system shall sense the point in time when the signal is sent to the solenoid valve(s) to switch from zero load
43、regulator (contact load) to the testing load regulator (test load). This is zero time. Using this time as a reference, the system shall provide a record of load and deflection measurements relative to this time. The system shall record the load and deflection at the loading times of 0.0, 0.5, 8.0, 1
44、5.0, 30.0, 60.0, 120.0, and 240.0 s. All readings shall be an average of three or more points within 0.2 s from the loading time, e.g., for a loading time of 7.8, 7.9, 8.0, 8.1, and 8.2 s. 6.1.3.1. Signal FilteringDigital or analog smoothing of the load and the deflection data may be required to eli
45、minate electronic noise that could otherwise affect the ability of the second-order polynomial to fit the data with sufficient accuracy to provide a reliable estimate of m-value. The load and deflection signals may be filtered with a low-pass analog or digital filter that removes signals of greater
46、than 4-Hz frequency. The averaging shall be over a time period less than or equal to 0.2 s of the reporting time. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS 2b T 313-6 AASHTO 6.2. Temperature Mea
47、suring EquipmentA calibrated temperature transducer capable of measuring the temperature to 0.1C over the range of 36 to 0C mounted within 50 mm of the midpoint of the test specimen supports. Note 1Required temperature measurement can be accomplished with an appropriately calibrated platinum resista
48、nce thermometer (RTD) or a thermistor. Calibrations of an RTD or thermistor can be verified as per Section 6.6. An RTD meeting DIN Standard 43760 (Class A) is recommended for this purpose. The required precision and accuracy cannot be obtained unless each RTD is calibrated as a system with its respe
49、ctive meter or electronic circuitry. 6.3. Test Beam MoldsTest beam molds of suitable dimensions to yield demolded test beam 6.35 0.05 mm thick by 12.70 0.05 mm wide by 127 2.0 mm long, fabricated from aluminum flat stock as shown in Figure 2. Figure 2Dimensions and Specifications for Aluminum Molds 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS 2b T 313-7 AASHTO 6
