1、Standard Method of Test for Determining the Flexural Creep Stiffness of Asphalt Mixtures Using the Bending Beam Rheometer (BBR) AASHTO Designation: TP 125-161Release: Group 3 (August 2016) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Was
2、hington, D.C. 20001 TS-2d TP 125-1 AASHTO Standard Method of Test for Determining the Flexural Creep Stiffness of Asphalt Mixtures Using the Bending Beam Rheometer (BBR) AASHTO Designation: TP 125-161Release: Group 3 (August 2016) 1. SCOPE 1.1. This test method covers the determination of the flexur
3、al creep stiffness or compliance of asphalt mixtures by means of a bending beam rheometer. It is applicable to material having a flexural stiffness value from 2 GPa to 20 GPa (creep compliance values in the range of 0.5 nPa1to 0.05 nPa1). The test apparatus is designed for testing within the tempera
4、ture range from 36 to 0C. 1.2. Test results are valid for beams of asphalt mixtures that deflect at least 15 m and less than 150 m (550 microstrains) during the entire duration of the test, when tested in accordance with this method. 1.3. This method has been verified with asphalt mixtures having a
5、nominal maximum aggregate size of 12.5 mm. 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 responsibility of the user of this procedure to establish appropriate safe
6、ty and health practices and to determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: Mechanistic-Empirical Pavement Design Guide T 313, Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR) 2.2.
7、ASTM Standard: E77, Standard Test Method for Inspection and Verification of Liquid-in-Glass Thermometers 2.3. Deutche Industrie Norm (DIN) Standard: 43760, Platinum Resistance Thermometer 3. TERMINOLOGY 3.1. Definition: 2016 by the American Association of State Highway and Transportation Officials.A
8、ll rights reserved. Duplication is a violation of applicable law.TS-2d TP 125-2 AASHTO 3.1.1. asphalt mixturean asphalt-based composite material that consists of asphalt binder, coarse and fine aggregates, filler, and air voids. 3.2. Definition of Terms Specific to This Standard: 3.2.1. contact load
9、load required to maintain positive contact between the beam and the loading shaft, and equal to 35 10 mN. 3.2.2. estimated flexural creep stiffness, S(t)the creep stiffness obtained by fitting a second-order polynomial to the logarithm of the measured stiffness, from 8.0 to 1000 s, as a function of
10、the logarithm of time. 3.2.3. flexural creepa test in which a simply supported asphalt mixture prismatic beam is loaded with a constant load at its midpoint and the deflection of the beam is measured with respect to loading time. 3.2.4. flexural creep compliance, D(t)ratio obtained by dividing the t
11、ime-dependent maximum bending strain in the beam by the time-independent maximum bending stress. 3.2.5. measured flexural creep stiffness, Sm(t)ratio obtained by dividing the maximum bending stress in the beam by the maximum bending strain. S(t) is the inverse of D(t). S(t) has been used historicall
12、y in asphalt technology while D(t) is commonly used in studies of viscoelasticity. 3.2.6. m-valueabsolute value of the slope of the logarithm of the estimated stiffness curves versus the logarithm of the time. Note that m-value estimation for any time during the test is based on the creep test resul
13、ts for the entire duration of the test. 3.2.7. seating loadload of 1-s duration required to seat the beam, and equal to 4000 100 mN. 3.2.8. test loadload of 1000-s duration required to determine the stiffness of the material being tested, and equal to 4000 100 mN. 3.2.9. testing zero time, stime at
14、which the signal is sent to the solenoid valve to switch from zero load regulator (contact load) to the testing load regulator (test load). 4. SUMMARY OF TEST METHOD 4.1. The bending beam rheometer measures the midpoint deflection of a simply supported beam of asphalt mixtures subjected to a constan
15、t load applied to the midpoint of the 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 1000-s. The test load (4000 100 mN) and the midpoint of deflection
16、 of the beam are monitored versus time 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. The maximum bending strain in the beam is calculated for
17、the same loading times from the dimensions of the beam and the deflection of the beam. The stiffness of the beam 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 that the full-testing load (4000 100 mN) during th
18、e 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 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a vi
19、olation of applicable law.TS-2d TP 125-3 AASHTO of the load (time to apply full load) can be affected by improper operation of the pressure regulators, improper air bearing pressure, malfunctioning air bearing (friction), and other factors. By reporting the 0.0 and the 0.5 s signals, the user of the
20、 test results can determine the conditions of the loading. 5. SIGNIFICANCE AND USE 5.1. The test temperature for this test is related to the temperature experienced by the pavement in the geographical area for which the asphalt binder is intended. For quality control purposes the single test tempera
21、ture shall be 10C above the specified binder grade required for the mixture. For performance prediction at least 3 temperatures shall be used at 6C intervals. The test temperatures of 4C, 10C, and 16C above the specified binder grade used in the mixtures have been successfully used. Other temperatur
22、es can also be used depending on the project requirements. 5.2. The flexural creep stiffness or flexural creep compliance, determined from this test, describes the low-temperature, stress-strain-time response of asphalt mixtures at the test temperature within the linear viscoelastic response range.
23、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 mixture. 5.4. The creep compliance is used in the low temperature algorithm of the AA
24、SHTO Mechanistic-Empirical Pavement Design Guide to calculate thermal stresses used in predicting pavement performance. 6. APPARATUS 6.1. Bending Beam Rheometer (BBR) Test SystemA bending beam rheometer (BBR) test system consisting of (1) a loading frame which permits the test beam, supports, and th
25、e lower part of the test frame to be submerged in a constant temperature fluid bath, (2) a controlled temperature liquid bath which maintains the test beam at the test temperature, and (3) a computer-controlled automated data acquisition component, and (4) items needed to standardize the BBR, verify
26、 it, or both. Note 1The buoyant force in the liquid of the bath provides partial counterbalance of the weight of the mixture beam. The remainder of the weight is approximately equal to 90 mN, which can be neglected for a testing load of 4000 mN. 6.1.1. Loading FrameA frame consisting of a set of sam
27、ple supports, a blunt-nosed shaft that applies the load to the midpoint of the test specimen, a load cell mounted on the loading shaft, a means for zeroing the load on the test specimen, a means for applying a constant load to the loading shaft, and a deflection measuring transducer attached to the
28、loading shaft. A schematic of the device is shown in Figure 1. 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d TP 125-4 AASHTO Figure 1Schematic of the Bending Beam Rheometer (T 313) 6.1.1.1. Loadi
29、ng SystemA loading system that is capable of applying a contact load of 35 10 mN to the test specimen and maintaining a test load of 4000 100 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
30、 the 35 10 mN contact load to the 4000 100 mN test load. During the rise time, the system shall dampen the test load to 4000 100 mN. Between 0.5 and 5.0 s, the test load shall be within 100 mN of the average test load, and thereafter shall be within 50 mN of the average test load. 6.1.1.3. Sample Su
31、pportsSample supports with specimen support strips 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 the supporting area of the s
32、upporting 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 the specimen measured during testing. The supports shall also include vertical alignment pins 2 to 4 mm in diameter
33、 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 center of the supports. See Figure 1 for details. 6.1.1.4. Loading ShaftA blunt-nosed loading shaft (with a spherical
34、contact point 6.25 (0.30) mm in radius) continuous with a load cell and a deflection measuring transducer which is capable of applying a contact load of 35 10 mN and maintaining a test load of 4000 100 mN. The rise 2016 by the American Association of State Highway and Transportation Officials.All ri
35、ghts reserved. Duplication is a violation of applicable law.TS-2d TP 125-5 AASHTO 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 4000 100 mN test load. During the rise time the system shall dampen the tes
36、t load after the first 5 s to a constant 50 mN value. 6.1.1.5. Load CellA load cell with a minimum capacity of 9,806 mN and 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 Differe
37、ntial Transducer (LVDT)A linear variable differential transducer or other suitable mounted device mounted axially above the loading shaft capable of resolving a linear movement 0.15 m with a range of at least 6 mm to measure the deflection of the test beam. 6.1.2. Controlled-Temperature Fluid BathA
38、controlled temperature liquid bath capable of maintaining the 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
39、 isothermal conditioning shall be allowed. 6.1.2.1. Bath AgitatorA 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 specifi
40、ed in Sections 6.1.3 and 6.1.3.1. 6.1.2.2. Circulating Bath (Optional)A circulating bath unit separate from the test frame which 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 t
41、han the resolution specified in Sections 6.1.3 and 6.1.3.1. 6.1.3. Data Acquisition SystemA data acquisition system that resolves loads to the nearest 2.5 mN, beam deflection to the nearest 0.15 m, and bath fluid temperature to the nearest 0.1C. The system shall sense the point in time when the sign
42、al is sent to the solenoid valve(s) to switch from zero load 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
43、 load and deflection every 0.5 s starting at time 0.0 when the instantaneous load is applied. 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 o
44、f the load and the deflection data may be required to eliminate 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
45、analog or digital filter that removes signals of greater than 4 Hz frequency. The averaging shall be over a time period less or equal to 0.2 s of the reporting time. 6.2. CuttingMasonry saw capable of cutting through 6-in. diameter cylindrical asphalt concrete samples prepared using the Superpave Gy
46、ratory Compactor (SGC) or cored from the road. Quality tile saw capable of cutting asphalt concrete beams 12.7 by 6.35 by 127 mm. 6.3. Temperature Measuring EquipmentA standardized temperature transducer capable of measuring the temperature to 0.1C over the range of 36 to 0C mounted within 50 mm of
47、the midpoint of the test specimen supports. Note 2Required temperature measurement can be accomplished with an appropriately standardized platinum resistance 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
48、(Class A) is 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d TP 125-6 AASHTO recommended for this purpose. The required precision and accuracy cannot be obtained unless each RTD is standardized as
49、a system with its respective meter or electronic circuitry. 6.4. Items for Calibration or VerificationThe following items are required to verify and standardize the BBR. 6.4.1. Stainless Steel (Thick) Beam for Compliance Measurement and Load Cell CalibrationOne stainless steel beam, 6.4 0.1 mm thick by 12.7 and 0.25 mm wide by 127 5 mm long, for measuring system compliance and calibrating the load cell. 6.4.2. Stainless Steel (Thin) Beam for Overall System CheckOne stainless
