1、Standard Method of Test for Pavement Deflection Measurements AASHTO Designation: T 256-01 (2016) Release: Group 1 (April 2016) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-5a T 256-1 AASHTO Standard Method of Te
2、st for Pavement Deflection Measurements AASHTO Designation: T 256-01 (2016) Release: Group 1 (April 2016) 1. SCOPE 1.1. This test method provides standards for measuring pavement surface deflections, directly under, or at locations radially outward (offset) from a known static, steady-state, or impu
3、lse load. Deflections are measured with sensors that monitor the vertical movement of a pavement surface due to the load. This test method describes procedures for the deflection measurement using various deflection testing devices and provides the general information that should be obtained regardl
4、ess of the type of testing device used. 1.2. This test method is applicable for deflection measurements performed on flexible asphalt concrete (AC), rigid portland cement concrete (PCC), or composite (AC/PCC) pavements. Rigid pavements may be plain, jointed, jointed reinforced, or continuously reinf
5、orced or fractured concrete. 1.3. The values stated in SI units are to be regarded as standard. The U.S. Customary system of units given in parentheses is for information purposes only. 1.4. This standard does not purport to address the safety concerns, if any, associated with its use. It is the res
6、ponsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 32, Calibrating the Load Cell and Deflection Sensors for a Falling Weight Deflectomet
7、er R 33, Calibrating the Reference Load Cell Used for Reference Calibrations for a Falling Weight Deflectometer 2.2. ASTM Standard: STP1026, Nondestructive Testing of Pavements and Backcalculation of Moduli 2.3. Other Documents: FHWA-HRT-07-040, FWD Calibration Center and Operational Improvements: R
8、edevelopment of the Calibration Protocol and Equipment FHWA-RD-98-085, Temperature Predictions and Adjustment Factors for Asphalt Pavements SHRP-P-661, Manual for FWD Testing in the Long-Term Pavement Performance Program 3. TERMINOLOGY 3.1. Definitions of Terms Specific to This Standard: 2016 by the
9、 American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 256-2 AASHTO 3.1.1. deflection sensorelectronic device(s) capable of measuring the relative vertical movements of a pavement surface and mounted in such a ma
10、nner as to minimize angular rotation with respect to its measuring plane at the expected movement. Such devices may include seismometers, velocity transducers, or accelerometers. 3.1.2. load cellcapable of accurately measuring the load that is applied perpendicular to the loading plate and is placed
11、 in a position to minimize the mass between the load cell and the pavement. The load cell shall be positioned in such a way that it does not restrict the ability to obtain deflection measurements under the center of the load plate. The load cell shall be water resistant, and shall be resistant to me
12、chanical shocks from road impacts during testing or traveling. 3.1.3. loading platecapable of an even distribution of the load over the pavement surface. Loading plates may be circular in shape (or rectangular in some cases), one piece or segmented, for measurements on conventional roads and airfiel
13、ds or similar stiff pavements. The plate shall be suitably constructed to allow pavement surface deflection measurements at the center of the plate. 3.1.4. deflection basinthe idealized bowl shape of the deformed pavement surface due to a specified load as depicted from the peak measurements of a se
14、ries of deflection sensors placed at radial offsets from the center of the loading plate. 3.1.5. deflection basin testa test with deflection sensors placed at various radial offsets from the center of the loading plate. The test is used to record the shape of the deflection basin resulting from an a
15、pplied load. Information from this test can be used to estimate material properties for a given pavement structure. 3.1.6. load transfer testa test, usually on PCC pavement, with deflection sensors on both sides of a transverse or longitudinal break in the pavement. The test is used to determine the
16、 ability of the pavement to transfer load from one side of the break to the other. Also, the load-deflection data can be used to predict the existence of voids under the pavement. 3.1.7. test locationthe point at which the center of the applied load(s) is located. 4. SUMMARY OF TEST METHOD AND LIMIT
17、ATIONS 4.1. This test method consists of standards for measuring pavement surface deflections directly under and/or at appropriate offset locations from the load center. Each nondestructive testing (NDT) device is operated according to the standard operating procedure applicable to the device. 4.2.
18、This test method includes general descriptions of the various types of static and semicontinuous deflection testing devices, and procedures for deflection measurement corresponding to each testing device. 4.3. Standards for collection of general information, such as test setup, ambient temperature,
19、pavement temperature, equipment calibration, number of tests, and test locations, pertain to all devices. 5. SIGNIFICANCE AND USE 5.1. NDT measurement of pavement surface deflections provides information that can be used for the structural evaluation of new or in-service pavements. These deflection
20、measurements may be used to determine the following pavement characteristics: 5.1.1. Modulus of each layer; 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 256-3 AASHTO 5.1.2. Overall stiffness
21、of the pavement system; 5.1.3. Load transfer efficiency of PCC pavement joints; 5.1.4. Modulus of subgrade reaction; and 5.1.5. Effective thickness, structural number, or soil support value. 5.2. These parameters may be used for the analysis and design of reconstructed and rehabilitated flexible and
22、 rigid pavements, pavement structural adequacy assessment including joint efficiency of PCC pavement, void detection in PCC pavements, research, and/or network structural inventory purposes. 6. APPARATUS 6.1. The apparatus used in this test method shall be one of the deflection measuring devices des
23、cribed in Section 6.2 and shall consist of some type of probe or surface contact sensor(s) to measure vertical pavement movements or deformations when subjected to a given load. 6.2. Deflection Measuring Devices: 6.2.1. Noncontinuous Static Loading Device1that operates on a single lever-arm principl
24、e. This device should have a minimum 2.5-m (8.2-ft) long probe, and the extension of the probe shall depress a dial gauge or electronic sensor that measures maximum pavement surface deflection with a resolution of 0.025 mm (0.001 in.) or better. The vehicle used to carry the static deflection device
25、 shall be a truck carrying an 80-kN (18,000-lbf) test load on a single rear axle. The loading configuration, including axle loads, tire sizes, and inflation pressures, can be obtained using the manufacturers specification; however, this information must be clearly indicated in the engineering report
26、. 6.2.2. Semicontinuous Static Loading Device2that operates on a double lever-arm principle. The vehicle used to carry this device shall be a truck carrying a l30-kN (29,000-lbf) single-axle test load. The loading configuration, including axle loads, tire sizes, and inflation pressures, can be obtai
27、ned using the manufacturers specification; however, this information must be clearly indicated in the engineering report. The test vehicle should be equipped with a double lever arm with probes, the geometry and size of which makes it possible to measure the maximum pavement surface deflection in bo
28、th wheel paths with a resolution of 0.025 mm (0.001 in.) or better. The extension of each lever arm holding the probe should depress an electronic sensor, which may be of any type provided the sensor delivers an analog or digital signal. The digital signal shall be correlated with the movement of th
29、is extension and, therefore, with the deflection of the pavement surface under the effect of the moving test load. The truck should be able to lift and move the probes from one measurement point to the next, lower them onto the pavement surface, and make another set of measurements in a fully automa
30、ted process at a constant vehicle speed. 6.2.3. Steady-State Loading Device3that uses a dynamic force generator to produce a dynamic load. The force generator may use, for example, a counter-rotating mass or a servo-controlled hydraulic actuator to produce the dynamic load. The device that uses a co
31、unter-rotating mass operates at a fixed frequency to produce a dynamic load under a static weight applied through a pair of rigid steel wheels. Both loading frequency and the magnitude of the dynamic loads may be varied by the operator of the devices that use a servo-controlled hydraulic actuator. D
32、epending on the model, normal operating frequencies range from 8 to 60 Hz and maximum dynamic forces range from 2.2 to 35.5 kN (500 to 8000 lbf) applied through a single circular or dual rectangular plate. These loading devices may be mounted in a van, on the front of a vehicle, or on a trailer. Def
33、lection measurement devices should have five or more sensors to satisfactorily measure the deflection basin with a resolution of 0.001 mm (0.00004 in.) or better. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applic
34、able law.TS-5a T 256-4 AASHTO 6.2.4. Impulse Loading Device4that creates an impulse load on the pavement by dropping a mass from different heights onto a rubber or spring buffer system. Generally known as a Falling Weight Deflectometer (FWD), the force-generating device shall be capable of being rai
35、sed to one or more predetermined heights and dropped. The resulting force pulse, transmitted to the pavement through a 300-mm (11.8-in.) diameter loading plate, shall not vary from each other by more than 3 percent. The force pulse shall approximate the shape of a haversine or half-sine wave and a p
36、eak force that can be varied within the range of 7 to 105 kN (1500 to 24,000 lbf) shall be achievable. The impulse loading device shall measure pavement surface deflections using six or more sensors with a resolution of 0.001 mm (0.00004 in.) or better. 7. CALIBRATION 7.1. The deflection sensor(s) a
37、nd load cell (if applicable) of the deflection device should be calibrated to ensure that all readings are accurate within specified limits. For devices in which the load is assumed to be constant and is not measured, the accuracy of the magnitude of load imparted should be checked periodically. 7.2
38、. Load Cell: 7.2.1. GeneralThe procedure for calibrating the load cell (if the device uses a load cell) depends on the type of device used. The calibration of the load cell may be checked informally by observing the load cell readings and comparing them against expected readings based on experience
39、or shunt calibration values in the case of a FWD. Load cell reference (or absolute) calibration shall be performed at least once a year except for the noncontinuous and semicontinuous loading devices. (See Table 1.) Table 1Load Cell Frequency of Calibration Device Type Frequency of Calibration Nonco
40、ntinuous and semicontinuous static loading types Prior to testing Steady-state loading types (see Section 7.2.3 for devices that do not have a load cell) At least once a year using manufacturers instructions or using the procedure in Appendix A of SHRP Report SHRP-P-661 Impulse loading types (fallin
41、g weight deflectometer) At least once a year using the procedure in R 32, Calibrating the Load Cell and Deflection Sensors for a Falling Weight Deflectometer 7.2.2. Noncontinuous and Semicontinuous Static Loading DevicesImmediately prior to testing, weigh the axle load of the truck if the ballast co
42、nsists of a material that can absorb moisture (sand or gravel, etc.) or could have changed for any reason. Trucks with steel or concrete block loads only need to be weighed if the loads are changed or could have shifted. 7.2.3. Steady-State Loading DevicesDevices that are equipped with load cells ma
43、y be calibrated by measuring the load cell output under known static loading conditions, such as the load of the device itself. Load cells should be calibrated at least once a year following the manufacturers instructions or R 32. Calibration of a dynamic load application device that does not have a
44、 load cell requires specialized equipment generally not available except at the manufacturers location. Potential error from variations in applied loads for this device is nominal; retesting after leaving the factory may not be considered a requirement. Calibration for applied load should be conduct
45、ed indirectly once a month by checking the frequency of the counter-rotating fly wheels with a strobe light. 7.2.4. Impulse Loading DevicesReference load cell calibration should be carried out at least once per year in accordance with R 33, Calibrating the Reference Load Cell Used for Reference Cali
46、brations for Falling Weight Deflectometer. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 256-5 AASHTO 7.3. Deflection Sensors: 7.3.1. GeneralThe procedure for calibrating the deflection sensor
47、s depends on the type of apparatus used. Calibration of the deflection sensors should be checked at least once a month during production testing except noncontinuous and semicontinuous loading devices. (See Table 2.) 7.3.2. Noncontinuous and Semicontinuous Static Loading DevicesStatic loading device
48、s should be calibrated daily with feeler gauges. When performing deflection sensor calibration, induced deflections should be similar in magnitude to the deflections encountered during normal testing. 7.3.3. Steady-State Loading DevicesA routine calibration check of the deflection sensors shall be c
49、onducted once a month. If significant differences are noted for a sensor, it shall be returned to the manufacturer for check or calibration under standard calibration oscillatory vibrations. Deflection sensors shall be calibrated annually. Table 2Deflection Sensor Frequency of Calibration Device Type Frequency of Calibration Min Frequency of Calibration Check Noncontinuous and semicontinuous Static loading types Daily during operation Daily during operation Steady-state loading types At least once a year Once a month during operation Impulse loading typ
