AASHTO T 340-2023
Determining Rutting Susceptibility of Asphalt Mixtures Using the Asphalt Pavement Analyzer (APA)
- Standard No.
- AASHTO T 340-2023
- Release Date
- 2023
- Published By
- American Association of State Highway and Transportation Officials US / AASHTO
- Latest
- AASHTO T 340-2023
- Introduction
Analysis of the Technical Framework of the AASHTO T 340-23 Standard
The T 340-23 standard, published in 2023 by the American Association of State Highway and Transportation Officials (AASHTO), is a key technical specification for evaluating the rutting resistance of asphalt mixtures. This standard details the complete process for rutting susceptibility testing using the Asphalt Pavement Analyzer (APA), providing a scientific basis for quality control of road materials.
Scope of Application and Technical Characteristics of the Standard
This standard applies to the rutting performance evaluation of asphalt mixtures prepared in the laboratory and sampled in the field. The core of the test is to quantify the mixture's resistance to permanent deformation under high-temperature conditions by simulating actual traffic loads. The standard clearly stipulates that the test temperature should be based on the high-temperature grade of the Superpave performance grade (PG) binder used in the project.
Test parameters Standard requirements Allowable deviation Test significance Specimen size Diameter 150mm × Height 75mm ±2mm Ensure comparability of test results Void ratio 7.0% ±0.5% Simulate actual road compaction state Wheel load 445N ±22N Simulate standard axle load Hose pressure 690kPa ±35kPa Control contact pressure consistency Test cycle 8000 times - Ensure sufficient rutting development
Equipment Configuration and Calibration Requirements
Asphalt Pavement Analyzer, as the core testing equipment, must have a precise temperature control system, load application system, and data acquisition system. The standard puts forward strict requirements on the key parameters of the equipment:
Temperature control system
APA must be able to accurately control the test temperature within the range of 4-72°C, with a fluctuation range of no more than 1°C. Temperature calibration requires the use of a NIST-traceable thermometer, verified for stability, uniformity, and accuracy.
Load Application System
Wheel load calibration requires a precise load of 445±5N at each test location. The impact of other wheel loading on the test location must be considered during the calibration process. Hose pressure must be stable within a range of 690±35kPa.
Specimen Mold Specifications
The test mold is constructed of ultra-high molecular weight polyethylene to ensure dimensional stability and durability. The cylindrical specimen mold contains two holes with a diameter of 150±2.0mm and a height of 75±2.0mm to ensure precise specimen positioning.
Key Technical Points for Sample Preparation
The quality of sample preparation directly affects the reliability of test results. The standard provides detailed preparation specifications for different types of samples:
Laboratory Sample Preparation
Specimens can be prepared using a Superpave Gyratory Compactor or a Vibratory Compactor. Gyratory compaction should be performed in accordance with Standard T 312, while vibratory compaction should follow the manufacturer's operating instructions. Regardless of the method used, the sample must achieve a target void ratio of 7.0±0.5%.
Field Core Sample Preparation
Road core samples should be between 140-152mm in diameter and have a minimum height of 50mm. For core samples that do not meet the size requirements, adjustments such as sawing or plaster filling are permitted, but testing must be performed on the uncut core surface.
Specimen Preconditioning
The compacted specimens must be cooled at room temperature (approximately 25°C) for at least 3 hours and then preheated at the test temperature for not less than 6 hours, but the total preheating time should not exceed 24 hours.
Test Procedure Execution Details
The standard test procedure consists of four main stages: specimen installation, initial measurement, load test, and final measurement:
Manual Rutting Depth Measurement
The specimen is first seated by applying 25 cycles, during which the hose pressure is adjusted. Using a dedicated rutting depth measurement template, initial and final measurements are taken at the four outer positions (the center position is not used), with a measurement accuracy of 0.01mm.
Automatic Rutting Depth Measurement
The test process is controlled by APA computer software, with a preset number of cycles of 8050-8100, ensuring that the specimen placement cycle and a full 8000 test cycles are included. Data files are automatically saved after the test.
Test Environment Control
The test chamber must not be open for more than 6 minutes during specimen installation. After closing the test chamber, wait at least 10 minutes for the temperature to stabilize before resuming testing.
Data Analysis and Quality Control
Rutting depth calculations utilize scientific data processing methods to ensure accurate and reliable results:
Outlier Handling
When three test locations are used, the sample standard deviation is calculated. If the standard deviation is ≥2.0mm, the test location with the largest deviation from the mean is eliminated. Possible causes should also be investigated, including the test procedure, equipment calibration, and specimen preparation.
Final result determination
The APA rutting depth of the asphalt mixture is the overall average of the rutting depths of all valid test positions, with two positions used for the four-wheel APA and three positions used for the six-wheel APA (after removing outliers).
Test Configuration Number of Specimens Test Locations Data Validity Requirements Two-round APA 4 cylindrical specimens 2 locations All valid Three-round APA 6 cylindrical specimens 3 locations Standard deviation <2.0mm or eliminate outliers
Calibration Procedure Technical Requirements
Appendix A1 of the standard specifies the detailed equipment calibration procedure to ensure the accuracy and comparability of test data:
Annual Calibration Items
The preheat oven, APA temperature, APA wheel load, and APA hose pressure must be calibrated at least annually. The horizontal and vertical components of the automatic rutting depth measurement system must be calibrated according to the manufacturer's schedule.
Temperature Calibration Accuracy
Temperature stability requires that the difference between two consecutive readings should not exceed 0.4°C. Temperature uniformity requires that the difference between the average temperature at different locations should not exceed 0.4°C. Temperature accuracy requires that the difference between the set temperature and the actual average temperature should not exceed 0.4°C.
Hose Replacement Procedure
After installation, new hoses must undergo a run-in test of 8,000 cycles at a temperature of at least 55°C to ensure that hose performance is stable before formal testing.
Analysis of Optional Test Parameters
Appendix X1 of the standard provides a variety of optional test parameters to meet different user needs:
Beam Specimen Testing
Some users use beam specimens instead of cylindrical specimens, with dimensions of 75×125×300mm. Beam specimens can only be prepared using a vibratory compactor, and rutting depth is measured at five locations during testing.
115mm High Cylindrical Specimen
Using cylindrical specimens with a height of 115mm requires a corresponding test mold. Research data for this type of specimen is not included in NCHRP 9-17.
Low Target Void Ratio
Some users use cylindrical specimens with a void ratio of 4.0% or beam specimens with a void ratio of 5.0%. NCHRP research indicates that lower void content better reflects actual pavement rutting performance.
High Wheel Load and Hose Pressure
Optional parameters include 534N wheel load and 830kPa hose pressure, but most users still use the standard 445N and 690kPa parameters.
Standard Implementation Recommendations
Based on the standard's technical requirements and operational experience, the following implementation recommendations are provided:
Laboratory Qualification Requirements
Testing laboratories should comply with the requirements of the R 18 standard and establish a comprehensive quality management system. Testing personnel should receive professional training and be familiar with equipment operation and standard procedures.
Equipment Maintenance Plan
Develop a detailed equipment maintenance plan, including daily inspections, regular calibration, and preventive maintenance. Pay particular attention to hose wear and promptly replace hoses that have reached the end of their service life.
Data Quality Control
Establish a data review mechanism to conduct root cause analysis of abnormal test results. Conduct regular inter-laboratory comparisons to ensure the comparability of test results.
Method Validation
New laboratories should undergo method validation before being put into use, including precision assessment, bias checking, and capability verification, to ensure the reliability of test results.
The implementation of the AASHTO T 340-23 standard will effectively improve the scientific nature and consistency of asphalt mixture rutting performance evaluation and provide strong technical support for road engineering quality management. As technology continues to develop, the standard will continue to be updated and improved to meet the testing needs of new materials and new processes.
AASHTO T 340-2023 history
- 2023 AASHTO T 340-2023 Determining Rutting Susceptibility of Asphalt Mixtures Using the Asphalt Pavement Analyzer (APA)
- 2010 AASHTO T 340-2010 Standard Method of Test for Determining Rutting Susceptibility of Hot Mix Asphalt (HMA) Using the Asphalt Pavement Analyzer (APA)
