AASHTO T 407-2023
Determining the Interlayer Shear Strength (ISS) of Asphalt Pavement Layers
- Standard No.
- AASHTO T 407-2023
- Release Date
- 2023
- Published By
- American Association of State Highway and Transportation Officials US / AASHTO
- Latest
- AASHTO T 407-2023
- Introduction
Standard Overview and Technical Background
AASHTO T 407-231 is a test method for interlaminar shear strength of asphalt pavements, officially released in 2023 by the American Association of State Highway and Transportation Officials. This standard, derived from the LISST apparatus technology developed at Louisiana State University, is specifically designed to evaluate the interfacial bond performance between asphalt pavement structural layers. With the increasing loads of modern traffic, interlaminar shear failure has become a major form of early damage to asphalt pavements, and the establishment of this standard provides an important technical basis for quality control.
Test Principle and Equipment Requirements
This standard utilizes the direct shear test principle, applying a vertical load to a cylindrical specimen using the Louisiana Interlaminar Shear Strength Tester (LISST) to measure the maximum bearing capacity at shear failure of the interface. The core of the apparatus consists of a shear frame and a reaction frame. The shear frame is movable in the vertical direction, while the reaction frame remains fixed.
Equipment components Technical requirements Accuracy requirements Loading device Displacement rate 2.54 mm/min ±1.0% Load sensor 0-25000 N Range ±1.0% LVDT Displacement Meter Vertical/Horizontal Displacement Measurement ±0.5% Specimen Size 150mm or 100mm Diameter ±1mm Detailed Explanation of Sample Preparation Specifications
Field Coring Samples
When drilling core samples from asphalt pavement, the traffic direction must be marked to ensure no prying during core extraction. The core sample diameter should be 150mm, and the thickness of each layer should be within 50±5mm. Core sample height exceeding 50mm requires trimming with a wet stone saw.
Laboratory Specimen Preparation
Double-layer specimens were prepared using a Superpave gyratory compactor according to the T 312 standard. The lower layer was compacted to a height of 50 mm, with a void ratio controlled at 6.0 ± 1.0%. The bond coat material was applied according to the design requirements using a 1-inch natural bristle brush and then properly cured before compacting the upper layer.
Test Procedure Critical Control Points
The following parameters were strictly controlled during the test: the specimens were maintained at a constant temperature of 25 ± 1°C for at least 2 hours; the traffic direction markings were ensured to be vertical during installation; the interlayer interface was precisely located at the center of the gap between the loading frame and the reaction frame; the normal load could reach 206.84 kPa; and the load was applied to failure at a constant displacement rate of 2.54 mm/min.
Typical Failure Mode Analysis
Interlaminar shear failure is primarily manifested as complete interface separation, partial bond failure, or mixed failure modes. Detailed documentation of failure surface characteristics, including contaminants, milling striations, debonding, and bondline striations, is crucial for analyzing the failure mechanism.
Calculation Results and Reporting Requirements
The interlaminar shear strength is calculated using the formula: ISS = 4Pult/(πD2), where Pult is the ultimate load (N) and D is the specimen diameter (m). Each test requires at least three valid specimens. The report should include specimen identification, porosity, failure surface location, interface surface characteristics, specimen dimensions, and complete test results.
Report Items Accuracy Requirements Units Ultimate Load ±4.4N N(lbf) Shear Strength ±1Pa Pa(psi) Deformation Data ±0.01mm mm(in) Statistical Parameters Mean + Standard Deviation - Standard Implementation Recommendations and Quality Control
Laboratory Qualification Requirements
Laboratories implementing this standard should meet the requirements of R R 18 quality management system requirements ensure that personnel qualifications, equipment calibration, and maintenance meet specifications. While compliance with R 18 does not fully guarantee the reliability of results, it provides a basic framework for quality control.
Safety Precautions
The standard addresses hazardous materials, operations, and equipment. Users must establish appropriate safety and health practices and determine the applicability of regulatory restrictions before use. Standard laboratory safety precautions must be followed when preparing and testing asphalt concrete specimens.
Technical Development Outlook
With the advancement of nondestructive testing technology, field testing equipment related to the LISST method may become available in the future. Currently, the standard's accuracy and deviation statements have not yet been finalized, and more data needs to be accumulated in practice to improve the evaluation system.
Engineering Application Value Analysis
The implementation of this standard has important guiding significance for preventing asphalt pavement defects such as interlayer slippage and surface cracks. By quantitatively evaluating the performance of the bonding layer, it provides a scientific basis for bonding material selection, construction process optimization, and pavement service life prediction, helping to improve the overall quality of road projects.
AASHTO T 407-2023 Referenced Document
- AASHTO M 231 Standard Specification for Weighing Devices Used in the Testing of Materials*， 2026-04-15 Update
- AASHTO R 18 Establishing and Implementing a Quality Management System for Construction Materials Testing Laboratories
- AASHTO T 312 Standard Method of Test for Preparing and Determining the Density of Asphalt Mixture Specimens by Means of the Superpave Gyratory Compactor
AASHTO T 407-2023 history
- 2023 AASHTO T 407-2023 Determining the Interlayer Shear Strength (ISS) of Asphalt Pavement Layers
