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CHAPTER 1
Introduction and Research Approach
measuring stiffness and permanent deformation properties
1.1 Problem and Purpose of asphalt concrete. Additional work, however, was needed
National Cooperative Highway Research Program (NCHRP) to further refine the SPT for use in routine practice. This
Project 9-19, "Superpave Support and Performance Models additional work was undertaken in Phases IV and V of NCHRP
Management" recommended three candidate simple perfor- Project 9-29. These phases of the project included four major
mance tests to compliment the Superpave volumetric mixture activities directed at implementation of the SPT in routine
design method. These tests are: flow time, flow number, and practice:
dynamic modulus. The recommended tests are conducted in
uniaxial or triaxial compression on cylindrical specimens that 1. Enhancement of the SPT to perform dynamic modulus
are sawed and cored from over-height gyratory compacted master curve testing required for pavement structural de-
samples. Data from all three candidates were shown to corre- sign and analysis.
late well with observed rutting in field pavements, and the 2. Procurement and evaluation of SPTs with dynamic modu-
dynamic modulus appears to have potential as a simple per- lus master curve testing capability.
formance test for fatigue cracking (1). The dynamic modulus 3. Development of equipment for rapid preparation of test
is also the primary material input for flexible pavement struc- specimens for the SPT.
tural design in the Mechanistic-Empirical Pavement Design 4. Ruggedness testing for dynamic modulus and flow num-
Guide (MEPDG) completed in NCHRP Project 1-37A (2). ber tests conducted in the SPT.
The use of this test for both mixture evaluation and structural
design offers a potential link between mixture design and This report documents the ruggedness experiments that were
structural analysis that has been an underlying goal of a sub- performed in Phase V of the project.
stantial amount of past flexible pavement research.
The objective of NCHRP Project 9-29 is to stimulate the de-
1.2 Scope
velopment of commercial testing equipment that is capable of
performing the NCHRP Project 9-19 performance tests. It is In Phase V of NCHRP Project 9-29 a series of experiments
envisioned that this equipment will be used for two purposes: were designed, conducted and analyzed to assess the SPT
(1) as a simple performance test to complement Superpave equipment and test procedures for the dynamic modulus and
volumetric mixture design and (2) for the asphalt concrete flow number tests. Phase V included two major experiments.
material characterization required by the MEPDG and other The first was a formal ruggedness experiment in accordance
similar flexible pavement structural design methods. with ASTM E1169, Standard Guide for Conducting Ruggedness
In Phase I of NCHRP Project 9-29, a detailed purchase Tests. The second was an experiment designed to investigate
specification for the Simple Performance Test System (SPT) whether there are significant differences in SPT data collected
was developed. The SPT is capable of performing the three with equipment from the three manufacturers: Interlaken
NCHRP Project 9-19 performance tests, and it standardizes Technology Corporation (ITC); IPC Global (IPC); and Med-
the instrumentation, data acquisition, and data analysis as- ical Device Testing Services (MDTS). Although the flow time
sociated with each test. In Phase II, two first article devices test was not formally included in the experiments, the find-
were procured and evaluated. This evaluation concluded ings from the flow number testing were also applied to the flow
that the SPT is a reasonably priced, user-friendly device for time test.
