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Aggregate Gradation Specification [3]) determined that the mance. New innovations in aggregate testing were also exam-
restricted zone was a redundant requirement when used in con- ined, especially those related to aggregate shape, angularity,
junction with the other aggregate and volumetric properties and texture.
specified in AASHTO M323. Pooled Fund Study 176, "Vali-
dation of SHRP Asphalt Mixture Specifications Using Accel-
erated Testing," examined the effects of VMA, fine aggregate 1.3 SCOPE
angularity (FAA), and gradation on the performance (pri-
To accomplish the research objectives, five tasks were con-
marily rutting) of HMA. Finally NCHRP Project 4-30, "Test
ducted; their descriptions are as follows:
Methods for Characterizing Aggregate Shape, Texture, and
Angularity," was recently awarded. It is expected that this
· Task 1--State of the Practice: In Task 1, a literature
study will provide new methods to more accurately measure
search and review was conducted to determine the cur-
the aforementioned properties with improved precision.
rent state of the practice on the evaluation and valida-
Evaluation of aggregate properties has been included in
tion of the Superpave aggregate criteria and the state of
some field and accelerated performance studies. The LTPP
the art on the development of promising new methods
Program documents the construction and tracks the perfor-
of aggregate characterization. The results from Task 1
mance of numerous HMA pavements. Some of the HMA
are presented in Chapter 2. The influence of aggregate
pavements in the Specific Pavement Studies (SPS) were
crushing operations is also discussed in Chapter 2.
designed with the Superpave methodology. The SPS-1, -5, and,
· Task 2--Survey of Ongoing Research: In Task 2, a sur-
particularly, -9 sections provide limited data relating aggregate
vey was conducted to identify the preliminary findings
properties to performance. Three test tracks--the MnRoad,
of ongoing research related to aggregate properties. The
WesTrack, and the NCAT Test Track--include Superpave-
results from Task 2 are presented in Chapter 2 in con-
designed HMA. The NCAT Test Track has a number of dif-
junction with the results from the literature review.
ferent aggregate sources and gradations represented by the test
· Task 3--Survey of Agency Specifications: A survey was
sections. Accelerated testing related to aggregate properties
conducted of state aggregate specifications for aggregate
has also been conducted by the FHWA's Accelerated Load-
used in the production of HMA. The survey provides
ing Facility (ALF) and the Indiana Department of Transporta-
insights into the widespread adoption of the Superpave
tion (DOT)Purdue University APT Facility.
method and into the aggregate tests that agencies ques-
Based upon performance histories of locally available mate-
tion. The survey results are summarized in Chapter 3; see
rials or research projects conducted to address concerns relat-
also the Appendix.
ing to the aggregate specifications included in AASHTO
· Task 4--Review Performance Data from Field Test Sec-
M323, numerous agencies have modified their aggregate
tions and Full-Scale Accelerated Testing: Results from
specifications for Superpave-designed HMA. Often times this
field test sections and accelerated test sites were reviewed
experience is not shared with other agencies that are using
to gather performance relationships for aggregate prop-
similar materials. A consensus among the states, based on their
erties. As expected, there are complex interactions when
experiences, may indicate the need to alter aggregate test pro-
aggregate properties are altered. These interactions tend
cedures or specifications on a national basis.
to dilute any correlations that may exist; however, trends
were identified. The results from the performance review
1.2 OBJECTIVE are summarized in Chapter 4. Specific experiments are
also discussed in relationship to specific test methods in
The objective of this study (NCHRP Project 9-35) was to Chapter 2.
review the technical literature and ongoing research to identify · Task 5--Final Report: The final report was prepared
the consensus, source, or other aggregate properties that sig- to document all of the research conducted in Tasks 1
nificantly impact HMA performance. The review also exam- through 4. Chapters 5 and 6 present (1) future work sug-
ined the effect of production and crushing operations on gested for validating new aggregate shape and texture
aggregate properties. The review concentrated on the effect parameters based on image analysis and evaluation of
of aggregate properties on HMA designed using the Super- the CAR test and (2) a summary of the conclusions of
pave methodology, HMA construction, and HMA perfor- NCHRP Project 9-35.
