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OCR for page 26
26 A Manual for Design of Hot Mix Asphalt with Commentary
and other major construction projects, reliability levels of at least 95% should be used when
selecting performance-graded binders.
Practical Selection of PG Binder Grades
for HMA Mix Design
Although the LTPPBind computer program is very useful, in practice most highway agencies
have, through experience, developed their own systems for selecting binder performance grades
depending on traffic level and location. This has been done in part because refineries are able to
produce only a limited number of binder grades, so engineers must determine two or three per-
formance grades that can be used to meet most or all of the paving needs in a given region. This is
sometimes referred to as a "binder slate" for a given state or region. For example, a common binder
slate in the Mid-Atlantic states involves only three performance grades: 58-28, 64-22, or 76-22.
Other binders might be occasionally used in this region, but typically only for small demonstration
projects. Engineers selecting performance-graded binders for paving applications should refer to
the appropriate specifications for their state or, if there are none, to those in neighboring states with
similar climates and conditions. Binder producers may also be useful in providing information
concerning what binder performance grades are available locally and which might be most
appropriate for a given application. Engineers and technicians using the LTPPBind program
without referring to the binders used by the local highway agency may find that the binder they
have specified for a given application is not locally available.
In selecting performance-graded binders from an available slate, it must be remembered that a
given performance grade will meet the requirements of many less extreme situations. For example,
in many areas of the Mid-Atlantic, LTPPBind (version 3.1) indicates that a PG 58-22 binder should
be used for light traffic. However, this binder may not be available in some Mid-Atlantic states.
If the PG 58-22 binder cannot be found (or found at a reasonable price), a PG 64-22 binder would
be selected and would perform perfectly well, since its extreme high and low temperature ratings
meet or exceed those for these applications. Care should however be used in selecting binders
that are much stiffer than required for a given application. Recently, many highway agencies have
noticed an increase in surface cracking in HMA pavements. Although such top-down cracking
is not yet fully understood, using unnecessarily stiff binders may contribute to the problem.
Additional details concerning the selection of asphalt binders for HMA mixtures are given in
Chapter 8 of this manual.
Bibliography
AASHTO Standards
M 320, Performance-Graded Asphalt Binder
M 323, Superpave Volumetric Mix Design
PP 42, Determination of Low-Temperature Performance Grade (PG) of Asphalt Binders
R 28, Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV)
R 29, Grading or Verifying the Performance Grade of an Asphalt Binder
R 35, Superpave Volumetric Design for Hot-Mix Asphalt (HMA)
T 48, Flash and Fire Points by Cleveland Open Cup
T 49, Penetration of Bituminous Materials
T 51, Ductility of Bituminous Materials
T 53, Softening Point of Bitumen (Ring-and-Ball Apparatus)
T 202, Viscosity of Asphalts by Vacuum Capillary Viscometer
T 240, Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test)
T 313, Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR)
OCR for page 27
Asphalt Binders 27
T 314, Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT)
T 315, Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR)
T 316, Viscosity Determination of Asphalt Binder Using Rotational Viscometer
Other Publications
The Asphalt Institute, Asphalt Binder Test Manual (MS-25).
The Asphalt Institute (2007) The Asphalt Handbook (MS-4A), 7th Ed., 832 pp.
The Asphalt Institute (2003) Superpave Performance Graded Asphalt Binder Specifications and Testing, 3rd Ed.,
72 pp.
