Fundamental Properties of Asphalts and Modified Asphalts, III

SUBTASK 2-5. MODIFIED ASPHALTS (continuing on Year-1 funds)
Statement of Problem
Asphalt modifiers are often added to meet binder purchase specifications. Common modifiers
include polymers to improve rutting resistance, lime and antistrip additives to mitigate moisture
damage, polyphosphoric acid for rutting resistance, and reclaimed asphalt pavement (RAP) for
reducing costs. New modifiers are also being introduced to enable warm-mix asphalt (WMA)
technologies where mix and compaction temperatures can be substantially reduced. One of these
modifiers is water (typically used to foam the asphalt), which improves the workability of
binders at mixing and laydown temperatures and appears to have little effect afterwards,
although there is some evidence that entrapped moisture may increase stripping [Hurley and
Prowell 2005]. In addition, the long-term effectiveness of some modifiers under highway
conditions is not known. Often, the mechanism of action of a modifier is understood only in an
empirical sense and the effective treatment levels and economical treatment levels may differ. It
is also important to point out that modifier interactions may reduce effectiveness and waste
resources.
Approaches
The sensitivity of PPA-modified asphalts to environmental factors is being determined using
laboratory PAV aging tests on modified and unmodified asphalts in the presence and absence of
moisture in the oven. Analytical tests applied include spectroscopic (FTIR) and rheologic (DSR)
of the aged materials. Master curve and shift factors are used to quantify changes.
Nuclear magnetic resonance techniques are being applied to study the reactions between
phosphorous-containing additives including antistrips and PPA in asphalts.
Goals
The goal of this research is to develop a detailed description of the actions of modifiers in
asphalts while varying environmental conditions. Where feasible, efforts are directed toward
developing relationships for predicting long-term behavior from initial laboratory tests.
Support of FHWA Strategic Goals
The work conducted in this subtask supports the FHWA strategic goal that addresses
environmental stewardship and safety. State agencies need a better understanding of how and
when to use additives, such as recycled asphalt pavement (RAP), polymers and/or
polyphosphoric acid (PPA), to improve the performance of asphalt pavements. Obviously, better
performing and longer lasting asphalt pavements, which incorporate the use of RAP, lead to the
utilization of less asphalt, thus decreasing the demand for reconstruction of pavements and
incidentally safer roads.
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