Page 396 - Mechanics of Asphalt Microstructure and Micromechanics

388 Ch a p t e r E l ev e n

some of these empirical relationship, one parameter on the gradation is difficult to be
carried in these formulations. Of the inputs on the material sides, representing a grada-
tion is challenging.
Taking the formulation for the compaction slope as an example, a reference case
may be specified, which might be a uniform size of marble spheres of 0.5 in as the refer-
ence gradation and aggregates. For this material, the gradation factor is defined as 1.0,
the combined aggregate shape, angularity, and texture contribution factor is also set
to 1.0 approximately. In order to calibrate it, three different aggregates (including the
uni-size marble spheres) shall be characterized for the shape, angularity, and texture
factors. For this case, uniform size aggregates, asphalt binder content, and asphalt rhe-
ology contributions can be well calibrated through mixing and compacting the mixture
at different temperatures. For this reference case, through X-ray scanning of the aggre-
gate locations, the compaction process can be accurately modeled.
Aggregate gradation design, as part of the SuperPave mixture design method, is a
process of selecting aggregate blends to ensure appropriate volumetric properties such
as VMA for the mix stability and durability; suitable maximum aggregate size for com-
paction; and adequate aggregate skeleton for strength. The current SuperPave mixture
design method, however, does not provide specific guidance in the selection of grada-
tion, and the gradation design is still a trial and error process. In addition, the tradi-
tional gradation design method requires a series of percentages of aggregate particles
passing a certain number of sieve size to describe a complete gradation blend. There is
no single parameter or parameters that can be used for evaluating a gradation and link-
ing the gradation to other performance parameters. Representing a gradation is still a
challenging problem.

11.7 Intelligent Compaction
One of the important applications of modeling and simulation of the compaction pro-
cess is interpretation of the compaction data collected automatically during the com-
paction. Intelligent compaction (IC) is supposed to provide oversight and better control
of the compaction process and results in improved quality and productivity of roadway
pavements.
IC originated in the late 1970s with the work of the European equipment makers
BOMAG, AMMANN, and Geodynamik that still dominate the market today. IC tech-
nology is currently used in Europe and Asia, and has recently been introduced in the
United States. IC refers to the compaction of subgrade soils, unbound aggregate base/
sub-bases, or AC using vibratory rollers equipped with an in-situ measurement and
feedback system. Global positioning system (GPS) based mapping is often used to au-
tomate the documentation of results. By integrating measurement, documentation, and
control systems, the use of IC rollers allows for real-time corrections in the compaction
process.
The most common quality control test method in road construction is the spot test,
including the static plate load test and the falling weight deflectometer (FWD) test for
modulus; and the nuclear gauge, the water balloon, and the sand replacement tests for
density. In asphalt compaction, the drilled cores, radiometric sounds (modulus), and
pavement quality indicator (PQI) tests are used.
IC technology combines the continuous measurement of absolute values (density
and/or stiffness) of the achieved compaction with a regulation system that uses the