Page 375 - Mechanics of Asphalt Microstructure and Micromechanics

CHAPTER11

Simulation of Asphalt Compaction

11.1 Introduction
Compaction of asphalt concrete (AC) is one of the most important steps in controlling
the quality of pavement construction. More importantly, many problems arise during
compaction: some mixes may not be easy to compact compared to others (perhaps indi-
cating a good mix); too thin a layer thickness may prevent effective compaction; a
weaker mastic may make compaction easy but it does not indicate good quality; a soft
base or sub-base may cause difficulties for compaction (compaction energy is absorbed
by the base or sub-base); the non-uniformity of the base or sub-base support causes
non-uniform compaction if operation parameters do not vary correspondingly; and a
change of environmental conditions such as temperature and wind speed results in a
change of viscosity and therefore compaction effectiveness. An understanding of how
these, and other factors, affect compaction in the point of view of fundamental mechan-
ics will help achieve better compaction and optimize layer thickness.
Due to the many influencing factors, it is difficult to develop simple mathematic
compaction models to relate these influencing factors with the end product properties
such as density, modulus, and performance. In addition, due to the significant differ-
ences between field conditions and laboratory conditions in loading, boundary, and
environmental constraints, it is challenging to develop the relationship between lab
compaction and field compaction. Research on compaction modeling may help: 1) re-
late laboratory to field compaction; 2) identify the controlling factors that affect density
and performance; and 3) provide guidance on construction process control for better
quality AC.
A tremendous amount of research has been conducted in recent years relating to lab
and field compaction (Huerne 2004; Masad et al., 2009; Wang et al., 2007; Partl, 2007a,
2007b). The following presents the modeling of AC in two categories—the lab compac-
tion and the field compaction.

11.2 Lab Compaction

11.2.1 Empirical Method-Soil Consolidation Analogy
Figure 11.1 presents a typical idealized gyratory compaction curve. Figure 11.2 pres-
ents the same curve in the air-void reduction view. It should be noted that the gyratory
compaction is similar to a one-dimensional (1D) consolidation. If the volumetric defor-
mation of asphalt binder and aggregates is neglected, the change of the air-void con-
tent is actually the incremental volumetric strain of the sample. In the 1D situation, the

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