DEF Grilli Andrea PhD Thesis 2007.pdf

Chapter 1: Introduction
The second section, related to water sensitivity of asphalt mixture, has
been developed in cooperation with EMPA (Swiss Federal
Laboratories for Materials Testing and Research).
Two mechanisms are related to water damage: cohesion failure and
adhesive failure (R. G. Hicks et al., 2003).
A loss of cohesion causes an overall weakening such as a reduction of
strength and stiffness, based on the emulsification of water in the
asphalt binder film, thus generating failure within the asphalt binder
film coat of the aggregate (Fromm, 1974) and reducing resistance
against stresses and strains. Adhesion failure, on the other hand,
typically results in debonding of aggregate and binder, implying
progressive loss of material and ravelling (Kandhal et al., 1989,
Kandhal and Rickards, 2001). Since, it is difficult to distinguish
between cohesion and adhesion failure modes, one can assume that,
generally, deterioration of asphalt pavements in presence of water is
caused by both failure modes in a coupled way.
Numerous research projects have been conducted to understand and
predict moisture damage in asphalt mixtures and remarkable progress
has been made up to now (Al-Swailmi and Terrel, 1992, Terrel and
Al-Swailmi, 1994, Nguyen et al., 1996, Epps et al., 2000, West et al.,
2004, Kim and Coree, 2005, Airey et al., 2003, Kim and Coree, 2006).
As a result, different test methods and procedures have been
developed. In particular, they may be generally classified into two
main categories: tests performed on loose mixtures and tests carried
out on compacted mixtures (Kiggundu and Roberts, 1988, Brown et
al. 2001, Airey and Choi, 2002, Solaimanian et al., 2003).
Tests on loose asphalt mixtures focus on moisture related adhesion
and cohesion failure for subjective evaluation and assessment of
stripping potential. Asphalt mixtures are usually immersed in water
for a specific time at constant temperature and visually inspected in
search of “stripped” or uncoated aggregates (Kennedy and Ping, 1991,
Dunning et al., 1993, Aschenbrener et al., 1995).
Tests on compacted asphalt mixtures may be further categorized into
both rutting tests on asphalt pavement slabs evaluating the
development of permanent deformation under repeated wheel loading
in presence of water (Smit et al., 2002, Raab et al., 2005, Solaimanian
et al., 2006) and static or cyclic loading tests where the reduction of
selected mechanical properties of compacted specimens or cores
during or after immersion in water are determined (Al-Swailmi and
Terrel, 1992, Aschenbrener et al., 1995, Kim and Coree, 2006,
Solaimanian et al., 2006).
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