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Pro037

Bottom-up fatigue cracking: myth or reality?



Title: Bottom-up fatigue cracking: myth or reality?
Author(s): A. A. A. Molenaar
Paper category : conference
Book title: Fifth International RILEM Conference on Reflective Cracking in Pavements
Editor(s): C. Petit, I.L. Al-Qadi and A. Millien
Print-ISBN: 2-912143-47-0
e-ISBN: 2912143764
Publisher: RILEM Publications SARL
Publication year: 2004
Pages: 275 - 282
Total Pages: 8
Nb references: 4
Language: English


Abstract: Mechanistic design procedures almost exclusively predict that the highest tensile strain occurs at the bottom of the asphalt layer especially when this layer is placed on an unbound base. Consequently fatigue cracking is predicted to initiate at the bottom of the asphalt layer and it is assumed that these fatigue cracks propagate upwards. If this is true then many cracks that are observed in practice should have propagated through the entire asphalt thickness. From coring it is however known that most of the longitudinal cracks observed at the pavement surface are wearing course cracks with a depth of only 40 - 50 mm. Furthermore one observes that cracks that have propagated through the entire asphalt thickness are mostly related to reflective cracking and not to bottom - up fatigue. The question therefore is "does bottom up fatigue cracking we predict with our mechanistic models exist or is it a myth which means that our design models are wrong". This paper shows that it is unlikely that fatigue cracks that initiate at the bottom of the asphalt layer really appear as well defined cracks. It will also be shown that it is much more likely that such cracks appear as a disintegrated zone. Furthermore it will be shown that such a zone is detected from full scale accelerated pavement testing where an increase in tensile strain at the bottom of the asphalt layer was measured and where, by means of falling weight deflectometer tests, a reduction of the effective stiffness of the asphalt layer of more than 50% was observed.


Online publication: 2004-04-15
Publication type : full_text
Public price (Euros): 0.00