The objective of this study was to develop models for predicting the
applications to the initiation of cracking for flexible pavements and to
develop models for
predicting crack propagation in flexible pavements. Crack initiation was
defined as the first
appearance of cracking in the wheel paths. The models are aimed for use in
Systems. Data used in the study consisted of data from a Swedish LTPP study
where over 600 test
sections have been monitored during more than ten years. Every year a
detailed distress survey,
measurements of rut depth and the longitudinal profile have been carried out
at each test section.
The database contains information about traffic, climate, pavement structure,
surface condition and
structural strength. Pavement response based explanatory factors included,
among other things,
tensile strain at the bottom of the asphalt layer and other deflection based
factors (i.e. surface
curvature index, curvature basin factor, bearing capacity).
The modelling of crack initiation models was carried out using a survival
The modelling of crack propagation models was carried out using linear
regression analysis. From
the data, describing the yearly development of cracks, a Cracking Index was
calculated. The same
approach of developing crack models was used in the PARIS (Performance
analysis of road
infrastructure) project carried out within the 4th European Framework
Programme Road Transport
Models were successfully developed to predict the cumulative number of
traffic loading to the
initiation of cracking in the wheel paths. The models included two
independent variables to
pavement response and ageing (a relationship between a response variable and
cumulative number of traffic loading). As response variables Surface
Curvature Index 300 or
Tensile Strain at the bottom of the asphalt layer can be used in the crack
Models were also developed to predict crack propagation in the wheel paths.
For any given
section of road, the slope of the linear model can be estimated from the
level of distress at the last
distress survey and the age of the pavement surface or the number of ESALs
carried by the
pavement at that time.
All models have been validated against independent data, not used in the
The results of the validation process show that the models meet the
requirements for models to be
used in Pavement Management Systems.
Linköping: Statens väg- och transportforskningsinstitut., VTI meddelande 916 , 2001.
Swedish, Sweden, Flexible pavement, Fatigue, Cracking, Rutting, Development, Forecast, Mathematical model, Input data