M.Sc Thesis

M.Sc StudentGoldman Ehud Hanoch
SubjectImplementation of Damage Mechanics to Characterize the
Mechanical Behavior of Asphalt Concrete
under Creep
DepartmentDepartment of Civil and Environmental Engineering
Supervisors DR. Arieh Sidess
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Hot Mix Asphalt (HMA) are used as the top layer in flexible pavements. Loading of the asphalt layer by the traffic loads may cause basic types of mechanical damages. The main ones are fatigue and rutting. Predicting the performance level of the HMA layers and analyzing their resistance to these damages requires characterizing the mechanical behavior of the HMA under conditions that maximally simulate pavement field conditions. Currently, a wide range of constitutive models have been used to characterize the behavior of HMA, such as Elasticity, Plasticity, Viscoelasticity, Viscoplasticity and Creep. Most of these HMA models are not considering damage evolution process during the continuous loading time. Ignoring this factor leads to inaccurate evaluation of pavement durability against various damage characteristics and unreliable prediction of pavement life.

The main goal of this research is to develop an integrated creep damage model for HMA. The damage approach used for developing the model is based upon Kachanov’s approach (1986). The development involves formulating the model, calibrating its parameters, applying Finite Element Analysis, and comparing experimental, analytical and computational results.

The study includes a literature review about the creep phenomenon and its characteristics in HMA. Within this framework, the creep phenomenon was defined, and characterization methods were introduced. The factors influencing the development of creep such as the composition of the asphalt mixture, loading conditions and environmental factors were presented. Furthermore, the study refers to linear mechanical models for describing viscoelastic behavior in static and cyclic loading. Also presented nonlinear mechanical models and non-linear empirical phenomenological models to describe the creep phenomenon. In addition to these models, integrated damage models were reviewed and divided into two main approaches: (a) Schapery approach, (1990), and (b) the Continuum Damage Mechanics (CDM) approach based on Kachanov's work (1986).
Most of the researchers who applied damage models followed Schapery's approach and very few followed the Kachanov's approach.

The model developed in the current research was formulated in the continuum damage mechanics approach according to Kachanov's (1986) theory. The model included six parameters that were calibrated modularly based on experimental creep test results. The model was broadened to the multiple axis loading case.

To calibrate the model parameters, a series of creep tests has been performed. The experimental framework includes a design and preparation sample process, and loading using static creep tests. The sample preparation process includes grading of the aggregate, classification of the bitumen type, preparation of the asphalt mixture, compaction and cutting, drilling, sample instrumentation etc. Continuous static creep tests were performed up to failure at various levels of stress in the range of 0.25-0.4 MPa. The experiments were performed at a uniform temperature of 54°C. At this temperature, the behavior of the asphalt mixture is mainly viscoplastic, which accumulates irreversible residual damage.

The model was implemented into one-dimensional (1D) Finite Element (FE) MATLAB code to predict the creep strain under various loading patterns. Good agreement was observed between our experimental, analytical and computational results.