Nonlinear Fatigue Damage Model of Asphalt Mixture Based on Dynamic Modulus and Residual Strength Decay

Abstract

In order to describe the fatigue damage state of asphalt mixture more reasonably, direct tensile tests of the fatigue and the residual strength under stress levels of 1.00 MPa, 0.50 MPa and 0.25 MPa with five parallel tests were carried out. The trabecular specimens of AC-13C asphalt mixture (25 cm × 5 cm × 5 cm) were manufactured with Styrene-Butadiene-Styrene (SBS) modified asphalt, aggregate basalt and limestone mineral filler. The optimum asphalt-aggregate ratio was 5.2%. The dynamic modulus decay and the residual strength decay were termed as the damage variables to evaluate the fatigue damage process of asphalt mixtures, respectively. Based on the test results, the decay patterns of the dynamic modulus and the residual strength during fatigue tests under different stress states were revealed, and the model and the parameters of fatigue damage according to the corresponding decay patterns were obtained. Then, based on the assumption that the residual strength and dynamic modulus depend on the same damage state, the relationship between the two damage definitions was given, and the residual strength-dynamic modulus coupled model was established. The results showed that the residual strength-dynamic modulus coupled model could better describe the fatigue damage evolution law of asphalt mixture, and the parameter of this coupled model could be obtained by less residual strength tests. A modified formula for calculating the damage variables associated with residual strength and dynamic modulus was proposed based on the relationship between two kinds of damage variables.

Research on the Modulus Decay Model under a Three-Dimensional Stress State of Asphalt Mixture during Fatigue Damage

“…The fatigue stress strength ratio ∆ is served as a fatigue resistance index, with Equation ( 22) defining its formula. ∆ = σ ei σ es (22) where σ ei represents the initial equivalent stress, while σ es represents the equivalent stress at the point of fatigue failure. The formula for equivalent stress is:…”

“…where σ 1 is the first principal stress; σ 2 is the second principal stress; σ 3 is the third principal stress. Equation (22) shows the ratio of the stress level to material resistance during asphalt mixture fatigue testing. Using the ratio ∆, which considers the stress state and loading rate, a normalized fatigue equation is established as follows.…”

“…It should be noted that one crucial mechanical parameter that plays a significant role in determining the asphalt pavement's service life is the modulus of pavement material [16][17][18]. An essential factor to take into account in pavement design and maintenance is the decay pattern of the modulus, which can serve as a general measure of asphalt pavement's damage law [18][19][20][21][22]. Thus, according to the strain equivalence assumption of viscoelastic damage mechanics theory, some scholars defined the reduction in modulus (stiffness) as a damage variable to study the asphalt mixes' fatigue damage features.…”

“…Lv et al [21] also analyzed the modulus decay characteristics of asphalt mixtures with various loading circumstances. By utilizing DT fatigue testing, Liu et al [22] revealed the attenuation law of remaining strength and dynamic modulus. Additionally, they established a coupled fatigue damage evolution model of remaining strength and dynamic modulus.…”

A Prediction Model on Viscoelastic Fatigue Damage of Asphalt Mixture

“…Mahmoud et al [ 10 ] applied viscoelastic continuum damage theory to simulate the asphalt fatigue properties, and found that there was a good correlation between viscoelastic parameters and anti-fatigue performance of asphalt mixture. Liu et al [ 11 ] found that the residual strength-dynamic modulus coupled model could better describe the fatigue damage evolution law of an asphalt mixture, and the parameter of this coupled model could be obtained by fewer residual strength tests. The fatigue life model of an asphalt mixture based on the definition of damage variable was put forward by Castro et al [ 12 ].…”