Damage-creep characteristics and model of asphalt mixture

The typical creep curve under uniaxial compression could be divided into three phases: decelerating creep phase,even creep phase and accelerating one.The three-phase creep course was the result of the competition between damage and hardening.The hardening of viscosity coefficient was the main cause of the decelerating phase of creep;and the accelerating phase was mainly due to the damage effect.The damage mechanism and the hardening one kept their balance in the even creep phase.It was unreasonable to describe and explain the three-phase creep by using the nonlinear viscosity coefficient or the damage only.So,based on the rheological component model,the damage and hardening effects were both introduced into the creep model to express the three-phase creep behavior.Hooker body and Kelvin model were adopted to represent the elastic and viscoelastic characteristics respectively,and Newton body was modified with a hardening variable.Then,a new damage-creep model was established for asphalt mixture by use of the complete decoupling method.Finally,the proposed model was verified through two experimental studies,and the results of model agreed with those of test perfectly.Damage was a linearly related with time in the most of the creep,but increased rapidly at the moment when the material was close to failure.In the primary and secondary phases,damage also existed and its value was small.But it was unreasonable to ignore the damage.The flow time,which was defined as the onset of the tertiary phase,could be used as an index to study the damage-creep characteristics of asphalt mixture,and the larger value denoted the longer time which was needed to enter into the tertiary phase for asphalt mixture.