沥青混合料损伤蠕变特性及模型研究

沥青混合料蠕变过程中,硬化、损伤两种机制同时存在。当硬化机制占主导地位时,蠕变呈现为衰减状态;当损伤机制占主导地位时,蠕变呈现为加速状态;两者互为接近时,则呈现为等速或者近似等速状态。只考虑损伤或黏滞系数的非线性变化均不能合理地描述和解析蠕变过程的3个阶段。以流变学模型理论为基础,综合考虑损伤和硬化效应,建立了一个统一的沥青混合料损伤蠕变模型。将该模型与试验曲线进行对比,两者吻合较好,说明该模型能够反映沥青混合料三阶段蠕变的全过程。在蠕变的大部分时间内损伤的发展都是平稳的,在接近破坏时损伤则会快速发展。在蠕变的第一、二阶段也存在损伤,只是损伤值较小,而将其忽略是不合理的。定义第三阶段起始的时间为流变时间,可作为研究沥青混合料损伤蠕变特性的指标,其值越大,表示蠕变变形进入破坏阶段所需要的时间越长。

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.