The aging of asphalt pavements is a key factor that influences pavement performance. Aging can be characterized by laboratory tests and prediction models. Common aging prediction models use the change of physical or chemical properties of asphalt binders based on regression techniques or aging reaction kinetics. The objective of this study was to develop a kinetics-based aging prediction model for the mixture modulus gradient in asphalt pavements to study long-term in-service aging. The proposed model was composed of three submodels for baseline modulus, surface modulus, and aging exponent to define the change of the mixture modulus with pavement depth. The model used kinetic parameters (aging activation energy and preexponential factor) of asphalt mixtures and combined the two reaction rate periods (fast-rate and constant-rate). Laboratory-measured modulus gradients of 29 field cores at different ages were used to determine the model parameters. The laboratory testing condition was converted to the field condition at a given age and corresponding temperature by introducing the rheological activation energy to quantify the temperature dependence of field cores at each age. The end of the fast-rate period or the beginning of the constant-rate period was accurately identified to model these two periods and to determine the associated parameters separately. The results showed that the predictions matched well with the measurements and the calculated model parameters were verified. The proposed aging prediction model took into account the major factors that affect field aging speed of an asphalt pavement, such as the binder type, aggregate type, air void content, pavement depth, aging temperature, and aging time.

Fatigue cracking and permanent deformation develop simultaneously in asphalt mixtures under repeated destructive loading regardless of temperature. Because these two distinctively different damage mechanisms always occur together, it is not possible to obtain pure cracking damage or pure permanent deformation damage in any asphalt mixture by varying the temperature or loading level. This paper develops an energy-based method to separate fatigue cracking from permanent deformation in terms of energy consumption. Specifically, the dissipated pseudostrain energy (DPSE) expended on cracking is separated from that expended on permanent deformation. Controlled-strain repeated direct tension (RDT) tests are performed on asphalt mixture specimens to determine their nondestructive properties, critical nonlinear viscoelastic properties, and destructive properties. The total DPSE, which is the amount of energy dissipated for the fatigue damage, including both fatigue cracking and permanent deformation, is ca...

With increased awareness of environmental protection, the output of traditional curing agents such as cement and lime is less and less, so it is urgent to develop new curing agents with high efficiency and environmental benefits. Thus, this study aims at investigating the application of rice husk ash (RHA) from agricultural waste to the soft soil stabilization. A series of tests are conducted to analyze the strength development process and soil–water characteristics of rice husk ash–lime (RHA–lime) stabilized soils. The results of the strength tests showed that by increasing the content of RHA, the unconfined compressive strength (UCS) and splitting strength of stabilized soils increased first and then decreased. The effective shear strength indexes of the three soil types (soft soil, lime-stabilized soil, and RHA–lime soil) are measured and compared. It is found that RHA can effectively improve the shear resistance and water resistance of stabilized soil. The results of methylene blue test demonstrated that RHA can also promote the reduction of the specific surface area and swelling potential energy of lime-stabilized soil. In addition, the influence of RHA on mineral composition and morphology change in stabilized soils is studied at the microscopic level. The X-ray diffraction tests and scanning electron microscope (SEM) tests showed that strength development and change of soil–water properties of RHA–lime stabilized soil are attributed to enhanced cohesion by cementation and pores filling with agglomerated mineral.

Fatigue cracking is a common distress in asphalt pavements, but most existing models to predict its growth are generally empirical or phenomenological in nature. To fill this gap, this paper aims at developing an energy-based mechanistic approach to model the fatigue crack growth in asphalt mixtures. The core of this approach is establishing the energy balance equations between the apparent energy of the bulk specimen and the true energy of the intact material. A controlled-strain repeated direct tension (RDT) test is used to generate fatigue cracking damage in asphalt mixtures. The true stresses, true strains, and true pseudostrains are simulated through the force equilibrium and energy balance equations. The true stress in a damaged asphalt mixture is found to be the driving force for crack growth; the crack growth in turn aggravates the localization of the true stress/true strain. The ratio of the true stress and the apparent stress in a damaged asphalt mixture is used to calculate the damage d...