Analysis of Factors Influencing the Modulus of Hot-Recycled Asphalt Mixture with High RAP.

Generally, the dynamic modulus and bending stiffness modulus are used to evaluate the mechanical properties of asphalt mixture, and they are also used as basic parameters for asphalt mixture design. Therefore, a study was conducted on changes in the dynamic modulus and bending stiffness modulus of hot-recycled asphalt mixture with high levels of reclaimed asphalt pavement (RAP) under the influence of different factors: dosage of regenerant, curing temperature, and curing time. The performance of reclaimed asphalt pavement (RAP) was first evaluated. Then, the hot-recycled asphalt mixture was adjusted and designed in order to conduct modulus experiments, composed of the dynamic modulus test and three-point bending test. Finally, the influencing factors were not only qualitatively but also quantitatively analyzed to clarify the change laws of the mechanical parameters of hot-recycled asphalt mixture. The results showed that the modulus of the recycled asphalt mixture first decreased, then increased, and then decreased with increasing dosage of regenerant. As the curing time or temperature increased, the modulus first decreased and then increased. In terms of the dynamic modulus of the hot-recycled asphalt mixture, the curing time had the greatest impact, followed by dosage of the regenerant and curing temperature. For bending stiffness modulus, the influence of dosage of the regenerant was the greatest, followed by curing time and curing temperature. For the bending stiffness modulus of hot-recycled asphalt mixture, the curing conditions had a greater influence compared with the dynamic modulus.

Comparative Study of Damage Detection Methods Based on Long-Gauge FBG for Highway Bridges.

Damage detection of highway bridges is a significant part of structural heath monitoring. Conventional accelerometers or strain gauges utilized for damage detection have many shortcomings, especially their monitoring gauge length being too short, which would result in poor damage detection results. Under this circumstance, long-gauge FBG sensors as a novel optical sensor were developed to measure the macro-strain response of the structure. Based on this sensor, many derived damage detection methods were proposed. These methods exhibit various characteristics and have not been systematically compared. As a result, it is difficult to evaluate the state of the art and also leads to confusion for users to select. Therefore, a strict comparative study on three representative methods using long-gauge FBG was carried out. First, these methods' theoretical backgrounds and formats were reformulated and unified for better comparison. Then, based on validated vehicle-bridge coupling simulation, these methods' performances were tested through a series of parametric studies including various damage scenarios, vehicle types, speeds, road roughness and noise levels. The precision and reliability of three methods have been thoroughly studied and compared.

Reasonable thickness design of expressway pavement structures based on gray relation analysis of subgrade soil improvement.

During the design of pavement structures, determining a reasonable thickness for pavement layers is critical. When an expressway is to be built in an area with a poor soil foundation, a reasonable subgrade treatment will make the pavement more durable. However, determining the optimal thickness of subgrade treatment is a difficult task for designers. A thicker treatment means a huge cost increase for the project, whereas a thinner treatment cannot achieve significant improvement in the mechanical behavior of pavement structures. This study used the finite-element method to analyze the mechanical response of real field pavement with subgrade treatments at certain depths. The study used an orthogonal design and gray relational theory to analyze the design indicators and make a better design for the pavement structure of a field expressway. The numerical calculation index and theoretical analysis results show that the treatment depth of subgrade soil has a significant influence on the stresses in an asphalt pavement structure and the bottom tensile strains of the asphalt layers. Therefore, designing a pavement structure with equal structural strength, using a reasonable depth for the cement-treated subgrade, instead of increasing the asphalt layer's thickness, is a more cost-effective solution.

Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation.

Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt-aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt.

Modelling and laboratory studies on the adhesion fatigue performance for thin-film asphalt and aggregate system.

Adhesion between asphalt and aggregate plays an important role in the performance of asphalt mixtures. A low-frequency adhesion fatigue test was proposed in this paper to study the effect of environment on the asphalt-aggregate adhesion system. The stress-based fatigue model had been utilized to describe the fatigue behavior of thin-film asphalt and aggregate system. The factors influencing the adhesion fatigue performance were also investigated. Experiment results show that asphalt has more important effect on the adhesion performance comparing with aggregate. Basalt, which is regarded as hydrophobic aggregates with low silica content, has better adhesion performance to asphalt binder when compared with granite. The effects of aging on the adhesion fatigue performance are different for PG64-22 and rubber asphalt. Long-term aging is found to reduce the adhesion fatigue lives for rubber asphalt and aggregate system, while the effect of long-term aging for aggregate and PG64-22 binder system is positive. Generally the increased stress amplitude and test temperature could induce greater damage and lead to less fatigue lives for adhesion test system.