Study on Microstructure Characteristics of Clay Rock of Xigeda Formation in Xichang City Based on Softening Test and Image Recognition

Based on the Xigeda clay rock exposed in the back mountain of Nanshan Villa in Xichang City, the microstructure changes of Xigeda clay rock before and after water softening were studied by scanning electron microscope and image recognition of PCAS software. The results show that: (1) the clay rock of Xigeda group has flake and layered micro structural characteristics, and the surface of aggregates in natural state has honeycomb characteristics. After water softening, the aggregate particles decompose, the average size of particles becomes smaller, the honeycomb characteristics disappear, and the surface contours of particles become smooth and round. (2) With the increase of water saturation time, the number of aggregate particles and pores increases, the porosity decreases in advance and increases in the later stage. (3) Micro structural changes of the clay rock in Xigeda formation have two stages, in the first stage, the aggregates decompose and the produced fine granular clays fill the original pores, resulting in the decrease of porosity.In the second stage, the fine clay particles further soften, decompose and lose in the water, the porosity increases suddenly.

Effect of Fractured Aggregate Particles on Linear Stress Ratio of Aggregate and Resilience Properties of Asphalt Mixes—A Way Forward for Sustainable Pavements

The interlocking and packing of aggregate particles play a key role in achieving high level of linear viscoelastic properties and rutting resistance in asphalt mix for sustainable pavements. In this study, the quantitative effect of fractured aggregate particles (FAPs) on loading (i.e., 500 kPa normal stress), along with the resilience properties of asphalt mixes, was evaluated. Linear and nonlinear stress behaviors of aggregates (from direct shear test) and asphalt mixes (from resilient modulus test) were analyzed. A new quantitative parameter (linear stress ratio), i.e., linear stress (Pi)/maximum stress (Pmax), is proposed to be used in selection of aggregates for asphalt mixes. It was observed that 15.5% increase in FAPs caused 19.5% increase in ϕ and 70.7% increase in linear stress ratio (LSR). The same content of FAPs resulted in 29.4% and 36% increases in total resilient modulus (MRT) and 34.2% and 24.5% increases in instantaneous resilient modulus (MRI) for 0.1 and 0.3 s load durations, respectively. The proposed LSR is observed to be superior to conventionally used ϕ for aggregate resistance in design of flexible pavements.

Study on Migratory Behavior of Aggregate in Asphalt Mixture Based on the Intelligent Acquisition System of Aggregate Attitude Data

In order to provide a new method to study the migration behavior of coarse aggregates in the compaction process of asphalt mixtures, the “Intelligent Aggregate Attitude Acquisition System (IAS)” is developed based on 3D printing technology and wireless intelligent sensing technology, and the “Intelligent Attitude Aggregate (IAA)” is prepared as the acquisition terminal. The Superpave Gyratory Compaction (SGC) test and the Internet of Things (IOT) wireless sensor technology are combined to collect and analyze the attitude data of an SMA-20 asphalt mixture built in IAA at different compaction stages, and the migration behavior of coarse aggregate in the compaction process is quantitatively characterized. The result shows that the IAA is suitable as a “tracking aggregate” to study the aggregate transfer behavior in asphalt mixtures. The IAA in the upper layer tends to move vertically downward, while the particles in the lower layer tend to move horizontally and spatial rotation in the process of rotating compaction. With the increase in asphalt content, the lubrication effect between aggregate particles is obvious, and the friction resistance of aggregate particles decreases when it is embedded downward. Affected by shear force in the process of rotary compaction, the aggregate particles are easier to overcome friction and cause large horizontal migration and spatial rotation. With the increase in compaction temperature, the viscosity of asphalt binder decreases, and the contact friction between aggregate particles decreases. The asphalt content has a significant effect on the displacement in the horizontal plane Dxoy of the aggregate. The asphalt content and compaction temperature have significant effects on the spatial rotation angle Φ of aggregate, but the asphalt content has a greater impact on it.

Study on the Accurate Measurement and Quantitative Evaluation Methods of Aggregate Surface Roughness

In this work, to quantitatively analyze the roughness of the surfaces of road aggregates, the contact measurement technique and contactless scanning technique were, respectively, used to capture the coordinate data of point clouds on the aggregate surface, which were then used to reconstruct the digital elevation models of aggregate particles. Then, the joint roughness coefficient (JRC) was used as an evaluation index, and the quantitative calculation methods of the two-dimensional (2D) contour line roughness and three-dimensional (3D) contour surface roughness of aggregate particles were, respectively, studied. Finally, the anisotropic characteristics and size effect of the roughness coefficients of aggregates with different lithologies were, respectively, investigated, based on which the practicability of the 3D roughness coefficient index was proven. The results demonstrate that the roughness of a road aggregate surface can be quantitatively described by the point cloud data. The 2D roughness of aggregate profile lines exhibits anisotropy, while the 3D roughness of the aggregate contour surface indicates the size effect. The subtle morphological changes of the surface textures of aggregates can be accurately described by the 3D joint roughness coefficient (JRC3D) calculated by the feature parameter method.

Influence of the Chemical Composition of Asphalt and the 3D Morphology of the Aggregate on Contact Surface Adhesion

The influence of the chemical composition of asphalt, the aggregate lithology, and the morphological characteristics of the aggregate on the level of adhesion between the asphalt and the aggregate is investigated. A contactless three-dimensional (3D) white-light scanning technique is used to obtain point cloud data of the aggregate particles. Six independent feature parameters are used as evaluation indices to quantitatively describe the multilevel features of the 3D morphology of road aggregates. Methods for analyzing the feature parameters based on the point cloud data of the aggregate are presented. Subsequently, the process and evaluation standard of the adhesion test are improved to quantify the spalling degree of the asphalt film on the aggregate surface under boiling conditions. The influences of the chemical composition of the asphalt and the aggregate morphology on the level of adhesion between the asphalt and aggregate are analyzed, and the compatibility between aggregates with different lithologies and the asphalt is assessed. The results show that the shape factor (SF) can be used to characterize the needle-flake shape of the particles, the ellipsoid index (E) is suitable to determine the angularity of the aggregate particles, and the 3D joint roughness coefficient (JRC3D) describes the roughness of the particle surface. The type of adhesion between the aggregate and the asphalt includes chemical and physical adsorption; chemical bonding is relatively strong, and the physical orientation force and mechanical interlocking force are relatively weak. Alkaline limestone aggregates should be used with asphalt with a high aggregate content of colloid and asphaltenes. Basalt aggregate with weak alkalinity should be used with asphalt with a high colloid content, and the use of angular aggregates should be avoided. Acidic aggregates with compact shapes, few edges and corners, and rough surfaces should be used prudently.