Recycled aggregates from construction and demolition wastes as alternative filling materials for highway subgrades in China

Aggregate occupies at least three-quarters of the volume of asphalt mixture and can significantly affect the performance of pavement. The geometrical morphology influences the slippage and interlock among aggregates for resisting and distributing applied loads. In recent years, the discrete-element method (DEM) has been employed for simulation of asphalt mixture structure. This paper introduces an approach for simulation of aggregate and asphalt mixtures using parameterized shape and size gradation. Both the plane geometry factor (PGF) and the section aspect ratio (SAR) were employed to describe the three-dimensional (3D) geometric characteristics of aggregates. A numerical technique of aggregate models was implemented with probabilistic parameters depending on statistical results of PGFs and SARs. The 3D numerical model of asphalt mixtures was assembled with three different components, and was validated by uniaxial compression tests via comparison with the laboratory result. It was found that the PGF and SAR are appropriate to describe the three-dimensional features of aggregate shapes, because a simplified space object can be described by a two-dimensional (2D) graphical projection and a vector scalar corresponding to the space vector. Probability distribution curves of PGFs and SARs between coarse aggregates were in concordance with the Gauss-type function, because their correlation coefficients were all greater than 95%. It was verified that the developed clumping algorithm of aggregates was reasonable in terms of the shape and size gradation. Based on the parallel-bond model and Burger's model, the results of virtual tests were in good agreement with those of laboratory uniaxial tests. The angularity (PGF) of aggregates has a beneficial effect on the strength and stability of asphalt mixtures, whereas the flat-elongated feature (SAR) has a negative effect on the strength and stability of asphalt mixtures.

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Three-dimensional simulation of aggregate and asphalt mixture using parameterized shape and size gradation

To solve the major issues that most carbon materials used as supercapacitors electrode should be prepared from complex chemical products with high cost and side effects to the environment. In this report, a novel kind of low-cost, abundant reserves and environmental friendly carbon materials derived from carbonaceous mudstone and lignin mixture have been prepared and the electrochemical performances have been investigated. By activation treatment with HNO3, the activated carbonaceous mudstone and lignin-derived carbons (ASLDC) has been successfully synthesized. The physical and electrochemical studies exhibit that the ASLDC electrode possesses porous structures and wonderful electrochemical behaviors, a high specific capacitance of 155.6 F g−1 can be achieved when first served as electrodes for supercapacitors, which is three times than that of the untreated carbon electrode. Meanwhile, the charge/discharge measurement further indicates that the ASLDC electrode possess the excellent supercapacitive characteristics. The results demonstrate that the as-prepared low-cost, renewable and environmental friendly carbon electrode materials can be a promising electrode material for high-performance supercapacitors. Furthermore, such abundant reserves materials would be useful for other energy storage and conversion devices.

Carbonaceous mudstone and lignin-derived activated carbon and its application for supercapacitor electrode

Soil contamination not only can cause environmental problems but also lead to a notable change in the mechanical properties of soil. Loess widely distributed over North-West (NW) China is featured with the metastable structure, and chemical contaminants produced especially during the rapid development of NW China in recent years seriously threaten the fragile loess environments. When exposed to chemical contaminants, the impacts on the microstructural characteristics of the loess and the resultant mechanical properties are deemed critical for land reclamation in NW China. In light of this, the microscale structural characteristics of the loess exposed to acetic acid, phosphoric acid, sodium hydroxide, and sodium sulfate respectively are studied using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy tests. Additionally, their resultant macroscale mechanical properties are determined by direct shear tests. The deterioration mechanism regarding the microscale structural characteristics when exposed to the contaminants is revealed, and the resultant macroscale mechanical properties present a good correspondence with the deteriorated microscale structural characteristics. The findings of this work provide some guideposts for contaminated land reclamation in NW China.

Effects of chemical contamination on microscale structural characteristics of intact loess and resultant macroscale mechanical properties

Mechanical and microstructural properties of recycling granite residual soil reinforced with glass fiber and liquid-modified polyvinyl alcohol polymer.

This study aims at developing an efficient and accurate methodology to estimate the resilient modulus of subgrade soils. First, a new resilient modulus model incorporating stress dependence and moi...

Jue Li

Papers

Three-dimensional simulation of aggregate and asphalt mixture using parameterized shape and size gradation

Rapid estimation of resilient modulus of subgrade soils using performance-related soil properties

Geometric anisotropy modeling and shear behavior evaluation of graded crushed rocks

Compaction process tracking for asphalt mixture using discrete element method

Modeling humidity and stress-dependent subgrade soils in flexible pavements