Surface Aggregation Research Articles

Palladium Single-Atom (In)Stability Under Aqueous Reductive Conditions.

Here, we investigate the stability and performance of single-atom Pd on TiO2 for the selective dechlorination of 4-chlorophenol. A challenge inherent to single atoms is their high surface free energy, which results in a tendency for the surface migration and aggregation of metal atoms. This work evaluates various factors affecting the stability of Pd single-atoms, including atomic dispersion, coordination environment, and substrate properties, under reductive aqueous conditions. The transition from single atoms to clusters vastly enhanced dechlorination kinetics without diminishing carbon-chlorine bond selectivity. X-ray absorption spectroscopy analysis using both in situ and ex situ conditions followed the dynamic transformation of single atoms into amorphous clusters, which consist of a unique unsaturated coordination environment and few nanometer diameter. The intricate relationship between stability and performance underscores the vital role of detailed characterization to properly determine the true active species for dehalogenation reactions.

Waste Plastic Powder Coating on Acidic Aggregates: A New Hydrophobic Coating Technology to Build Moisture-Resistant Asphalt Mixtures

The surface energy of aggregate in asphalt pavements has a huge impact on its moisture susceptibility. The commercial antistripping agents widely used in asphalt may not be effective enough to enhance the moisture resistance if large quantities of acidic aggregates exist in pavements. This is also the reason why moisture damage is still an issue in many U.S. regions primarily supplied with “problematic” aggregates. In this regard, a promising solution is to use waste-plastic-coated aggregate, the surface of which is fundamentally modified and has a high affinity with asphalt because of the hydrophobic nature of plastic. However, it has not been widely promoted in the industry since there needs to be a practical and reliable method for uniform coating and avoiding the agglomeration of fine aggregate. To this end, an entirely new coating technology (thermoplastic polyethylene powder coating [TPPC]) was developed to coat aggregate using polyethylene (PE) powder. This technology utilizes a cheap but highly wettable fluidized bed to stably disperse the hydrophobic PE powder. Then, the dispersion liquid is sprayed onto the hot aggregate where the fluidized bed will evaporate fast while the PE particles stay, melt, and coat the aggregate surface. The microstructures of the coated aggregate were directly observed by scanning electron microscopy. Surface energy-based thermodynamic parameters were used to demonstrate the effect of TPPC on the moisture resistance of asphalt mixtures. This technology can be extended to other types of waste plastic if suitable fluidized beds are developed.

Change Characteristics of Soil Organic Carbon and Soil Available Nutrients and Their Relationship in the Subalpine Shrub Zone of Qilian Mountains in China

Studying the spatial and temporal distribution of soil organic carbon (SOC) content in high-altitude mountainous areas and its correlation with soil nutrients provides a basis for understanding soil carbon stocks and the factors affecting the local carbon cycle. Based on soil samples collected from a semi-sunny slope and semi-shady slope in the subalpine shrub zone of the eastern Qilian Mountains from May to October 2019, we studied the temporal and spatial changes in SOC and soil available nutrients and their relationships. The results showed that SOC content and soil nutrients were greater on the semi-shady slope than on the semi-sunny slope during the growing season and decreased with an increase in soil depth in different slope directions, showing obvious surface aggregation. The soil available nitrogen (SAN) content was consistent with the SOC content and exhibited greater synchronization. SOC was significantly positively correlated with soil available nutrients in the study area during the whole growing season. However, the correlation between SOC and soil nutrients varied among the different soil layers and slope orientations. The SOC content was more obviously correlated with the SAN content in the soil layer at a depth of 30–40 cm (r = 0.67, p < 0.05) on the semi-shady slope. The SOC content was more obviously correlated with soil-available phosphorus (SAP) content in the soil layer at a depth of 30–40 cm (r = 0.57) on the semi-sunny slop. The SOC content was more obviously correlated with the SAP content in the soil layer at a depth of 60–70 cm (r = 0.55) and with the soil-available potassium (SAK) content in the soil layer at a depth of 70–80 cm (r = 0.84) on the semi-sunny slope.

Optimization of a small molecule inhibitor of secondary nucleation in α-synuclein aggregation.

Parkinson's disease is characterised by the deposition in the brain of amyloid aggregates of α-synuclein. The surfaces of these amyloid aggregates can catalyse the formation of new aggregates, giving rise to a positive feedback mechanism responsible for the rapid proliferation of α-synuclein deposits. We report a procedure to enhance the potency of a small molecule to inhibit the aggregate proliferation process using a combination of in silico and in vitro methods. The optimized small molecule shows potency already at a compound:protein stoichiometry of 1:20. These results illustrate a strategy to accelerate the optimisation of small molecules against α-synuclein aggregation by targeting secondary nucleation.

(Invited) Precise Evaluation of Functional Group Distribution and Reaction Yield for Chemically Treated Carbon Nanohorns by Highly Sensitive SEM-EDS

Single-walled carbon nanohorns (CNHs) have great potential in diverse applications such as catalyst support, energy conversion, and drug carriers. Although chemical functionalization of CNHs is critical for these applications, they inherently form robust spherical “dahlia-like” aggregates, which may inhibit chemical reactivity. Herein, highly sensitive energy-dispersive X-ray spectrometry (EDS) analysis in scanning electron microscopy (SEM) is employed to elucidate the functional group distribution and the reaction yield of CNH dahlia aggregates. First, the technique clearly visualizes the elemental distribution associated with the functional groups on dahlia structures with a sufficient spatial resolution of <10 nm.1 The result exposes that the outer surface of an individual aggregate is functionalized while the inner core remains almost unreacted. Second, the SEM-EDS precisely assesses the reaction yield for functionalized CNHs.2 The sensitive elemental analysis enables the evaluation of functionalization efficiency for sequentially grown polyamidoamine dendrimers on CNH surface, which consistently explains the change of chemical structure according to the reaction process. The details about the functionalization mechanism on CNH surface will be discussed in the conference.[1] H. Nakajima, T. Morimoto, K. Kobashi, M. Zhang, I. K. Sideri, N. Tagmatarchis, and T. Okazaki, Outer-Surface Covalent Functionalization of Carbon Nanohorn Spherical Aggregates Assessed by Highly Spatial-Resolved Energy-Dispersive X-ray Spectrometry in Scanning Electron Microscopy, J. Phys. Chem. C 2020, 124, 25142-25147.[2] H. Nakajima, K. Kobashi, C. Stangel, T. Morimoto, M. Zhang, N. Tagmatarchis, and T. Okazaki, Step-by-step Characterization of a Series of Polyamidoamine Dendrimers on Carbon Nanohorn Surface, submitted.

Effect of continuous instant pressure drop treatment on the rheological properties and volatile flavor compounds of whole highland barley flour

Continuous instant pressure drop (CIPD) treatment effectively reduces microbial contamination in whole highland barley flour (WHBF). Base on it, this study further investigated its effects on flour properties (especially rheological properties) and volatile compounds (VOCs) profile of WHBF, and compared it with that of ultraviolet-C (UV-C), ozone and hot air (HA) treatments. The results showed that the damaged starch content (6.0%) of CIPD-treated WHBF was increased, leading to a rough surface and partial aggregation of starch particle, thereby increasing the particle size (18.06 μm of D10, 261.46 μm of D50 and 534.44 μm of D90). Besides, CIPD treatment exerted a positive influence on the structure and rheological properties of WHBF, including an elevation in pasting temperature and viscosity. Notably, CIPD-treated WHBF exhibited higher storage modulus and loss modulus compared to the other three groups of sterilization treatments, contributing to the formulation of a better-defined and stable gel strength (tan δ = 0.38). UV-C and ozone, as cold sterilization techniques, also induced alterations in specific characteristics of WHBF. UV-C treatment led to changes in WHBF's crystallinity, while ozone treatment caused modifications in the secondary protein structure of WHBF. A total of 68 VOCs were identified in raw WHBF (including 3 acids, 19 alcohols, 25 aldehydes, 1 alkene, 8 esters, 2 ethers, 3 furans, and 7 ketones). The maximum flavor-contributing VOC in CIPD-treated WHBF remained dimethyl sulfide monomer (cabbage aroma), consistent with the raw WHBF. Conversely, in HA-treated WHBF, the maximum flavor-contributing VOC shifted to 2-furanmethanethiol monomer (roasted coffee aroma), altering the initial flavor presentation. These findings will provide strong support for the application of CIPD technology in the powdery foods industry.

Optimized aggregate height measurement by laser with nonlinear fitting

The measurement of shape parameters of coarse aggregate is the premise to ensure the quality of concrete engineering. In the measurement of particle shape based on laser triangulation method, the selection of polynomial fitting parameters between different test scene displacement and image offset is often different. For coarse aggregate height measurement, an optimal laser triangulation method is proposed, and the best polynomial fitting times of aggregate measurement is obtained through data extraction and error analysis. Firstly, the laser streak information is collected from the aggregate surface based on the industrial camera, and the laser streak is processed by Gaussian filtering and color space transformation, and then the center line of the laser streak is obtained by the center method to obtain the corresponding aggregate height information. Finally, based on the comparison between the experimental measurements and the height values calculated by different polynomial fits, the laser triangulation solution method is optimized by different error factors analysis. The experimental results show that in the process of aggregate height measurement, the cubic term fitting solution is optimal with an average relative error of only 0.693%.

Hexaphenyl-butadiene derivative with aggregation-induced emission characteristic for high-sensitive detection of ursolic acid, oleanolic acid, and glycyrrhizic acid

Plant natural products (PNPs) have a wide range of pharmacological effects and biological activities, including antitumor, antiinflammatory, antibacterial, and antiviral properties. These properties can be beneficial for their use in the health care industry. As representative PNPs, ursolic acid (UA), oleanolic acid (OA), and glycyrrhizic acid (GA) have been efficiently biosynthesized in microbial cells. In this study, hexaphenyl-butadiene methylpyridine salt (HPB-I) with an aggregation-induced emission characteristic (AIE) was developed as a simple, real-time, and efficient quantitative probe for detection of PNPs. Experimental results showed that HPB-I has a highly selective fluorescence response to UA, OA, and GA among 18 PNPs. Three detection methods were employed. Dilution of a PNP aqueous solution with dimethyl sulfoxide was optimal with low limits of detection of 0.16 (UA), 0.23 (OA), and 0.066 (GA) nmol/mL. Scanning electron microscopy, dynamic light scattering, and zeta potential analyses revealed that the PNPs were effectively adsorbed on the surface of HPB-I aggregates, which resulted in an increase in the fluorescence response based on restriction of intramolecular motion. HPB-I could also effectively and quantitatively detect the three PNPs in a synthetic dropout (SD) culture medium. This study provides a valuable approach toward the development of a real-time low-cost method for in-situ PNP detection of biosynthesis processes in microbial cells.

Geometrical characteristics of aggregates: The influence of sphericity, angularity, and surface texture on the workability of asphalt mixtures

Workability of asphalt mixtures is considered as an essential factor in quality control of asphalt pavement construction. However, there are fewer studies related to the influence of geometric properties of aggregates on the workability of asphalt mixture. The main purpose of this paper is to explore the influence of aggregate sphericity, angularity and surface texture on the workability of asphalt mixture during the mixing process. Firstly, a self-developed workability equipment of asphalt mixture was used to analyze the differences in the asphalt mixture workability of three materials, namely, basalt, limestone and pebble. Next, using the Aggregate Image Measurement System (AIMS), the geometric characteristics of the aggregates were determined. Accordingly, the correlation between the geometric characteristics of the aggregates and the workability index was established through linear correlation analysis. Finally, investigating the distribution uniformity of asphalt film by scanning electron microscope (SEM), the influence of the geometric characteristics of the aggregates on the workability of the asphalt mixture was determined. The results demonstrated that, compared with limestone and pebble asphalt mixtures, a significantly greater workability value was observed for the basalt asphalt mixture. Moreover, the geometric characteristics of the aggregates were found to influence the change rule of workability in the following order: sphericity > surface texture > angularity. Furthermore, the geometric characteristics revealed to have a significant effect on the uniformity of the asphalt film.

MATLAB image analysis approach for adhesion and moisture susceptibility assessment of modified asphalt concrete

This research aimed to examine the adhesion and moisture susceptibility of asphalt concrete, which are crucial for its durability. Three types of asphalt (40–50, 60–70 and 80–100 penetration grade asphalt) were modified with low-density polyethylene (LDPE), hydrated lime (HL) and paraffin wax (PW). These modified asphalts were mixed with lime stone aggregate at optimum dosage. The Rolling Bottle Tests (RBT) were performed to quantify the moisture susceptibility of the asphalt concrete while pneumatic adhesion tensile testing instrument (PATTI) was used to perform the bitumen bond strength (BBS) tests. The images of virgin and modified asphalt concrete samples were taken before and after performing RBT and BBS tests using high resolution cameras. The analysis of images was carried out using MATLAB software. The RBT and BBS tests standards recommend using visual assessment of asphalt area coverage on aggregate surface. Image analysis using MATLAB gives more precise and accurate asphalt coverage area on aggregate. The LDPE modified concrete showed more asphalt area on aggregate surface than others. The results showed that the 40–50 pen asphalt modified with LDPE and HL had higher bond strength (66%) and less moisture susceptibility (19%) compared to the softer grade (60–70 and 80–100 pen) asphalt. The PW-modified asphalt concrete showed less (4%) bond strength and more moisture susceptibility (5%) compared to the virgin asphalt concrete. Asphalt coverage area from visual and MATLAB image analysis were found in variation of frequency distribution from −4% to 16%. Based on the findings of the research it is proposed to use MATLAB image analysis in place of visual inspection for the determination of asphalt coverage on aggregate surface.

Skid-resistance durability and wear/polish-resistance behaviors of ultra-thin friction course designed based on the differential polishing of aggregates

To improve the skid-resistance durability of asphalt pavements in a cost-effective manner, this study introduced a differential-polishing principle based on blending various aggregates. SMA-5 ultra-thin friction courses (UTFC) were prepared using mineral aggregates consisting of 88# calcined bauxite and limestone blended in six proportions. Long-term simulated traffic polishing tests were performed on six types of UTFC surfaces in the laboratory. Direct skid-resistance indexes, BPN20 and μ80, were used to evaluate skid resistance at low and high velocities after different polishing cycles, respectively. Surface texture evolution during long-term polishing was analyzed using bearing area ratio, mean profile depth, and fractal dimension D. Additionally, an attenuation prediction model for skid resistance was developed. Aggregate mechanical properties affecting skid-resistance durability of UTFC were investigated through grey correlation analysis. The results show that a significant differential-polishing effect was generated during long-term polishing due to large differences in the two aggregates’ wear/polish resistance, which can effectively reduce the attenuation rate of skid resistance of UTFC and improve skid-resistance durability by decreasing wear loss of UTFC surface aggregate and forming texture structure difference between aggregates to maintain rough surface texture. The reasonable blending proportion of 88# calcined bauxite was determined to be 40%–60% of the mineral aggregate mass. It was also found that the developed predictive model can reflect the attenuation law of skid resistance, and PSV and LAA loss of aggregates are well correlated with the skid-resistance durability of UTFC.

Clarifying the effects of volume proportion and surface area of aggregate on chloride diffusivity of concrete through microstructural design

Increasing the aggregate proportion usually reduce the chloride diffusivity of concrete, but may also increase the chloride diffusivity as more interfacial transition zone (ITZ) is introduced with increased surface area of aggregate. Since both packing density and surface area of aggregate varied simultaneously with its particle size distribution (PSD), effects of volume proportion and surface area of aggregate on the chloride diffusivity of concrete has not been clarified separately yet. In the present study, we established a database containing over 500,000 aggregate PSDs and their corresponding packing density and specific surface area using the Compressible Packing Model (CPM) and photogrammetric 3D reconstruction. By individually controlling target volume proportion or surface area of aggregate, effects of aggregate volume proportion and surface area on the mechanical properties and chloride diffusivity of concrete were evaluated. Then an empirical equation, in consideration of aggregate size-dependent ITZ thickness the tortuosity, was proposed to describe the relationship between chloride diffusion coefficient and aggregate proportion and surface area, and a strategy for aggregate PSD optimization was provided to meet chloride diffusivity requirement, which offer an approach for enhancing the chloride resistance of concrete.

Chemical Etching, Thermally Driven Combination Strategy to Fabricate Superhydrophobic Fe-Based Amorphous Coatings with Excellent Anticorrosion Property: Based on Hydroxylation Effect.

Fe-based amorphous coatings are ideal materials for surface protection due to their outstanding mechanical properties and corrosion resistance. However, coating defects are inevitably formed during the preparation of coatings by thermal spray technology, which seriously affects the corrosion performance. Inspired by bionics, conceiving superhydrophobic surfaces with liquid barrier properties has become a new idea for the corrosion protection of metal surfaces. In this work, based on surface hydroxylation, we designed a superhydrophobic Fe-based amorphous coating with corrosion resistance by chemical etching combined with a thermally driven preparation strategy. The obtained superhydrophobic coatings exhibit liquid repellency (contact angle >150°) and excellent corrosion resistance (corrosion current density and passive current density reduced by 3 orders of magnitude). The results revealed that the superhydrophobic behavior stems from the construction of hydroxyl-induced surface micro-/nanomultilevel aggregates (cluster structures). The hydrophobic agent layer deposited on the surface of cluster aggregates and the nanoparticle elements that constitute the clusters dominate the corrosion resistance of the coating. This work provides an effective guide to the design of high-corrosion-resistant Fe-based amorphous alloy coatings and promotes their engineering applications.

Image-based indices of aggregates for predicting the initial skid resistance of bituminous pavements

The objective of this study is to propose image-based indicators of microtexture and macrotexture for pavement surfaces that can predict the initial skid resistance. To achieve this objective, images of different types of aggregates that were collected from quarries were processed. Based on the outcome of the image processing, suitable indicators of shape, angularity, and surface texture of coarse aggregates were proposed. Skid resistance data were collected from pavements constructed with the aggregates used in the image processing, as well as with different surface course mixes commonly used in India, such as Bituminous Concrete (BC), Stone Matrix Asphalt (SMA), and Gap-Graded Rubberized Bituminous mix (GGRB).Through a detailed investigation of the image processing outcome and field data, this study introduces the Aggregate Surface Texture Index (STI) as a means of quantifying microtexture, which can be obtained by processing images of the aggregate using wavelet decomposition technique. Additionally, the study proposes Shape Index (SI) and Angularity Index (AI) as indicators for macrotexture, which can be obtained from the processing of digital images of aggregates. For determining the skid resistance of newly constructed pavements, the study suggests using the Surface Macrotexture Index (SMI), which can be obtained by processing digital images of the pavement surface. Furthermore, this study proposes statistical models for predicting the initial skid resistance of pavement based on these indicators. Overall, the proposed image-based indicators of microtexture and macrotexture have the potential to provide valuable insights for designing and maintaining safe and durable pavement surfaces.

Evaluating the interfacial properties between crumb rubber modified asphalt and aggregates using molecular dynamics simulation methods

In the present study, the molecular dynamics (MD) simulation methods were used to investigate the interfacial properties of crumb rubber modified asphalt (CRMA)-aggregates considering the effects of crumb rubber (CR) degradation behavior and moisture. The interface models with different CR degradation degrees were then constructed. The interfacial adhesion properties between CRMA and aggregates were discussed by the interaction energy and work of adhesion; the agglomeration characteristics of CRMA on aggregates surface were evaluated by the radial distribution function (RDF); the diffusion behaviors of CRMA on aggregates surfaces were investigated using the mean square displacements (MSD); the asphalt adhesion strength test was performed to further verify the reliability of the simulation results. The results showed that the incorporation of CR into asphalt could significantly improve the adhesion and moisture damage resistance of the asphalt mixtures, while the CR degradation would slightly decrease these properties. The results of asphalt adhesion strength test exhibited similar trends with those of the work of adhesion, indicating that the simulation possessed a certain rationality. The RDF curves showed that the intrusion of water enlarged the distance between the polar components and aggregates, whereas the CR molecules displayed satisfactory agglomeration properties. Furthermore, the addition of CR weakened the mobility of asphalt on aggregates surface. This was mainly attributed to the poor mobility of the CR and its limitation on the mobility of the constituent components of asphalt. However, these problems would be alleviated as the CR degradation.

Interfacial interaction behavior of recycled asphalt pavement: Molecular dynamics simulation

Recycling waste asphalt mixture (WAM) to prepare recycled asphalt pavement (RAP) is an important measure to handle road construction waste. Asphalt-aggregate interface (AAI) and matrix-aged asphalt interface (MAI), as weak interfaces in RAP, interface interaction behavior directly affects the road performance of RAP. In this paper, molecular models of asphalt and aggregate were constructed. Molecular dynamics simulation was used to analyze and evaluate the interaction behavior of the AAI and the MAI in RAP. The mean square displacement (MSD), relative concentration function (RCP), and radial distribution function (RDF) were used to quantitatively analyse the interface interaction behavior. The research results are as follows: For the AAI, the temperature, the aging level of asphalt, and chemical composition of aggregates will affect the interaction behavior of the AAI. Increasing temperature accelerates the diffusion of asphalt on the surface of aggregate. However, the increase of the aging level of asphalt and the alkalinity of aggregate will decrease the interaction rate of asphalt on the surface of aggregate. For the MAI, the temperature and the ratio of filler-asphalt (RFA) significantly affect the interaction behavior of the MAI. The molecular diffusion rate of matrix asphalt and aged asphalt increases significantly with the increasing temperature. The addition of filler will decrease the diffusion rate of asphalt, and the diffusion rate decreases with the increase of RFA. This article comprehensively and systematically studies and evaluates the effect of various factors on the interface interaction behavior. The results provide guidance for improving the adhesion ability of AAI and enhancing the degree of incorporation of MAI.

Investigation on the wetting behavior of asphalt emulsion on aggregate for asphalt emulsion mixture

The wetting behavior of asphalt emulsion on aggregate greatly influences the physical bonding interface between asphalt emulsion and aggregate. However, the wetting behavior of asphalt emulsions has not been widely considered. In this work, the wetting behavior of asphalt emulsion on aggregate was investigated in terms of dynamic contact angle. Firstly, the quantitative indicators for evaluating the wetting behavior are proposed. Then, the factors influencing the wetting behavior are analyzed, such as emulsifier dosage, asphalt dosage, wetting agent dosage, aggregate type and surface roughness. Finally, the primary factor affecting the wetting behavior is analyzed using the grey correlation method. The result shows that the wetting process of asphalt emulsion on the aggregate surface could be divided into two stages: the initial linear rapid wetting stage driven by inertial force, the second slow wetting stage driven by viscous forces, which the development of dynamic contact angle can be well illustrated by the power function. The equilibrium contact angle (θe) and wetting velocity (v) are recommended as quantitative indicators of wetting behavior. Grey correlation analysis shows that the emulsifier dosage and wetting agent dosage can significantly affect the wetting behavior. Increasing the emulsifier dosage can increase the equilibrium contact angle and decrease the wetting velocity. Adding the wetting agent can reduce the equilibrium contact angle and increase the wetting velocity. Therefore, to guarantee the good wetting behavior, the emulsifier dosage should not be too high, provided that good emulsification effect is achieved and the wetting agent can be added in asphalt emulsion.

Investigating the deterioration mechanism of adhesion between asphalt and aggregate interface under acid rain erosion

To further reveal the effect of acid rain on the interfacial adhesion of asphalt mixtures, molecular dynamics (MD) simulation was used to investigate the interfacial damage mechanism. A water layer containing hydrogen ions, sulfate ions, and nitrate ions was inserted between the asphalt and aggregate to simulate the effect of acid rain attack on the interface. The interfacial bonding strength under three conditions of dry, pure and acidic water was analyzed. The effect of acidic ions on the spatial arrangement and movement of asphalt molecules was discussed. The damage of the asphalt-aggregate interface under both pure water and acidic water attack was investigated. The results showed that the acidic ions promote the rearrangement distribution of asphalt molecules at the interface, reduce the concentration of asphalt molecules at the interface, and weaken the adhesion ability at the interface. The degree of aggregation of polar components increases, resulting in a reduction in the movement migration capacity of asphalt and poor mobility, increasing the possibility of asphalt stripping from the aggregate surface. Under the influence of acidic ions, less separation energy is required for interfacial adhesion damage to occur between asphalt and aggregate, and the amount of deformation at interfacial failure is smaller.

Thermodynamic Properties of Aggregate Coated by Different Types of Waste Plastic: Adhesion and Moisture Resistance of Asphalt-Aggregate Systems

The utilization of acidic aggregates in hot-mix asphalt (HMA) is often inevitable due to the limited supply of locally available aggregates, posing a potential threat of moisture damage to asphalt pavements. In this regard, the use of urban waste plastic to coat the low-quality aggregates is a promising way to improve the moisture resistance. This study fundamentally evaluated the compatibility between asphalt and plastic-coated aggregate by measuring surface energy, and for the first time compared the effects of different types of waste plastic including high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polypropylene (PP). The plastic-coating significantly altered the chemistry of aggregate surface by increasing the nonpolar components and reducing the polar components. Such changes remarkably increased the dry adhesion energy between asphalt and aggregate and enhanced the wettability of aggregate. For the acidic aggregates, the polymeric treatment could decrease the value of wet adhesive, which indicated the debonding tendency in the presence of water was reduced. Finally, the energy ratios of the asphalt-aggregate combinations significantly increased by the surface pretreatment, which proved the effect of waste plastic coating on improving the moisture damage resistance of asphalt mixtures. By comparison, the HDPE coating was the most effective way to enhance the compatibility with asphalt, followed by PP and LDPE coatings. The PVC and PET coatings were investigated as the least effective way. This study cannot only contribute to the potential large-scale utilization of waste plastic but also remove the obstacles of using large quantities of acidic natural aggregate in asphalt pavements.

Spatial distribution of soil organic carbon and its response to forest growth and soil layer in Cunninghamia lanceolata plantations in mid-subtropical China

To investigate the effects of stand age and soil layer on the temporal and spatial distribution of soil organic carbon (SOC) in Cunninghamia lanceolata plantations, five experimental plots and 15 soil sampling sites were established in five stands of different ages (3, 6, 9, 15, and 25 years) in Huitong, Hunan Province. Tree diameter at breast height, tree height, canopy density and elevation in sample plots, and soil organic carbon concentrations (SOCC), soil enzyme activity, soil pH, and soil bulk density at 0–15, 15–30, 30–45 cm soil layers were measured during stand development. The change in SOC distribution with stand age and soil layer, and soil enzyme activity were investigated using ANOVA, LSD test, and inter-subject effect test and simulation analysis. The results showed that the SOC distribution in Cunninghamia lanceolata plantations had spatiotemporal heterogeneity and surface aggregation. The SOC increased with increasing stand age and decreased with increasing soil depth. Furthermore, SOCC and SOC density (SOCD) were strongly correlated with environmental factors; however, the interaction between forest growth and soil layer reduced the variation of SOC distribution. Forest growth and soil enzyme activity were important factors that affect the temporal and spatial distribution of SOC. Therefore, the management measures to promote the growth of the plantation and improve soil enzyme activity can enhance the SOC storage capacity from the angle of balancing ecological and economic benefits, and contribute to the achievement of the goal of “carbon neutrality”.