Laboratory evaluation of the residue of rubber-modified emulsified asphalt

Emulsified asphalt has been widely used in various surface treatment methods such as chip seal for low-volume road preservation. Using modified emulsified asphalt made it possible to use chip seal technology on medium-and even high-volume traffic pavements. The main objective of the study is to quantify the residue characteristics of rubber-modified emulsified asphalt and to assess the effectiveness of using crumb rubber to modify emulsified asphalt binder. The four emulsified asphalt residues used the distillation procedure. Then, the rheology characteristics of emulsified asphalt residue were evaluated. The Fourier transform infrared spectroscopy (FTIR) test analyzed the chemical change of emulsified asphalt during the aging procedure. The results indicate that the evaporation method cannot remove all the water in emulsified asphalt. The mass change during the rolling thin film oven (RTFO) process only represented the component change of emulsified asphalt binder residue. Both the high-temperature and low-temperature performance grade of the two emulsified asphalt binders with rubber were lower. The original asphalt binder adopted to emulsification had a crucial influence on the performance of emulsified asphalt. The rubber modification enhanced the property of the emulsified asphalt binder at low temperatures, and the improvement effect was enhanced as the rubber content in the emulsified asphalt was raised. The C=O band was more effective in quantifying the aging condition of the residue. The findings of this study may further advance the emulsified asphalt technology in pavement construction and maintenance

Cold in-place recycling asphalt mixtures: Laboratory performance and preliminary m-e design analysis

Cold in-place recycling (CIR) asphalt mixtures are an attractive eco-friendly method for rehabilitating asphalt pavement. However, the on-site CIR asphalt mixture generally has a high air void because of the moisture content during construction, and the moisture susceptibility is vital for estimating the road service life. Therefore, the main purpose of this research is to characterize the effect of moisture on the high-temperature and low-temperature performance of a CIR asphalt mixture to predict CIR pavement distress based on a mechanistic–empirical (M-E) pavement de-sign. Moisture conditioning was simulated by the moisture-induced stress tester (MIST). The moisture susceptibility performance of the CIR asphalt mixture (pre-mist and post-mist) was estimated by a dynamic modulus test and a disk-shaped compact tension (DCT) test. In addition, the standard solvent extraction test was used to obtain the reclaimed asphalt pavement (RAP) and CIR asphalt. Asphalt binder performance, including higher temperature and medium temperature performance, was evaluated by dynamic shear rheometer (DSR) equipment and low-temperature properties were estimated by the asphalt binder cracking device (ABCD). Then the predicted pavement distresses were estimated based on the pavement M-E design method. The experimental results revealed that (1) DCT and dynamic modulus tests are sensitive to moisture conditioning. The dynamic modulus decreased by 13% to 43% at various temperatures and frequencies, and the low-temperature cracking energy decreased by 20%. (2) RAP asphalt incorporated with asphalt emulsion decreased the high-temperature rutting resistance but improved the low-temperature anti-cracking and the fatigue life. The M-E design results showed that the RAP incorporated with asphalt emulsion reduced the international roughness index (IRI) and AC bottom-up fatigue pre-dictions, while increasing the total rutting and AC rutting predictions. The moisture damage in the CIR pavement layer also did not significantly affect the predicted distress with low traffic volume. In summary, the implementation of CIR technology in the project improved low-temperature cracking and fatigue performance in the asphalt pavement. Meanwhile, the moisture damage of the CIR asphalt mixture accelerated high-temperature rutting and low-temperature cracking, but it may be acceptable when used for low-volume roads

Thiophene antibacterials that allosterically stabilize DNA-cleavage complexes with DNA gyrase

A paucity of novel acting antibacterials is in development to treat the rising threat of antimicrobial resistance, particularly in Gram-negative hospital pathogens, which has led to renewed efforts in antibiotic drug discovery. Fluoroquinolones are broad-spectrum antibacterials that target DNA gyrase by stabilizing DNA-cleavage complexes, but their clinical utility has been compromised by resistance. We have identified a class of antibacterial thiophenes that target DNA gyrase with a unique mechanism of action and have activity against a range of bacterial pathogens, including strains resistant to fluoroquinolones. Although fluoroquinolones stabilize double-stranded DNA breaks, the antibacterial thiophenes stabilize gyrase-mediated DNA-cleavage complexes in either one DNA strand or both DNA strands. X-ray crystallography of DNA gyrase–DNA complexes shows the compounds binding to a protein pocket between the winged helix domain and topoisomerase-primase domain, remote from the DNA. Mutations of conserved residues around this pocket affect activity of the thiophene inhibitors, consistent with allosteric inhibition of DNA gyrase. This druggable pocket provides potentially complementary opportunities for targeting bacterial topoisomerases for antibiotic development

Discrete Element Simulation of the Internal Structures of Asphalt Mixtures with High Content of Tire Rubber

Increasing rubber content in asphalt mixtures is recognized as a practical approach to consume fast-growing waste tires. The reacted rubber technology using the dry process was developed to address the rubber swelling and poor performance of rubber asphalt mixtures. Although the tire rubber has proved to increase the low-temperature performance, fatigue life, cracking resistance, and rutting resistance of asphalt mixtures, the impacts of high content tire rubber on the mixtures’ internal structures have not been revealed. This study is a preliminary research that utilized the laboratory and numerical simulation approach to investigate the strength, skeleton structures, and stress distribution of the tire rubber asphalt mixtures. The discrete element method (DEM) was employed to establish asphalt mixture models with a high content of tire rubber. New modeling procedures were developed to incorporate coarse aggregate shapes and rubber particles. Indirect tensile strength (ITS) values of specimens with rubber content up to 4.5% by mass were tested in laboratory and simulation. The results from DEM simulation had better consistency than the laboratory results. However, the test results showed that as the rubber content increased, the ITS of asphalt mixtures significantly decreased. Besides, the simulation indicates that the ITS decreased linearly as the percentage air void increased. The specimen ITS value decreased by half as the void ratio reached 15%. Furthermore, the internal structures and stress distribution of specimens with different rubber content were analyzed. The gap gradation proved to have a functional capacity of accommodating fine aggregates and rubber particles, all while forming a coarse aggregate skeleton

Pavement conductive wearing surface with graphite heating film de-icing potential and performance experimental study

It is known that the freezing of the road brings high risks to the traffic in winter. However, Traditional deicing technology has low deicing efficiency and severe damage to the road surface. Therefore, the new develop pavement conductive wearing surface with graphite heating film (PCWSG) could be one option to solve this problem. So the main objective of this paper is to investigate the road performance (high-temperature, low-temperature, moisture susceptibility, friction-resistance) of pavement conductive wearing surface with graphite heating film (PCWSG) and then evaluate its deicing potential. In this paper, several tests are conducted to evaluate the performance of PCWSG. The high-temperature performance is conducted by the laboratory wheel-tracking rut test. Low-temperature performance is characterized by the low-temperature bending test. Moisture susceptibility is studied by the freeze-thaw split test. Friction-resistance performance is estimated by the pendulum type friction coefficient measuring instrument and the small acceleration loading device. Furthermore, removing ice potential is studied by asphalt rutting slabs (various gradations) with graphite conductive wearing surface. The results show that pavement conductive wearing surface with graphite heating film (PCWSG) could improve the high-temperature, low-temperature, and friction-resistance compared with the original asphalt mixture. Although moisture susceptibility and wear performance decrease lightly but also satisfy the specification requirement. Moreover, removing ice potential of asphalt slabs with PCWSG results shows that AC-20 asphalt concrete with higher porosity has better deicing and snow removal effect. The PCWSG has lower heating and deicing cost and more effective deicing effects

(Table B2) Relative abundances of diatom species used in the Canoco analysis at sediment surface samples from the Chinese inshore waters

Canonical correspondence analysis has been used to analyze and to visualize the relationships between the main species and selected environmental variables in a study of diatoms from surface sediment samples in Chinese inshore waters. The result shows that the diatom distribution in Chinese inshore waters is closely correlated with the environmental variables and that the measured environmental variables account for the major changes of the diatom composition. Winter sea-surface temperature (WST), winter sea-surface salinity (WSS), water depth and summer sea-surface salinity (SSS) play an important role for the diatom distribution. Among the environmental factors, winter sea-surface temperature is the most important, controlling the distribution of diatoms in the surface sediments in Chinese inshore waters, and therefore, it may be potentially reconstructed in palaeoceanographic studies. Three diatom assemblages are distinguished, representing environments with different hydrological characteristics. The temperate-water diatom assemblage may be used as an indicator of the coastal circulation system of Bohai Sea and Yellow Sea. While the warm-temperate water diatom assemblage is closely related to Shanghai-Zhejiang-Fujian coastal currents and Northern Bay coastal currents of South China Sea. The deep water diatom assemblage is a response to that the waters are less controlled by coastal currents, but are more influenced by open sea currents, such as Kuroshio

Investigation of asphalt mixture internal structure consistency in accelerated discrete element models

The discrete element method (DEM) requires an enormous amount of computational resources when applied to asphalt mixture simulation. Reducing material modulus is recognized as an efficient method to cut down the computational cost. However, over-reduced material modulus would case unacceptable calculation errors for DEM models, and the allowable modulus reduction range is not clear. Based on the small displacement assumption in the DEM modeling, the overlap ratio between particles should be small enough to ensure efficient force transition and discrete system stability. Combining this assumption with time step determination and force-displacement law, a theoretical inference that specified a material modulus reduction range without causing an exceeded overlap ratio can be derived. To verify this theoretical inference, a three-step DEM compaction model, including gravity fall, static compaction, and gyratory compaction processes was established for asphalt mixtures. Three groups of asphalt mixtures with different mixture designs were tested both in the laboratory and in simulation. To evaluate the effects of the reduced material modulus on the internal-structure of asphalt mixture specimen under three compaction states, this study proposed 4 categories of internal-structure indexes in respect of specimen’s height, average coordination number, rotation angles of coarse aggregates, and spatial distribution of mastic particles. In the presented case, when the modulus reduction was 1/100 times, the maximum simulation error of internal-structure indexes (except the average coordinate number) was around 4% compared to the control group. Meanwhile, the model’s calculation efficiency was increased by 8–10 times depending on the mixture design

Identify the Micro-Parameters for Optimized Discrete Element Models of Granular Materials in Two Dimensions Using Hexagonal Close-Packed Structures

The widely used simple cubic-centered (SCC) model structure has limitations in handling diagonal loading and accurately representing Poisson’s ratio. Therefore, the objective of this study is to develop a set of modeling procedures for granular material discrete element models (DEM) with high efficiency, low cost, reliable accuracy, and wide application. The new modeling procedures use coarse aggregate templates from an aggregate database to improve simulation accuracy and use geometry information from the random generation method to create virtual specimens. The hexagonal close-packed (HCP) structure, which has advantages in simulating shear failure and Poisson’s ratio, was employed instead of the SCC structure. The corresponding mechanical calculation for contact micro-parameters was then derived and verified through simple stiffness/bond tests and complete indirect tensile (IDT) tests of a set of asphalt mixture specimens. The results showed that (1) a new set of modeling procedures using the hexagonal close-packed (HCP) structure was proposed and was proved to be effective, (2) micro-parameters of the DEM models were transit form material macro-parameters based on a set of equations that were derived based on basic configuration and mechanism of discrete element theories, and (3) that the results from IDT tests prove that the new approach to determining model micro-parameters based on mechanical calculation is reliable. This new approach may enable a wider and deeper application of the HCP structure DEM models in the research of granular material