THE LABORATORY PERFORMANCE AND AGING CHARACTERISTICS OF RUBBER MODIFIED ASPHALT MIXTURE USING A DRY PROCESS

The accumulation of waste tires generates severe environmental issues. Using crumb rubber processed from waste tires on the pavement could relieve the pressure of waste tire on the environment and improve the performance of the pavement as well. The application of crumb rubber on the pavement using the dry process was proved to be a cost-effective strategy in some projects, however, the interaction between the rubber and asphalt binder was unknown in the rubber modified asphalt mixture using the dry process, especially when reclaimed asphalt pavement was adopted. The performance improvement of the rubber particle to the asphalt mixture was closely related to the interaction. The influence of aging on the characteristics of rubber modified asphalt mixture using the dry process is critical to its long-term performance. The scope of the dissertation is to evaluate the performance of rubber modified asphalt mixture using a dry process when reclaimed asphalt pavement was adopted. The influence of aging on the characteristics of the rubber modified asphalt mixture and the extracted asphalt binder were investigated. This dissertation proposed the volumetric design of rubber modified asphalt mixture using the dry process. The aggregate gradation determination, rubber modified asphalt mixture preparation, design binder content determination, and moisture susceptibility evaluation were proposed. The quality control of the laboratory mixture design procedure was critical to guarantee the consistency of the asphalt mixture design in the laboratory and the results of mixture construction in the plant. The high temperature rutting performance and the low temperature cracking performance of plant mixed and laboratory compacted asphalt mixture was evaluated. The influence of various factors, which included mixture design parameters of the asphalt mixture (nominal maximum aggregate size, reclaimed asphalt pavement content, and asphalt content), rubber modification, mixture air void content, test temperature, and aging procedure, on the rutting and low temperature characteristics of asphalt mixtures were evaluated. Based on the evaluation of different assessment parameters, the rubber addition and the rubber addition and aging were the two most critical factors that influenced the rutting and low temperature cracking performance of different asphalt mixtures. The effect of the Trichloroethylene solvent in asphalt binder was investigated, and the extracted asphalt binder was assessed and compared with the base asphalt binder and rubber modified base asphalt binder. Both the existence of Trichloroethylene and the content of Trichloroethylene had a significant influence on the |G*| of unaged and PAV aged asphalt binder. The Trichloroethylene in the extracted asphalt binder significantly influenced the actual performance of the asphalt binder in the reclaimed asphalt binder, thus potentially compromising the success mixture design. The modified extraction procedure was proposed to improve the accuracy of the extraction procedure. The rubber particles in the asphalt mixture using the dry process were not totally interacted with asphalt binder, only the interacted rubber particles were extracted, and the influence of the interacted rubber particle was assessed. The aged asphalt binder weakened the low temperature performance of the extracted asphalt binder. The aged asphalt binder and rubber in extracted asphalt binder guaranteed the asphalt binder to sustain heavy traffic load, thus improved the permanent deformation resistance of asphalt binder

An Improved Algorithm for Fixed-Hub Single Allocation Problem

This paper discusses the fixed-hub single allocation problem (FHSAP). In this problem, a network consists of hub nodes and terminal nodes. Hubs are fixed and fully connected; each terminal node is connected to a single hub which routes all its traffic. The goal is to minimize the cost of routing the traffic in the network. In this paper, we propose a linear programming (LP)-based rounding algorithm. The algorithm is based on two ideas. First, we modify the LP relaxation formulation introduced in Ernst and Krishnamoorthy (1996, 1999) by incorporating a set of validity constraints. Then, after obtaining a fractional solution to the LP relaxation, we make use of a geometric rounding algorithm to obtain an integral solution. We show that by incorporating the validity constraints, the strengthened LP often provides much tighter upper bounds than the previous methods with a little more computational effort, and the solution obtained often has a much smaller gap with the optimal solution. We also formulate a robust version of the FHSAP and show that it can guard against data uncertainty with little cost

The progenitors of type Ia supernovae in the semidetached binaries with red giant donors

Context. The companions of the exploding carbon-oxygen white dwarfs (CO WDs) for producing type Ia supernovae (SNe Ia) are still not conclusively confirmed. A red-giant (RG) star has been suggested to be the mass donor of the exploding WD, named as the symbiotic channel. However, previous studies on the this channel gave a relatively low rate of SNe Ia. Aims. We aim to systematically investigate the parameter space, Galactic rates and delay time distributions of SNe Ia from the symbiotic channel by employing a revised mass-transfer prescription. Methods. We adopted an integrated mass-transfer prescription to calculate the mass-transfer process from a RG star onto the WD. In this prescription, the mass-transfer rate varies with the local material states. Results. We evolved a large number of WD+RG systems, and found that the parameter space of WD+RG systems for producing SNe Ia is significantly enlarged. This channel could produce SNe Ia with intermediate and old ages, contributing to at most 5% of all SNe Ia in the Galaxy. Our model increases the SN Ia rate from this channel by a factor of 5. We suggest that the symbiotic systems RS Oph and T CrB are strong candidates for the progenitors of SNe Ia.Comment: 8 pages, 6 figure

Asphalt Mixture with Scrap Tire Rubber and Nylon Fiber from Waste Tires: Laboratory Performance and Preliminary M‐E Design Analysis

Scrap tire rubber and nylon fiber are waste materials that could potentially be recycled and used to improve the mechanical properties of asphalt pavement. The objective of this research was to investigate the properties of scrap tire rubber and nylon fiber (R‐F) modified warm mix asphalt mixture (WMA). The high‐temperature performance was estimated by the Hamburg wheel-tracking testing (HWTT) device. The low‐temperature cracking performance was evaluated by the disk‐shaped compact tension (DCT) test and the indirect tensile strength (IDT) test. The stress and strain relationship was assessed by the dynamic modulus test at various temperatures and frequencies. The extracted asphalt binder was evaluated by the dynamic shear rheometer (DSR). Pavement distresses were predicted by pavement mechanistic‐empirical (M‐E) analysis. The test results showed that: (1) The R‐F modified WMA had better high‐temperature rutting performance. The dynamic modulus of conventional hot mix asphalt mixture (HMA) was 21.8% ~ 103% lower than R‐ F modified WMA at high temperatures. The wheel passes and stripping point of R‐F modified WMA were 2.17 and 5.8 times higher than those of conventional HMA, respectively. Moreover, the R‐F modified warm mix asphalt had a higher rutting index than the original asphalt. (2) R‐F modified WMA had better cracking resistance at a low temperature. The failure energy of the R‐F modified WMA was 24.3% higher than the conventional HMA, and the fracture energy of the R‐F modified WMA was 7.7% higher than the conventional HMA. (3) The pavement distress prediction results showed the same trend compared with the laboratory testing performance in that the R‐F modified WMA helped to improve the IRI, AC cracking, and rutting performance compared with the conventional HMA. In summary, R‐F modified WMA can be applied in pavement construction

Learning to Pivot as a Smart Expert

Linear programming has been practically solved mainly by simplex and interior point methods. Compared with the weakly polynomial complexity obtained by the interior point methods, the existence of strongly polynomial bounds for the length of the pivot path generated by the simplex methods remains a mystery. In this paper, we propose two novel pivot experts that leverage both global and local information of the linear programming instances for the primal simplex method and show their excellent performance numerically. The experts can be regarded as a benchmark to evaluate the performance of classical pivot rules, although they are hard to directly implement. To tackle this challenge, we employ a graph convolutional neural network model, trained via imitation learning, to mimic the behavior of the pivot expert. Our pivot rule, learned empirically, displays a significant advantage over conventional methods in various linear programming problems, as demonstrated through a series of rigorous experiments

Cardinal Optimizer (COPT) User Guide

Cardinal Optimizer is a high-performance mathematical programming solver for efficiently solving largescale optimization problem. This documentation provides basic introduction to the Cardinal Optimizer

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