SGC Tests for Influence of Material Composition on Compaction Characteristic of Asphalt Mixtures
Compaction characteristic of the surface layer asphalt mixture (13-type gradation mixture) was studied using Superpave gyratory compactor (SGC) simulative compaction tests. Based on analysis of densification curve of gyratory compaction, influence rules of the contents of mineral aggregates of all sizes and asphalt on compaction characteristic of asphalt mixtures were obtained. SGC Tests show that, for the mixture with a bigger content of asphalt, its density increases faster, that there is an optimal amount of fine aggregates for optimal compaction and that an appropriate amount of mineral powder will improve workability of mixtures, but overmuch mineral powder will make mixtures dry and hard. Conclusions based on SGC tests can provide basis for how to adjust material composition for improving compaction performance of asphalt mixtures, and for the designed asphalt mixture, its compaction performance can be predicted through these conclusions, which also contributes to the choice of compaction schemes.
Using discrete element models to track movement of coarse aggregates during compaction of asphalt mixture
Abstract The objective of this study is to analyze the movement characteristic of differently-shaped compositions in the Superpave Gyratory Compactor (SGC) test through tracking coarse aggregates and the numerical simulation of Discrete Element Method (DEM). First, the coarse aggregates were classified into five shape types (rounded, fractured, angular, elongated and flat) and scanned by a 3D scanner. Second, seven groups of asphalt mixtures with different combination types of hybrid, 100%fractured, 100%angular, 80%fractured + 20%rounded, 60%fractured + 40%rounded, 80%fractured + 20%elongated, and 80%fractured + 20%flat groups were simulated by Particle Flow Code (PFC) Version 5. Third, numerical simulations were conducted to analyze the SGC test process and the movement paths of differently-shaped coarse aggregates were obtained. Finally, statistical analysis on the results from the modeling test were used to study the movement characteristics of asphalt mixtures with differently-shaped aggregate compositions. Through this study, it was found that: (1) there were three main stages of particle movement in the SGC test; (2) the ratio of vertical displacement was obviously larger than that of horizontal displacement, while the variation of vertical rotation was obviously smaller than that of horizontal rotation in asphalt mixtures with differently-shaped compositions; (3) the rounded, elongated and flat coarse aggregates have greater influence on horizontal displacement compared with vertical displacement, but have adverse effects on particle rotations during the compaction process; (4) the effects of elongated coarse aggregates on particle movement were larger than those of flat coarse aggregates, but the flat coarse aggregates have more influence on particle rotation for the variations of horizontal and vertical rotational angles.
Toluene degradation via a unique metabolic route in indigenous bacterial species
Tanneries are the primary source of toluene pollution in the environment and toluene due to its hazardous effects has been categorized as persistent organic pollutant. Present study was initiated to trace out metabolic fingerprints of three toluene-degrading bacteria isolated from tannery effluents of Southern Punjab. Using selective enrichment and serial dilution methods followed by biochemical, molecular and antibiotic resistance analysis, isolated bacteria were subjected to metabolomics analysis. GC–MS/LC–MS analysis of bacterial metabolites helped to identify toluene transformation products and underlying pathways. Three toluene-metabolizing bacteria identified as Bacillus paralicheniformis strain KJ-16 (IUBT4 and IUBT24) and Brevibacillus agri strain NBRC 15538 (IUBT19) were found tolerant to toluene and capable of degrading toluene. Toluene-degrading potential of these isolates was detected to be IUBT4 (10.35 ± 0.084 mg/h), IUBT19 (14.07 ± 3.14 mg/h) and IUBT24 (11.1 ± 0.282 mg/h). Results of GC–MS analysis revealed that biotransformation of toluene is accomplished not only through known metabolic routes such as toluene 3-monooxygenase (T3MO), toluene 2-monooxygenase (T2MO), toluene 4-monooxygenase (T4MO), toluene methyl monooxygenase (TOL), toluene dioxygenase (Tod), meta- and ortho-ring fission pathways. But additionally, confirmed existence of a unique metabolic pathway that involved conversion of toluene into intermediates such as cyclohexene, cyclohexane, cyclohexanone and cyclohexanol. LC–MS analysis indicated the presence of fatty acid amides, stigmine, emmotin A and 2, 2-dinitropropanol in supernatants of bacterial cultures. As the isolated bacteria transformed toluene into relatively less toxic molecules and thus can be preferably exploited for the eco-friendly remediation of toluene.