Water and sediment quality in Qinghai Lake, China: a revisit after half a century.

Qinghai Lake, situated on the Qinghai-Tibet plateau, is the largest lake in China. In this study, the water and sediment quality were investigated in Qinghai Lake, three sublakes, and five major tributaries. Both Na+ and Cl- were found to be the major ions present in Qinghai Lake and the three sublakes, while Ca2+ and HCO3- dominated the tributaries. Compared with historical data from the 1960s, the concentrations of NH4 (+), NO3 (-), and soluble reactive silica have increased considerably, likely caused by increased human activities in the area. Compared to the historical data, chemical oxygen demand has increased and lake water transparency has decreased, likely related to an increase in nutrient levels. Relatively high concentrations of total nitrogen (TN) and total phosphorus (TP) were observed in Qinghai Lake sediments, although P fraction types and low water concentrations of these two indicate low possibility of transfer into the water column. The ratios of C/N suggest that the organic matter in the sediments are primarily from autochthonous sources. TN and total organic carbon in the sediment cores increased slowly up the core while TP and total inorganic carbon have been fairly constant

Ageing of bituminous materials: Experimental and numerical characterization

Research of the ageing mechanisms in the Netherlands is crucial to deal with ageing infrastructure and the growing pressure on and lack of natural resources. The use of porous asphalt incurs the additional costs because of the shorter service life and the more expensive maintenance required. On the other hand, the Dutch road engineering community has made significant efforts in recycling of pavements after the end of their service life. Currently, 90% of the asphalt is demolished and used in new asphalt pavement. Ideally, it would be nice to keep recycling asphalt concrete indefinitely, but this should be done without loss of functionality or environmental risks.This thesis aims to acquire an advanced understanding of the fundamental thermal ageing processes of bituminous materials, by conducting a series of experiments and developing a set of computational models. A greater understanding of the bitumen ageing mechanisms and how they change physico-chemical properties of bitumen can help to accurately predict the service life of an asphalt pavement and develop high performance bituminous products that are less sensitive to ageing...Pavement Engineerin

环氧沥青固化过程中的粘度特性

In this study, a series of viscosity tests were performed to investigate various conditions, i.e. temperature, shear rate and dilution level, on the curing behavior of epoxy bitumen. The results show that curing rate of epoxy bitumen increased with temperature; high shear rate would interfere the formation of crosslinks in epoxy bitumen, resulting in a negative effect on curing rate; diluting epoxy bitumen by a base bitumen was an effective way to control the curing rate and reduce the material cost. Considering the workability and durability of paving materials, it is recommended that dilution level of epoxy bitumen is 25%, mixing rate is 20 r/min, curing temperature is 130 ℃, and the pavement construction should be finished within 5 hours.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Pavement Engineerin

Comprehensive review on the transport and reaction of oxygen and moisture towards coupled oxidative ageing and moisture damage of bitumen

Oxidative ageing and moisture damage are key factors in bitumen degradation and asphalt pavement deterioration. The effects of oxygen and moisture on bitumen are governed by their transport and reaction processes. This paper provides an overview of theories and concepts developed to describe the kinetics, thermodynamics and mechanisms of transport and reaction of moisture and oxygen within bitumen. The moisture- and oxygen-induced changes of the physicochemical and mechanical properties of bitumen are also discussed. The aim is to summarize literature findings and conclusions and discuss the possibilities of establishing coupled moisture-oxygen models to be used for long-term pavement performance predictions.Pavement Engineerin

Effect of filler properties on the hydrothermal ageing of bituminous mastics

Moisture sorption can significantly influence hydrothermal ageing and alter the chemical and rheological properties of bituminous mastics. Mineral filler particles are added to bituminous binders to form mastics with increased stiffness. The addition of fillers can considerably change the moisture sorption and the physico-chemical properties of binders by surface interactions and physical presence. This study aims to investigate the effect of filler type on the moisture-induced changes of bituminous mastics after wetting-drying cycles by means of sorption, rheological and infrared spectrometry tests. The results show that mineral fillers with higher diffusivity increase the overall capacity of mastics to absorb moisture, but at the same time allow for moisture desorption during drying. Nevertheless, it has been found that it is not the diffusivity properties but rather the bitumen and filler interactions that control the hydrothermal ageing of the mastics.Pavement Engineerin

Recyclability of epoxy-modified open-graded porous asphalt

Epoxy asphalt attracted the attention of road authorities in many countries as a solution for du-rable open-graded porous asphalt (OGPA) surface layers with enhanced longevity. Nevertheless, the recycla-bility of aged epoxy asphalt materials has not been thoroughly studied yet. This research presents an experi-mental program conducted in the laboratory to assess the potential recyclability of epoxy-modified open-graded porous asphalt (EMOGPA) mixes. Results indicate that the aging increased the tensile strength of studied mixes, with the strength and strength development rate of aging EMOGPA mixes to be almost identi-cal to standard OGPA mixes. The EMOGPA mixes have shown higher resistance against water damage than the OGPA mixes supporting the claim that the stone-mastic adhesion is improved with the use of epoxy bind-er. It was also proven that the aged material containing the epoxy binder could be re-melted to produce new pavement materials. The new EMOGPA mixes with the recycled epoxy material exhibited similar durability characteristics with the recycled standard OGPA mixes.Pavement Engineerin

Life cycle assessment of epoxy-modified asphalt pavement

This research aims to evaluate the potential environmental impact of epoxy-modified asphalt used as a pavement material for roadways in the Netherlands and identify what determines the environmental performance of the epoxy asphalt technology through life cycle assessment. Results indicated that the incor-poration of epoxy binder in asphalt could lead to significantly lower environmental impact than the unmodi-fied asphalt. Such benefits are attributed by the minimal maintenance interventions of a pavement with epoxy and their remarkably higher service life over the analysis period. Finally, although the initial price of epoxy-modified asphalt production and construction was substantially higher than of standard asphalt mixtures, the overall score of epoxy-modified asphalt pavement in all weight scenarios was lower than that of the reference structures reflecting the sustainability benefits of using this technology for roadway pavements.Pavement Engineerin

Effect of mineral fillers on epoxy-modified open-graded porous asphalt durability

Epoxy-asphalt (EA) attracted the attention of road authorities in many countries as a solution for open-graded porous surface layers with enhanced durability and longevity. This research presents an experimental programme to assess the durability of epoxy-modified open-graded porous asphalt (EMOGPA) mixes, emphasising the effects of the reactivity of two mineral fillers on mixes containing various EA proportions. Results indicate that the EMOGPA mixes have shown a high sensitivity to the conditioning time before compaction (aka. preconditioning). The materials produced exclusively by EA are the most sensitive to preconditioning, reducing their water and ravelling resistance with increased preconditioning time lengths. The number of gyrations has also been proven as an efficient quantity of the compaction effort required to reach the target mix properties. Moreover, the proportional increase of EA in mixes led to substantially improved durability. Hydrated lime in epoxy-modified asphalt mixes also affected their mechanical response. The indirect tensile strength and toughness of EA mixes were higher than other mixes, while mixes with limestones were stronger and tougher than those with hydrated lime. This attribute reflects the positive contribution of apolar fillers to strengthen and toughen the EA mixes.Pavement Engineerin

Ageing effect on the relaxation properties of bitumen

The ageing of bitumen has a significant impact on the mechanical behavior of asphalt concrete. In this study, Dynamic Shear Rheometer (DSR) tests were utilized to investigate the effect of ageing on the relaxation properties of bituminous materials. PEN 70/100 bitumen films with thickness of 2 mm were exposed to laboratory ageing at various conditions. Specifically, different combinations of ageing time, temperature and pressure were applied on the bitumen films. Three evaluation indices, explicitly the shear stress at 0 s and 100 s, the ratio of shear stress at 0 s and 100 s and the time that shear stress reduces to 50% and 25% of the initial value, were used to determine the evolution of the relaxation properties of bitumen. The results show that, in comparison to fresh bitumen, aged samples show higher residual shear stresses after relaxation and are more susceptible to stress accumulation thus cracking. In addition, temperature, followed by pressure and ageing time, was found to have the stronger impact on bitumen ageing.Pavement Engineerin

Thermodynamics and kinetics of moisture transport in bitumen

Moisture in bitumen and at the bitumen-aggregate interface affects the cohesive and adhesive properties of asphalt mixtures, which are critical for the service performance and durability of pavements. This paper aims to investigate the kinetics and thermodynamics of moisture transport in bitumen at various temperatures and relative humidity for different bitumen types. Transport models are introduced to study the moisture transport mechanisms. A parameter optimization approach combined with the finite element method is applied to simulate moisture transport behavior. Results show salient sorption increase at higher relative humidity levels (more than 70%), indicating the occurrence of clustering of water molecules in bitumen, which can lead to a significant decrease of the diffusion coefficient. Transport models show great quality in simulating experimental results, in which the S-Cluster model provides a detailed explanation of the moisture transport mechanisms and describes better the performance at high sorption levels. The diffusion coefficient, cluster size and activation energy were determined and were found to be linked to the bitumen chemical and structural properties. The transport kinetics and thermodynamics are expected to contribute to a comprehensive understanding of moisture transport behavior in bitumen and further of pavement moisture damage at complex and interacting environmental conditions.Pavement Engineerin