Analysis of the effect of wax content on bitumen under performance grade classification

This paper describes an analysis of the effect of wax content on bitumen under performance grade (PG) classification. Wax content affects the performance and rheological behavior of bitumen. Bituminous mixtures with bitumen of high wax content tend to become very soft at high temperatures leading to rutting problem on pavement. Also the rheological behavior of bitumen has a great influence on the behavior of bituminous mixtures.To address the potential adverse effect of wax on bitumen, countries in Europe limit the wax content to 2.2% (BS EN 12606-1). In Mainland China, the standard (JTG F40-2004) classifies bitumen into three grades (Grades A, B and C). Grade A, with wax content below 2.2%, is used for highway pavement construction. Grades B and C, with wax content limits of 3.0% and 4.5% respectively, can only be used on roads with relatively lower traffic. The current binder specifications in Hong Kong Special Administration Region is based on penetration testing, which does not properly account for pavement performance. This paper assesses the effects of wax content and the rheological properties of seven types of bitumens and provides the basis for a performance grading binder standard for Hong Kong.     

Effect of bitumen wax on asphalt mixture performance

This paper mainly deals with waxes which are naturally present in bitumens, and does not include synthetic waxes that sometimes are proposed as bitumen additives. The main objectives were to study the rheological effect of bitumen waxes and the impact of waxy bitumens on asphalt mixture performance, such as rutting, low temperature cracking, and water sensitivity. In the rheological characterisation of bitumens, a dynamic shear rheometer (DSR) and bending beam rheometer (BBR), as well as various conventional methods, were used. For asphalt mixtures, rutting, low temperature cracking and water sensitivity were evaluated by wheel tracking test (WTT), thermal stress restrained specimen test (TSRST), and modified Lottman test, respectively. It was found that, at high service temperatures and within the same bitumen grade, differences in rutting between the asphalt mixtures made with waxy and non-waxy bitumens were relatively small. However, the presence of wax in bitumen resulted in physical hardening at low temperatures. Using waxy bitumens, asphalt mixtures tended to show higher fracture temperature. As regards water sensitivity, no effect of the wax content in bitumen was seen. The water sensitivity was however heavily influenced by type of aggregate and to less extent by bitumen type. The present study implies that the effect of wax on bitumen quality and asphalt mixture performance depends on many factors. Those may include the chemical composition of the bitumen and particularly the nature of the wax.     

Rheological evaluation of ethylene vinyl acetate polymer modified bitumens

The morphological, thermal and fundamental rheological characteristics of ethylene vinyl acetate (EVA) copolymer modified bitumens are studied in this paper. Nine plastomeric EVA polymer modified bitumens (PMBs) have been produced by laboratory mixing bitumen from three sources with an EVA copolymer at three polymer contents. The morphology, thermal properties and rheological characteristics of the EVA PMBs have been analysed using fluorescent microscopy, differential scanning calorometry and dynamic mechanical analysis using a dynamic shear rheometer, respectively. The results of the investigation indicate that EVA polymer modification increases binder stiffness and elasticity at high service temperatures and low loading frequencies with the degree of modification being a function of bitumen source, bitumen–polymer compatibility and polymer concentration. Filler type modification is evident at low temperatures, temperatures above the melting temperature of the semi-crystalline EVA copolymer and for those modified binders that do not exhibit a dominant polymer network.     

Morphology and image analysis of polymer modified bitumens

This paper presents a laboratory study of styrene butadiene styrene (SBS); ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA) based polymer modified bitumen samples (PMBs). The PMBs have been produced by mixing a 50/70 penetration grade unmodified (base) bitumen with copolymers at different proportions. The fundamental characteristics of the PMBs have been determined using conventional methods. The morphology of the samples as well as the percent area distribution of polymers throughout the base bitumen have been characterized and determined by means of fluorescent light optic microscopy and Qwin-Plus image analysis software, respectively. The results indicate that the fundamental properties and morphology of the modified bitumens are dependent on the type of polymer and polymer content. Polymer modification improves the conventional properties of the base bitumen such as penetration, softening point, temperature susceptibility. At low polymer contents, the samples reveal the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase is observed. Moreover it is found out that a relationship exists between the polymer content and percent area distribution of polymers.     

Preparation and properties of bitumen modified by EVA graft copolymer

This paper presents a laboratory study of modified bitumen containing ethylene vinyl acetate (EVA) and ethylene vinyl acetate grafted maleic anhydride (EVA-g-MAH) copolymers. When the different polymers were added, the physical properties of modified bitumens, such as softening point, ductility at low temperature and storage stability at high temperature are changed. The polymer modified bitumens (PMBs) were analyzed by thermogravimetry (TG), derivative thermogravimetry (DTG) and fourier transform infrared spectroscopy (FTIR). Thermal characterizations showed that the main decomposition stage refers to samples with modifiers exhibited a slight increase in thermal stability and the sample with the highest stability was EVA-g-MAH PMBs. FTIR analysis suggested that it is difficult to prove the EVA-g-MAH has reacted with the functional group in bitumen by FTIR spectrum. The dynamic shear rheometer (DSR) tests reported that added content of EVA-g-MAH has great effect on the rheological properties of the binder and its high temperature performance was improved while its temperature susceptibility was reduced in compare to EVA modified bitumens binder.     

Rheological effects of commercial waxes and polyphosphoric acid in bitumen 160/220 – high and medium temperature performance

The effects of adding three commercial waxes and a polyphosphoric acid to three bitumens of 160/220 penetration grade were studied using different types of laboratory equipment, such as Dynamic Shear Rheometer (DSR), Differential Scanning Calorimeter (DSC), Force Ductilometer (FD) as well as equipment for determining conventional parameters like penetration, softening point and Fraass breaking point. The paper deals with effects at medium and high in-service temperatures likely to affect the rutting performance of an asphalt concrete pavement. The results show that magnitude and type of effect on bitumen rheology depend on the bitumen as well as type and amount of additive used. Bitumen composition was found to be of decisive importance. Adding polyethylene wax or polyphosphoric acid especially to a non-waxy bitumen, showed considerable positive effects on the rheological behaviour at medium and higher temperatures.     

Effect of ageing on bitumen chemistry and rheology

Effect of ageing on bitumen chemistry and rheology was studied. Seven bitumens were aged according to the thin film oven test (TFOT) and the rolling thin film oven test (RTFOT). The binders were characterised using infrared spectroscopy, chromatography and dynamic mechanical analysis. Statistical correlation between different chemical parameters, as well as between chemical and rheological parameters, was examined. The relationship between TFOT and RTFOT was also investigated. It was observed that ageing influenced bitumen chemistry and rheology significantly. However, chemical and rheological changes were generally not consistent, and consequently, ageing susceptibility of bitumens may be ranked differently when different evaluation methods are used. Regardless of the type of the parameters measured, a strong correlation was observed between TFOT and RTFOT, and the two ageing procedures show similar severity.     

Rheological properties and storage stability of bitumen/SBS/montmorillonite composites

Styrene–Butadiene–Styrene triblock copolymer is commonly used for modifying physical, mechanical and rheological properties of bitumen. Because of the poor compatibility between SBS and bitumen, SBS modified bitumen is not storage stable at high temperature. To obtain more compatibility between SBS and bitumen, several methods have been suggested. In this study, organophilic montmorillonite/SBS modified bitumen mixtures were prepared by melt intercalated blending. Physical and rheological properties of polymer modified bitumen were compared before and after adding nanoclay to the bitumen. Results showed that the presence of nanoclay improves the storage stability of PMB significantly without adverse effect on other properties of it. The structure of OMMT/SBS/bitumen blend was characterized by XRD. The spectra indicated that proper dispersion of OMMT in SBS led to a homogenous blend which is named exfoliated structure. The result of storage stability test showed that the difference in softening point was in good accordance with ASTM standard limitation which means that OMMT can improve the storage stability of PMB. Also morphological analysis confirmed storage stability results.     

聚合物改性剂对沥青中蜡含量的影响

通过试验研究，论述了含蜡量对沥青性质的影响，证明高聚物改性剂能有效地吸收沥青中的蜡分。     

Modelling the linear viscoelastic rheological properties of bituminous binders

An extensive literature review on the modelling of the linear viscoelastic (LVE) rheological properties of bitumen over the last six decades is presented in this paper. The use of reliable models can, in general, be considered as a valuable alternative tool for estimating the LVE rheological properties of bitumen. These properties are normally presented in terms of complex modulus and phase angle master curves at a particular reference temperature. The review in this paper consists of three nonlinear multivariable models, 13 empirical algebraic equations and four mechanical element approaches. The details as well as the advantages and disadvantages of the models are discussed. In general, all the models are able to predict the LVE rheological properties of unmodified bitumen as well as follow the time–temperature superposition principle (TTSP). However, the observations suggest a lack of agreement between predicted and experimental LVE rheological properties for materials that contain a phase transition, such as found for highly crystalline bitumen, structured bitumen with high asphaltenes content and highly modified bitumen.     

Effects of nanoclay on rheological properties of bitumen binder

Nanoclays are the new generation of processed clays of interest in a wide range of high performance composites. In other words, nanoclay is defined as clay that can be modified to make the clay complexes compatible with organic monomers and polymers. Here, it can be said that the polymeric nanocomposites are among the most exciting and promising classes of materials discovered recently. A number of physical properties can be enhanced successfully when as a polymer is modified with small amount of nanoclay on condition that the clay is dispersed at nanoscopic level. This research has accomplished a comparative rheological test on the unmodified and nanoclay modified bitumen. For that matter, so, two types of nanoclay were used: nanofil-15 and cloisite-15A. The nanostructure exfoliation of nanoclay platelets in bitumen has been studied using X-ray diffraction (XRD). In the present research, although the empirical rheological test on bitumen are penetration, softening point, ductility and ageing effect, the fundamental rheological test by dynamic shear rheometer (DSR) is conducted on modified and unmodified bitumen. Test results show that while nanoclay changes rheological properties of bitumen and increases stiffness, it also decreases angle phase and improves ageing resistances, as well.     

Aqueous leaching of polycyclic aromatic hydrocarbons from bitumen and asphalt.

The application of bitumen in, e.g. asphalt roads, roofs and hydraulic applications will lead to the leaching of compounds from the bitumen/asphalt into the environment. Because polycyclic aromatic hydrocarbons (PAHs) are present in bitumen, static and dynamic leach tests have been performed to study the leaching behaviour of this class of compounds. Nine petroleum bitumens covering a representative range of commercially available products and one asphalt made from one of the bitumens have been tested in a static leach test. The asphalt has been also subjected to a dynamic leach test. The main conclusions are that a 30h dynamic leach test is sufficient to determine the equilibrium concentration that will be reached after bitumen or asphalt has been in contact with the water for more than 3-6 days. As an alternative to performing a leach test, this concentration can be calculated from the PAH concentrations in the bitumen, and their distribution coefficients, as calculated here, or from their aqueous solubilities. The equilibrium PAH concentrations in the leach water from bitumens stay well below the surface water limits that exist in several EEC-countries and are also more than an order of magnitude lower than the current EEC limits for potable water.     

Decay properties of the foamed bitumens

This paper presents study on decay properties of two foamed bitumens. Foaming tests under various conditions were carried out to investigate decay properties of two types of bitumen: Penetration-grade 60 (PG 60) and Penetration-grade 100 (PG 100). Decay data were recorded and analyzed. It is found that water content has a significant effect on the bitumens’ decay, and the time at which the maximum expansion ratio appears advances with an increase of temperature. PG 60 achieves the maximum expansion ratio at an earlier time than PG 100. The effect of viscosity on the two bitumens’ decay properties was discussed and explained; and the observation of the tests confirms this explanation is rational. For developing the bitumens’ decay functions, a four-parameter power function and a three-parameter exponential function were selected to fit the testing data of PG 60 and PG 100 bitumen, respectively. Two bitumens’ decay functions were established by a two-stage method. Non-linear fitting analysis exhibits that two functions can well fit the data of the foaming tests. Decay functions’ parameters were obtained by using the best subset regression method. Two decay functions can be used to calculate the maximum expansion ratios and half-lives of PG 60 and 100 bitumen under various conditions.     

基于时间和温度依赖性的SBS/ 多聚磷酸复合改性沥青流变性能研究

为分析多聚磷酸掺量对SBS/多聚磷酸复合改性沥青高温流变特性的影响,对比复合改性沥青与基质沥青、SBS改性沥青流变特性的差异,本文采用SK90号基质沥青、制备4.5%SBS改性沥青以及SBS/多聚磷酸复合改性沥青。对沥青试样进行60℃频率扫描和30℃-60℃温度扫描试验,分析沥青结合料复数模量、相位角随加载频率和温度的变化规律。结果表明:SBS改性沥青、SBS/多聚磷酸复合改性沥青的复数模量值远大于基质沥青,SBS/多聚磷酸复合改性沥青的复数模量随着多聚磷酸掺量的增多而增大;SBS改性沥青和SBS/多聚磷酸复合改性沥青的相位角随荷载作用频率上升而迅速增大;SBS改性沥青和SBS/多聚磷酸复合改性沥青的温度敏感性较基质沥青有了显著的改;3.5%SBS+1.6%PPA复合改性沥青的复数剪切模量大于改性剂掺量为4.5%的SBS改性沥青。     

Evaluation of the improved properties of SBR/weathered coal modified bitumen containing carbon black

One problem of polymer modified bitumens (PMBs) is the poor compatibility between polymer and bitumens. In this paper, the improved properties of bitumen binders containing various kinds of additive including styrene butadiene rubber (SBR), weathered coal (WC) and carbon black (CB) under different concentrations are investigated. To assess the effects of the type and concentration of the additive on classical properties of bitumen binders, the softening points, penetration, penetration index (PI), ductility and Fraass breaking points before and after RTFOT aging are tested. The dynamic mechanical analysis (DMA) of these binders before and after ageing had been characterized by dynamic shear rheometer (DSR) using a combination of temperature and frequency sweeps. With higher polymer concentrations, it produced a highly elastic network which increases the viscosity, complex modulus and elastic response of the PMBs, particularly at high service temperatures. However, ageing of PMBs tended to result in a decrease in the elastic response of the modified bitumens. It also has been confirmed that the morphology observed by optical microscopy and scanning electron microscope (SEM) revealed the compatibility among SBR, WC and bitumen. The storage stability of binder was also improved significantly.     

石油沥青油毡的耐低温性能

讨论了油毡的耐低温性能,石汕沥青改性的技术路线。介绍了丁苯橡胶改性沥青油毡的研究及其技术性能,指出今后在寒冷地医防水工程中应大力推广应用改性沥青油毡。     

SBS对基质沥青低温性能改善效果研究

通常认为SBS可以同时改善基质沥青的高、低温性能。以三种常用的国产沥青和一种进口沥青作为基质沥青,采用四种不同的SBS对其进行改性,分别制得成品SBS改性沥青。运用SHRP试验方法中的弯曲梁流变仪(BBR)分别对制得的这些SBS改性沥青的RTFO／PAV残留物的流变特性进行了试验研究。结果表明,用物理意义上的共存共混方法制备得到的SBS改性沥青,其低温等级基本保持在基质沥青的低温等级上,即从流变学的意义上来说,SBS对基质沥青低温抗裂性能的改善效果仍值得探讨。     

香港特区强制性建造业工人注册制度及借鉴

2.北京交通大学应用经济学博士后流动站,北京100044)[摘要]实施强制性建造业工人注册制度是香港特区建造业的一件大事,是建立新文化的一项重要措拖。分析了香港特区实施强制性建造业工人注册制度的目的和注册管理等基本内容,探讨了该制度对于内地建筑业的可借鉴之处。     

Experimental and numerical investigation of high strength stainless steel structures

The paper summarises research on high strength stainless steel tubular structures conducted at the University of Hong Kong, and the Hong Kong University of Science and Technology. Square and rectangular hollow sections were investigated. The test specimens were cold-rolled from high strength austenitic and duplex stainless steel sheets. The material properties of the test specimens were determined by tensile coupon tests at normal room and elevated temperatures. The initial geometric imperfection and residual stress of the specimens were measured. The experimental and numerical investigation focused on the design and behaviour of cold-formed high strength stainless steel structural members. The results were compared with design strengths calculated using the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures.     

Blowing in the wind: the impact of China's Pearl River Delta on Hong Kong's air quality

The local versus regional nature of Hong Kong's air pollution remains an unresolved issue with important policy implications. Specifically, the potential benefits of different air quality improvement efforts will vary dramatically, depending upon the nature of the pollution. This multi-disciplinary paper attempts to resolve the issue, using a time series, cross-sectional panel of pollution data from Hong Kong and southern China, along with weather variables from Hong Kong. An econometrically-based structural model of Hong Kong pollution levels is constructed, and Granger causality tests are conducted. Then, using results from the structural model, the health impacts on Hong Kong residents of reductions in mainland China's pollution are estimated and valued in economic terms. Results indicate that for the pollutants PM(10) and NO(2) causality runs in both directions, highlighting the regional nature of the air pollution problem. However, the potential health benefits resulting from reductions in southern China's pollution are relatively small. In US dollar terms, the averted mortality benefits of a large China-focused clean up are approximately $40 million, but the benefits of a more modest Hong Kong-focused effort are nearly $200 million. The resulting policy implication is that Hong Kong's primary pollution control efforts should lie at the local level.