Improving the performance of Crumb Rubber bitumen by means of Poly Phosphoric Acid (PPA) and Vestenamer additives

Paralleled to the numerous researches on Crumb Rubber (CR) modified bitumen, some limited work-studies have also been implemented on the effects of specific chemical modifiers, such as Poly Phosphoric Acid (PPA) and Vestenamer, on the performance of bitumen. The main difference between present research and previous ones is simultaneous evaluation of these additives on bitumen performance grade. In this research, five samples of modified bitumen were prepared using PG58-22, PPA, Vestenamer, and various CR percentages. The samples were classified according to the superpave performance grading system. The results indicate that these modifiers have significantly improved the performance of bitumen.     

Technical study on the Iranian Gilsonite as an additive for modification of asphalt binders used in pavement construction

In this research, effects of the Iranian natural bitumen (gilsonite) on two types of asphalt binders produced in the country with the performance grades of PG58-22 and PG64-22 were studied according to superpave performance grading (PG) system. Results of conducted tests on the modified asphalt binders with 4%, 8% and 12% gilsonite show that although addition of gilsonite to base bitumens can cause improvement in high performance temperature (HT) of mentioned bitumens, it has no positive impact on low performance temperature (LT) of them.     

Investigation of rutting performance of asphalt mixtures containing polymer modifiers

The purpose of this study is to evaluate mechanical properties of control and modified asphalt mixtures. Conventional and five modified asphalt mixtures were studied on hot mix asphalt permanent deformation resistance. Amorphous polyalphaolefin, cellulose fiber, polyolefin, bituminous cellulose fiber and styrene butadiene styrene were used as modifiers. Indirect tensile strength, indirect tensile, static and repeated creep and LCPC wheel tracking tests were used for different loading conditions and temperatures. Research was focused on comparing the interaction between LCPC wheel tracking and other mechanical tests. According to the LCPC wheel tracking and repeated creep test results SBS mixtures were found as the most resistance mixtures in view of the rutting. Additives performed different performance levels but showed more resistance to permanent deformation according to the conventional mixtures. As far as the static creep test results are concerned there are controversial results because conventional mixtures are better. It is thought that this result may stem from the static behavior of the load and rheological change of bitumen with modifiers.     

Performance evaluation of a high durability asphalt binder and a high durability asphalt mixture for bridge deck pavements

This paper describes the results of laboratory and full-scale performance tests for a high durability asphalt binder (HDAB) and high durability asphalt mixture (HDAM) applicable to the wearing course in a bridge deck system. The HDAB was developed using a styrene–butadiene–styrene (SBS) modifier and hydrocarbon for improving construction workability and resistance to fatigue cracking. Various binder tests were conducted on the HDAB, and test results showed that the resistance to fatigue and low temperature cracking of the HDAB increased significantly compared to that of the PG 64-22 and PG 76-22 binders. For the mixtures, the fatigue test results showed that the HDAM has a three times longer fatigue life than the SBS-modified asphalt mixture. It was also found that the HDAM has a higher resistance against moisture-induced damage. Results from full-scale accelerated testing on the bridge deck pavement system proved that the HDAM can significantly improve pavement performance.     

Laboratory comparison of the crumb-rubber and SBS modified bitumen and hot mix asphalt

The use of crumb rubber (CR) recycled from waste tires using an ambient grinding process was evaluated at two stages in asphalt formulation. First, bitumen modified with crumb rubber was evaluated by rotational viscometery (RV), dynamic shear rheometry (DSR) and conventional binder tests. Hot asphalt mixtures including crumb-rubber-modified bitumen were then evaluated by determining the permanent and fatigue characteristics and stiffness moduli of control and modified mixtures. The properties of the crumb-rubber-modified bitumen and asphalt mixtures were compared to different contents of styrene–butadiene–styrene (SBS) modified-bitumen and asphalt mixtures. The tests showed that to achieve the same performance, as with SBS-modification, the CR-content must be used at much higher than SBS. 8%-CR modification was determined as the most suitable content according to both binder and mixture tests.     

A model for dynamic creep evaluation of SBS modified HMA mixtures

The specimens, according to the Marshall Stability testing procedure, of hot mix asphalt (HMA) containing bitumen modified with styrene–butadiene–styrene (SBS) have been constructed in the laboratory and tested under dynamic loading for permanent deformation using Suleyman Demirel University Asphalt Tester equipment (SDU-Asphalt Tester). Analysis of data shows that the permanent deformation of the samples may be modeled in terms of the specimen’s characteristics in a very satisfactory manner. Benefits of adding styrene–butadiene–styrene (SBS) in variant quantities and in variant types of additive to asphalt cement (AC-60/70) were investigated. Initial research was done to determine the physical properties of asphalt cement and modifiers. Fifteen asphalt binder recipes were prepared with two types of gradation, six different contents of bitumen, four different contents of polymer, three different types of polymer. After that, Marshall samples were prepared by using the modified and unmodified control asphalt binders. The results of investigation indicate that asphalt mixtures modified by any SBS additive gives the best permanent deformation resistance in the tests carried out in this study, so that, this modification increases physical and mechanical properties of asphalt binder. In this study, total deformation of each sample was calculated using a newly developed equation containing variables of mixture characteristics. In addition to these, to develop a model that could fit the creep curve a new logarithmic model derived from first 100 preconditioning loading was developed instead of power law function model for first stage of permanent deformation curves.     

Laboratory study on the low temperature physical hardening of conventional and polymer modified bitumens

Physical hardening is a reversible process that may influence the long-term performance of a material. In this paper, physical hardening of five unmodified and 35 polymer modified bitumens was studied using a bending beam rheometer (BBR). The modified binders were prepared by mixing 3, 6 or 9% styrene–butadiene–styrene (SBS), styrene–ethylene–butylene–styrene (SEBS), ethylene vinyl acetate (EVA) or ethylene butyl acrylate (EBA) polymers with different base bitumens. The binders were isothermally stored at low temperatures (−15, −25 and −35°C) for different times ranging from 0.5 to 32 h. The results indicated that physical hardening significantly influenced the creep response of the binders, and the hardening index and horizontal shift factor were strong functions of isothermal storage temperature. Unlike the shift factor, the hardening index did not always increase with decreasing storage temperature. At a given storage temperature, a statistical correlation was observed between the two parameters. It was also shown that degree and kinetics of physical hardening were dependent on the base bitumens, and in most cases, the effect of polymer modification was insignificant.     

基于PG值的机场道面沥青抗老化性能预估模型

从沥青老化机理出发,提出了预测机场道面沥青抗老化性能的预估模型.在标准大气压下针对1种基质沥青和2种改性沥青进行4种温度下不同时间段的老化处理,同时采用动态流变剪切仪(DSR)对沥青试样的PG上限温度值进行测试,研究其在老化作用下的变化规律.结果表明:3种沥青的PG上限温度值随老化条件的变化均存在一定的规律,但在相同老化条件下,沥青种类不同,其老化速率不同;无论是基质沥青还是改性沥青,其实测数据与预估模型吻合良好,PG上限温度值可作为评价机场沥青道面抗老化性能的指标.     

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.     

常用改性材料对沥青的改性研究

常用的沥青改性材料有SBS、SBR、聚乙烯、聚丙烯、胶粉等,本文通过实验研究总结了上述材料对改性沥青性能的影响,讨论了各自的最佳改性温度和最佳加入量,并分析了改性机理。     

Characterization of warm mix asphalt binders containing artificially long-term aged binders

Reclaimed asphalt pavement (RAP) comprises one of the largest recycled materials, and warm mix asphalt (WMA) technologies become more commonly used due to their promising advantages in the United States and Europe. This paper addresses the laboratory investigation of performance properties of WMA binders containing aged binders. The recycled binders with the additives were produced using two (i.e., zeolite Aspha-min^® and wax Sasobit^®) of the available warm asphalt processes. The recycled WMA binders were artificially short-term and then long-term aged through the rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. Superpave binder tests were carried out on the binders through the rotational viscometer, the dynamic shear rheometer (DSR), and the bending beam rheometer (BBR). In general, the results of this study indicated that (1) the additives and aged binders played an important role in determination of the binder properties; (2) the use of lower PG grade as a virgin binder (PG 58-28 in this study) was critical on offsetting the increase of binder stiffness caused by the addition of WMA additives and aged binders; and (3) even at the low recycling percentage of 15%, the lower PG grade was needed to get the results meeting current Superpave binder requirements.     

Rheology of warm mix asphalt binders with aged binders

This study addresses the rheological investigation of properties of warm mix asphalt (WMA) binders containing long-term aged binders. The recycled binders with the additives were produced using two (i.e., zeolite Aspha-min® and wax Sasobit®) of the available warm asphalt processes. The main rheological factors selected in this study were relationships between loading and response as a function of time, temperature and frequency using a Bohlin Dynamic Shear Rheometer II. The results indicated that the addition of Sasobit® into recycled binders played an important role in determination of the binder properties evaluated in this study. The use of lower performance grade (PG) as a virgin binder (PG 58-28 in this study) was critical on offsetting the change of rheological binder properties due to the warm additives and the aged binders.     

Dimensional stability of waterproofing bituminous sheets used in low slope roofs

Lap joints between waterproofing bituminous sheets, applied in either single or multiple layers, are one of the most critical areas of roofs, especially when the waterproofing systems comprise only a single sheet. In fact, the way how lap joints are executed is highly associated with the occurrence of anomalies in such systems. With this regard, the dimensional stability of the sheets is one of their most important characteristics, as it that can strongly influence the performance of the lap joints and the details on roof upstands. In this context, with the aim of contributing to improve the understanding of this characteristic of bituminous sheets, the present paper presents results of an experimental study on the dimensional changes suffered by bituminous sheets when subjected to temperature variations. Different types of traditional and non-traditional sheets, with various types of bituminous mixtures (oxidised bitumen and atactic polypropylene (APP) and styrene–butadiene–styrene (SBS) modified bitumen) and reinforcements (polyester, glass fibre and polyethylene) were tested according to EN 1107-1 standard. For most of the sheets, the isolated reinforcements were also subjected to dimensional stability tests in order to evaluate their influence on the overall performance of the waterproofing layer. The results of these experimental investigations confirm that sheets with polyester reinforcement are much less stable than sheets reinforced with glass fibre. In addition, it was concluded that the influence of the type of polymer–bitumen is negligible when compared to the influence of the type of reinforcement – in general, the dimensional stability of the sheets is worse than that of the corresponding reinforcement. Finally, it is shown that the dimensional stability performance of similar products produced by different manufacturers is similar, both for the isolated reinforcements and for the waterproofing sheets.     

Laboratory evaluation of flexible pavement materials containing waste polyethylene (WPE) film

This paper presents a research to recycle the waste vinyl (waste polyethylene film: WPE film) in asphalt mixtures for improving the performance properties of the mixtures. Conventional Marshall mix designs were carried out with varying WPE contents, and the best performing content of WPE film was determined from the previous study. Also, asphalt mixtures with two commercial polymer modifiers, low-density polyethylene (LDPE) and a styrene–butadiene–styrene (SBS), were used to compare the effectiveness of WPE-modified mixture. The strength characteristics such as Marshall stability and indirect tensile strength (ITS) were evaluated, and the wheel tracking test, result of which is generally considered to reflect the field performance, was conducted to measure the rutting resistance of the asphalt mixtures. From the results of this study, asphalt mixture with waste vinyl showed much better rutting resistance than normal asphalt mixture without WPE. It is hypothesized if an optimum content of waste vinyl is used, it is expected that the waste vinyl will be effective as much as commercial modifier in improving the performance of asphalt pavements.     

Mechanistic analysis of ST and SBS-modified flexible pavements

This paper deals with the viability of using starch (ST) and styrene–butadiene–styrene (SBS) as an additive in stone matrix asphalt (SMA) mixtures. A 5% of ST and SBS by weight of bitumen were blended with (70/100)-paving grade asphalt. Unmodified and modified bitumen were subjected to physiochemical tests. The performance tests including, Marshall stability, tensile strength, tensile strength ratio and resilient modulus were carried out on unmodified and modified SMA mixtures. A mechanistic-empirical design approach was used for estimating the improvement in service life of the pavement or reduction in thickness of SMA and base layer for the same service life due to modification the SMA mixtures. The analyses of test results show that the moisture damage and temperature susceptibility can be reduced by the inclusion of ST and SBS in the asphalt mixture. The results also revealed that ST-modifier can be used as anti-stripping agent, and reduced plant emissions and energy consumption by 30%, as well as it shows resistant to fuels, most common chemicals and solvents. The results of multi-layer elastic analysis presented herein indicate that the pavement consisting of ST and SBS-modified SMA as a surface layer is beneficial in reducing the construction materials. In addition, the safe pavement design criteria of unmodified and modified SMA mixtures based on the anisotropic elasticity analysis through finite-element simulation were obtained and reported herein.     

Interpreting SuperPAVE PG test results with confidence intervals

The innovative method to interpret SuperPAVE PG test results using regression analysis and confidence intervals is evaluated in this research. Till now, most of researches and conclusions in the field of bitumen rheological aspects are based on the mean values of test results. Using the mean values does not show the reliability of the test results and in many cases two bitumen with the same PG show different performances, due to different data variances. In this study the confidence intervals method is implemented to interpret the results of SuperPAVE PG tests and notify that the mean values of the variables are occasionally misleading and always some uncertainty exists when using bitumen. This study presents a new formulation that quantifies the uncertainties in bitumen behavior to obtain the true temperature grade of the bitumen with different confidence levels (75% and 95%). Two samples of bitumen with same PG were evaluated with this formulation and the interesting results were found. The behavior of these samples with same PG was significantly different regarding the higher confidence intervals.     

Starch as a modifier for asphalt paving materials

This paper investigates the viability of using starch (ST) as a new modifier for asphalt paving materials. Different ratios of ST (2.5, 5.0, and 7.5% by weight of asphalt) were blended with 70/100 paving grade asphalt. Unmodified and modified asphalt binders were subjected to physicochemical, alkali, acid and fuel resistance tests. The performance tests including, Marshall stability, Marshall Quotient (MQ), tensile strength, tensile strength ratio, flexural strength, rutting resistance and resilient modulus (MR) were carried out on unmodified and modified stone matrix asphalt (SMA) mixtures. The analyses of test results show that the performance of ST-modified asphalt mixtures are better than conventional and styrene–butadiene–styrene (SBS)-modified mixtures. The rutting potential, moisture susceptibility and temperature susceptibility can be reduced by the inclusion of ST in the asphalt mixture. The laboratory MR values are lower than the calculated ones using the empirical equations. The results also revealed that this modifier can be used as anti-stripping agent. It also shows resistance to fuels and most common chemicals. A ST content of 5% by weight of asphalt is recommended for the improvement of the performance of asphalt concrete mixtures similar to that investigated in this study.     

SBS改性沥青热储存及运输过程中的降解研究

通过室内模拟低空气浓度(或相对绝氧)环境下苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)改性沥青的热降解过程,测试和分析了不同条件下SBS改性沥青的性能.结果表明:在热降解过程中,SBS改性沥青低温抗裂能力随时间的延长或温度的升高而逐渐降低;与低空气浓度下热降解对SBS改性沥青微观结构的影响相比,SBS改性沥青在高空气浓度下热降解过程中有更高的羰基和更低丁二烯含量.在生产、储存和运输SBS改性沥青时,需要充分考虑时间、温度以及空气浓度对其性能的影响.     

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.     

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.