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.     

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 flame retardant high impact polystyrene

Flame retardant high impact polystyrene (HIPS) was prepared by melt blending HIPS with nano-modified aluminum trihydrate (nano-CG-ATH) and red phosphorus masterbatch (RPM). Styrene–butadiene–styrene (SBS) was used as a strengthener in this research. The effects of the nano-CG-ATH, RPM, and SBS on properties of HIPS composites were studied using mechanical and combustion tests, and thermogravimetric analysis. The morphologies of fracture surfaces and char layers were characterized through scanning electron microscopy (SEM). The HIPS/nano-CG-ATH/RPM (68/20/12) composite and its combustion residues at various temperatures were characterized by Fourier transform infrared (FTIR) spectra analysis. The results show that the UL-94 rating of the HIPS/nano-CG-ATH/RPM (68/20/12) composite reached V–0 and that its char layer after flame test was well-developed and robust, but that its impact performance was poor. The addition of the SBS improved its impact performance but did not influence its thermal and flame retardant properties, but lowered its tensile strength and flexural modulus to some extent. The FTIR spectra confirm that both P–O–P and P–O–C groups were present in the char.     

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.     

SBS改性沥青低温性能研究

为了研究BBR试验方法对SBS改性沥青低温性能评价的合理性,采用3种基质沥青、3种SBS改性剂,制备了5种SBS改性沥青,通过BBR试验得到沥青的劲度模量S和劲度模量变化率m,计算得到其低温等级温度TLC,并与各沥青的延度值进行比较,结果表明用TLC评价SBS改性沥青的低温性能更加合理,并分析了基质沥青和SBS类型对TLC的影响规律,结果表明,基质沥青中胶质和芳香酚含量越高改性沥青低温性能越好,线型SBS改性沥青低温性能优于星型SBS改性沥青。     

Effect of wax on basic and rheological properties of bitumen with similar Penetration-grades

This paper presents the results of a study on the wax content, the basic and rheological properties of seven unmodified bitumens with Penetration-grades 60–70 and the effect of wax on these bitumens. Among the bitumens, one (currently used in Hong Kong) was supplied by a manufacturer in Singapore while the other six bitumens were obtained from manufacturers in Mainland China. The results of the basic tests show that all bitumens are Penetration-grade 60–70 and have similar basic properties. The test results comply with the Hong Kong bitumen specification. However, the wax contents of some of the bitumens manufactured from crude oil deposited in China are relatively high. The test results obtained by the dynamic shear rheometer further indicate that the bitumens with low wax content performed better than those with high wax content under a high temperature environment. The test results exhibit relatively good correlation between the wax contents and the rheological properties of the bitumens. Therefore, standards and procedures should be established in Hong Kong to specify requirements on wax content or Performance-grade for bitumen used in road paving.     

SBS改性剂与沥青的相容性分析

分别采用4303、LG501两种SBS改性剂与辽河90#基质沥青进行相容性试验。沥青胶浆性能结果表明两种改性剂与基质沥青相容性良好,在掺量一定的情况下,两种SBS改性剂制成的改性沥青的感温性能、高温稳定性能是4303优于LG501;低温延伸性LG501优于4303;弹性恢复、抗老化性两者性能相当。混合料性能试验结果表明,室内制成的改性沥青与成品改性沥青拌制混合料性能相当,在高温抗车辙方面稍优于取样改性沥青。     

SBS掺量对改性沥青技术指标的影响

通过对韩国SK沥青和壳牌沥青,分别掺入T161B和4303星型改性剂以及YH1301-1和1320-115线性改性剂,制备出SBS改性沥青,深入的分析了改性沥青各项性能随SBS掺量的变化规律。结果表明：改性剂掺量为4．4％的时候,改性沥青各项性能达到了最优,而且SBS改性剂掺量超过了4．8％的时候,其低温延度就会下降。     

Effect of styrene-butadiene-styrene copolymer on the aging resistance of asphalt: An atomistic understanding from reactive molecular dynamics simulations

To reveal the potential influence of styrene-butadiene-styrene (SBS) polymer modification on the anti-aging performance of asphalt, and its mechanism, we explored the aging characteristics of base asphalt and SBS-modified asphalt by reaction force field (ReaxFF) and classical molecular dynamics simulations. The results illustrate that the SBS asphalt is more susceptible to oxidative aging than the base asphalt under oxygen-deficient conditions due to the presence of unsaturated C=C bonds in the SBS polymer. In the case of sufficient oxygen, the SBS polymer inhibits the oxidation of asphalt by restraining the diffusion of asphalt molecules. Compared with the base asphalt, the SBS asphalt exhibits a higher degree of oxidation at the early stage of pavement service and a lower degree of oxidation in the long run. In addition, SBS polymer degrades into small blocks during aging, thus counteracting the hardening of aged asphalt and partially restoring its low-temperature cracking resistance.     

TB胶粉复合SBS改性沥青及混合料的低温性能

通过小梁弯曲蠕变试验(BBR)以及半圆弯拉试验(SCB),对不同TB胶粉掺量和苯乙烯丁二烯苯乙烯嵌段共聚物(SBS)掺量的TB胶粉复合SBS改性沥青及其混合料的低温性能进行研究,并对其低温性能指标进行相关性分析.结果表明:与基质沥青相比,TB胶粉改性沥青具有优异的低温性能,且随着TB胶粉掺量的增加,其低温PG分级温度下降,沥青低温应力变小,混合料低温抗裂性增强;TB胶粉复合3%SBS改性沥青及其混合料的低温性能高于基质沥青,且随着TB胶粉掺量的增加,其低温性能改善效果较为显著,但低于相应掺量的TB胶粉改性沥青;随着SBS掺量的增加,10%TB胶粉复合SBS改性沥青的低温性能变化不明显,混合料的低温抗裂性变差;TB胶粉改性沥青的低温PG分级可以很好地反映沥青及其混合料的低温性能,而TB胶粉复合SBS改性沥青不能通过单一的PG分级来评价其低温性能,需要结合其他指标共同评价.     

高黏SBS改性沥青的流变性能与化学特性

为研究SBS掺量、稳定剂含量和老化对高黏SBS改性沥青流变性能与化学特性的影响,针对SBS掺量和稳定剂含量不同的高黏SBS改性沥青,分别采用动态剪切流变仪(DSR)和凝胶渗透色谱(GPC)试验对老化(短期老化和长期老化)前后的改性沥青进行流变性能与化学特性分析.结果 表明:相位角主曲线可以很好地表征高黏SBS改性沥青在老化过程中的流变性能;高黏SBS改性沥青中由于广泛的交联作用,使得SBS中形成了大量共价键,因此即便是长期老化,仍有足够数目的共价键来维持SBS结构的完整性;相比无稳定剂的SBS改性沥青,稳定剂的添加大幅度改善了高黏SBS改性沥青的性能,但在已有稳定剂的基础上再增加稳定剂的含量对其性能的提升有限;SBS掺量高的改性沥青需要更长的搅拌时间,以保证SBS在沥青中发生充分溶胀;稳定剂含量高的改性沥青也需要更长的搅拌时间,使SBS分子之间发生交联作用.     

Polymer modified asphalt binders

This paper is a review of research that has been conducted on polymer modified binders over the last three decades. Polymer modification of asphalt binders has increasingly become the norm in designing optimally performing pavements, particularly in the United States, Canada, Europe and Australia. Specific polymers that have been used include rubber, SBR, SBS and Elvaloy^®. Specifications have been designed and pre-existing ones modified to capture the rheological properties of polymer modified binders. The elastic recovery test is good at determining the presence of polymers in an asphalt binder, but is less successful at predicting field performance of the pavement.     

Sick building syndrome—A case study in a multistory centrally air-conditioned building in the Delhi City

Recently, airtight envelope system has become popular in the design of office buildings to reduce heating and cooling loads. Maintaining allowable indoor air quality (IAQ) for such airtight buildings totally depends on mechanical ventilation systems. Subsequently, poor operation of the ventilation system in such office buildings causes ineffective removal of polluted indoor air, and displays a sign of “sick building syndrome” (SBS). User's perception is an important parameter for evaluating IAQ. A questionnaire study was carried out to investigate the prevalence of the SBS at a multistory centrally air-conditioned Airport Authority of India (AAI) building in the New Delhi city. Quantification of the perceptions of the users regarding IAQ was done by converting their responses to a SBS score. The quantified answers were then subjected to statistical analysis. Qualitative analysis of the questionnaire was carried out to evaluate relationships between SBS score and carbon dioxide (CO₂) and other parameters related to building and work environment. Quantitative analysis of IAQ was also conducted by monitoring indoor concentrations of four pollutants, namely, nitrogen dioxide (NO₂), sulphur dioxide (SO₂), suspended particulate matter (SPM) and carbon monoxide (CO). Concentrations of pollutants were complying with IAQ standards as given by ASHRAE and WHO. The SBS was higher on the third floor as compared to other floors and the control tower. The main symptoms prevailing were headache (51%), lethargy (50%), and dryness in body mucous (33%). The third floor and the control tower were affected by infiltration, mainly from entrance doors. A direct relation between the average SBS score and CO₂ concentration was found, i.e., the average SBS score increased with CO₂ concentration and vice versa, clearly signifying the usefulness of SBS score in IAQ.     

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.     

The effects of using lime and styrene–butadiene–styrene on moisture sensitivity resistance of hot mix asphalt

This study focuses on determining the effects of styrene–butadiene–styrene (SBS) and using mineral filler with lime on various properties of hot mix asphalt especially moisture damage resistance. The asphalt cement was modified with 2%, 4% and 6% SBS. The lime treated mixtures containing 2% lime by weight of the total aggregate as filler. The physical and mechanical properties of polymer modified binder and binder–aggregate mixes were evaluated through their fundamental engineering properties such as dynamic shear rheometer (DSR), rotational viscosimeter (RV) for binders, Marshall stability, stiffness modulus, indirect tensile strength and moisture susceptibility for mixes. The retained Marshall stability (RMS) and tensile strength ratio (TSR) values were calculated to determine the resistance of mixtures to moisture damage. To investigate clearly the effective of SBS and lime seven freeze–thaw cycle was applied to specimens at TSR test. The results indicate that application of SBS modified binders and lime as mineral filler one by one improves the stability, stiffness and strength characteristic of hot mix asphalt. According to retained Marshall stability it is concluded that addition of only 2% lime have approximately same effect with addition of 6% SBS. Using lime together within the SBS modified mixes exhibit high accordance and exacerbates the improvement of properties. Specimens containing both 2% lime and 6% SBS, have the highest stiffness modulus which is 2.3 times higher than those of the control mixture and showed the least reduction in tensile strength ratio while maintaining 0.70 tensile strength ratio after seven freeze–thaw cycle.     

SBS/ 多聚磷酸复合改性沥青低温蠕变特性分析

为分析多聚磷酸掺量对SBS/多聚磷酸复合改性沥青低温性能的影响,采用弯曲梁流变仪对SBS/多聚磷酸复合改性沥青和SBS改性沥青的低温蠕变劲度(S)与松弛特性(m)进行了试验测试,分析多聚磷酸掺量以及测试温度对其粘弹性组成的影响,并与SBS改性沥青进行比较。结果表明:SBS/多聚磷酸复合改性沥青的S和m值在很大程度上取决于多聚磷酸的掺量,多聚磷酸掺量越大,复合改性沥青的S值越大,m值越小,SBS/多聚磷酸复合改性沥青的低温性能随多聚磷酸掺量的增加而降低。     

PVP修饰石墨烯对SBS改性沥青流变性能的影响

为研究经聚乙烯吡咯烷酮(PVP)处理后的石墨烯对SBS改性沥青流变性能的影响,通过高速剪切机在SBS改性沥青中掺入PVP修饰石墨烯,制备了石墨烯-SBS复合改性沥青,并采用动态剪切流变仪、温度扫描和线性振幅扫描试验,对复合改性沥青流变性能及抗疲劳性能变化规律进行研究,同时结合弯曲梁流变仪试验探索了复合改性沥青低温抗裂性的变化规律.试验结果表明:PVP修饰石墨烯的掺入能够有效改善SBS改性沥青在高温条件下的抗变形、弹性恢复能力以及抗疲劳性能;PVP修饰石墨烯的掺入对复合改性沥青的低温抗裂性能存在负面影响,但影响不明显.     

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.     

SBS C9石油树脂改性沥青的研究

选择SBS改性剂与C9石油树脂对辽河90#基质沥青进行改性,通过常规试验、梁弯曲流变(BBR)试验考察了该改性沥青的感温性能、高温稳定性能、低温抗裂性能和抗老化性能,并利用电子显微镜对其结构进行了观察.结果表明:当SBS-C9石油树脂的质量分数为5%时,SBS-C9石油树脂改性沥青的感温性能、高温性能均优于SBS改性沥青,而低温性能、抗老化性能与之相差不大;C9石油树脂可提高SBS改性剂与基质沥青之间的结合力及SBS改性剂对基质沥青的约束力,使之形成新的交联网络结构.     

Effect of different high viscosity modifiers on rheological properties of high viscosity asphalt

High viscosity asphalt (HVA) has been a great success as a drainage pavement material. However, the larger porosity of drainage asphalt mixtures weakens the cohesion and adhesion and leads to premature rutting, water damage, spalling and cracking. The purpose of this study was to investigate the rheological properties of HVA prepared using different high viscosity modifiers through conventional tests, Brookfield viscosity tests, dynamic shear rheometer tests and bending beam rheometer tests. The conventional performance results demonstrated SBS + rubber asphalt (SRA-1/2) exhibited excellent elastic recovery and low-temperature flexibility. The 60°C dynamic viscosity results indicated TPS + rubber asphalt (TRA) had the excellent adhesion. The rotational viscosity results and rheological results indicated that SRA-2 not only exhibited excellent temperature stability and workability, as well as excellent resistance to deformation and rutting resistance, but also exhibited excellent low-temperature cracking resistance and relaxation performance. Based on rheological results, the PG classification of HVA was 16% rubber + asphalt for PG76-22, 20% rubber + asphalt for PG88-22, TRA and SRA-1/2 for PG88-28. From comprehensive evaluation of the viscosity, temperature stability and sensitivity, as well as high/low temperature performance of HVA, SRA-2 was found to be more suited to the requirements of drainage asphalt pavement materials.