Effect of polyethylene on life of flexible pavements

The present study investigates the potential use of pyrolysis low density polyethylene (LDPE) as a modifier for asphalt paving materials. Five different blends including conventional mix were subjected to binder testing such as rheological tests, as well as to some other tests related to the homogeneity of the system. Further, its effect on the moisture sensitivity and low temperature performance of stone matrix asphalt (SMA) mixtures was studied. Research results indicate that modified binders showed higher softening point, keeping the values of ductility at minimum range of specification of (100⁺ cm), and caused a reduction in percentage loss of weight due to heat and air (i.e. increase durability of original asphalt). The results indicated that the inclusion of LDPE in SMA mixtures can satisfy the performance requirement of high-temperature, low temperature and much rain zone. In addition, the horizontal tensile strain at the bottom of asphalt concrete layer (Ε_t) and the vertical compressive strain at the top of subgrade layer (Ε_c) were calculated using multi-layer elastic analysis program, BISAR under 50KN set of dual tires with 106.5 mm contact radius. These responses were 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.     

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.     

Thiopave改性沥青路面力学响应研究

基于Thiopave改性沥青路面良好的高低温稳定性,采用有限元软件对典型半刚性基层沥青面层进行计算,得到不同沥青面层层底力学响应,并对计算结果进行对比研究,得到的主要结论如下：Thiopave沥青路面层底弯拉应力显著大于SBS沥青及基质沥青路面,路表轮隙中心处弯沉值小于SBS沥青及基质沥青路面;随着SEAM掺量的增加,...     

Fatigue behavior of rubberized asphalt concrete mixtures containing warm asphalt additives

The long-term performance of pavement is associated with various factors such as pavement structure, materials, traffic loading, and environmental conditions. Improving the understanding of the fatigue behavior of the specific rubberized warm mix asphalt (WMA) is helpful in recycling the scrap tires and saving energy. This study explores the utilization of the conventional fatigue analysis approach in investigating the fatigue life of rubberized asphalt concrete mixtures containing the WMA additive. The fatigue beams were made with one rubber type (?40 mesh ambient crumb rubber), two aggregate sources, two WMA additives (Asphamin^® and Sasobit^®), and tested at 20 °C. A total of eight mixtures were performed and 29 fatigue beams were tested in this study. The test results indicated that the addition of crumb rubber and WMA additive not only reduced the mixing and compaction temperatures of rubberized asphalt mixtures offset by crumb rubber but also effectively extended the long-term performance of pavement when compared with conventional asphalt pavement. In addition, the exponential function forms are efficient in achieving the correlations between the dissipated energy and load cycle as well as mixture stiffness and load cycle.     

Fatigue of asphalt binder,mastic and mixture at low temperature

The fatigue damage is one of the most common distresses observed on the asphalt concrete pavement. To thoroughly understand the fatigue of asphalt concrete, the behaviors of the major components of asphalt concrete under cyclic loading are investigated respectively in this study. A new experiment method is developed to evaluate the performances of asphalt binder, mastic and fine aggregates mixture under cyclic tensile loading. The fatigue test results of asphalt binder show that the fatigue performance of asphalt binder is closely related with loading magnitude, temperature and loading rate. Mastic specimens with different filler content are tested and the results indicate that mastic specimens with 30% filler content show better fatigue resistance and higher permanent strain. The micro-structure analysis of mastic and mixture indicates that the fatigue resistance is closely related with the air void content of specimen. 3D digital specimens are developed to model the fatigue of the asphalt binder, mastic and mixture specimens based on the finite element method (FEM). Fatigue damage of asphalt concrete is simplified by a damage model. With proper selection of damage parameters, the simulation results agree well with laboratory test results and can be used as a basis for future fatigue research.     

Bridging the gap between laboratory and field moduli of asphalt layer for pavement design and assessment: A comprehensive loading frequency-based approach

Asphalt pavement is a key component of highway infrastructures in China and worldwide. In asphalt pavement design and condition assessment, the modulus of the asphalt mixture layer is a crucial parameter. However, this parameter varies between the laboratory and field loading modes (i.e., loading frequency, compressive or tensile loading pattern), due to the viscoelastic property and composite structure of the asphalt mixture. The present study proposes a comprehensive frequency-based approach to correlate the asphalt layer moduli obtained under two field and three laboratory loading modes. The field modes are vehicular and falling weight deflectometer (FWD) loading modes, and the laboratory ones are uniaxial compressive (UC), indirect tensile (IDT), and four-point bending (4PB) loading modes. The loading frequency is used as an intermediary parameter for correlating the asphalt layer moduli under different loading modes. The observations made at two field large-scale experimental pavements facilitate the correlation analysis. It is found that the moduli obtained via laboratory 4PB tests are pretty close to those of vehicular loading schemes, in contrast to those derived in UC, IDT, and FWD modes, which need to be adjusted. The corresponding adjustment factors are experimentally assessed. The applications of those adjustment factors are expected to ensure that the moduli measured under different loading modes are appropriately used in asphalt mixture pavement design and assessment.     

Performance evaluation of high modulus asphalt mixtures for long life asphalt pavements

This paper describes the results of laboratory and full scale performance tests for a high modulus asphalt binder (HMAB) and mixes (HMAM) developed in this study for long life asphalt pavements. Various binder tests were first conducted on the HMAB and test results showed that the stiffness of the HMAB was significantly increased compared to the conventional binder without changing the low temperature properties of the binder. Laboratory tests for the mixes included dynamic modulus, moisture susceptibility, wheel tracking and fatigue tests.Dynamic modulus test results showed that the modulus of the HMAM was 50% higher than those of the conventional mix at the high temperatures. The results of performance test indicated that the resistances of the HMAM against moisture, rutting, and fatigue damage were better than those of the conventional mix. It was also found from the full scale test sections that the tensile strain values at the bottom of the asphalt layer for the HMAM sections were lower than those of the conventional mix sections although the asphalt layer thicknesses of the HMAM sections were thinner than those of the conventional sections. All the tensile strain values measured from the HMAM sections were within the fatigue endurance limit of 70 microstrain which is the fatigue criterion of a long life asphalt pavement. Similar to the wheel tracking test results, the rut depth occurred in the thick HMAM test section was two times smaller than the conventional pavement section.     

Dynamic behavior of a Mediterranean natural stone under tensile loading

Historical buildings are important structures commonly occurring in Mediterranean cities. The behavior of their constituent materials under high dynamic loads is fundamental to investigate the vulnerability of such structures under extreme dynamic events. The main aim of our investigation was to study the effect of high dynamic loading conditions on a classical porous natural stone from the Naples area, namely yellow tuff, used in hundreds of historical buildings and monuments in Naples and other Mediterranean cities. Hence, dynamic characterization was performed through high strain-rate failure tensile tests. A wide range of strain-rates was investigated, from 10^?5 s^?1 to 50 s^?1. The obtained data were processed to obtain stress–strain relationships at different strain-rate levels. The results reveal that Neapolitan yellow tuff presents a significantly strain-rate sensitive behavior, exhibiting dynamic tensile strength increasing with strain-rate, up to about three times that from quasi-static conditions in the case of very high strain-rates. Dynamic increase factors (DIFs) vs. strain-rate curves for tensile failure stress were also evaluated and discussed.     

钢桥面沥青混合料铺装应变动态响应实测研究

掌握钢桥面沥青混合料铺装层在车载作用下的真实力学特性对桥面铺装体系设计有重要意义,而现阶段现场桥面铺装层的力学实测数据仍偏少,尤其缺乏对铺装层不同温度下服役时力学特性的长期监测。为此,该研究对钢桥面双层SMA混合料铺装进行现场实桥加载试验,实测铺装层在低温、中温、高温3种服役温度下的应变响应数据。试验结果表明,钢桥梯形肋正上方铺装层混合料在中低温服役状态下主要承受压应变的作用,而在高温服役时则主要承受拉应变的作用;动载作用过程中铺装层底纵向应变会出现拉压应变交替作用的现象,而横向应变只体现为拉应变或压应变的形式;加载车行驶速度对混合料的应变极值均有明显的影响,加载车低速行驶时混合料层底横向及纵向变形最为显著。同时,研究利用加载试验中铺装层应变响应时程曲线,计算不同加载状态下混合料对应的加载频率数值,计算结果可为钢桥面铺装混合料室内试验中加载频率参数的确定提供参考。     

Improving the compressive strengths of cold-mix asphalt using asphalt emulsion modified by polyvinyl acetate

Rut is the type of flexible pavement distress mostly occurring in Mexico, generally caused by exceedingly heavy axle loads. Therefore, the compressive strengths of cold-mix asphalt (CMA) must be improved, for this reason a polyvinyl acetate emulsion (PVAC-E) was added to a cationic quick set emulsified asphalt to obtain a modified asphalt emulsion that was mixed with a local aggregate in order to prepare two types of CMA. In the type I mix, aggregates were coated by a film of asphalt–polyvinyl acetate (A–PVAC) binder. In the type II mix, before the A–PVAC binder was layered, the aggregate was covered with the polymer by mixing the aggregate in a diluted PVAC-E. Since the microparticles of the polyvinyl acetate were well dispersed in the asphalt paving mixture matrix for modified CMA type II, the compressive strengths of test specimens were improved by 31% compared to the values obtained with the unmodified CMA.     

Performance based binder type selection using mixed integer programming technique

The rationale behind an asphalt mix design is optimizing the binder content for the desired aggregate gradation to satisfy the specified volumetric and strength requirements. The designed asphalt mix should be durable and cost effective. The mechanical behavior of a designed asphalt mix is affected by the traffic loading and climatic variations. To improve the mechanical properties of asphalt mixes, additives are added to the base asphalt binder. These binders are called modified asphalt binders. The objectives of the present study are to compare the performance of asphalt mixes with different binders by two different mix design methods and to optimize the asphalt binder type to achieve the desired performance. Two methods of mix design namely, Marshall and Superpave mix design methods are considered. The performances of asphalt mixes viz., tensile strength, moisture damage, densification and rutting resistance were compared. The results indicated a statistically significant difference in the optimum asphalt binder content from the two mix design methods. The Marshall method of asphalt mix design is found to yield lower optimal asphalt binder content when compared to the Superpave method of mix design. The moisture susceptibility and construction densification index of asphalt mixes designed using Superpave method were found to be significantly lower than that of the mixes designed by Marshall method. Optimization using a Mixed Integer Linear Program (MILP) indicated that the polymer modified asphalt binder outperforms the requirements of engineering properties when compared to other commercial binders used in the study.     

沥青混合料配合比设计方法

通过材料选择、目标配合与设计、施工配合比设计 ,介绍了沥青路面混合料设计的方法 ,指出沥青混合料配合比设计是沥青路面质量控制的首要条件     

Laboratory evaluation of the effects of short-term oven aging on asphalt binders in asphalt mixtures using HP-GPC

Both the RTFO (rolling-thin film oven) aging of asphalt binders and the STOA (short-term oven aging) of asphalt mixtures are designed to simulate aging during the construction of hot mix asphalt (HMA) pavements. Many studies have been conducted evaluating the aging effects on asphalt binders since their properties can be easily measured using many conventional tests, such as rotational viscometer, DSR (dynamic shear rheometer), and BBR (bending beam rheometer). However, studies on asphalt mixture aging have been limited to mechanical properties such as strength and fatigue characteristics because considerable effort is required to identify the aging of the asphalt binder in a mixture. This study evaluated the effects of short-term oven aging on asphalt mixtures using the GPC (gel-permeation chromatography) procedure. Nine asphalt mixtures, using three different binder sources, were prepared and five short-term aging methods were used to evaluate these mixes. For comparison, the RTFO aging was also conducted for nine asphalt binders. The aging of a binder within asphalt mixtures, including polymer-modified mixtures, could be identified under various short-term aging conditions. Statistical analysis of the GPC test results indicated that two commonly used short-term aging methods in the laboratory, a 154 °C oven aging for 2 h and a 135 °C oven aging for 4 h, are not significantly different, based on the increase in the large molecular size (LMS) ratios. The RTFO aging method was found to have less effect on binder aging than the short-term oven aging methods of asphalt mixtures.     

Effect of polyester resin additive on the properties of asphalt binders and mixtures

The properties of AC-5 control asphalt binder, mixture containing the same asphalt were compared with the properties of AC-10 asphalt binder modified by 0.75%, 1%, 2%, and 3% of polyester resin (PR), mixture containing pure AC-10 and AC-10 modified by 0.75% of PR, respectively.Initial research was done to determine the physical properties of unmodified and PR modified asphalt binders. The AC-10 asphalt binder modified by 0.75% of PR had good results compared to AC-5 control asphalt binder and all other modified binders, and hence this modified binder as well as unmodified binders were used to prepare Marshall samples for Marshall stability and flow, indirect tensile stiffness modulus (ITSM), indirect tensile strength (ITS) and creep stiffness tests.The results of investigation indicate that AC-10 + 0.75% PR binder has better physical properties than AC-5 control asphalt binder and, at the same time, PR improves mechanical properties of asphalt mixture.     

Multiaxial tensile–compressive strengths and failure criterion of plain high-performance concrete before and after high temperatures

Multiaxial tensile–compressive tests were performed on 100 mm × 100 mm × 100 mm cubic specimens of plain high-performance concrete (HPC) at all kinds of stress ratios after exposure to normal and high temperatures of 20, 200, 300, 400, 500, and 600 °C, using a large static–dynamic true triaxial machine. Friction-reducing pads were three layers of plastic membrane with glycerine in-between for the compressive loading plane; the tensile loading planes of concrete samples were processed by attrition machine, and then the samples were glued-up with the loading plate with structural glue. The failure mode characteristic of specimens and the direction of the crack were observed and described, respectively. The three principally static strengths in the corresponding stress state were measured. The influence of the temperatures, stress ratios, and stress states on the triaxial strengths of HPC after exposure to high temperatures were also analyzed respectively. The experimental results showed that the uniaxial compressive strength of plain HPC after exposure to high temperatures does not decrease completely with the increase in temperature, the ratios of the triaxial to its uniaxial compressive strength depend on brittleness–stiffness of HPC after different high temperatures besides the stress states and stress ratios. On this basis, the formula of a new failure criterion with the temperature parameters under multiaxial tensile–compressive stress states for plain HPC is proposed. This study is helpful to reveal the multiaxial mechanical properties of HPC structure enduring high temperatures, and provides the experimental and theory foundations (testing data and correlated formula) for fire-resistant structural design, and for structural safety assessment and maintenance after fire.     

基于光纤光栅传感技术的沥青路面行车工况下力学响应研究

为揭示半刚性基层沥青路面内部真实力学响应规律,为耐久性路面设计提供参考。通过现场埋设光纤光栅传感器,基于真实荷载工况开展了不同车速与轴载作用下沥青路面应变测试试验。测试结果表明：沥青面层轮载中心拉应变最大,为该层最不利荷载点位|静载应变历时曲线黏弹性明显,且很好地符合Bugers模型,拟合判定系数为0.98|动载应变曲线呈现明显的压-拉-压波形。水稳碎石基层轮隙中心拉应变最大,为该层最不利荷载点位|静载应变历时曲线符合弹性性质,动载应变曲线主要表现为拉峰波形。构建了路面结构层层底应变随轴载和车速变化的理论函数模型,并得到了纵向动应变压峰与拉峰的峰值比值随车速变化的规律。其研究成果可供耐久性沥青路面设计及室内疲劳试验参考。     

Experimental study of recycled asphalt mixtures with high percentages of reclaimed asphalt pavement (RAP)

This paper presents an experimental study to characterize the mechanical behaviour of bituminous mixtures containing high rates of reclaimed asphalt pavement (RAP). Two semi-dense mixtures of 12 and 20 mm maximum aggregate size and containing 40% and 60% RAP, respectively (S-12 and S-20, in accordance with Spanish specifications), which were used for rehabilitation of a highway section, were evaluated. First, the effect of RAP variability on the recycled mixtures was analyzed. Their mechanical properties were then studied by determining the stiffness modulus and indirect tensile strength and cracking and fatigue behaviour. Results show that high rates of recycled material can generally be incorporated into bituminous mixes by proper characterization and handling of RAP stockpiles.     

Laboratory evaluation of WMA mixture for use in airport pavement rehabilitation

The concept of warm mix asphalt (WMA) gives a promise for rehabilitating airport pavement to realize quick turnover to traffic after construction, however, laboratory and field data in terms of the performance-related properties are significantly lacking for using WMA in airfield in Japan. To fill this gap, three WMA mixtures (different gradations) were systematically investigated compared with the conventional airfield used hot mix asphalt (HMA) through a series of laboratory tests in terms of wheel tracking test, submerged wheel tracking test, raveling test, static bending and fatigue bending test. These WMA mixtures were made at two production temperatures (30 and 50 °С lower than the normal, respectively) by incorporating a commercially sold additive. Results showed that overall, the WMA mixture with a coarse gradation produced at the temperature 30 °С lower than the normal exhibited a comparable performance compared with the control HMA mixture, and it was further recommended for use in airport pavement rehabilitation.     

A dimensional analysis on asphalt binder fracture and fatigue cracking

Fracture and fatigue cracking in asphalt binder are two of most serious problems for pavement engineers. In this paper, we present a new comprehensive approach, which consists both of dimensional analysis using Buckingham Π Theorem and J-integral analysis based on classic fracture mechanics, to evaluate the fracture and fatigue on asphalt binder. It is discovered that the dimensional analysis could provide a new perspective to analyze the asphalt fracture and fatigue cracking mechanism.     

半刚性基层沥青路面的破损原因和改进措施

该文通过对海宁市东西大道沥青路面病害情况的调查,分析造成半刚性基层沥青路面基层疲劳破坏的主要原因。据此提出了防止路面破损的改进措施;设计阶段调查交通量时,要充分考虑转移交通量和超载因素,并且有余地;面层应采用抗车辙、抗浸水的改性沥青和SMA混合料;半刚性基层上最好铺一层土工合成材料。