Hainian Wang

The Effect of Morphological Characteristic of Coarse Aggregates Measured with Fractal Dimension on Asphalt Mixture’s High-Temperature Performance

The morphological properties of coarse aggregates, such as shape, angularity, and surface texture, have a great influence on the mechanical performance of asphalt mixtures. This study aims to investigate the effect of coarse aggregate morphological properties on the high-temperature performance of asphalt mixtures. A modified Los Angeles (LA) abrasion test was employed to produce aggregates with various morphological properties by applying abrasion cycles of 0, 200, 400, 600, 800, 1000, and 1200 on crushed angular aggregates. Based on a laboratory-developed Morphology Analysis System for Coarse Aggregates (MASCA), the morphological properties of the coarse aggregate particles were quantified using the index of fractal dimension. The high-temperature performances of the dense-graded asphalt mixture (AC-16), gap-graded stone asphalt mixture (SAC-16), and stone mastic asphalt (SMA-16) mixtures containing aggregates with different fractal dimensions were evaluated through the dynamic stability (DS) test and the penetration shear test in laboratory. Good linear correlations between the fractal dimension and high-temperature indexes were obtained for all three types of mixtures. Moreover, the results also indicated that higher coarse aggregate angularity leads to stronger high-temperature shear resistance of asphalt mixtures.

Effects of Physio-Chemical Factors on Asphalt Aging Behavior

Based on an accelerated asphalt-aging test in the laboratory, the authors evaluated the physical and chemical properties of asphalt at different aging times and temperatures for this paper. They evaluated the properties of the asphalt binder, such as saturates, aromatics, resins, asphaltenes, penetration, softening point, and molecular distribution of the asphalt, by using experimental results from the accelerated asphalt-aging tests. They employed gel permeation chromatography (GPC), Fourier transforms infrared spectroscopy, asphalt constituents fraction analysis, and rheological test techniques to analyze the effects of asphalt from different crude oil sources on antiaging performance. They used asphalt-aging tests to determine the relevant kinetic parameters needed in the aging kinetics equation. They found that the asphalt-aging reaction perfectly fits to the first order kinetics equation, and during the asphalt-aging process, the asphalt had a higher activation energy and a lower reaction rate coefficient. Moreover, the molecular weight (MW) of asphalt increased, whereas the dispersity decreased. The asphalt-aging process was divided into two stages: one stage is from aliphatic sulfide to sulfoxide and the other stage was from benzylic carbon to carbonyl. The aging resistance of asphalt was influenced by the asphalt fraction, wax content, and molecular weight.

Determination of Flow Number in Asphalt Mixtures from Deformation Rate During Secondary State

Numerous research studies have been conducted on the connection between asphalt material properties and pavement performance. Asphalt mixture performance tests (AMPTs) have been part of these efforts in the past few years. One such test is the flow number test, the output of which is the flow number. Recent studies have found that flow number correlates well with the rutting potential of asphalt pavement. However, the current method used in AMPTs to examine the flow number also was highly sensitive to the variation of testing data (resulting in inaccurate flow number values) and time-consuming, especially when used on stiff asphalt mixtures. The main goal is to determine the flow number with the use of the deformation rate at the secondary state from the result of the flow number test. One hundred twenty-two flow number tests were conducted. A stepwise method was used to overcome variations in results from the flow number test. The flow number was determined with the stepwise method, then compared with the flow deformation rate. A strong correlation between flow number and deformation rate was found. Therefore, the deformation rate can be used to estimate flow number, which significantly reduces testing time. The proposed method also allows the flow number test to be terminated as soon as the permanent strain reaches 1.2%.

Characterization of Low Temperature Crack Resistance of Crumb Rubber Modified Asphalt Mixtures Using Semi-Circular Bending Tests

The objective of this study was to assess the low temperature anti-cracking performance of crumb rubber modified asphalt mixtures by performing the semi-circular bending tests. The flexural tensile strength, fracture energy density, and fracture resistance were used to evaluate the rubber modified asphalt mixtures performance based on fracture mechanics J-integral concept. The semi-circular bending (SCB) tests were conducted to study the effect of crumb rubber dosage, crumb rubber size, and testing temperature on the low temperature anti-cracking performance of rubber modified asphalt mixtures. Two gradations (a dense gradation mixture and a gap-gradation mixture) were selected, and five rubber application dosages (15, 18, 20, 22, and 25 %, all by the weight of base binder) were studied in the paper. The tests were performed at temperatures of 0, −10, and −20°C. The testing results indicated that the flexural tensile strength and fracture energy density increased initially, reached to a peak point and then decreased with the increase of rubber dosage. Flexural tensile strength and fracture energy density reached its maximum value at the 20 % rubber dosage among the five rubber application dosages. The flexural tensile strength, fracture energy density, and the J-integral fracture toughness of the gap-graded rubber asphalt mixture specimens were higher than those of the dense gradation. The smaller sized particle rubber modified mixture provided a better low temperature anti-cracking performance as compared to those with bigger particle sizes. Through the comprehensive consideration of laboratory test results and field results, it was recommended that the J-integral fracture toughness should be no less than 2.8 KJ/m2 for new asphalt rubber pavement in Shannxi province.

Analysis of the Low-Temperature Rheological Properties of Rubberized Warm Mix Asphalt Binders

Warm mix asphalt (WMA) has generated a lot of interest worldwide based on the potential to realize environmental benefits related to lower production temperature and safe disposal of crumb rubber (tires). However, barriers to complete implementation of WMA technology still exist because of the lack of understanding of how different additives affect the performance of crumb rubber modified (CRM) binders. This paper investigates the effects of three WMA additives and crumb rubber concentration on the low-temperature performance of the CRM binders. The WMA additives used in this study were Sasobit, RH, and Advera, and the ambient 40 mesh tire rubber at different concentrations of 10 %, 15 %, 20 %, and 25 % by the weight of asphalt binder were applied in this paper. Burgers model was used to describe the relationship between deformation and time for rubberized WMA binder. The models parameters such as relaxation time, delay time, creep stiffness, m-value and m/S(t)-ratio were applied to evaluate the low-temperature performance of the rubberized WMA binders. Furthermore, the statistical analysis of variance (ANOVA) technique was applied to quantify the effects of different WMA additives and crumb rubber concentrations on the rubberized asphalt binders’ low-temperature performance. It was found that Advera could be used to enhance the low-temperature performance by enhancing the stress relaxation, whereas RH and Sasobit did not exhibit this ability, thereby weakening the low-temperature performance of the CRM binders. The crumb rubber concentration could significantly increase the rubberized WMA binders’ low-temperature performance by influencing the flexural creep stiffness of the control binders.

Evaluation of Coarse Aggregate in Cold Recycling Mixes Using X-ray CT Scanner and Image Analysis

The performance of cold recycling (CR) mixtures has been widely evaluated, but these studies rarely focused on the internal structure of CR mixtures. The objective of this research is to investigate the distribution, orientation, and shape properties of coarse aggregates in CR mixtures with emulsion by processing a series of sectional images from an X-ray CT scanner. The uniformity index (UI) was derived to describe the distribution of coarse aggregates. The aggregate orientation was obtained by calculating the average angle of inclination θ and the coherence of orientation Δ. The morphological indices, such as the flat and elongated ratio (FER), angularity index (AI), and surface texture index (STI) were used to address the shape properties of CR mixtures. According to the results, the distribution uniformity of CR aggregates becomes worse with coarser gradation. Compaction methods significantly influence the aggregate orientation in CR mixtures. The superpave gyratory compaction (SGC) method makes the best coherence of aggregate orientation, but the static load compacted specimen shows the opposite result. The CR mix tends to have worse uniformity of aggregate distribution, larger angle of aggregate inclination, and more random aggregate orientation compared with the HMA mix. It is estimated that more crushed faces of aggregates are produced in the process of pavement milling and the surface texture of RAP materials decreases with the long-term effects of traffic loading and environment. Adding new coarse aggregates to CR mixtures disturbs the aggregate distribution, but it can improve the average surface texture of aggregates in CR mixtures.

Applying Method of Moments to Model the Reliability of Deteriorating Performance to Asphalt Pavement under Freeze-Thaw Cycles in Cold Regions

AbstractAccurate deterioration models play a critical role in designing and managing transportation infrastructure. Regular models simply consider loading factor and its relative uncertainties. However, climate and environment impacts are not considered, or are just used as certain variables. Thermal cracks and moisture distresses are principal distress forms in cold regions. In this study, a freeze-thaw (F-T) cycle test was used to simulate the influence of adverse weather conditions in cold regions, like moisture and temperature impact. Then method of moments was applied to analyze the pavement reliability functions with various uncertainties. The analytical results showed that the resilient modulus of asphalt concrete mixture declined under F-T cycles. Consequently, pavement structure capacity was reduced. The results also illustrated that the reliability method was capable of accommodating uncertainties in pavement parameters. The sensitivity analysis indicated that F-T cycles had a significant impact...

Characterization of the Viscoelastic Property of Asphalt Mastic

The mechanical performance of asphalt mixture is highly dependent on the viscoelastic property of asphalt mastic, which is usually composed of asphalt binder and fine aggregates with sizes smaller than 2.36 mm. The viscoelastic property of asphalt mastic was analyzed and tested by uniaxial creep tests in the laboratory and fitted using Burgers model in this paper. Three asphalt mastics, dense graded mixture (DGM), stone mastic asphalt (SMA), and open graded friction course (OGFC), were applied and tested at -10 °C and 15 °C separately. Test results show that Burgers can well present the viscoelastic property of asphalt mastic. The viscoelastic property of asphalt mastic was characterized in this paper. The viscoelastic property of asphalt mastic is significantly influenced by its constituents and testing temperature.

Intermediate Temperature Fatigue and Low Temperature Cracking Properties of Rubber Asphalt Binder

As an environmentally friendly pavement material, a 20 mesh crumb rubber was blended in Superpave performance grade PG64-22 binder to make crumb rubber modified (CRM) binders with 10%, 15%, 20% and 25% content, respectively. Two main indices, |G*|.sin(δ) obtained from the dynamic shear rheometer (DSR) test, and creep stiffness obtained from the bending beam rheometer (BBR) test, were applied to characterize the intermediate and low temperature rheological performance of CRM binders. Statistical analysis of variance (ANOVA) was applied to investigate the significance level of testing temperature, rubber content and their interaction on the rheological performance of CRM binders. The test results show that the addition of crumb rubber significantly improves the intermediate temperature fatigue and low temperature cracking performance of asphalt binder. 10% content crumb rubber lowers the low temperature grade from -22 to -28 °C. Higher rubber content makes better rheological performance of the CRM binder. From the point of view of cost-efficiency, the suggested rubber content should not exceed 20%.

Synthesis and thermal properties of novel microencapsulated phase-change materials with binary cores and epoxy polymer shells

A series of novel epoxy polymer shell microcapsules with n-tetradecane and dimethylbenzene as binary core materials are successfully synthesized via interfacial polymerization. Dimethylbenzene is used as the solvent for epoxy and n-tetradecane. The chemical structure, surface morphology, and thermal properties of the microencapsulated phase-change materials (micro-PCMs) are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscope. Results show that the micro-PCMs have relatively spherical profiles and smooth surfaces with diameters ranging from 10 to 70xa0μm. The epoxy shell successfully encapsulates the binary core. Phase-change enthalpy and binary core content in the micro-PCMs increase with the increasing mass ratio of the binary core to the epoxy resin. The micro-PCMs degrade in two steps, and the resulting microcapsules exhibit good thermal stabilities. The degradation temperature decreases, as the core-to-shell mass ratio increases.