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    <title>Transport Research International Documentation (TRID)</title>
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    <language>en-us</language>
    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
    <docs>http://blogs.law.harvard.edu/tech/rss</docs>
    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Transport Research International Documentation (TRID)</title>
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      <link>https://trid.trb.org/</link>
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    <item>
      <title>Stabilisation of tropical soils with lime mud: materials characterisation and pavement structural analyses</title>
      <link>https://trid.trb.org/View/2618022</link>
      <description><![CDATA[Road construction often depends on limited natural resources, prompting researchers to explore waste reuse for eco-efficient solutions. The effects of lime mud (LM), a residue from the cellulose industry, on the stabilisation of different soil types have not been previously studied. The influence of curing period on different geotechnical properties of soil-LM mixtures remains unknown. Their resilient behaviour and plastic deformations were not investigated in previous works. This study addresses these gaps by evaluating the mechanical behaviour of different soils with varying LM contents and subjected to different curing times. Uniaxial Compressive Strength (UCS), California Bearing Ratio (CBR), swelling, resilient modulus, and plastic strain were determined. Results showed that LM improved UCS, reduced swelling, enhanced resilient behaviour, and decreased soil deformability. Structural analyses explained the mechanical performance of asphalt pavements incorporating the soil-LM mixtures. Therefore, LM from the cellulose industry can be a promising alternative for sustainable road construction.]]></description>
      <pubDate>Mon, 09 Feb 2026 13:55:11 GMT</pubDate>
      <guid>https://trid.trb.org/View/2618022</guid>
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    <item>
      <title>Investigation of rheological properties of asphalt-based materials under physical hardening</title>
      <link>https://trid.trb.org/View/2643721</link>
      <description><![CDATA[Physical hardening is widely recognized to significantly deteriorates the low-temperature performance of asphalt-based materials. However, the response mechanisms and patterns of physical hardening under the influence of multiple variables remain insufficiently understood. In this study, a Bending Beam Rheometer was employed to investigate the response of asphalt-based materials to physical hardening, taking into account storage temperature, storage time, aging degree, and additives. Temperature-related performance indicators were statistically analyzed, and master curves for both stiffness modulus and stiffness modulus change rate were established. The results indicate that the deterioration of low-temperature performance in asphalt-based materials due to physical hardening is influenced by the incorporation of filler and SBS modifiers, which play negative and positive roles, respectively. Additionally, during the construction of stiffness modulus master curves, a ‘tail drift’ phenomenon was observed in some asphalt-based materials. Based on the competitive relationship between physical hardening and material relaxation characteristics, this study proposes a quantitative criterion to identify the occurrence of this phenomenon. These findings provide a theoretical basis for the development and characterisation of asphalt-based materials suitable for cold regions, and are expected to establish a three-dimensional predictive model considering storage temperature, storage duration, and loading time in future research.]]></description>
      <pubDate>Mon, 26 Jan 2026 08:41:42 GMT</pubDate>
      <guid>https://trid.trb.org/View/2643721</guid>
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    <item>
      <title>Enhancing performance and fuel resistance of modified epoxy asphalt using amine and carboxyl terminated PET co-hardener</title>
      <link>https://trid.trb.org/View/2582187</link>
      <description><![CDATA[In this study, a fuel-resistant modified epoxy asphalt was formulated using a co-hardener containing a commercial amine and carboxyl terminated PET (CTPET). Rheological, physical, mechanical, and fuel-resistance properties were evaluated across various epoxy polymer-to-asphalt ratios. The CTPET co-hardener enables blending with up to 85% epoxy polymer, preserving viscoelastic behaviour comparable to base asphalt. Notably, higher epoxy-to-asphalt ratios enhanced the complex shear modulus, phase angle, rutting resistance, and cohesion bonding. Furthermore, weight loss measurements after immersing the specimens in kerosene at 80°C for 24 h revealed losses of 1.08%, 0.24%, 0.18%, and 0.01% for blends containing 70, 75, 80, and 85 wt% epoxy, respectively, all well below the standard limit of 2%. The material also retained an elongation at break exceeding 1000%. Additionally, the penetration values, softening points, and tensile strengths remained stable before and after immersion, confirming the material’s durability and suitability for fuel-resistant applications.]]></description>
      <pubDate>Fri, 24 Oct 2025 16:53:56 GMT</pubDate>
      <guid>https://trid.trb.org/View/2582187</guid>
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    <item>
      <title>Exploring the physical hardening characteristics of asphalt mortars and mixtures based on gradient particle size</title>
      <link>https://trid.trb.org/View/2590955</link>
      <description><![CDATA[Current research on asphalt physical hardening predominantly focuses on the polymer scale and microscopic characterization, while systematic studies on the response mechanisms of asphalt mortars and mixtures remain limited. In this study, six asphalt mortars and mixtures with gradient nominal maximum aggregate sizes (2.36–10 mm) were designed, and small-scale specimens were prepared. Utilizing a self-designed loading device, stress relaxation and low-temperature bending tests were conducted to reveal the particle size effect and multivariable response mechanisms under the physical hardening. The results show that in destructive tests, 4.75 mm serves as the critical particle size threshold for studying physical hardening effects. When the nominal maximum aggregate size exceeds 4.75 mm, the inhomogeneity in specimen composition tends to obscure the observable physical hardening effects. Moreover, the aggregate gradation—specifically gradation type and nominal maximum aggregate size—substantially impact the susceptibility of asphalt-based materials to physical hardening, through their effects on the distribution of free and structured asphalt and on asphalt–aggregate interface defects. In addition, this study introduces a set of quantitative evaluation indices for physical hardening effects, defining the residual stress ratio difference (ΔRSR) to assess the degradation of relaxation performance, and proposing the physical hardening rate (PHR) based on fracture energy decay rate. The findings provide a theoretical basis for particle size control and gradation optimization in anti-cracking design of asphalt pavements in cold regions.]]></description>
      <pubDate>Thu, 16 Oct 2025 17:02:35 GMT</pubDate>
      <guid>https://trid.trb.org/View/2590955</guid>
    </item>
    <item>
      <title>Oxygen Consumption by Asphalt Films and Resulting Viscosity Changes</title>
      <link>https://trid.trb.org/View/2543328</link>
      <description><![CDATA[The objective of this research was to determine the amount of oxygen consumed by thin films of different asphalts heated in a closed air cell for 3 hours at 225°F and measure the increase in viscosity of each asphalt caused by this treatment. The following conclusions are drawn from the data given in this report: (1) For a particular asphalt the moles of oxygen consumed per unit weight of asphalt usually decreases with increasing thickness of the asphalt film; (2) When essentially the same film thickness (14±1 microns) is used, the consumption of oxygen by the seven asphalts investigated varied from 0.033 to 0.016 moles of oxygen per gram of asphalt; (3) Relative Viscosities (hardening) of the asphalt films heated for 3 hours at 225°F, in an enclosed cell filled with air, did not correlate with the amount of oxygen consumed, because polymerization (by heat), which also results in hardening, occurs simultaneously with oxygen consumption; and (4) The hardening effect of heat alone on each asphalt when subtracted from the hardening obtained from the treatment in the air filled cell indicated that rather small amounts of hardening of the asphalts were caused by oxidation alone. In fact asphalts Nos. 5 and 6 appeared to be slightly softened by the consumption of oxygen.]]></description>
      <pubDate>Mon, 19 May 2025 17:32:51 GMT</pubDate>
      <guid>https://trid.trb.org/View/2543328</guid>
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    <item>
      <title>Hardening of 85-100 Penetration Asphalt Cements During Service in Pavement</title>
      <link>https://trid.trb.org/View/2543326</link>
      <description><![CDATA[The objective of this research was to determine changes in hardness that occur in an asphalt cement while the hot paving mixture is being prepared and laid and during the early (one year) service life of the pavement surface. Hot mix surfacing projects using 85-100 penetration grade asphalt cements were located in 13 widely separated Districts of the Texas Highway Department. Asphalts were supplied by 9 different producers in Texas. Conclusions were as follows: (1) Rates of asphalt hardening are moderate during careful preparation and handling of hot mixes and through the first two weeks of service in the pavements; (2) The average Relative Viscosities of the extracted asphalts between 2 weeks and 12 months service give a straight line when shown against time on a log-log plot; (3) Asphaltene contents (n-pentane insolubles) of the asphalts after one year of service are greater than for the original asphalt cements, with the increase ranging from 1.4 to 8.3 percent; (4) The laboratory hardening test, which is a part of the Texas Highway Department Specifications for asphalt cements, is an indicator of the hardening of the asphalts in service; and (5) Sensitiveness of some asphalts to the effect of mineral matter in the pavement may be one of several causes for the few large and unexplained deviations from the average relationship between laboratory and field hardening.]]></description>
      <pubDate>Mon, 19 May 2025 17:32:50 GMT</pubDate>
      <guid>https://trid.trb.org/View/2543326</guid>
    </item>
    <item>
      <title>Susceptibility of Paving Asphalts to Hardening by Heat, Oxygen and Sunlight</title>
      <link>https://trid.trb.org/View/2543322</link>
      <description><![CDATA[The objective of this research was to investigate paving asphalts used by the Texas Highway Department  to determine how they can be evaluated for quality. Increases in hardness of asphalt films caused by oxidation, photooxidation, volatilization, photochemical action, and polymerization were determined by the microfilm technique. Relative viscosities were evaluated on asphalts extracted after two years of service. Hardening caused by hot mixing, transportation, and laying on the pavements was determined. The following conclusions were reached: (1) Oxidation in the dark is a very important factor contributing to the hardening of films in an asphalt pavement; (2) Photooxidation probably is of secondary importance followed by volatilization; (3) Photochemical action and polymerization are of minor importance; (4) All effects are accentuated by increases in time and temperature; (5) Asphalts recovered from pavements after two years usually are quite hard because of the effect of asphalt composition, nature of the aggregate, and design and constructional factors;  (6) Asphalts increase in viscosity considerably during hot mixing, transport to paving site, and laying of the pavement; (7) Laboratory oxidation tests give valuable information concerning the potential hardening of asphalt during construction and service life of a pavement.]]></description>
      <pubDate>Sun, 18 May 2025 17:56:43 GMT</pubDate>
      <guid>https://trid.trb.org/View/2543322</guid>
    </item>
    <item>
      <title>Oxidation (Durability) Tests on Asphalts Used by the Texas Highway Department</title>
      <link>https://trid.trb.org/View/2543325</link>
      <description><![CDATA[The objective of this research was to establish specifications to assure use of superior asphalts by the Texas Highway Department. Sixty asphalts were tested for susceptibility to hardening by oxidation. The test used was similar to that tentatively proposed by Sub-Committee B-19 of ASTM D-4 on Road and Paving Materials. Fifteen-micron films of each asphalt were oxidized in an air oven in the dark at 225°F for 2 hours. The hardened material and the original asphalt were tested in the Hallikainen viscometer at 77°F and the viscosities calculated at 5 x 10 to the -2 power/sec rate of shear. The quotient obtained by dividing the viscosity of an original asphalt into that of the hardened film was called the relative viscosity and used as an aging index. The following conclusion is drawn from the data presented in this report: About 60 percent of the asphalts supplied to the Texas Highway Department during 1959 and 1962 passed these proposed minimum relative viscosities (hardening indices): AC-20, 5.0; AC-10, 4.5; and AC-5, 4.0.]]></description>
      <pubDate>Sun, 18 May 2025 17:56:43 GMT</pubDate>
      <guid>https://trid.trb.org/View/2543325</guid>
    </item>
    <item>
      <title>Antioxidants for Paving Asphalts</title>
      <link>https://trid.trb.org/View/2543318</link>
      <description><![CDATA[The objective of this project was to determine how the durability of paving asphalts can be improved. Sixteen chemical additives from two different manufacturers were evaluated as antioxidants for 85-100 penetration paving asphalts. The following conclusions are drawn from the data given in this report: (1) Chemical compounds are available which serve rather effectively as antioxidants and free radical inhibitors when added to asphalt cements; (2) The retardation of hardening by these chemicals is most effective in asphalts that are highly susceptible to oxidation; (3) One to two weight percent of the additive material appears to be the optimum concentration; and (4) The additives investigated are more effective against oxidation in the absence of light than against the severe hardening caused by photo-oxidation.]]></description>
      <pubDate>Tue, 13 May 2025 10:37:54 GMT</pubDate>
      <guid>https://trid.trb.org/View/2543318</guid>
    </item>
    <item>
      <title>Hardening of Paving Asphalts and Relation to Composition</title>
      <link>https://trid.trb.org/View/2543314</link>
      <description><![CDATA[The objectives of this project were to: (1) Investigate the paving asphalts used by the Texas Highway Department and determine how these binders can best be classified as to quality; (2) Establish specifications to assure use of superior asphalts by the Department; and (3) Determine how the durability of paving asphalts can be improved. A modified Shell Film Test was found to be more satisfactory than the Bureau of Public Roads Film Test. Data obtained by heating 15 micron films of asphalts in air at 275 to 350°F for times ranging from 15 to 60 minutes are useful for calculating the hardening of a particular asphalt for many of the temperature-time combinations that may be encountered in the preparation and laying of hot paving asphalts. Most asphalts show less hardening by volatilization than by oxidation. Causes for hardening of asphalts in decreasing order of importance are oxidation, volatilization, polymerization induced by actinic light (sunlight) and condensation polymerization (caused by relatively high temperatures). Less stable asphalts may show a decrease in viscosity when subjected to elevated temperatures for several hours. This is caused by depolymerization or thermal cracking. Component analyses together with the asphaltene content of an asphalt can be used to calculate a Dispersion Coefficient which, in most cases, predicts the resistance of the asphalt to hardening.]]></description>
      <pubDate>Tue, 13 May 2025 10:37:54 GMT</pubDate>
      <guid>https://trid.trb.org/View/2543314</guid>
    </item>
    <item>
      <title>Microstructural analysis of the phase separation of epoxy-modified bitumen</title>
      <link>https://trid.trb.org/View/2446231</link>
      <description><![CDATA[This research provided quantitative evidence on the microstructural transformation due to the phase separation in epoxy-modified bitumen in the domain of epoxy contents from 10 to 90 % by confocal fluorescence microscopy (with the effective pixel size of 21.5 μm) as the systems approached their ultimate state of hardening. The image analysis of phases representing bitumen and epoxy included particle size distributions and spatial arrangement (of discrete droplets) and the local thickness distributions (of percolated structures). The results showed that these systems underwent substantial transformed from a solution of epoxy droplets in bitumen to a quasi-bimodal dispersion of bitumen within an epoxy networked structure, with the catastrophic phase inversion taking place between 40 and 50 % of epoxy. The morphology of phases and their spatial arrangement confirmed that mechanical interactions determined the packing of hyperdispersed droplets (as the systems approached the phase inversion), while the relaxation of surface tensions weakened the interlocking and eased the movability of droplets (far away from the inversion point). This contributed to understand how the microstructure directly resulted from the interfacial tensions between phases. Transformation in the phase inversion zone and the interfacial diffusion, including spectroscopic techniques, were recognised as particularly relevant for further research.]]></description>
      <pubDate>Thu, 21 Nov 2024 09:26:09 GMT</pubDate>
      <guid>https://trid.trb.org/View/2446231</guid>
    </item>
    <item>
      <title>The influence of oxidative aging and wax structure on bitumen physical hardening: Insights from model wax compounds</title>
      <link>https://trid.trb.org/View/2424551</link>
      <description><![CDATA[Physical hardening (PH) significantly affects bitumen's low-temperature performance. This paper investigates the effect of oxidative aging and wax structure on PH using 4-mm dynamic shear rheometer (4-mm DSR) and differential scanning calorimetry (DSC) tests. The results show that the wax chain length has a pronounced effect on the PH. Short-chain waxes, such as C18 and C24 affect the PH while longer-chain n-paraffins like C40 or Sasobit have almost no effect. In addition, the physical hardening index (PHI) is not linearly increasing with wax content but shows a maximum at a particular wax percentage. Wax-doped samples that crystallize before reaching the hardening temperatures typically show a reduced PHI compared to those with crystallization temperatures just below the hardening temperature. When crystallization and melting temperatures are not close to the hardening temperatures, the PHIs are typically reduced. Oxidative aging also influenced the PHI and in most cases the hardening decreased after aging. The highest PHI of almost all investigated samples occurs at 0 °C among the four typical temperatures. This investigation provides insights in the mechanism of PH and in the relations between wax contents, the hardening temperature, and the PHI. It also shows that while long-chain waxes used as warm mix additives, will not cause a PH risk, short-chain waxes present in pyrolyzed waste plastic, for example, should be handled with care. In addition, PH is also crucial for the intermediate service temperatures and not exclusively for thermal cracking at low temperatures.]]></description>
      <pubDate>Fri, 27 Sep 2024 13:48:26 GMT</pubDate>
      <guid>https://trid.trb.org/View/2424551</guid>
    </item>
    <item>
      <title>Evaluation of physical hardening of wax-based warm mix asphalt binders from low-temperature rheological properties</title>
      <link>https://trid.trb.org/View/2345243</link>
      <description><![CDATA[The effects of eight representative commercial waxes on low-temperature properties of asphalt binders after long-term cold storage were investigated using extended bending beam rheometer (ExBBR) test, thermal stress calculation, and statistical analysis. The results showed that the addition of F-T waxes and Montan waxes with typical paraffin characteristics significantly reduced the low temperature rheological properties of asphalt binders after 1 h conditioning. However after 72 h conditioning, all waxes affected the low temperature properties of asphalt binders to varying degrees, especially F-T waxes. The grade loss of 3% F-T wax-doped asphalt binders reached 6.2°C and 4.5°C, respectively. After 72 h conditioning, thermal stresses of wax-doped asphalt binders increased significantly, confirming the effect of physical hardening. Statistical analysis of test results showed that the incorporation of F-T wax, montan wax, naphthenic wax and amide wax significantly increased thermal stresses of asphalt binders, while the incorporation of P (Synthesis of palm wax and polyethylene wax) and L (Amide-functionalized hydrocarbon wax) did not cause significant changes.]]></description>
      <pubDate>Fri, 19 Apr 2024 09:38:52 GMT</pubDate>
      <guid>https://trid.trb.org/View/2345243</guid>
    </item>
    <item>
      <title>Research on the response of bitumen binder and bitumen mastic to physical hardening effect based on rheological properties</title>
      <link>https://trid.trb.org/View/2320461</link>
      <description><![CDATA[Bitumen materials will occur a physical hardening effect when stored isothermally in a low-temperature environment, and ignoring the physical hardening factor has become one of the important reasons for premature cracking of asphalt pavement during the service period. This paper investigates the response of bitumen binder and bitumen mastic to physical hardening effects at different storage temperatures and times using the bending beam rheometer and dynamic shear rheometer. The response of the material to physical hardening effects is analyzed through temperature index system changes, mathematical model fitting, and stiffness master curve fitting. Results indicate that the response of the material to physical hardening effects can be classified into two stages: the rapid growth and the gradual stabilization periods. The response time of these two stages is related to factors such as aging degree and storage temperature. The physical hardening effect will cause the temperature loss of the material at low temperature, and its influence law on TS60=300MPa and Tm60=0.300 is different. It is recommended to extend the isothermal storage time specified in the test from 1 h to 9 h, considering the time cost and the change in temperature index. Moreover, the stiffness master curve study revealed the occurrence of the "tail drift" phenomenon.]]></description>
      <pubDate>Thu, 22 Feb 2024 09:06:19 GMT</pubDate>
      <guid>https://trid.trb.org/View/2320461</guid>
    </item>
    <item>
      <title>Mechanism of physical hardening on the fracture characteristics of polymer-modified asphalt binder</title>
      <link>https://trid.trb.org/View/2290027</link>
      <description><![CDATA[This article aims to reveal the physical hardening mechanism of polymer-modified asphalt binder (PMA) and accurately assess its impact on the low-temperature fracture properties of asphalt binders. Base asphalt binder (BA), styrene–butadiene–styrene modified asphalt binder (SBSMA), and crumb rubber modified asphalt binder (CRMA) were used as the research objects. Molecular dynamics (MD) simulation and differential scanning calorimetry (DSC) test were used to investigate the physical hardening mechanism of PMA at the microscopic level. The fracture characteristics of PMA under physical hardening were analyzed based on the single-edge notched beam (SENB) test. The results show that under prolonged cold service conditions, the asphalt molecular mobility is weakened, the non-bond energy and the free volume are reduced, and the molecules undergo aggregation state transformation, leading to the physical hardening of asphalt materials. In the process of physical hardening of asphalt molecules in the micro-Brownian motion of the main active force from the aromatic and saturate fractions. Considering the effect of physical hardening, it is recommended that the method used to test the low temperature properties of asphalt binders should ensure a constant temperature for at least 24 h. The crack tolerance (Ct) is recommended as the evaluation index of low-temperature cracking resistance of PMA in cold regions. The Ct of BA, SBSMA, and CRMA are reduced by 52.88 %, 12.04 %, and 35.24 %, respectively, after 24 h of constant low temperature. This indicating that the polymer modifiers can improve the fluidity of asphalt molecules, inhibit molecular aggregation, and reduce the effect of physical hardening on asphalt binders. Thermo-oxidative aging can aggravate the physical hardening phenomenon of asphalt binder, and the higher the degree of thermo-oxidative aging, the more severe the physical hardening of asphalt binder. The related research results provide the theoretical basis and technical support for the accurate design and development of the low-temperature performance of asphalt binders for roads in cold regions.]]></description>
      <pubDate>Fri, 15 Dec 2023 08:45:18 GMT</pubDate>
      <guid>https://trid.trb.org/View/2290027</guid>
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