Asphalt Aggregate Research Articles

Effect of Binder Rheology and Aggregate Gradation on the Permanent Deformation of Asphalt Mixtures

Rutting is one of the main sources of distress in asphalt pavements and has been widely studied because it influences safety and maintenance costs. To mitigate this distress, the selection of adequate asphalt binder and aggregates and an appropriate balance between them are key elements. This paper analyzed seven asphalt binders (2 neat, 3 polymer-modified, and 2 rubber-asphalt binders) and asphalt mixtures with different gradations (19-mm dense-graded and 12.5-mm gap-graded asphalt mixtures). The asphalt binders were evaluated in terms of rheology with the use of a dynamic shear rheometer (DSR) and a bending beam rheometer (BBR) to obtain the high- and low-performance grade (PG) temperatures. Additionally, multiple stress creep and recovery (MSCR) tests were performed to analyze the rutting potential of the materials at different temperatures. To evaluate the effect of the mineral skeleton on the asphalt mixtures, the Laboratoire Central des Ponts et Chaussees (LCPC) wheel tracking rutting test was performed. The polymer-modified binders (PMBs) and the asphalt mixtures produced with them were the most resistant to permanent deformation with low values of rut depth (< 2.5%). In general, the gap-graded mixtures had better resistance than the dense-graded mixtures; however, this comparison is dependent on the type of asphalt binder. Relationships between the binder and mixture parameters were also proposed and they demonstrated a good relationship between the nonrecoverable creep compliance of the binders (Jnr) and the rut depth of the dense mixtures (R2 = 0.81); however, no significant relationship was found for the gap-graded mixtures (R2 = 0.52).

Automatic Classification of Coarse Aggregate Particle Size Based on Light Gradient Boost Machine

Aggregate plays an important role in the performance of asphalt mixture. In order to complete the intelligent online monitoring of asphalt aggregate quality, an automatic classification algorithm for coarse aggregate particle size based on LightGBM classification algorithm is proposed. Firstly, OpenCV is used to extract the two-dimensional morphological features of coarse aggregates, and then the correlation between these features and the classification of aggregates is analyzed. Finally, the accurate classification of coarse aggregate particles is achieved through grid search and cross-validation optimization model. The results show that the average classification precision of coarse aggregate can reach 84.7%. Compared with the classification method based only on image processing technology, the precision is increased by about 20%, and the efficiency of classification is greatly improved.

Influence of Coarse Aggregate Morphological Properties on the Performances of Warm-Mix Asphalt Containing Recycled Asphalt Pavement

The properties of asphalt and aggregate in the warm-mix asphalt (WMA) containing recycled asphalt pavement (RAP) are critical to the mixture performances. This study quantified the effects of the morphological properties of WMA-containing RAP through the gray correlation analysis. The properties of asphalt and aggregate involved in this study included RAP content, two-dimensional morphological properties of recycled coarse aggregate, three-dimensional angle of recycled coarse aggregate, and surface free energy of recycled asphalt. The high-temperature performance represented by dynamic stability, low-temperature indicated by maximum bending strain, and moisture susceptibility characterized by the tensile strength ratio were chosen as the criteria for evaluating the impacts of different factors. The results showed that the RAP content had the greatest influence on high-temperature performance, followed by recycled asphalt’s surface free energy (SFE), and aggregate sphericity. The irregular shape factor of aggregate particles significantly influenced the mixture’s low-temperature properties. The SFE of asphalt was pivotal to the moisture susceptibility, and samples with higher SFE of asphalt presented better moisture damage resistance.

Effect of aggregate type and polishing level on the long-term skid resistance of thin friction course

• Thin friction course with 88# calcined bauxite shows satisfactory skid resistance. • Aggregate mineral/chemical compositions affect the long–term skid resistance of TFC. • The attenuation rate of aggregate’s PSV has a strong correlation with that of μ 40 . This study was attempted to investigate the influence of aggregate type and polishing level on the long–term skid resistance of thin friction course particularly with calcined bauxite. The PSV (Polished Stone Value) test, self-designed three wheel polishing device (TWPD) and dynamic friction tester (DFT) were applied to examine the friction performance of asphalt mixture and aggregate at different polishing cycles in laboratory. The mineral hardness of aggregate was linked with the skid resistance of aggregate and thin friction course by regression analysis. The grey correlation and t -test were utilized to evaluate the factors that influenced the skid resistance of thin friction course. It is found that better skid resistance value is observed for thin friction course by 88# calcined bauxite than by limestone, basalt and 75# calcined bauxite at each polishing level. PSV presents most significant influence for both terminal value and initial value of μ 60 . The PSV attenuation rate of aggregate has a strong correlation with the attenuation rate of μ 40 . The aggregate hardness parameter presents the ability of the aggregate and asphalt mixture to keep long–term skid resistance. In addition, calcined bauxite aggregate owns extensively applied potential in the thin friction course in China.

Newly Developed Aggregate Gradation for Five Asean Countries

This paper presents the new aggregate gradation of the porous asphalt (PA) mixture in five Asean countries including Malaysia, Indonesia, Vietnam, Thailand and Singapore. The PA aggregate gradation need to be developed as it may suit all of the countries and the air voids content for Asean countries can be standardized. This study was carried out to investigate the air voids properties. Several aggregate testing should be conducted in order to get the new porous asphalt aggregate gradation that suits all Asean countries. Sieve analysis test was conducted to see the patterns of the aggregate gradation curve. Sieve analysis test were tested three times for each of the countries to get the best average. The results were then plotted in one graph for all countries to be evaluated. From the analysis, Singapore specification started with 0.075mm, followed by 0.15mm, 0.3mm, o.6mm and 2.36mm are seems to have all the criteria in terms of aggregate gradations for fine aggregate and the rest are from Thailand aggregate specification for lower line while for upper line, Vietnam specifications were proved to have all the criteria within all five countries gradations.

Aggregate Weight Prediction Based on Two-dimensional Image Feature Extraction

The weight of aggregates of different particle sizes is vital for the online monitoring of the gradation of asphalt mixtures. In order to complete the online intelligent detection of asphalt aggregate gradation, an automatic coarse aggregate weight prediction algorithm based on the feature extraction of aggregate two-dimensional images is proposed. First, use OpenCV to extract the two-dimensional morphological features of coarse aggregate and use high precision electronic gram scale to obtain the actual weight of the aggregate. Then analyze the correlation between these characteristics and aggregate weight. Finally, the weight of coarse aggregate particles can be accurately predicted by establishing a BPNN (Back-Propagation Neural Network) model. The results show that the weight prediction accuracy of coarse aggregate can be achieved 89.49%. The manual weighing process is reduced, which greatly improves the efficiency of online intelligent detection.

An Experimental Investigation into the Effect of Asphalt Binder Modified with SBR Polymer on the Moisture Susceptibility of Asphalt Mixtures

There are several experimental methods for improving the moisture strength of asphalt mixtures. Utilization of anti-stripping materials is the most prevalent method. In the present paper, the influence of polymer materials on asphalt binder was investigated using repetitive loading test in wet and dry conditions along with thermodynamic parameters based on the Surface Free Energy components of asphalt binder and aggregates. The results obtained from the present study indicated that using Styrene Butadiene Rubber polymer has improved the asphalt mixtures strength against the moisture damage, especially in the specimens made of granite aggregates. Also, Styrene Butadiene Rubber polymer increased the cohesion free energy and reduced the energy released by the system during the stripping event, which represented a decrease in the tendency for stripping. The stripping percentage index, which is obtained by a combination of the results of the repetitive loading test in wet and dry conditions along with the results of thermodynamic parameters, represented that the specimens made of controlled asphalt binder in the loading cycles under wet conditions had a higher stripping rate. It was also concluded that the modulus loss rate in the control asphalt mixtures was faster than the modified specimens.

Evaluation of the Performance of Asphalt Mixes for Airport Pavements

AbstractThis paper summarizes the results of a research study that was conducted to evaluate the effects of asphalt binder and aggregate gradation on the rutting and cracking resistance of asphalt ...

Investigating the Effective Laboratory Parameters on the Stiffness Modulus and Fatigue Cracking of Warm Mix Asphalt

Lack of attention to the effect of laboratory conditions on the results of asphalt mixture tests, especially these of the warm mix asphalt (WMA), makes the analysis of results misleading. Thus herein, after examining the research on WMA and factors affecting test results in laboratory conditions, the effect of three parameters including short-term aging (asphalt binder storage in the oven), curing time (from construction to placement in the test chamber), and thermal equilibrium time (from placement in the test chamber to the test onset) were investigated on the characteristics of WMA at mid-temperature. To simultaneously examine these three factors, 36 modes were developed to evaluate their effect on the stiffness modulus and fatigue cracking, using the indirect tensile stiffness modulus test (ITSM) and indirect tensile fatigue test (ITFT), respectively. Results of the experiments showed that increasing the time of asphalt binder placement in the oven for 2–6 h significantly increased the stiffness modulus of the mixture, which reduced the fatigue life of the WMA. With increasing the curing time and improving the adhesion between asphalt binder and aggregates, the stiffness modulus and fatigue life of the specimens increased; however, by increasing the thermal equilibrium time, the stiffness modulus and fatigue life of the specimens decreased due to asphalt binder viscoelastic behavior and temperature sensitivity. Results of statistical analyses revealed that short-term aging, curing time, and thermal equilibrium time in laboratory conditions were effective on the stiffness modulus and fatigue life of WMA at a 95% confidence level.

Meso-structural evaluation of asphalt mixture based on pore cellular structure model

ABSTRACT To provide a reference for the gradation-refined design of asphalt mixtures, pore cellular structure model was developed to evaluate the meso-structure of asphalt mixture, and corresponding meso-structural evaluation indices of the coarse aggregate main skeleton and asphalt mortar interference were obtained. Then three different asphalt mixtures were selected to study the influence of gradation and asphalt mortar performance on the meso-structure of pore cellular structures. The gradual behaviour characteristics of the meso-evaluation indices subjected to load, as well as the correlation between the main skeleton meso-evaluation indices and macro deformation were studied. The results indicated that gradation is a key determinant of the contact point, number of pore cells, and area of pore cell distribution. Under the action of loads, the number of contact points and pore cells within the asphalt mixture increase, interference coefficient decreases, and skeleton rate increases gradually; coarse aggregates with contact that are not involved in the pore cellular structure are the main factor affecting skeleton rate. Meso-structural evaluation indices including interference coefficient and skeleton rate can effectively evaluate the meso-structure of the asphalt mixture, ensure that the coarse aggregates are interlocked with each other to form a stable main skeleton.

Failure of the Asphalt–Aggregate Interface under Tensile Stress: Insight from Molecular Dynamics

Interfacial strength between asphalt binder and aggregate plays a vital role in maintaining the mechanical integrity of asphalt mixture. Given the lack of accurate testing instruments for the interaction of asphalt–aggregate interface, the adhesive interaction and failure evolution occurring at this interface has not been fully understood. In this study, molecular dynamics (MD) simulation was utilized to elucidate the mechanical and deformation behavior of the asphalt–aggregate interface under tensile stress from the atomic perspective. The interface system was constructed with a 12-component asphalt molecular model bonding on a silica substrate. This asphalt molecular model, combining the polymer consistent force field (PCFF) adopted to describe the inter-/intra-action of the system, was first validated. A stress-separation law of this interface can be obtained by tracing the atomic force during the tensile process. From this stress-separation law, the interfacial strength and work of adhesion can be derived. The influences of model size, loading rate, asphalt film thickness, and moisture were investigated. It was found that the interfacial failure type transfers from adhesive failure to cohesive failure as the loading rate decreases to a certain level. Moreover, the interfacial strength is highly associated with the failure type. The interfacial strength of the adhesive failure is about five times that of the cohesive failure, which demonstrates the traditional method of improving the adhesion performance of asphalt on aggregate through increasing its viscosity from the aspect of atomic modeling. Furthermore, the water molecules absorbed at the interface are crucial to the durability of the asphalt–aggregate system. This study provides deep insight into the interfacial failure of the asphalt–aggregate system and could serve as an initial step in multiscale modeling using bottom-up approaches for asphalt mixture.

Improving the Moisture Sensitivity of Asphalt Mixtures by Simultaneous Modification of Asphalt Binder and Aggregates with Carbon Nanofiber and Carbon Nanotube

Moisture sensitivity of asphalt mixtures may cause damage due to cohesion in asphalt binder membrane and adhesion between aggregate and asphalt binder that result in considerable damage to the pavements. Therefore, by determining the adhesion quality in a modified aggregate‐asphalt binder system, one can choose the suitable material compositions to decrease the moisture sensitivity of mixtures. In this study, the effects of modified asphalt binder with carbon nanofiber and modified aggregates with carbon nanotube on the moisture sensitivity of asphalt mixtures were simultaneously explored. For investigating the moisture sensitivity, the indirect tensile strength test and surface free energy concept were implemented. The results of the indirect tensile strength test revealed that modification of asphalt binder and aggregates with carbon nanofiber and carbon nanotube, respectively, increased the indirect tensile strength and tensile strength ratio values of mixtures. The results of surface free energy indicated that using carbon nanofiber and carbon nanotube enhanced the adhesion free energy of the aggregate‐asphalt binder system. Moreover, utilizing carbon nanofiber to modify asphalt binder enhanced the cohesion free energy values in the asphalt binder membrane. Also, carbon nanofiber and carbon nanotube brought detachment energy of the system toward zero, indicating less desire for the mixtures to be stripped. Generally, investigations performed by the two methods showed that covering aggregates by carbon nanotube as well as utilizing carbon nanofiber as an asphalt binder modifier had a positive impact on decreasing moisture sensitivity of asphalt mixtures.

Study on the Change Law of Interfacial Bond Strength Between Asphalt and Aggregate Under the Influence of Salt Freezing and Water Immersion

In order to study the interfacial bond strength of asphalt aggregate under immersion and salt freezing conditions, the influence of immersion time, freeze-thaw cycles and salt concentration on the interfacial bond strength under different temperature conditions was discussed. The orthogonal test was used to determine the mass of the sample after the freeze-thaw cycle, and the water absorption rate was obtained. The influence of soaking time, freeze-thaw cycle times and salt concentration on the water absorption rate was studied by range analysis method. The self-designed drawing test device was used to obtain the stress change of each sample during tensile test at room temperature, so as to achieve tensile failure After that, the range analysis method is still used to deal with the test data. According to the test results, the influence of the above three factors on the interfacial bond strength at different temperatures is qualitatively analyzed. The results show that: under the action of immersion and salt freezing, the interfacial bond strength decreases significantly, and the asphalt aggregate specimen is more sensitive to the change of perceived temperature. When the environmental temperature of the specimen changes, the bond strength fluctuates obviously; under the influence of three factors, the salt concentration has a greater impact on the water absorption and interfacial strength of the specimen than the other two factors. Therefore, in engineering application, we should attach great importance to this problem. And through this research, it provides reference for similar engineering construction and related research.

Physio-Mechanical Properties and Geological Features of the Gharam Chashma Granitic Batholith, Southern Margin of Asian Plate, Nw Pakistan: A Regional Geoheritage Diversity

For centuries, the Granite have been used as a lavish, high-end building material with a rich history due to its strength and beauty. Ancient monuments and buildings made from granite still are standing today. Among these granites, the Granitic batholith Karakoram, in the village of Chitral has tremendous potential to be used as aggregates for heavy duty concrete floor, dimension stone, asphalt and concrete work and other engineering projects. The current study focused on the physcio-mehcnial properties and petrographic characterization of the granitic batholith to highlight the importance of these rocks as a regional geoheritage diversity for construction industry. The interrelationship between the mechanical properties and petrographic features of granites were studied. Field observation shows that the granites are sub-equigranular to inequigranular, coarse to fine grained and without any preferred orientation. Different textural varieties of granites (coarse-grained, fine-grained) were collected. Based on the experimental results, the Petrographic studies demonstrate euhedral to subhedral grains. The fine-grained granite yield more UCS (169.55 MPa) than coarse-grained granite (79.46 MPa) due to its less degree of mineral alteration, fine grains size, relatively low porosity (0.43%) and water absorption (0.39%). Based on physico-mechanical properties including unconfined compressive strength (UCS), specific gravity, water absorption, porosity, soundness, and Loss Angeles abrasion (L.A), the fine-grained granite can be used variety of construction materials, while the coarse grained granite cannot be used as building stone and asphalt in roads. However, petrographic investigations reveal that both fine and coarse grained varieties contain less than 5 percent of strained quartz, which categories these rocks as innocuous for Alkali Silica Reaction (ASR) but according to alkali silica reactivity test (Chemical method ASTM C 289-02) the fine grained variety is considered as innocuous and the coarse grained variety as deleterious.

Study on Influencing Factors of Asphalt‐Aggregate Stripping Mechanism

In order to study the stripping mechanism of asphalt aggregate comprehensively, the conditions of the stripping of asphalt aggregate are divided into two types, which are anhydrous environment and water environment. The stress generation and release of asphalt film under anhydrous environment and the differences in stripping mechanism of asphalt film under tensile and pressure stress were analyzed. The existence of water in the mixture and its harmfulness to stability were also described in this paper. Moreover, the transport behavior of water in asphalt was studied by the principles of electrochemical testing. The test results show that the diffusion rate of water in modified asphalt film is one half of that of base asphalt, so the blocking water ability of modified asphalt is better than that of matrix asphalt. Moreover, the condition of water spalling the asphalt‐aggregate interface is characterized by a change in the mass of asphalt film before and after boiling. It can be concluded that the mass loss of asphalt film is minimal with limestone and modified asphalt, which shows that it has the best spalling resistance.

Study on the adhesion performance of medium weathered igneous rock aggregate and asphalt

In view of the current situation of the shortage of alkaline aggregate and the abundance of weakly acidic weathered igneous rocks around Nairobi, Kenya, in order to fully improve the adhesion performance of asphalt and acidic igneous rocks, this paper studies the effects of different anti-stripping agents separately and combined on the adhesion performance of asphalt aggregates. The results show that the anti-stripping agent can improve the anti-stripping property of the medium weathered igneous rock aggregate and asphalt, and the effect is better when the anti-stripping agent is combined.

Design Optimization and Performance Evaluation of the Open‐Graded Friction Course with Small Particle Size Aggregate

This study aims to optimize the bonding performance between the wearing course and the used pavement or the underlying layer and further improve the service quality and durability of the open‐graded friction course with small particle size aggregate (ultrathin OGFC). The ultrathin OGFC including waterborne epoxy resin emulsified asphalt (WEA) bonding layer and open‐graded asphalt concrete with 9.5 mm nominal maximum aggregate size gradation was optimized. The construction timing of the open‐graded asphalt mixture was determined. The road performance, wear resistance, and interlaminar bonding durability of the ultrathin OGFC were comprehensively evaluated. The results show that, based on the basic properties of the open‐graded asphalt mixture, its asphalt aggregate ratio is recommended to be 5.0–5.5%. Based on interlaminar shear strength, it is recommended that the open‐graded asphalt mixture is paved immediately after WEA bonding material was sprayed, and the bonding layer does not spread aggregate. The WEA containing 20% waterborne epoxy resin (WER) is recommended as bonding layer for the ultrathin OGFC, and the optimized spraying amount is 1 kg/m2. The ultrathin OGFC has good antisliding, drainage, and wear resistance properties. The interlaminar bonding performance, water stability, and durability of WEA bonding layer are obviously better than those of high viscosity asphalt (HVA) and SBS‐modified asphalt. The WEA bonding layer can better resist interlaminar shear failure and improve the service quality and service life of the ultrathin OGFC.

Effects of cellulose fibers on the properties of asphalt mixtures

• Mechanical properties were more sensitive to CF addition methods than volumetric. • CF orientation and distribution may affect the variation in measured properties. • No unique CF-asphalt mixture met all the required properties. • The determination of optimum CF content was inconclusive. Various types of additives have been used in asphalt pavement industry to improve the performance. Among these additives, fibers have received increasing attention to achieve the desired improvement. This investigation aims to evaluate the effect of applying dry and wet methods separately to introduce the cellulose fibers (CF) into the local hot mix asphalt (HMA). The evaluation was carried out by measuring the volumetric and mechanical proprieties of conventional (control) and CF-asphalt mixtures. This study also aims to examine the possibility of using the cellulose fiber as a sustainable material in the local asphalt pavement industry. The effect of variations in cellulose fibers content; 2.5%, 5.0%, 7.5%, and 10.0% by the weight of asphalt cement, aggregate source (Al-Nibaay and Al-Suddor aggregates), and two methods (wet and dry) for adding cellulose fibers to asphalt mixtures are evaluated. Marshall methodology and indirect tensile strength test (ITS) were applied to investigate the effects of these variables. The results of this study showed that the difference in mechanical properties of the fiber-reinforced asphalt mixtures was more sensitive to CF application methods in these mixtures than the difference in volumetric properties. In addition, the wet method improved most properties of Al-Nibaay aggregate asphalt mixtures while the dry method improved most properties of Al-Suddor aggregate asphalt mixtures. Determination of optimum CF content was found inconclusive due to the wide variation in the measured properties. CF can be recommended as a promising sustainable additive to improve the properties of local asphalt pavement. However, further investigation remains necessary to precisely determine the optimum CF content in parallel with the optimum asphalt content and it is also important to assess the resistance of CF-asphalt mixtures to moisture damage and aging.

Study on Mesoscopic Mechanics of Recycled Asphalt Mixture in the Indirect Tensile Test

Reclaimed asphalt pavement (RAP) mainly contains asphalt binder and aggregates, and the RAP materials used in paving roads could save virgin materials. This paper studied the following: asphalt mixture with different RAP material contents was prepared; then the indirect tensile test was carried out, and the mesoscopic model of the recycled asphalt mixture was reconstructed digitally. Discrete element method (DEM) of indirect tensile test was carried out to analyze the mechanical properties of recycled asphalt mixture in mesoscopic perspective. The results showed that there were some gaps between the simulation result of the digital specimen model and the test value of the recycled asphalt mixture, but the velocity vector and the law of force chain development of the recycled asphalt mixture could be explained in mesoscopic perspective. It proved that the virtual simulation test of the mechanical test was effective. The damage process of recycled asphalt mixture was analyzed in mesoscopic perspective, and the unification of mechanical response and macroscopic appearance was completed. Meanwhile, the simulation method of mesoscopic mechanics was an effective supplement to traditional tests, and guided tests method theoretically.

Using Silane Coupling Agent Coating on Acidic Aggregate Surfaces to Enhance the Adhesion between Asphalt and Aggregate: A Molecular Dynamics Simulation

Acidic aggregates have the merits of high strength and good abrasion resistance capacity. However, its poor adhesion with asphalt binder constrains its application in pavement construction. Among these, the granite aggregate is the typical one. Therefore, this study modified granite aggregates’ surface to improve their adhesion property with the asphalt binder. Specifically, the silane coupling agent (SCA) KH-560 was adopted to achieve the modification purpose. Subsequently, asphalt mixtures with modified and unmodified granite, basalt, and limestone were subjected to the boiling test, immersion test, and freeze-thaw splitting test to estimate the asphalt adhesion property. Moreover, a molecular dynamic simulation was employed to characterize the asphalt-aggregate interface from the molecular scale. The radius distribution function (RDF) and interaction energy were used as the primary indicators. The results showed that the SCA could efficiently improve the adhesion between asphalt and granite aggregates, comparable with the alkaline aggregates. In terms of the molecular scale, the incorporation of SCA could significantly increase the concentration distribution of asphalt molecules on the aggregate surface. Meanwhile, the interaction energy was correspondingly increased due to the considerable growth of non-bond interaction.