Coarse Gradation Research Articles

Investigation of Performance Specifications for Marshall Mixes Using Performance-Based Mix Design Methodology

This paper presents a comprehensive study for developing the performance specifications for the Marshall mixes using the performance-based mix design (PMD) methodology. The specification describes the desired levels of fundamental engineering properties for predicting performance during mix design or quality assurance checks at the time of construction. In this study, the bituminous concrete mixture was designed through complementing volumetric criteria with performance tests such as dynamic creep and the indirect tensile asphalt cracking test for evaluating resistance against rutting and fatigue cracking, respectively. This study considers different factors such as five different types of design aggregate gradations (mid-gradation, fine-coarse gradation, coarse gradation, coarse-fine gradation, and fine gradation), three binder types (VG-30, VG-40, and PMB-40), and five levels of compactive efforts (35, 50, 75, 90, and 110 blows on each face). The study finds the effect of design aggregate gradation, binder type, and compactive effort on the rutting and cracking resistance of bituminous mixes. The research study also comprehends the influence of volumetric properties on the performance parameters. Further, it establishes the initial performance criteria for rutting and cracking for Marshall mixes. The performance space diagram (PSD) has also been plotted, portraying the overall performance (acceptable, desirable, or unsatisfactory performance regions) of bituminous mixtures based on rutting resistance and cracking resistance. This paper highlights and advocates the integration of these performance-based specifications into the Marshall mix design specifications for improving pavement characteristics and extending overall service life.

Size effect analysis of mode I fracture performance of hot mix asphalt

The diameters of asphalt concrete cylindrical specimens typically measure either 100 mm or 150 mm, as these are the standard sizes for almost all conducted tests. However, the impact of specimen size on the fracture performance of asphalt mixtures has not been extensively explored. This study aimed to address this gap by performing laboratory tests on semi-circular bending (SCB) specimens. These tests were designed to apply the Size Effect Law (SEL) in evaluating the fracture performance of two asphalt mixture types (AC10 and AC16) at −10 ℃. The experiment selected four different diameters (76 mm, 100 mm, 125 mm, and 150 mm) and two notch-radius ratios (α0 = 0.2 and 0.4) to investigate the relationship between the specimen dimensions and both the nominal stress and fracture toughness (KIC). Results indicated that the nominal stress and KIC adhered to the SEL. It was observed that both aggregate gradation and notch-radius ratio (α0) significantly influenced the SEL’s effect on nominal stress. An increase in α0 from 0.2 to 0.4 shifted the fracture failure towards a more linear elastic fracture behavior. Specifically, the coarser gradation in AC16, compared to AC10, predisposed the fractures towards linear elastic behavior. Moreover, an increase in α0 notably augmented the brittleness number. For specimens with identical dimensions and α0, AC16 exhibited higher D/D0 values, indicating a stronger alignment with Linear Elastic Fracture Mechanics (LEFM) principles for the tested specimen sizes compared to AC10. As the size of the specimen increased, there was a gradual rise in KIC, with the enlargement from 76 mm to 150 mm resulting in KIC increases of 25.2 % and 12 % for α0 values of 0.2 and 0.4, respectively, in the AC10 mixture. Conversely, the AC16 mixture saw respective enhancements of 15.8 % and 7.6 % for the same α0 values. The influence of α0 on the apparent fracture toughness became less pronounced with its increase; KIC gradually decreased for AC10, yet increased for AC16 with rising α0 levels. For the same asphalt mixture type, KIC was found to escalate with both D/D’0 and α0. At an α0 of 0.4, the disparities between KIc and KIcm, – expressed as (KIcm- KIc)/ KIcm, – stood at 13.9 % and 9.2 % for AC10 and AC16, respectively, with a diameter of 150 mm. Based on these findings, it is recommended to utilize an SCB specimen with a diameter of 150 mm and an α0 of 0.4 for fracture performance testing, as these parameters appear to provide the reliable assessment of the materials’ fracture behavior.

Exploring the relationship between pavement mean texture depth and mean profile depth: from theoretical derivation to field results

Pavement mean texture depth (MTD) and mean profile depth (MPD) are common evaluation indicators for characterizing the pavement surface. Clarifying the relationship between the two contributes to coordinate various measurement methods and evaluation criterions. The calculation methods of MTD and MPD were first introduced to trace the similarity between the indicators. Subsequently, the tortuosity area of surface texture was observed using x-ray Computer Tomography (CT). To further determine the model parameter, over 3000 sets of field data in Research Institute of Highway Ministry of Transport (RIOH) track were measured. Meanwhile, the field results of another track and existing recommended model were also used to validate the model. The results show that the shift relationship between MTD and MPD is theoretically unified into a linear model with a slope of 1 and an intercept related to the surface tortuosity. These tortuous areas, the main difference source between the two indicators, would lead to a greater equivalent texture depth under the coarser gradation or lower the compactness of the asphalt mixture. Even for the different track roads, the determined model (MTD = MPD + 0.03) has a lower mean relative estimation error, indicating good applicability. This study provides theoretical explanation and empirical references for the automated laser-based texture detection.

A multi-gradient analysis of microscopic void characteristics' influence on the mechanical properties of open-graded friction course bituminous pavement

The mechanical properties of the open-graded friction course (OGFC) bituminous pavement are tied to its microscopic void structure, but multiple void parameters influence void formation and distribution. Solely using air voids as an indicator of pavement stability is challenging. Thus, a multi-gradient analysis of void structure factors is vital for advancing OGFC pavement's mechanical property research. This study used computerized tomography (CT) and digital image processing (DIP) to gather data on void structure distribution, size, and complexity in OGFC bituminous mixtures. Mechanical experiments assessed high-temperature deformation, low-temperature cracking, and water damage resistance. Analysis of void parameters' influence led to a predictive model for mechanical property in OGFC mixtures. The study found that as air voids increase within the 18 %–24 % range, both equivalent void diameter and void fractal dimension increase, while void count decreases. Conversely, coarser gradation and a larger nominal maximum aggregate size (NMAS) lead to increased equivalent void diameter but decreased void fractal dimension, reducing void complexity. The mechanical properties of OGFC mixtures decline with rising air voids but improve with coarser gradation and larger NMAS. The predictive model highlights the void fractal dimension and NMAS as critical indicators, with other factors showing weaker influence or multicollinearity issues that are unfit for model fitting. The findings could provide useful references for the structural design, property evaluation, and quality control of OGFC bituminous pavements in actual road construction.

Accelerated Pavement Testing of Re-Recycled Cold Central Plant Recycled Asphalt Mixtures

Cold central plant recycled asphalt mixtures (CCPR) have been shown to provide a high-quality, economical, and environmentally conscious asphalt base mixture. Existing literature, however, does not indicate what would be an appropriate future rehabilitation method for a pavement that includes CCPR. Given the previously cited benefits of CCPR, it is logical to ask whether a CCPR can be re-recycled and, if so, how will it perform? This paper presents a study of a test section containing a re-recycled CCPR placed at the National Center for Asphalt Technology Test Track. CCPR from a Virginia Department of Transport study on the Test Track was recovered, re-recycled, and placed at 5-in. thick with a 2-in. asphalt concrete (AC) overlay. In preparing for a re-recycled CCPR layer, milling an existing CCPR layer resulted in a coarser gradation and lower indirect tensile strength values. Initially, the re-recycled CCPR test section did not perform well owing to moisture in the aggregate base present during construction of the re-recycled CCPR layer. It is suspected that this moisture negatively affected the curing of the re-recycled CCPR layer. Thus, the re-recycled CCPR layer was milled and re-recycled again (3rd generation re-recycled CCPR) and placed at 5-in. thick with a 2-in. AC overlay. The 3rd generation re-recycled CCPR performed well through 3 million equivalent single axle loads (ESALs), the same number of ESALs that resulted in fatigue cracking and rutting failures in the initial re-recycled CCPR.

Structure stability and shear failure behaviors of asphalt mixtures from the perspective of aggregate particle migration

Shear deformation of asphalt mixtures is the macroscale accumulation of aggregate migration, addressing excessive aggregate slip and rotational migrations can reduce shear failure. In this research, the slip failure and torsional failure tests were introduced to achieve targeted investigations using developed instruments. Deformation resistance of the asphalt mixture was analyzed from the granular properties. The results indicate that shear energy is dissipated by structural self-organization induced by aggregate migration. Coarse gradation and complex aggregate morphology enhance the structure stability. The shear failure threshold resulting from aggregate slip exceeds that of rotation over fourfold. The packing coefficient (PC) and the critical moment of inertia (IC) were proposed to evaluate the slip and rotation resistances of asphalt mixtures, the indicators show good parabolic and linear relationships with the peak forces of slip and rotation as gradation changes, which can be illustrated by the interfacial friction and the spatial hindrance provided by the aggregate morphologies of texture and form. Finally, the findings were validated by the discrete element method.

Study on Compaction Properties and Skeleton Structural Characteristics of Porous Asphalt Mixture

Porous asphalt pavements have a skeletal structure with a large number of interconnecting pores, which can improve drainage, ensure traffic safety, and reduce tire noise. However, it can weaken the mechanical properties of the pavement. One of the key factors affecting the performance of porous asphalt pavements is the quality of compaction, the assessment of which is difficult to accurately quantify. Therefore, Superpave gyratory compaction (SGC) and skeleton penetration tests of porous asphalt mixtures were carried out using three engineering-differentiated gradations in this paper to investigate the gyratory compaction characteristics and the skeleton contact state during penetration. The results show that obvious stages with the increase in number of cycles can be observed during the compaction process. All gradations can achieve the maximum porosity requirements within a reasonable number of compaction cycles, while only the medium and fine gradations can approximately meet the minimum porosity requirements. The coarse gradation takes too long to finish compaction and is almost impossible to meet the minimum porosity. The optimum match between the void ratio of the design gradation and the skeleton contact state can be verified using the VCA ratio and void ratio curves. This is a new method to determine the corresponding target compaction number that can ensure better accuracy and ease of engineering application. Moreover, medium-graded mixtures with better skeletal embedding exhibit greater skeletal strength than coarse-graded aggregates, which provide theoretical support for the establishment of material grade optimization methods.

Investigation on the effects of physical property and stress state of graded crushed stone on resilient modulus and permanent deformation

The graded crushed stone has been widely used in flexible pavement structures to reduce the reflective crack and optimize pavement performance. The most important performance indexes are the mechanical property characterized by resilient modulus and permanent deformation. This paper is aimed to study the effects of the physical property and stress state on the performance of graded crushed stone to provide the basis of the pavement design. The results show that: the fine gradation has a higher increasing magnitude as the bulk stress increases, indicating a more significant stress dependence, while the coarse and middle gradations have a similar changing trend. The increase in water content could reduce the resilient modulus and enhance permanent deformation due to the lubricating effect. The deviatoric stress has a prominent effect on the resilient modulus for coarse gradation, while the confining stress is for fine gradation. Then the permanent deformation is significantly affected by the stress ratio, in which accumulated permanent strain and deformation rate all increase with the increasing of stress ratio. The critical stress ratio should be determined to control the stress state of graded crushed stone to a limited range to prevent unstable failure.

Influence of Morphological Characteristics of Coarse Aggregates on Skid Resistance of Asphalt Pavement.

This research aims to improve the durability of skid resistance of asphalt pavement from the perspective of coarse aggregates based on on-site investigation. Firstly, the skid resistance of six representative actual roads was tested during two years by employing the Dynamic Friction Tester and the attenuation characteristics of skid resistance of different types of asphalt pavements were analyzed. Secondly, core samples were drilled onsite and coarse aggregates were extracted from the surface layer of the core samples. The morphological parameters of coarse aggregates were collected by a "backlighting photography" system and three-dimensional profilometer, and the variation rules of angularity and micro-texture of coarse aggregates were investigated. Finally, the correlation between the morphological characteristics of coarse aggregates and the pavement skid resistance was established based on the grey correlation entropy. The research results show that with the increase in service time, the attenuation rate of skid resistance of asphalt pavement gradually slows down; the angularity of coarse aggregates gradually decreases, and the micro-texture on the wearing surface gradually wears away. The grey correlation entropy between all the micro-texture indexes of coarse aggregates and dynamic friction coefficient, as well as between the roundness and skid resistance is more than 0.7, whereas the correlation between other evaluation indicators and the dynamic friction coefficient is poor, indicating that compared with the angularity of coarse aggregates, the micro-texture affects the skid resistance of actual asphalt pavement more greatly. In engineering applications, the use of coarse gradation, coarse aggregates with high roughness or high anti-wear performance can slow down the attenuation of pavement skid resistance, so that the pavement can maintain superior long-term anti-skidding performance.

Effect of aggregate gradation and asphalt mix volumetrics on the thermal properties of asphalt concrete

The objective of this study is to investigate the impact of aggregate gradation and Superpave volumetrics on thermal properties of asphalt mixtures. Thirty asphalt concrete specimens with three different Nominal Maximum Aggregate Sizes (NMAS) of 19.0, 12.5 and 9.5 mm and two levels of gradation coarseness: fine gradation (FG) and coarse gradation (CG) were prepared. The Transient Plane Source (TPS) method was used to determine thermal properties. Based on the analyses performed, it was concluded visually that heat transfer is highly dependent on the contact area which, in turn, is related to air void volume. Unlike NMAS, the gradation coarseness (G) has some effect on thermal conductivity (TC) (p-value = 0.008 < 0.05). On the contrary, the NMAS, unlike gradation coarseness, has a significant effect on thermal diffusivity (TD) with a p-value of 0.025. Both gradation coarseness and NMAS have a significant effect on thermal diffusivity (p-value = 0.029 < 0.05) and do not have much effect on specific heat (SH) where p-value is greater than 0.05. Nevertheless, it was noticed that the thermal diffusivity increased linearly with an increase in aggregate size from 85.64 mm2/s to 125.79 mm2/s at 9.5 NMAS FG and 19 mm NMAS FG, respectively. Whereas the specific heat and thermal conductivity increase as the asphalt content (AC) increases. Consequently, the highest average values of thermal conductivity and specific heat are 2 W/m.K and 0.025 M.J/m3. K, respectively, at the highest asphalt content of 6.1%. Multiple linear regression, non-linear regression and deep learning (MLR, NLR and DL) equations were developed. The non-linear regression resulted relatively in the best predictive power of all equations. Finally, larger datasets are needed to predict thermal properties with higher confidence.

Study on Low-Temperature Index and Improvement Measures of Emulsified Asphalt Cold Recycled Mixture.

With the promotion of cold recycled mixture (CRM) in cold areas and the improvement of its application layer, the enhancement of the low-temperature performance of mixtures is particularly important. The applicability of the current low-temperature bending test method to CRM is controversial. Firstly, the low-temperature crack resistance of CRM with different gradations and emulsified asphalt contents was studied by the indirect tensile (IDT) test and the semi-circular bending (SCB) test. Thereafter, the low-temperature performance evaluation index suitable for CRM was put forward. Then, the low-temperature performance of CRM with different gradations, fiber types, and contents was evaluated by using the above low-temperature evaluation index. The results show that the low-temperature performance of CRM with different gradations and emulsified asphalt contents can be distinguished by fracture work (W) and fracture energy (Gf). Not only do the test results have little variability (about 12% and 15%, respectively), but also the correlation coefficient with the new asphalt film thickness is the highest (0.8595 and 0.8939, respectively). Compared with coarse gradation (AC-25) and fine gradation (AC-13), medium-gradation (AC-20) CRM has higher low-temperature performance, and polyester fiber can significantly improve the low-temperature performance of CRM. Compared with non-fiber, the W and Gf of CRM of polyester fiber (0.3% content) can be increased by at least 42% and 30%, respectively.

Investigation on low-temperature cracking characteristics of asphalt mixtures: A virtual thermal stress restrained specimen test approach

In order to characterize the effects of aggregate characteristics on the low-temperature cracking characteristics of asphalt mixtures, a virtual approach for the thermal stress restrained specimen test (TSRST) was established based on the discrete element method (DEM) and the simulation software particle flow code in two-dimension (PFC2D). A two-dimensional (2D) virtual specimen was established according to the random generation algorithm. The meso contact parameters between each phase in materials at different temperatures were determined through laboratory tests. The internal thermal stress curve of the specimen and the meso mechanism of crack propagation were analyzed during the virtual test, and the reliability of the virtual test was confirmed by the results of laboratory tests. Finally, the effects of aggregate properties on the low-temperature crack resistance of asphalt mixtures were analyzed. The results of the virtual test and the laboratory test are highly consistent, which proves that the virtual TSRST can be used as a reliable method to evaluate the low-temperature crack resistance of asphalt mixtures. The damage of the specimen can be divided into three stages: crack initiation, stable propagation, and unstable propagation. The asphalt mixture with less aggregate content, coarser gradation and smaller flat ratio has better low-temperature crack resistance.

Effects of particle size optimization of quartz sand on rheology and ductility of engineered cementitious composites

In this study, the effect of particle size of quartz sand on the fresh and hardened properties of engineered cementitious composites (ECC) was investigated. For this purpose, three ECC mixtures that are identical except for the gradation of quartz sands used in their composition were designed. One of the mixtures includes a combination of quartz sands with amounts determined by the Andreasen and Andersen particle size optimization model while the remaining two have a finer and a coarser gradation. In the fresh state, mini slump, mini V-funnel and bleeding tests were applied, and rheological parameters were determined according to Bingham and modified Bingham models by using a rotational viscometer. In the hardened state, flexural strengths, mid-span deflections and numbers of microcracks formed under flexural loading were determined at 7 and 28 days. It was observed that the particle size optimization of the quartz sand can provide a balance between flow and bleeding characteristics of ECC mixtures. Although a reduction in flexural strength occurred at both ages in the optimized ECC mixture, the deflection capacity and the crack formation capacity under loading were significantly increased, reaching a deflection value of over 10 mm with at least 11 cracks formed during the test. As a result, it was revealed that particle size optimization can yield a mixture with the highest ductility without compromising the workability of ECC.

Relative Contribution of Process Control Parameters on the Raveling Resistance of Microsurfacing Mix

Raveling is one of the key performance parameters of microsurfacing treatment. During the material handling and mix production, process control parameters including aggregate gradation, emulsion content, and water content vary inevitably and might increase the risk of raveling. The objective of this study was to quantify the relative contribution of these process control parameters on the raveling resistance of the microsurfacing mix. For this purpose, a total of 30 combinations of aggregate gradation, emulsion content, and water content were subjected to raveling using wet track abrasion test. The investigations showed that the raveling increased for coarser gradation and lower emulsion content, whereas the variation in raveling was minimal with water content. Further, the test results were modeled using an artificial neural network (ANN). The ANN model was able to capture the influence of process control parameters on the raveling resistance of the microsurfacing mix. Garson’s algorithm was used to quantify the relative contribution of each process control parameter on raveling. It was found that the relative contributions of aggregate gradation, emulsion content, and water content were 40%, 28%, and 32%, respectively. Because of their substantial contribution, it is critical to ensure proper quality control of process control parameters during material handling and production of microsurfacing mix. In particular, coarser aggregate gradation in conjunction with lower emulsion content should be avoided to minimize the risk of raveling.

Influence of Aggregate Gradation on the Compactability of Asphalt Mixtures Utilizing Locking Point

Aggregate gradation is crucial for the performance of asphalt mixtures. However, the adequate mix design must include the compromise between performance and workability. This study used two compaction methods: the impact (Marshall Hammer, Humboldt, Elgin, Illinois) and gyratory [Superpave Gyratory Compactor (SGC), Pine Instrument Company, Grove City, Pennsylania], to investigate the influence of aggregate gradation on the compaction of asphalt mixture utilizing the concept of the locking point. For the impact compaction, an accelerometer was placed on the falling mass of the Marshall Hammer to record the asphalt mix response, with which the impact locking point was defined. For the gyratory compaction, the densification curves were utilized to define the locking point. Twelve mixes, three for each mixture type (base, intermediate, and surface) were designed and prepared in the laboratory. The asphalt mixes were tested for their locking points in relation to their type and gradation. Results indicated that the locking point could be determined for the majority of the mixtures compacted by both the impact and gyration methods, except for the mixture composed of the bigger stone and coarser gradation. The locking point of the asphalt mixture was strongly dependent on its gradation. A coarser mix resulted in a higher locking point. Thus, the maximum aggregate size was not the only factor that determined the locking point but the whole gradation.

Determination of Construction Parameters of Porous Ultra-Thin Overlays Based on Laboratory Compaction Studies.

To address the severe distresses of asphalt pavement, a new type of pavement maintenance treatment, porous ultra-thin overlay (PUTO) with small particle size was proposed. The PUTO has a thickness of 1.5–2.5 cm and a large void ratio of 18–25%. As a newly asphalt mixture, the structure characteristics differ from poor traditional pavement. Therefore, it is necessary to investigate the fabrication schemes in laboratory and on-site, respectively. In this study, the optimal fabrication schemes, including compaction temperature and number of blows of PUTO were determined based on Cantabro test and volumetric parameters. Then, the corresponding relationship between laboratory and on-site compaction work was then established based on the energy equivalent principle. On this basis, the numbers of on-site rolling passes and the combination method were calculated. The results show that increased compaction temperature and number of blows reduce the height and enhance the compaction of the Marshall sample. With the same temperature and number of blows, the raveling resistance of coarse gradation, Pavement Asphalt Concrete-1 (PAC-1) is better than that of fine gradation, Pavement Asphalt Concrete-2 (PAC-2), and the increased asphalt viscosity significantly improves the raveling resistance of the asphalt mixture. To ensure the scattering resistance and volumetric characteristic, the initial compaction temperature of the PAC-1 and PAC-2 should not be lower than 150 °C and 165 °C, respectively. Then, the laboratory compaction work and on-site compaction work were calculated and converted based on the principle of energy equivalence. Consequently, the on-site compaction combination of rolling machines for four asphalt mixtures was determined. According to the volumetric parameters, the paving test section proved that the construction temperature and the on-site rolling combination determined by laboratory tests are reasonable, and ultra-thin overlay has good structural stability, drainage, and skid resistance.

Meso-scale study on compaction characteristics of asphalt mixtures in Superpave gyratory compaction using SmartRock sensors

Compaction degree is an essential parameter to characterize the construction quality and performance of asphalt pavement. Under the same compaction conditions, asphalt mixtures with different aggregate sizes and gradation may exhibit different compaction characteristics. Accordingly, this paper aims to study the compaction characteristics of asphalt mixture at the meso-scale through particle response of the mixture by using SmartRock sensor. Firstly, a laboratory test scheme of the asphalt mixture is designed and the SmartRock sensors are used to obtain the internal stress of the mixture during compaction. By comparing the particle stress with the height of the specimen, it is inferred that the stress state of the particles can reflect the compactness of the compacted material, and the change rate of compaction degree in logarithmic coordinates is proposed to characterize the compaction performance of the asphalt mixture. Furthermore, the quantitative analysis is comprehensively conducted related to the different nominal maximum aggregate size (NMAS), locations and gradation types. The results reveal that the asphalt mixture with larger NMAS has a better compactibility in terms of forming a stable skeleton structure, and the mixture in the middle of specimen can be compacted more easily than that in the top and bottom area of specimen. It can be aslo found that the gradation type affects the compaction performance through the probability of coarse aggregates interlocking with each other. The open-graded mixture (i.e, PAC-16) is relatively faster to achieve the target compaction degree than gap-graded and dense-graded mixtures (i.e, SMA-16 and AC-16, respectively). Although the asphalt mixture with larger NMAS and coarser gradation can reach a certain compaction degree with a rapid speed, it doesn't mean the mixture can achieve higher compaction degree finally under the action of subsequent compaction work. The test result shows that the asphalt mixture with coarser aggreages is relatively difficult to compact with lower final compactness. The experimental research sheds substantial light on the internal relationships between the response of the particles and compaction charateristics of asphalt mixture at meso-scale.

Drainage Capacity and Resistance to Clogging of Porous Asphalt Concrete Based on the Water Penetration Test and Constant Head Permeability Test

Abstract Porous asphalt concrete (PAC) can decrease the risk of hydroplaning, reduce splashing and spraying, improve visibility, reduce traffic noise, and improve driving safety, but the clogging of the void affects its durable function. To investigate this, the fine aggregate was chosen as a plugging agent, and the permeability coefficients and water permeability coefficients were measured by using an asphalt mixture permeability testing device and pavement surface permeameter to simulate a multicycle drainage clogging experiment of PAC. The influence of asphalt mixture design parameters, including voids volume (VV), the nominal maximum aggregate sizes (NMASs), grading types on the drainage capacity, and resistance to clogging, was investigated. The two test results indicated that VV has a manifest influence on both drainage capacity and resistance to clogging. The NMAS has an obvious influence on resistance to clogging but no clear influence on the drainage capacity. PAC with the coarser gradation has better performance on drainage capacity and resistance to clogging. The clogging location is concentrated on the top 40 mm of the PAC-13 specimen. The fine particles with diameters of 0.15 to 2.36 mm are the key particles causing the clogging in the PAC-13 specimen. Water permeability coefficients and permeability coefficients have a very high correlation.

Measurement of coarse aggregates movement characteristics within asphalt mixture using digital image processing methods

The movement of aggregates plays an important role in the permanent deformation of asphalt mixture. To provide a reference for the design of asphalt mixture, this study conducted in-depth analyses of the mechanisms involved in coarse aggregate movement and rutting subjected to load by using digital image processing (DIP) technique. The movement characteristics of coarse aggregates within different asphalt mixtures were investigated from a mesoscopic perspective, and correlations between meso-parameters of coarse aggregates movement and rut depth (RD) were analyzed. Finally, a meso-structural model of coarse aggregate movement was proposed. The results indicated that the anti-rutting performance of asphalt mixture is closely related to the meso-movement parameters of coarse aggregates. The movement regions of coarse aggregates subjected to load can be divided into a compacted flow zone, uplifted zone, and a disturbed zone, depending on the movement characteristics of coarse aggregates. There is an obvious linear correlation between the RD and the movement parameters of coarse aggregates in the compacted flow and uplifted zones. Material design measures of asphalt mixture can effectively improve the rutting resistance include using materials that have a coarse gradation and asphalt with high cohesion.

Laboratory Performance Evaluation of Hot-Mix Asphalt Mixtures with Different Design Parameters

Aggregate gradation and asphalt type are traditional variables that affects mix design of Hot-Mix Asphalt (HMA). Recently, the number of design gyrations (Ndes) has been increasingly accepted as another variable parameter during the design process. Due to the growing shortage of high-quality raw materials, it is necessary to make full use of the combined roles between these design parameters, instead of solely relying on their individual effect, to improve the HMA properties. Therefore, this study comprehensively explored the effect of aggregate gradation, Ndes, and asphalt type on the performance of HMAs. Seven different combinations of aggregate gradation, Ndes, and asphalt type were evaluated. The volumetric indicators, uniaxial penetration shear test (UPST), unconfined compression test (UCT), low-temperature bending test (LBT), four-point bending test (FPBT), and dynamic modulus test (DMT) were used to assess the performance of HMAs designed by various parameter combinations. It was found that the contribution of adopting harder asphalt binder was able to make up for the high-temperature resistance loss caused by lower Ndes or coarser gradation. The dynamic modulus exhibited the similar phenomenon. By contrast, the harder asphalt binder led to the worse tenacity of HMAs at low temperature; however, the tenacity can be restored through using lower Ndes or coarser gradation by increasing asphalt content. In addition, the fatigue life of HMAs went up significantly by about 36 ~ 41%, when both Ndes and asphalt penetration grade decreased to one lower level.