Graded Asphalt Mixtures Research Articles

Gradation optimization of AC-20 asphalt mixture based on the fuzzy analytic hierarchy process and comprehensive evaluation method

The aggregate gradation of asphalt mixture is one of the most important factors affecting the service life of asphalt pavement. In order to study the gradation of asphalt mixture with the best comprehensive performance, this study puts forward a new method of mineral aggregate gradation optimization based on the fuzzy analytic hierarchy process and comprehensive evaluation method, aiming at the multi-level and multi-index evaluation of the road performance of asphalt mixture. First, the orthogonal test design method is applied to design nine target gradations with coarse aggregate (>4.75 mm) and fine aggregate (<4.75 mm) of AC-20 (asphalt concrete) mixture serving as two factors and the upper, middle, and lower positions of the gradation curve as three levels, and then the road performance test research is carried out. Second, a comprehensive model for evaluation of road performance of mineral aggregate gradation is established. A fuzzy complementary judgment matrix is constructed, and the index weights of each level and the hierarchical total ranking weight are calculated. Then, the membership function is introduced into the comprehensive evaluation model for the road performance of mineral aggregate gradation, and the membership values of each index of asphalt mixture road performance are obtained. Finally, the fuzzy comprehensive evaluation method is used to find out the comprehensive evaluation value of the road performance of the nine graded asphalt mixtures, and the mineral aggregate gradation is optimized. The research results show that the 1# gradation of the asphalt mixture has the highest comprehensive road performance evaluation value, and the combination of the fuzzy hierarchical analysis process and comprehensive evaluation method can more objectively and comprehensively evaluate the comprehensive road performance of the asphalt mixture and provide a useful reference for the optimal selection of asphalt mixture mineral gradation.

Damage evolution in asphalt mixtures based on in-situ CT scanning

A novel approach utilizing in-situ Computed Tomography (CT) scanning and digital image processing techniques was developed to overcome the limitations of traditional CT image analysis in studying microcrack evolution in asphalt mixtures. Two types of graded asphalt mixtures (continuous gradation/AC and intermittent gradation/SMA) were scanned in-situ to capture internal structural changes. Digital image processing distinguished primary voids from cracks and extracted crack evolution. Multivariate regression analysis linked crack parameters to compressive strain. The study found that crack evolution during uniaxial compression in asphalt mixtures can be divided into densification, linear elastic deformation, and nonlinear failure stages. As load increases, the number, volume, and void percentage occupied by cracks rise, peak, and then decrease due to merging and engulfing after the ultimate load. The skeletal structure of cracks was obtained, and a damage evolution equation was established, linking crack parameters to damage evolution. Crack tortuosity was used to characterize the resistance effect of different gradations on crack propagation. This methodology provides new insights and technical support for studying damage evolution and understanding the failure mechanisms of asphalt mixtures.

Investigation of key morphological parameters of pores in different grades of asphalt mixture based on CT scanning technology

The internal pore structure of asphalt mixtures directly influences their permeability characteristics. Current research has not yet clarified the quantitative characterization of different types of meso-pore structures and their impact mechanisms on permeability characteristics. Therefore, this study, based on the acquisition of the internal pore structure of asphalt mixtures through CT non-destructive scanning technology, classifies pores according to their characteristics. It conducts a multi-dimensional and multi-scale qualitative and quantitative analysis of the meso-pore structures of asphalt mixtures in terms of pore distribution, equivalent radius of pore throats, inclination angle of pore throats, tortuosity of pore throats, and pore connectivity. The results indicate that the internal pore distributions of AC-16, SMA-16, OGFC-13, and OGFC-16 gradation asphalt mixtures are uniform, without noticeable segregation. The results of porosity obtained through non-destructive CT scanning technology demonstrate good consistency with those of macroscopic experiments. This demonstrates that analyzing CT images can accurately acquire pores and quantify pore characteristics. The number of pores in AC-16 gradation specimens is approximately 3–5 times that of other groups of gradation specimens, but the average volume of the pores is only 0.98 mm3. The average pore volume for SMA-16 gradation is 5.1 mm3, while for OGFC-13 and OGFC-16 gradation, the average pore volumes are 28.3 mm3 and 29.6 mm3, respectively. In SMA-16 grade specimens, the volume of open pores accounts for 95% of the total pore volume, despite the fact that open pores make up only 1% of the total number of pores. In the OGFC-13 and OGFC-16 graded asphalt mixtures, the volumes of interconnected pores account for 88.7% and 88.9% of the total pore volume, respectively. The number and volume proportion of pore throats decrease with the increase in pore throats angle, indicating that there are more pore throats with smaller angles, which are conducive to longitudinal drainage, and fewer pore throats with larger angles, which are conducive to lateral drainage. This suggests that the vertical permeability of samples formed by traditional Marshall compaction is usually greater than their horizontal permeability.

Characterization of rutting damage based on two-dimensional image analysis of changes in mesoscopic aggregate properties of asphalt mixtures

Accurately predicting the rutting development law of asphalt pavement is of great significance for preventing and controlling pavement diseases. The aggregate skeleton of the asphalt mixture is the main load-bearing part and plays an important role in its anti-rutting performance. However, quantitative and mesoscopic evaluation indicators and standards for aggregate skeletons have not been established. This study aims to reveal the relationship between the mesostructured characteristics of asphalt mixtures and rutting damage. This paper uses two-dimensional image technology to analyze the dynamic change process of internal skeleton information of two graded asphalt mixtures under cyclic wheel load. According to the fractal theory, the fractal dimension and multifractal spectrum of the full-depth aggregate were calculated. The results indicate that the linear regression model between the mesoscopic skeleton information of asphalt mixture and the average rutting depth during the rutting test can be used to quantify the rutting performance. There is an obvious correlation between the fractal dimension of the section aggregate and the loading times, and there is a certain linear relationship between the multifractal spectrum indexes and the loading times. It indicates that the fractal theory index of aggregate can reflect the change of the macro performance of loading times.

Study of the Influence of Sisal Fiber Length on Cement Emulsified Asphalt Mixture and Its Strengthening Mechanism

Abstract In order to explore the suitable length of sisal fibers used in cement emulsified asphalt mixtures, this paper refers to the AC-20 gradation of hot mix asphalt mixture, and adds 3 mm, 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm sisal fibers to cement emulsified asphalt mixture. The effects of different sisal fiber lengths on the performance of cement emulsified asphalt mixture were investigated by low temperature splitting tests, high temperature stability tests, and water stability tests. The influence of different fiber lengths on the performance of cement emulsified asphalt mixture was investigated by grey correlation theory. The results show that there is a correlation between the length of the sisal fiber and the performance of the cement emulsified asphalt mixture. The length of sisal fiber has the greatest influence on the splitting tensile strength of cement emulsified asphalt mixture, followed by dynamic stability, freeze-thaw splitting strength ratio, immersion Marshall residual stability, vacuum saturation residual stability, and permeability coefficient. The enhancement mechanism of sisal fiber on cement emulsified asphalt mixture was explored by means of infrared spectroscopy and electron microscope scanning. The results show that after adding sisal fiber to cement emulsified asphalt mixture, the overall stability of cement emulsified asphalt mixture is increased under the action of “pulling anchor” of sisal fiber. According to the research results of this paper, it is suggested that sisal fiber with a length of 9 mm is added to cement emulsified asphalt mixture under AC-20 gradation.

Research on the evolution of aggregate skeleton characteristics of asphalt mixture under uniaxial compression loading

The aggregate skeleton is the intrinsic core of asphalt mixtures for load transfer, which is quite different under various gradations. For evaluating the loading characteristics of the aggregate skeleton, this research combined the 3D blue-ray scanning technology and discrete element method (DEM) to establish the numerical models of different graded asphalt mixtures considering the real aggregate morphology. A linear parallel bond model was used to simulate the adhesion effect of asphalt, and the uniaxial compression numerical simulation was verified by indoor tests. In addition, the contact force, contact number, anisotropy, and rotation angle were used to evaluate the aggregate skeleton evolution under uniaxial compression loading. Furthermore, the contribution of each grade aggregate in the gradation to the skeleton structure was analyzed. Results show that the average contact force is higher in large-size aggregates above 9.5 mm, which exhibit greater load transfer efficiency. Moreover, 4.75–9.5 mm size aggregates combine the functions of bearing and filling, and its role is significantly affected by the gradation. It is also found that the internal skeleton structure can be optimized and adjusted under stress. The contact numbers of different graded mixtures follow a close decrease, and the strong contacts are mostly provided by coarse aggregates above 4.75 mm. The anisotropy development of aggregate skeleton contact force is induced by the stress, and the deviator fabric of asphalt mixtures show a good linear positive correlation with the uniaxial compressive strength (UCS). Besides, fine aggregates exhibit greater cumulative rotation angle and instability effect, it is feasible to detect asphalt mixture deformation by the rotation angle of particles.

Exploring the short-term water damage characteristics of asphalt mixtures: The combined effect of salt erosion and dynamic water scouring

In icy or snowy conditions, improper application and uneven dispersion of deicing salts on roadways can lead to saltwater accumulation, subsequently causing roadway scouring when vehicles transit. This study aims to assess the combined influence of salt erosion and dynamic water scouring on short-term water damage of asphalt mixtures. A custom-designed dynamic water scouring simulation apparatus is used, employing three diverse deicing salt solutions as agents for dynamic water scouring. Numerous iterations of dynamic water scouring tests are conducted on two types of graded asphalt mixtures. Post-scouring, alterations in air void content and water stability are evaluated through void content tests, Marshall water immersion tests, and freeze-thaw splitting tests. Additionally, the GM (1,N) damage prediction model from gray theory is applied for data modeling and prediction. The results reveal a significant impact of the combined effects of salt erosion and dynamic water scouring on the short-term performance of asphalt mixtures. In the early phase, dynamic water scouring primarily influences the asphalt composite, augmenting micro-cracks and causing aggregate disintegration. The intermediate phase sees the disintegration of the asphalt membrane by deicing salts, disrupting adhesion between asphalt and aggregate, and progressively leading to the emergence of new micro-cracks. During later stages, dynamic water scouring continues to deteriorate the asphalt composite, building on the erosion instigated by deicing salts, resulting in the expansion of newly formed micro-cracks and further aggregate disintegration. Among the three deicing salts, CH4N2O exhibits the most pronounced impact on short-term water damage, followed by NaCl, while CH2CH3OH has the least effect. Increasing the fine aggregate proportion in the asphalt mixture enhances water damage resistance. The GM (1,N) damage prediction model effectively anticipates air void content and water stability of asphalt mixtures. The research outcomes offer theoretical and technical support for understanding the durability and service lifespan of asphalt pavements in cold regions.

Drainage Performance of Long Longitudinal Slope and High Safety Permeable Asphalt Pavement

Permeable asphalt pavement refers to an asphalt mixture layer with an air void content of more than 18% and internal water permeability and drainage capabilities that can quickly drain away water on the road surface, improve rainy day travel safety, and improve ride comfort. This paper aims to explore the optimal asphalt mixture design for long longitudinal slope pavement (referred to as the FAM mixture). By using CT scanning technology to analyze the air void content of different rotated and compacted asphalt mixture specimens and extensively testing and evaluating the performance of permeable pavement mixtures, the following conclusions are drawn: Based on the research philosophy of functional integration, a new asphalt mixture gradation suitable for long longitudinal slope roads is proposed, with the optimal key factor composition being: 0.075 mm passing rate of 7%, 2.36 mm passing rate of 20%, 9.5 mm passing rate of 55%, and an oil-stone ratio of 4.8%. The FAM mixture was divided into three parts for air void analysis, with the upper part having a slightly higher air void content than the lower part. The air void distribution diagram of the FAM mixture is concave, with higher air void rate curves on both sides and a lower middle curve. Through dynamic modulus testing, the strength requirement for the road asphalt mixture in the pavement structure design was evaluated. It was found that at high temperature conditions (50 °C), the minimum dynamic modulus value of the FAM mixture was 323 MPa, with a peak value of 22,746 MPa at a temperature of −10 °C and a frequency of 25 HZ. The dynamic modulus value at high temperature conditions is lower than at low temperature conditions, while the dynamic modulus value at high frequency conditions is higher than at low frequency conditions. This study provides useful information and experimental data for the design of new asphalt mixtures for long longitudinal slope roads and has conducted in-depth research on the air void distribution and performance of the mixture, providing strong support for related research fields and practical applications.

Characterization of internal pore size distribution and interconnectivity for asphalt concrete with various porosity using 3D CT scanning images

The open pore characteristics of asphalt mixtures play a crucial role in their resistance to water-induced damage. Accurate extraction and analysis of the pore structures at a micro level can reveal the seepage characteristics of asphalt pavements. However, existing studies mainly focus on the through-pore characteristics of porous asphalt mixtures and there is a lack of research on the open pore characteristics and interconnected paths of dense graded asphalt mixtures. This study aims to fill this gap by using 3D X-ray computed tomography technology to analyze the digital images of three typical asphalt mixtures with different porosities. The study quantitatively and statistically analyzes several new pore structure parameters at a micro level, such as porosity, equivalent diameter, coordination number, pore throat dimension, and tortuosity. The interconnected paths of the pores are also compared and analyzed. The results show that as the total pores content increases, the difference between the pore fraction and open pores fraction decreases. The porosity of porous asphalt mixtures is high, but mainly composed of interconnected pores with only a small proportion of closed pores. The coordination number determines the connectivity and thus the porosity of the asphalt mixture, and larger open pore channels lead to larger pore diameters and greater permeability. As the porosity of the asphalt mixture increases, the average coordination number of its internal pores also increases, leading to better pore connectivity and a more complex pore network.

Investigation on flow resistance of fluid in permeable asphalt mixture

Flow resistance distribution of fluid is the basis of comprehensively grasping the permeability of permeable asphalt mixture. This study aimed to investigate the flow resistance of fluid in permeable asphalt mixture. Considering the influence of anisotropy of permeable asphalt mixture, the vertical and transverse permeability tests of five types of permeable asphalt mixture were carried out using multidirectional permeability test instrument developed by our research group. The fitting equation of permeability was determined by comparing Darcy's law with Forchheimer equation. Moreover, the flow resistance is usually considered as an effective parameter to reveal the structural permeability. The connective void content of permeable asphalt mixture is important to calculate flow resistance. Accordingly, it is necessary to obtain the transverse and vertical connective voids of the asphalt mixture considering the influence of anisotropy. Therefore, a program for calculating the multi-directional connective void content was developed based on the theory of projection reconstruction. On this basis, a pore throat model was applied to reveal the variation of flow resistance of asphalt mixture. The results show that the weight of inertia resistance and viscous resistance is different in various seepage velocities. The viscous resistance is dominant when the fluid flow velocity is less than 0.0087 m/s under experimental conditions, and the inertial resistance is dominant when the fluid flow velocity is greater than 0.0087 m/s. The viscous resistance and inertia resistance of fluid are affected by the anisotropy and structure type of permeable asphalt mixture. When the vertical void content decreases by 3.3%, the corresponding viscous and inertial resistance increase by 7.92 kPa/m and 0.84 kPa/m, respectively. For the transverse void, the viscous and inertial resistance increase by 3.19 kPa/m and 2.02 kPa/m respectively as the content decreases by 3.5%. The influence of void structure of permeable asphalt mixtures on fluid flow is revealed from a microscopic perspective, which can be used to guide the optimization design of gradation of permeable asphalt mixtures.

A New Framework for Determining the Gradation of Asphalt Mixtures

Strength and rutting resistance as well as durability are the main quality measures for any asphalt mix. While the strength and resistance of the asphalt mixture to permanent deformation are controlled by the aggregate interlock and aggregate packing, the durability of asphalt mixture depends on adequate volumetric characteristics and film thickness of asphalt mixture. Accordingly, providing an adequate interlock between aggregates and the aggregate packing is of high importance in designing a new asphalt mixture in order to produce desirable volumetric characteristics in asphalt mixture. A new framework for asphalt mixture gradation has been developed and designed following an intensive review of the various currently used approaches. The new framework considers all the controlling factors in the aggregate gradation design for optimum gradation of the asphalt mixtures. Satisfactory interlocking between aggregate particles, proper skeleton within the asphalt mixture, and acceptable volumetric properties are the main parameters to be considered for optimum gradation design for asphalt mix. The framework provides a systematic approach for the gradation process starting from the concentration at different sieves to finally account for the Other parameters including ratio, CA ratio and are also considered through the current framework.

A scientometric study and a bibliometric review of the literature on the design and construction of semi-flexible pavement

In last years, a new type of pavement has gained popularity, this type is called Semi-Flexible Pavement (SFP). It consists of porous asphalt with high air voids between (25-35) % filled with cementitious grout materials. This type of pavement substance offers substantial advantages over both common types of pavements (concrete and flexible) such as good resistance to rutting and durability. SFP is considered an alternative pavement to exceed the drawbacks that occur for both flexible and concrete pavements. SFP has good features against permanent deformation, oil spillage, and fatigue resistance. Previous studies have shown that it can be used in a variety of applications such as highways, motorways, bridge deck pavement, tunnels, industrial areas with industrial equipment traffic, airport aprons, and stations. The goal of this research is to identify and compile the most significant research papers using the Web of Science (WOS), analyze the data using the VOS viewer software, as well as learn which countries and institutions had published the most articles relating to the subject of cementitious grout material as it relates to semi-flexible. It was also done to learn more about the authors and their collaboration. In addition to knowing the keywords that will aid researchers in their research on this topic, using these studies to better understand the elements that affect how well semi-flexible mixtures and grouts perform such as porous asphalt Mixture gradation and grout material components.

Mesoscopic Mechanical Properties of Aggregate Structure in Asphalt Mixtures and Gradation Optimization.

Particle media are widely used in engineering and greatly influence the performance of engineering materials. Asphalt mixtures are multi-phase composite materials, of which coarse aggregates account for more than 60%. These coarse aggregates form a stable structure to transfer and disperse traffic loads. Therefore, knowing how to adjust the structural composition of coarse aggregates to optimize their performance is the key to optimize the performance of asphalt mixtures. In this study, the effects of different roughness and different sizes on the interlocking force and contact force of coarse aggregates were investigated through means of simulation (DEM), and then the formation-evolution mechanism of the coarse aggregate structure and the role of different sizes of aggregates in the coarse aggregate structure were analyzed. Subsequently, the optimal ratio of coarse aggregates was explored through indoor tests, and finally, the gradation of asphalt mixture based on the optimization of fine structure was formed and verified through indoor tests. The results showed that the major model can effectively reveal the role of different types of aggregates in the fine structure and the relationship between the strength of contact forces between them and clarify that the strength of the fine structure increases with the increase in aggregate roughness. Hence, the coarse aggregate structure can be regarded as a contact force transmission system composed of some strong and sub-strong contact forces. Their formation-evolution mechanism can be regarded as a process of the formation of strong and sub-strong contact forces and the transformation from sub-strong contact force to strong contact force. Moreover, the dynamic stability of the optimized graded asphalt mixture was increased by 30%, and the fracture toughness was increased by 26%.

Research on thermal stress fracture performance of low-temperature asphalt concrete in castel high altitude area

The temperature in the southwest Castel highland area is relatively low, and the asphalt concrete on the road surface is in a low-temperature state all year round. Strong ultraviolet radiation will interfere with the material and cause it to fracture and damage. This paper uses a low-temperature bending test and thermal stress constrained specimen test (TSRST) to test the low-temperature performance of asphalt mixtures with different gradation and asphalt types under different ultraviolet (UV) aging conditions. Existing studies are mainly based on asphalt aging, which cannot take into account the interactions between the binder and aggregate phases during aging. This paper analyzes the correlation between test indexes after UV aging and asphalt mixture parameters, as well as the impact of UV on asphalt mixtures, and the mechanical strength prediction model was established. The results indicate that when the aging time is less than 2 months, the low-temperature performance degradation rate of the asphalt mixture first accelerates and then gradually slows down. The degree of influence of ultraviolet radiation on different graded asphalt mixtures is in descending order: stone asphalt concrete, AC 16 asphalt concrete, and AC-13 asphalt concrete. The relationship between fracture thermal stress and asphalt mixture parameters is strong. It is suggested that the appropriate equivalent outdoor aging time is 2 months in the low-temperature performance test of asphalt mixture after UV aging. At the point when there is no UV test condition, the worth acquired by the test is prescribed to consider the UV aging attenuation coefficient, and the matrix asphalt can allude to 0.84; modified asphalt has a value of 0.9. This article is of great significance for guiding the research on thermal stress fracture of low-temperature asphalt concrete in Castel high-altitude areas.

Neural Network Aided Homogenization Approach for Predicting Effective Thermal Conductivity of Composite Construction Materials.

Thermal conductivity is a fundamental material parameter involved in various infrastructure design guides around the world. This paper developed an innovative neural network (NN) aided homogenization approach for predicting the effective thermal conductivity of various composite construction materials. The 2-D meso-structures of dense graded asphalt mixture, porous asphalt mixture, and cement concrete were generated and divided into 2n × 2n square elements with specific thermal conductivity values. A two-layer feed-forward neural network with sigmoid hidden neurons and linear output neurons was built to predict the effective thermal conductivity of the 2 × 2 block. The Levenberg-Marquardt backpropagation algorithm was used to train the network. By repeatedly using the neural network, the effective thermal conductivities of 2-D meso-structures were calculated. The accuracy of the above NN aided homogenization approach was validated with experiment, and various factors affecting the effective thermal conductivity were analyzed. The analysis results show that the accuracy of the NN aided approach is acceptable with relative errors of 1.92~4.34% for the dense graded asphalt mixture, 1.10~6.85% for the porous asphalt mixture, and 1.13~3.14% for the cement concrete. The relative errors for all the materials are lower than 5% when the heterogeneous structures are divided into 512 × 512 elements. Ignoring the actual material meso-structures may lead to significant errors (134.01%) in predicting the effective thermal conductivity of materials with high heterogeneity such as porous asphalt mixture. While proper simplification is acceptable for dense construction composite materials. The effective thermal conductivity of composite cement-asphalt mixtures increases with higher saturation of grouted material. However, the improvement effect of the high-conductive cement paste on the composite cement-asphalt mixtures could be significantly reduced when the cement paste concentrates at the bottom of the mixture. Cracked aggregates and segregation of material components tend to decrease the effective thermal conductivity of construction materials. The NN aided homogenization approach presented in this paper is useful for selecting the effective thermal conductivity of construction materials.

Correlation model between mesostructure and gradation of asphalt mixture based on statistical method

<abstract> <p>Asphalt mixture has complex gradation and mesostructure. Accurate prediction of the relationship between gradation and mesostructure is of great significance for the establishment of mesostructure numerical simulation model and image-based gradation detection. In this paper, featurization, stepwise regression, econometric hypothesis test are utilized for establishing the predicting models. Firstly, asphalt mixtures with 64 kinds of gradation are scanned by Computed Tomography (CT) to obtain the mesostructure images; Then a series of mesostructure parameters of voids and aggregates are put forward. On this basis, the relationship model between gradation and mesostructure is established and verified by featurization and statistical modeling method. The results show that for predicting the passing percentage of the 4.75 mm sieve and the mean value of average distance between aggregate centroids for 9.5–4.75 mm aggregates, the prediction error of passing percentage is acceptable. It illustrates that the relationship model between gradation and mesostructure established by statistical method is effective, and it is significance for material design and testing under the condition of big data in the future.</p> </abstract>

Research on the characteristics of asphalt mixture gradation curve based on Weibull distribution

Gradation design is the critical procedure for asphalt mixture design, a proper mineral gradation could provide excellent volumetric and mechanical properties for asphalt mixture. Most previous studies were focused on the effect of single particle content on the properties of mixture, which could result in uncontrolled and unpredictable mixture performances, and the comprehensive characterization of the entire gradation curve needs to be extensively explored. Therefore, this research proposed a two-parameter Weibull distribution model to describe the aggregate gradation, and the applicability of the Weibull model and the fractal model was compared for different gradations. Besides, the influence of the gradation characteristics parameters on the volumetric indexes of mixture was evaluated by 332 groups of field and experimental gradation design. Finally, the factors influencing the uniaxial compressive strength (UCS) of the porous asphalt concrete were evaluated by the grey correlation analysis, and a multiple regression model for the UCS of mixture was developed. The results indicated that there were linear correlations between gradation characteristics parameters and mixture volumetric indexes, and it was feasible to predict the UCS of asphalt mixture by known material parameters.

Low temperature performances of fiber-reinforced asphalt mixtures for surface, binder, and base layers

In the present study, the effects of adding fibers and Reclaimed Asphalt Pavement (RAP) on the low temperature performances of open graded asphalt mixtures for surface layer and dense asphalt mixtures for surface, binder, and base layers were investigated. Two different kinds of fibers were used: a combination of aramid and polyolefins fibers were utilized for preparing fiber reinforced porous asphalt mixtures, while polyacrylonitrile fibers were employed for producing conventional dense asphalt mixtures for surface, binder, and base layers. Reference mixtures were made with virgin materials as a benchmark to study the effects of the fibers' addition. Moreover, asphalt mixtures for surface layers composed of 30% RAP and mixtures for binder layers containing 50% RAP were produced to study the combined effects of fibers and RAP on the low temperature's performance. Thermal Stress Restrained Specimen, Uniaxial Tension Stress, and Semi-Circular Bending tests were used to evaluate the response against thermal distresses. The addition of the fibers showed no significant effects on the low temperature strength, while a remarkable improvement in the failure temperature and crack propagation resistance properties was found. The use of fibers has also shown to be beneficial in combination with mixtures designed with RAP and higher binder content suggesting a dedicated study on mix design for future research.

Effect of low dosage crumbed rubber on the mechanical properties of a dense graded asphalt mixture

The benefits of crumb rubber modification of bituminous binder for asphalt mixture production is well established. Although most research has used high (20–30% by mass of the bitumen) crumb rubber dosages, there is now interest in low (5–15%) dosages for use in local road surfacing, where mechanical properties are less important. This paper quantifies the effects of low-dosage crumb rubber on the mechanical properties of a typical dense graded local road surface mixture. It was concluded that 5–10% crumb rubber dosage significantly increased the deformation (rutting) resistance and crack (fatigue) resistance of the asphalt. The effect of crumb rubber on mixture stiffness (modulus), moisture damage (stripping) resistance and workability (compactability) was mixed but was unlikely to present any practically important benefit or detriment. Consequently, 5–10% was concluded to be the preferred range of crumb rubber dosage for dense graded asphalt for local road surfacing.

Characterization of Rutting Damage by the Change of Air-Void Characteristics in the Asphalt Mixture Based on Two-Dimensional Image Analysis.

In the process of the rutting test, the air-void characteristics in asphalt mixture specimens are a dynamic change process. It is of great significance to systematically study the correlation between the change of air-void characteristics and the depth of the rutting slab and establish a relationship with damage. In this paper, the air-void information of rutting specimen sections with different loading cycles (500, 1000, 1500, 2000, 2500, and 3000 times) is obtained by two-dimensional image technology. The dynamic change process of the micro characteristics of internal air voids of two graded asphalt mixtures (AC-13 and AC-16) under cyclic wheel load is analyzed, and it is used as an index to characterize the microstructure damage of the asphalt mixture. The results show that the variation of air-void distribution, air-void shape characteristics, and air-void fractal dimension with the loading process can well characterize the permanent deformation law of the rutting slab. The fractal dimension of the air void increases with the increase in load. It is a dynamic process in which the air-void content changes with crack initiation and propagation. After rutting deformation, the total air-void area and average air-void size of the sample increase, and the total air-void number decreases. Because microcracks are formed in the specimen after rutting damage, the aspect ratio of the air void increases, and the roundness value decreases.