Asphalt Concrete Mix Design Research Articles

Harmonizing Flexible Pavement Rutting Design with Balanced Mix Design

The state-of-the-practice in asphalt concrete mix design and pavement structural design are two divergent concepts. The simulative laboratory performance tests such as Hamburg Wheel Tracking (HWT) and Asphalt Pavement Analyzer (APA) that are used primarily for balanced mix design are pragmatically accelerated surrogate tests developed to ensure the stability or ranking of mixes. Pavement structural design methods, being empirical or mechanistic-empirical, do not consider these laboratory test results in their analyses, in favor of other fundamental mechanical parameters such as dynamic modulus. As such, the selection of the type of mix to be placed on a project is based on the local experience, and a set of consensus limits, rather than the demand of the pavement section. A harmonized strategy that integrates the results from mix tests with the pavement structure, material properties, environmental conditions, and traffic levels can lead to an optimized pavement system. A framework is proposed to incorporate the laboratory HWT and APA device results into the rutting analysis associated with most mechanistic-empirical structural design algorithms. The proposed framework was applied to the results from two accelerated pavement testing facilities and six in-service pavement test sections to demonstrate its feasibility. The proposed strategy can be potentially used to predict the rutting life of the pavement reasonably well. By balancing the rutting demand of an asphalt layer with the rutting capacity of a given mix, the proposed method can potentially lend itself to the use of local materials for a more economical and sustainable pavement structure.

Leaching of PAHs from rubber modified asphalt pavements

The present study aimed to, for the first time, quantify the total content of 16 priority EPA PAHs in end-of-life tyre derived crumb rubber granulates and various manufactured rubberised asphalt mix designs. After identifying the availability of 16 EPA PAHs, the leaching behaviour of rubberised asphalt specimens, were evaluated using the Dynamic Surface Leaching Test (DSLT) based on CEN/TS 16637-2:2014 standard. This was prior to modelling the release mechanisms of PAHs by utilizing a mathematical diffusion-controlled leaching model. According to the results, the total content of 16 EPA PAHs in crumb rubber granulates ranged between 0.061 and 8.322 μg/g, which were associated with acenaphthene and pyrene, respectively. The total content of PAHs in rubberised asphalt specimens varied between 0.019 and 4.992 μg/g depending on the volume of crumb rubber granulates in the asphalt concrete mix design, and type of binder. Results of the leaching experiments revealed that the highest leached PAHs were benzo[b]fluoranthene, benzo[k]fluoranthene and naphthalene with a 64-days cumulative release per specimen surface area > 1 μg/m2. Acenaphthylene, fluoranthene, fluorene and indeno[1,2,3-c,d]pyrene were released in cumulative concentrations between 0.1 and 1 μg/m2. The PAHs with a cumulative release potential below 0.1 μg/m2 during DSLT were benzo[a]anthracene, benzo[a]pyrene, benzo[g,h,i]perylene and chrysene. The diffusion coefficients, which were calculated by mathematical modelling of DSLT data, revealed that the leaching process of 16 EPA PAHs from surface of rubberised asphalt concrete mix designs fitted all the criteria set by the NEN 7345 standard for diffusion-controlled leaching during all stages of leaching experiments.

The effect of using activated dates seed on Hot Mix Asphalt performance

The increasing demand for construction materials and the need to improve the performance of asphalt mixes have led to the depletion of available resources of aggregates. Lots of aggregate alternatives had been studied to partially or fully replace aggregate in asphalt concrete mixes. Indeed, date seeds are found easily in Kuwait. Their properties; such as light weight, very low crushing strength, and low impact value; represent a potential domain to enhance asphalt mix performance. The main objective of this paper is investigating the possibility of using activated date seeds additives in Hot Mix Asphalt (HMA) as a partial replacement of Fine Aggregates (sand). A total of 3 asphalt concrete mixes with different percentages by weight were prepared. Physical and mechanical properties of date seeds and Fine Aggregates (sand) were determined and compared in the asphalt concrete mix design of ratios 7, 10, and 15%. Compressive Strength and Marshall Stability tests were performed to investigate the effect of activated date seeds additives on HMA. Eventually, the findings indicated that the ratio of 10% gave the highest Marshall Stability. On the other hand, the ratio of 7% found to give the highest retained strength index. a deeper statistical analysis is performed to evaluate the robustness and significance of studied factors on response variables represented in Marshal Stability and Flow. The first part of the analysis included recognizing data outliers in data sets and eliminating them to compare basic statistical values with raw data. The minor differences in these values implies minor variability in the measurement and indicates minimal experimental error. T-test analysis was performed to study the influence of date seed percentages on different performed measurements. ANOVA tests were also represented to demonstrate the statistical significance factors on considered response variables. The results supported the significant influence of the included measurements on Marshal stability and flow values.

Laterite Rock Modified Asphalt Concrete Mix Design Properties and Swell Behaviour under Soaked Conditions for Rural Roads

Laterite Rock Modified Asphalt Concrete Mix Design Properties and Swell Behaviour under Soaked Conditions for Rural Roads

Micromechanical modeling of I-FIT asphalt concrete specimens

Analytical and numerical micromechanical models have been previously used to understand fracture behavior of heterogeneous materials like Portland cement concrete or asphalt concrete (AC). In this study, the behavior of asphalt concrete was studied during a semi-circular bending (SCB) fracture test, Illinois Flexibility Index Test (I-FIT), using micromechanical level finite element models. The models were validated in multiple steps using the strain fields calculated with the digital image correlation (DIC) technique as well as the global scale forces measured in the same experiment. The micromechanical model was developed to evaluate the effects of microstructural features such as aggregate gradation, aggregate distribution, and void space on fracture behavior of AC. The model focused on pre-peak behavior and assumed that AC consists of aggregates and mortar. Aggregates were considered linear elastic with material constants reported in the literature, while the mortar was assumed linear viscoelastic. Mortar was defined as the combination of binder, air voids, and material passing 2.36 mm sieve. Mixture theory was utilized to characterize the mortar as viscoelastic using binder’s dynamic shear rheometer results, elastic properties of fine aggregate material, and air voids volume from the AC mix design. The validated FEM was used to perform a parametric study aimed at determining the effect of aggregate gradation and binder properties on the applied load, opening strains and stresses, and energy around the crack tip. Nine aggregate gradations and three binders were studied; ten replicates for each aggregate gradation-binder combination were considered. In order to create the replicates, a Python script that fabricates artificial aggregate gradations and randomly distributes aggregates in the I-FIT geometry was created. It was found that mortar properties, rather than air voids, binder content, or fine material, were heavily correlated to energy and applied load of the I-FIT specimen.

Application of compressible packing model for optimization of asphalt concrete mix design

Packing of an aggregate blend is a measure reflecting how solid part and air voids would share the volume occupied by the blend. It is usually measured in terms of “packing density”. In this paper, Compressible Packing Model (CPM) is described as a potential technique to optimize aggregate blend by optimizing the packing density in asphalt mixes. Gradation envelops for high-performance asphalt mixes or Enrobé à Module Élevé (EME) were determined for two different mix types (12.5 mm NMAS and 19 mm NMAS) using CPM. Further, asphalt mixes were fabricated using two types of modified asphalt binders. Compactibility and volumetrics of the mixes were assessed. Dynamic modulus test was performed to evaluate the rheological behavior of the mixes at elevated temperatures as well as loading frequencies to develop master curves. Results of this study showed that the gradation limits obtained from CPM were very close to the grading control points of EME mixes and that the asphalt mixes had higher compactibility than the conventional mix. Dynamic modulus test results also depicted the designed mixes could meet stiffness requirement of EME mixes, and the mixes behaved more elastically.

Experimental Characterization of Rutting Performance of HMA Designed with Aggregate Gradations According to Superpave and Marshall Methods

The permanent deformation (rutting) of pavement is a major distress in flexible pavement. It is related to vehicles properties and/or pavement materials and conditions. This article presents an extensive experimental investigation in order to compare between the aggregate gradation according to Superpave and Marshall methods of asphalt concrete mix design on pavement rutting and to examine the sensitivity of rutting resistance to aggregate gradation. A wheel truck machine has been used for measurement of pavement rutting (permanent deformation). The tests were carried out at two controlled different air temperature 55℃ and 25℃. The results obtained showed that the adopting of aggregate gradation procedure of Superpave method of pavement mix design for Marshall method of asphalt concrete mix design can reduce the pavement rutting by about 50%. This achievement may be related to missing of three sieves in aggregate gradation procedure of Marshall method which controls rounded and finer aggregate particles. These sieves provide more continuity for aggregate gradation to ensure filling unnecessary gaps and produce more contact points between the aggregates in Hot Mix Asphalt (HMA). The outputs of the research support modifying Marshall method of asphalt concrete mix design by adopting aggregate gradation proposed in Superpave method. The results of study also showed that the coarser aggregate provided more resistance to pavement rutting.

A Performance-based Evaluation of Superpave Design Gyrations for High Traffic Surface Mixes

The number of design gyrations (Ndes) is an extremely important parameter in the asphalt concrete mix design procedure using the Superpave method. The choice of Ndes is a function of total traffic during the pavement service life, expressed in ESALs. Asphalt concrete mixes for higher traffic levels are compacted to a higher Ndes as a denser mix resists rutting more effectively. However, this leads to a lower design asphalt content, which decreases fatigue performance of the mix. Therefore, a performance-oriented approach to determine Ndes was developed that optimizes mix performance with respect to both rutting and fatigue cracking.In this paper, the research methodology adopted to compare the relative performance of surface mixes with 12.5mm nominal maximum aggregate size is presented, along with recommended Ndes values for C and D-level mixes, designed to handle traffic levels of 3-30 Million and greater than 30 Million ESALs, respectively. Asphalt concrete mixes were designed at Ndes levels of 50, 75, 100 and 125 gyrations to determine asphalt content using Superpave design method. Dynamic modulus (E*) was measured at design asphalt content for different gyration levels using the Asphalt Mixture Performance Tester device. The E* data and corresponding binder properties were used as input in the AASHTO Darwin-ME software to predict rutting and fatigue performance of the mixes by assuming a model pavement section and appropriate traffic levels. Relative performance indicators were developed for both rutting and fatigue, and plotted against the asphalt content to determine optimum Ndes. For both surface mixes, the optimum Ndes value was determined to be 85 gyrations.

CRITICAL EVALUATION OF ASPHALT CONCRETE MIXES CONTAINING GRANULAR VOLCANIC ASH MATERIAL

Granular volcanic ash material is spread over considerable parts of Yemen, including urban and suburban areas. Due to the inferior properties of this material in its natural state, it can not be used as a foundation layer either for roads or buildings. However, when improved it can be used in different applications. A recent study by the author has indicated that using granular volcanic ash as a partial replacement of conventional basalt aggregate in hot asphalt concrete mixes is technically feasible. All conventional criteria requirements suggested by Marshal Mix Design Method for hot asphalt concrete mix design were achieved with samples at different levels of granular volcanic ash content. In this paper, further evaluation was performed to provide critical evaluation of some important mix characteristics. Samples, at different volcanic ash content, were prepared at optimum asphalt content and subjected to different advanced tests. These include dynamic creep, modulus of resilient, fatigue and permanent deformation tests. Results indicated that mixes containing volcanic ash aggregate had performed well in terms of creep and permanent deformation. However, improvements in fatigue life and in modulus of resilience were observed at volcanic ash contents up to 10% and 20%, respectively. Further investigation is recommended to find ways for improving the properties of volcanic ash material so that the negative trends in fatigue life and modulus of resilience can be dealt with at higher volcanic ash content.

Using X-ray computed tomography to study paving materials

X-ray computed tomography, a non-destructive three-dimensional imaging tool, has been very helpful in medical diagnosis since the first commercial tomographs were constructed in 1973. In recent years it has gained increasing applications in civil engineering materials research. Several investigators have illustrated the use of computed tomography scans for the non-destructive evaluation of soils and have shown promising applications in characterisation, modelling and computational simulation to optimise asphalt concrete mix design, predict performance and conduct investigative forensic studies. This paper provides a detailed review of X-ray computed tomography applications in characterising asphalt concrete and also describes preliminary studies conducted at the Center for Nondestructive Evaluation (CNDE) at Iowa State University for characterising asphalt and concrete materials using X-ray microcomputed tomography or micro-computed tomography. Researchers are currently using the advanced imaging facilities available at the CNDE to develop a deeper understanding of the pavement internal structure, to develop and optimise the various parameters that describe the internal structure and to relate them to the performance of pavements in a scientific way. This will provide the foundations for building more durable and long-lasting transportation infrastructure systems.

Effects of Asphalt Content and Air Void Content on Mix Fatigue and Stiffness

The primary objective of most procedures for asphalt concrete mix design is to find an asphalt content that minimizes the possibility of stability failure while providing adequate fatigue and other durability characteristics. To date, the consequences of asphalt content selection and construction compaction on fatigue performance and flexural stiffness have not been thoroughly investigated and documented with experimental data. The results of laboratory-controlled strain flexural beam testing, (i.e., fatigue life and flexural stiffness) for one aggregate and asphalt cement combination, five asphalt contents, and three air void contents are presented. The results clearly indicate the benefits of a lower air void content on both fatigue life and initial stiffness. Increased asphalt content was found to increase fatigue life and reduce stiffness. Alternative models for predicting fatigue life and initial stiffness using asphalt content, air void content, voids filled with bitumen, and the volume concentrations of asphalt and aggregate were evaluated. Elastic-layer theory was used to simulate the effects of air void content and asphalt content on the fatigue life of several example overlays using the models for stiffness and fatigue life from the laboratory testing. The simulations indicated an increase in predicted pavement fatigue life for lower air void contents and higher asphalt contents. Example simulations of the effects of increased asphalt content and decreased air void content at the bottom of thick overlays indicated a marked increase in predicted fatigue life. It was also concluded that stiffness should not be included in regression for fatigue life models for mix design unless there is a clear understanding of the effects of other variables in the model that correlate with both fatigue life and stiffness.

Effects of Asphalt Content and Air Void Content on Mix Fatigue and Stiffness

The primary objective of most procedures for asphalt concrete mix design is to find an asphalt content that minimizes the possibility of stability failure while providing adequate fatigue and other durability characteristics. To date, the consequences of asphalt content selection and construction compaction on fatigue performance and flexural stiffness have not been thoroughly investigated and documented with experimental data. The results of laboratory-controlled strain flexural beam testing, (i.e., fatigue life and flexural stiffness) for one aggregate and asphalt cement combination, five asphalt contents, and three air void contents are presented. The results clearly indicate the benefits of a lower air void content on both fatigue life and initial stiffness. Increased asphalt content was found to increase fatigue life and reduce stiffness. Alternative models for predicting fatigue life and initial stiffness using asphalt content, air void content, voids filled with bitumen, and the volume concentrations of asphalt and aggregate were evaluated. Elastic-layer theory was used to simulate the effects of air void content and asphalt content on the fatigue life of several example overlays using the models for stiffness and fatigue life from the laboratory testing. The simulations indicated an increase in predicted pavement fatigue life for lower air void contents and higher asphalt contents. Example simulations of the effects of increased asphalt content and decreased air void content at the bottom of thick overlays indicated a marked increase in predicted fatigue life. It was also concluded that stiffness should not be included in regression for fatigue life models for mix design unless there is a clear understanding of the effects of other variables in the model that correlate with both fatigue life and stiffness.

Experimental Analysis and Numerical Simulation of Marshall Method of Asphalt Concrete Mix Design

Abstract The results of a numerical simulation of the Marshall testing procedure used in asphalt concrete mix design are reported in this work. The numerical simulation uses the finite element method to model both the asphalt concrete specimen as well as the surrounding testing heads. Linear elastic material behavior and plane stress conditions are assumed to hold in the finite element analysis of the Marshall testing procedure. The elastic modulus required for this analysis is obtained from a separate unconfined compression test on long cylidrical specimens made of the same asphalt concrete mixture as that used in the Marshall test. Although the assumption of linear elastic material behavior is restrictive, a qualitative picture of the displacements and stresses developed in the specimen during the Marshall test emerges from this work.

Properties of Asphalt-Stabilized Aggregates from Evaluation of Laboratory Prepared Specimens

Abstract The tensile and resilient characteristics of the cold-mixed asphalt-stabilized aggregates were investigated in the laboratory using the indirect tensile and resilient modulus techniques. The mixture was also characterized by using the Marshall equipment that is frequently used in asphalt concrete mix design. Specimens were fabricated with emulsified asphalt, two aggregate types, two emulsion contents, and two initial added moisture contents. The properties of the mixture were evaluated at different curing conditions and test temperatures. Comparisons were made between dry and vacuum saturated specimens to evaluate the moisture resistance of the mixture. It was found that the mixture properties were largely affected by temperature. In addition, curing increased the tensile resistance and the resilient modulus values. Aggregate type, asphalt content, and initial added moisture content altered the properties of the mixture at different degrees. Vacuum saturation affected the mixture characteristics to some extent. Other properties such as density, moisture content, and air voids were evaluated.