Superpave Mix Design Research Articles

Risk and expected pay factor analysis for assessing gap and dense-graded Superpave mixture specifications

With the implementation of the Superpave mix design method, some state highway agencies have experienced significant problems in durability of hot mix asphalt (HMA) mixtures due to lower binder content. With the adoption of revised HMA specifications for the state of Maryland, it was desired to evaluate the potential risks to both agency and contractors. This was achieved by calculating the α and β risks through the construction of operating characteristic curves. Furthermore, simulation analyses were conducted for assessing the impact of the current HMA production quality on the specification tolerances percent within specification limits and mixture pay factor. The findings of this study are based on a large set of quality control and quality acceptance data since the analyses were based on 7 consecutive years of production and paving of Superpave mixtures in the state. The risk analysis indicated that the agency bears a significant risk on accepting low-quality material, and thus changes in the current State Highway Administration specification are needed and discussed in this paper. The simulation analysis illustrated that the correlation among mixture parameters had minimal impact on pay factors. Furthermore, it was concluded that the asphalt content has a more pronounced impact on the pay factor than any other mixture property. Overall, the analysis indicated that significant changes in the acceptance specifications are needed in order to reduce the risks of accepting lower quality, or rejecting good quality, HMA mixtures. Furthermore, changes of the order of 10%, 20% even 50% in specification tolerances represent feasible and currently achievable levels of production quality by the paving industry, and thus no increase in the production cost of HMA is expected. Such change in the specification tolerances is expected to promote an overall improvement in quality of Superpave mixtures in the state and the region. The approach used in this study can be used by highway agencies and the pavement industry to evaluate risks related to the acceptance of hot asphalt mixtures. The pay factor analysis can aid in adjusting pay schedules and specification tolerances for accepting higher quality materials.

Evaluation of stiffness to predict rutting resistance of hot-mix asphalt: a Canadian case study

This paper investigates the relationship between the stiffness and rutting resistance of hot-mix asphalt. Ten different types of hot-mix asphalt were examined. The Superpave mix design method was utilized to produce nine mixes; the remaining mix was designed using the Marshall method. The asphalt mixes were tested for stiffness and rutting resistance under the Centre for Pavement and Transportation Technology research program at the University of Waterloo. The stiffness was determined by the laboratory resilient and dynamic moduli tests. The dynamic modulus test was conducted at six different loading frequencies and five different temperatures. The rutting test was executed by the Hamburg Wheel Rut Tester and the French Laboratory Rutting Tester to obtain rutting depth. The regression analysis was performed to examine the relationships of resilient and dynamic moduli with rutting depth. The results of the regression analysis revealed that resilient modulus did not correlate well with rutting depth. In contrast, dynamic modulus showed strong correlation with rutting depth for a number of loading frequencies and temperatures. The strong relationship was observed at the higher temperatures of +46.1 oC and +54.4 oC. Moreover, the relationship between dynamic modulus and rutting depth was better for lower loading cycles/wheel passes applied in the rutting test. It was also noticed that dynamic modulus exhibited a better relationship with rutting depth obtained from the French Laboratory Rutting Tester. The overall findings indicate that the dynamic moduli obtained at 0.1–1.0 Hz and +46.1–(+54.4) oC are useful to predict the rutting resistance of hot-mix asphalt.

Investigation into hot-mix asphalt moisture-induced damage under tropical climatic conditions

A major concern for highway industries in tropical climatic countries is the excessive moisture-induced damage to hot-mix asphalt (HMA) pavements as a result of frequent passes by heavy axle loads. Therefore, in this study, two different approaches, the Superpave and Marshall mix design methods, were used to design HMA mixes and a comparison was made to identify how susceptible these mixtures are to moisture damage. The Modified Lottman test and Simple Performance Test (SPT) were performed on unconditioned and conditioned specimens tailored to suit tropical climatic conditions, omitting freeze and thaw. The Modified Lottman test showed that the tensile strength values of Superpave-designed mixtures are higher than Marshall-designed mixtures. The tensile strength ratio (TSR) values decreased from unconditioned to conditioned specimens, suggesting that there is damage to the mixtures. The results also show good agreement between the TSR and ESR in the two tests, with a coefficient of determination value of 0.78. This relationship indicates that the SPT dynamic modulus test was effective and suitable to evaluate the lab-measured moisture susceptibility of HMA mixes. Since the dynamic modulus test provides a full characterisation of the mix over a broad range of temperatures and loading frequencies, this test is highly recommended for Superpave mixture characterisation in tropical climatic conditions.

중온화 액상형 화학첨가제 개발과 이를 적용한 중온 아스팔트의 성능 평가

PURPOSES: The liquid-type chemical warm-mix asphalt (WMA) additive has been developed. This study evaluates the basic properties of the additive and the mechanical properties of WMA asphalt and mixture manufactured by using the newly developed chemical additive. METHODS: First, the newly developed WMA additive was applied to the original asphalt by various composition of additive components and dosage ratio of additive. These WMA asphalt binders were evaluated in terms of penetration, softening point, rotational viscosity, and PG grade. Based on the binder test results, one best candidate was chosen to apply to the mixture and then the mechanical properties of WMA mixture were evaluated for moisture susceptibility, dynamic modulus, and rutting and fatigue resistance. RESULTS : According to the binder test, WMA asphalt binders showed the similar properties to the original asphalt binder except the penetraion index of WMA additive was a little higher than original binder. From the Superpave mix design, the optimum asphalt content and volumetric properties of WMA mixture were almost the same with those of hot mix asphalt (HMA) mixture even though the production and compaction temperatures were <TEX>$30^{\circ}C$</TEX> lower for the WMA mixture. From the first set of performance evaluation, it was found that the WMA mixture would have some problem in moisture susceptibility. The additive was modified to improve the resistance to moisture and the second set of performance evaluation showed that the WMA mixture with modified chemical additive would have the similar performance to HMA mixture. CONCLUSIONS : Based on the various laboratory tests, it was concluded that the newly developed chemical WMA additve could be successfully used to produce the WMA mixture with the comparable performance to the HMA mixture. These laboratory evaluations should be confirmed by applying this additive to the field and monitoring the long-term performance of the pavement, which are scheduled in the near future.

An artificial neural network model for virtual Superpave asphalt mixture design

This study presents an artificial neural network (ANN) model to predict the asphalt mixture volumetrics at Superpave gyration levels. The input data-set needed by the algorithm is composed of gradation of the mix, bulk specific gravity of aggregates, low- and high-performance grade of the binder, binder content of the mix and the target number of gyrations (i.e. Nini, Ndes and Nmax). The proposed ANN model uses a three-layer scaled conjugate gradient back-propagation (feed-forward) network. The ANN was trained using data obtained from numerous roads with a total of 1817 different mix designs. Results revealed that the ANN was able to predict Va within Va (measured) ± 1.0% range 85–93% of the time and within Va (measured) ± 0.5% range 60–70% of the time. Currently with the developed ANN model, Superpave mix design can take approximately between 1.5 and 4.5 days, which corresponds to 3–6 days of savings.

Design a Thermosetting Asphalt Mixture for Surfacing on Orthotropic Steel Deck Bridge

According to Superpave mix design method, a thermosetting material (Epoxy Asphalt mixture) was designed for surfacing on orthotropic steel deck bridge. Firstly, based on the thermosetting feature, the viscosity increasing law of EA binder was studied by Brookfield test. Then, some characteristic indexes of EA mixture, such as the prior mixing time and the reserved time, were determined according to the viscosity increasing law and recommended viscosity range for mixing and compaction. Finally, using these characteristic indexes, an EA mixture with 3.0% air voids was designed by volumetric mixture design procedure of Superpave method. The results show: 1) different from other asphalt mixtures, the characteristic indexes of end mixing time and reserved time should be applied in EA mixture design because of the thermosetting character of EA binder; 2) the EA mixture designed by Superpave method in this paper has a higher EA binder content than that designed by conventional Marshall method.

Laboratory evaluation of the mechanical properties of plant-produced warm-mix asphalt mixtures

This paper presents a laboratory evaluation of plant-produced asphalt mixtures containing the control hot-mix asphalt (HMA) and four warm-mix asphalt (WMA) technologies: an organic additive (Sasobit®) and three foaming processes (Advera®, low-emission asphalt, and Gencor). These asphalt mixtures were produced using a single binder performance grade (PG 64-22) and 9.5-mm nominal maximum aggregate size Superpave mix design compacted to 75 design gyrations. Dynamic modulus (E*), flow number, and Hamburg wheel–track tests were utilised to evaluate the mechanical properties of the asphalt mixtures. The PG of the asphalt binders containing the WMA technologies was also verified. In addition, their rheological properties were evaluated using shear modulus master curves and multiple stress creep recovery tests. It was found that the asphalt binder containing Sasobit® technology increased the continuous high-temperature binder grade by 6°C and measured higher elastic properties. In general, the asphalt mixture prepared with Sasobit® technology and the control HMA mixture measured higher stiffness than those prepared with the other WMA technologies and measured the highest dynamic modulus rutting parameter and fatigue cracking parameter. In addition, these mixtures demonstrated increased resistance to rutting and moisture damage. Statistical analysis indicated that the binder rheological properties, WMA dosage rates, and production temperatures influenced the performance of the WMA mixtures.

Application of discrete element method to Superpave gyratory compaction

Superpave mix design method is one of the major asphalt mixture design methods and has been widely used worldwide. However, the Superpave laboratory mix design process is time-consuming and requires significant human and material resources. In this study, the discrete element method (DEM) was used to simulate the compaction of hot-mix asphalt (HMA) with the Superpave gyratory compactor (SGC). The open source DEM code, YADE, was modified and implemented with C++programming language to conduct virtual SGC compaction. The effects of aggregate gradation, gyration number, gyration angle, and parameters of contact model during the SGC compaction were investigated. Also, the clump technique was utilised to study the effect of aggregate shape. To verify the DEM simulation results, a laboratory SGC compaction was conducted. The results from the DEM virtual compaction were generally in agreement with the experimental data, indicating that DEM provides a feasible way to simulate asphalt mixture compaction. With further research, DEM has the potential to be a helpful tool for aggregate selection in asphalt mix design.

Preliminary evaluation of the materials in Egypt for Superpave implementation

The Egyptian code of practice for the design of asphalt mixtures is based on Marshall mix design methodology. There is a significant shift to Superpave mix design worldwide and Egypt is one of the countries that is expected to follow this shift. For the transition to be smooth and easy for practitioners, an analysis was done to evaluate the compliance of the gradation bands available in the current Egyptian code of practice to Superpave requirements. This showed that only a few of the gradation bands could still be used with Superpave mix design, and these only with some considerations. Four gradations were developed from two of the gradation bands, and these mixes were designed using both Superpave and Marshall mix design methods. The Superpave mix design samples were tested for stability and flow. A comparison was made between both designs. The results showed that Superpave mix design yielded lower optimum binder content and that its samples had higher values of stability and flow.

Criteria for using the Superpave gyratory compactor to design airport HMA mixtures

Asphalt concrete pavements for commercial airport applications in the USA are constructed according to guidelines in Item P-401, ‘Plant Mix Bituminous Pavements’, Federal Aviation Administration (FAA) Advisory Circular 150/5370-10E. Item P-401 specifies the material characteristics and construction requirements for airport asphalt pavements, but does not currently provide guidance for using the Superpave gyratory compactor (SGC) in the preparation of specimens used in the design of hot mix asphalt (HMA) mixtures. Nearly all state departments of transportation in the USA use the SGC along with the Superpave mix design procedure. Since most HMA mixes are used in roadways, many asphalt contractors no longer maintain expertise and equipment for conducting the Marshall mix design procedure currently used by the FAA. The lack of contractors familiar with the Marshall method may become a significant problem for the FAA in the future. This paper describes a laboratory study of the HMA mix design for airport pavements, which uses the SGC. The purpose of the study was to determine the number of gyrations with the SGC needed to design asphalt pavement mixtures for airports. A value of 70 gyrations is recommended for further evaluations based on the comparisons of volumetric measurements of HMA mixture specimens compacted using Marshall compaction with specimens from the same mixture compacted using Superpave gyratory compaction.

On the Road to Sustainability

Most state departments of transportation (DOTs) adopted the Superpave® mix design method in the late 1990s. The Superpave mix design method replaced the Marshall method and became mainstream. Superpave came with aggregate, binder, and mix requirements to control rutting and cracking. With a life expectancy of about 15 years, many Superpave roads are now becoming candidates for resurfacing or recycling. Can Superpave mixes undergo hot in-place recycling with success? In fact, Superpave mixes contain expensive and high-quality aggregates, which meet the consensus properties, and high-quality binder, which meets the performance grade (PG) requirements. If these mixes can be recycled in place and meet the original Superpave properties, then substantial savings can be realized. The potential savings are in the 30% to 50% range of the cost to mill and resurface. In addition, emissions could be reduced by 70%, while 100% of the existing material could be reused. This paper reports on an experiment conducted in Gainesville, Florida, in 2010 at the Florida DOT State Materials Office, in which a Superpave mix underwent the hot in-place recycling process. The properties of the aggregate, binder, and mix were compared to answer certain questions about aggregate degradation, binder rejuvenation, and mix properties. The answers to these questions shed light on the possibility of the 100% recycle of Superpave mixes. The results showed that minimal aggregate degradation took place. The recycled mixes met Superpave gradation requirements for the most part. The rejuvenated binder met or exceeded the PG requirement. The mix could be engineered to meet the air voids requirement of Superpave.

Disruption factor of asphalt mixtures

Typically, aggregate gradation is selected to meet Superpave mix design specification; however, many Superpave mixtures have exhibited deficient field performance. The porosity of the dominant aggregate size range (DASR), which is the primary structural network of aggregates, has been extensively validated as a tool to evaluate coarse aggregate structure of laboratory and field asphalt mixtures. Mixtures identified by the system as having poor or marginal gradations resulted in poor rutting resistance. This study focused on how asphalt mixture performance is affected by changes in interstitial component (IC), which is the material between DASR particles. Laboratory testing clearly showed that IC characteristics may have a significant effect on rutting and cracking performance of mixtures. The disruption factor (DF) was developed to evaluate the potential of IC aggregates to disrupt the DASR structure. DF satisfactorily distinguished poor performing mixtures; therefore, it may eventually be used in combination with DASR porosity as a design parameter for rutting and cracking resistant asphalt mixtures.

Evaluation of Superpave HMA Mixture Properties at the Plant versus behind the Paver: Statistical Comparison of QC and QA Data

State highway agencies concerned with lower asphalt levels and potential durability problems in hot-mix asphalt (HMA) mixtures designed with superior performing asphalt pavements (Superpave) have lead efforts to explore strategies for improving Superpave mix design. This study addressed the differences in HMA properties that have been observed over the years between samples taken at the plant versus behind the paver for Superpave designed mixtures in Maryland. A large set of Maryland State Highway Administration (MSHA) quality assurance (QA) and quality control (QC) data were analyzed statistically in the context of current specifications. Statistical analysis found that the means and standard deviations of the QC and QA data represent different populations. Because the material leaving the asphalt plant is the same material that is compacted behind the paver, some relationship between the plant and field properties is expected. However, attempts to define transfer functions between QA and QC measurements to use both data sets in HMA acceptance testing encountered low levels of statistical significance.

Feasibility of Superpave gyratory compaction of rubberized asphalt concrete mixtures containing reclaimed asphalt pavement

Recently, some specific materials such as ground crumb rubber are widely being used to save money (e.g. longer life) and protect the environment. In addition, the utilization of reclaimed asphalt pavement (RAP) is an acceptable practice in many states. However, the use of these materials in the Superpave mix design system is not standardized, so it is essential to investigate whether a rubberized asphalt concrete (RAC) mixture containing RAP can be used in the Superpave mix design procedure. In general, the use of RAP in the past has proven to be economical, environmentally sound, and effective for enhancing the engineering properties of asphalt mixtures. Crumb rubber has also been used successfully in improving the mechanical characteristics of an HMA mixture. The objective of this research was to investigate the feasibility of the Superpave mix design of rubberized asphalt mixtures containing RAP through volumetric analysis of various mixtures with respect to crumb rubber type, percentage and RAP percentage in the mixture. The results of this limited study indicated that increasing the rubber content led to an increase of the optimum binder content; the two rubber types had good workability with virgin and RAP mixtures; and the Superpave mix design method and volumetric analysis can be used for the rubberized asphalt mixtures containing RAP.

The application of Recycled Concrete Aggregate (RCA) for Hot Mix Asphalt (HMA) base layer aggregate

Recycled Concrete Aggregate (RCA) is different from natural aggregate because of RCA’s cement paste and contaminants that cause low density and high porosity. In many cases, these properties of RCA that lead to poor engineering qualities are the major reasons that RCA is not recommended as aggregate for Hot Mix Asphalt (HMA). In this research, the performance of HMA mixtures with RCA is quantitatively evaluated using various tests to verify the applicability of RCA as aggregate for HMA material. For this verification, the Indirect Tensile (IDT) strength test, Kim test, wheel tracking test, and tensile strength ratio test accompanied by fundamental material property tests were performed on asphalt mixtures with four types of aggregate blends. In addition, asphalt mixtures with RCA, whose binder contents were determined from the Superpave mix design method, were utilized and evaluated against Marshall design criteria in order to effectively reflect both field specifications and field compaction conditions in South Korea. As a result of this study, it is observed that the study asphalt mixtures with RCA (Mixes II and III) show good performance compared to the asphalt mixture with natural aggregate only (Mix I) in terms of indirect tensile strength ratio, deformation strength, rut depth, and IDT strength, whereas Mix IV, which consists of coarse and fine RCA, does not exhibit good performance. By evaluating the Marshall test properties of each mixture, it is also concluded that the dynamic loading in the Marshall test compaction method possibly causes friction in the RCA of the asphalt mixtures and, therefore, leads to an underestimation of the engineering properties of HMA with RCA.

Polyvoids: Analytical Tool for Superpave HMA Design

This paper demonstrates the application of the polygon of voids, or “polyvoids,” as an analytical technique to produce a hot-mix asphalt (HMA) job-formula based only on voids specifications, to Superpave hot-mix asphalt design and analysis. Polyvoids is one of the original analytical tools of RAMCODES (an acronym for rational methodology for compacted geomaterials’ densification and strength analysis). Functions for the definition of voids (i.e., air voids, voids in mineral aggregate, and voids filled with asphalt) as used in this paper are the same as found in the Asphalt Institute’s MS-2: Mix Design Methods and SP-2: Superpave Mix Design manuals. Definition and construction of polyvoids are herein described completely from a logical point of view. The polyvoids centroid is proposed as the job-formula or optimum-binder content for HMA design, based on voids specifications only. Three actual examples of Superpave hot-mix design were used to prove that the asphalt-binder content of the centroid is roughly ...

Evaluation of North Dakota's 4.75-mm Superpave Mixes for Thin Overlay Applications

Because of the decline in aggregate supplies and the need for durable and rut-resistant hot-mix asphalt (HMA), the use of surplus fine aggregates in 4.75-mm mixes could be beneficial for HMA producers, aggregate suppliers, and highway agencies. The primary focus of this paper is to describe the development of and evaluate 4.75-mm Superpave® mixes for use in thin overlays on non-Interstate highway pavements and maintenance applications. The asphalt pavement analyzer (APA) is used to examine the rut resistance of the 4.75-mm mixes. The acceptable APA rut depth was specified to be 9.5 mm. Because of the nature of the 4.75-mm mixes, the Superpave mix design was adjusted to avoid the production of mixes with excessive asphalt contents. A 6% air void design was crucial for the success of North Dakota's 4.75-mm mixes. The research study entailed four mix design cases involving two binders and two aggregate blends with different proportions of natural and crushed fines. Laboratory specimens were produced at 7.0% air voids, heated to either 64°C or 58°C for 6 h, and made to endure 8,000 APA loading cycles. The results indicate that all mix design cases were rut resistant and that mixes with higher percentages of crushed fines performed the best. For the design cases in which only the asphalt binder grade (PG) is the variable, the specimens were tested at different temperatures, so the results could not be compared, but a trend for an increase in rut depth with higher asphalt concrete contents was observed. Trial mixes with high percentages of natural fines failed the APA rut depth tests.

Analysis of Aggregate Gradation and Packing for Easy Estimation of Hot-Mix-Asphalt Voids in Mineral Aggregate

The voids in mineral aggregate (VMA) design parameter is one of the most important in the current Superpave mix design procedure that links hot-mix-asphalt (HMA) mix properties to field performance. The success of achieving the appropriate VMA at an early stage of the mix-design process not only significantly impacts the design time and effort but also can produce an economical and reasonable design with good field performance. Although several current mix and gradation design methods have provided some guidance on adjusting gradation to achieve target VMA, these approaches still have to rely on initial experimental results with some degree of trial and error, and provide no direct correlation between aggregate gradation and VMA. This paper presents an analysis of aggregate packing and discrete-element modeling (DEM) simulation to link the aggregate gradation property to the VMA of HMA. A new definition is proposed for characterizing traditional dense-graded aggregate gradations into three types: coarse-graded, medium-graded, and fine-graded. A gradation weighing factor, fv, defined as the percentage of voids change by volume caused by unit additional aggregate, is developed to theoretically evaluate the packing of an aggregate structure. A method of VMA estimation based on the generated fv values is thus provided. Eleven mix designs from different states are used for verifying the accuracy of the prediction. Most predictions are within 1% difference of the design VMA. Using one nominal maximum aggregate size (NMAS) of 12.5 mm as an example, this study provided a promising method for a fast and accurate VMA estimation. It can be used directly in the HMA mix design to reduce the design time and effort, and contribute to the estimation of the HMA mixture performance at an early stage of the design period.

Comparison of the rutting potential of paving mixes produced from different asphalt binders with the same superpave high-temperature performance

Asphalt binders with the same high-temperature performance grade (PG 64-xx), but prepared by different methods to cover the spectrum of conventional, oxidized, and polymer and crumb rubber modified binders, were selected for the testing of the rutting potential of paving mixes with these asphalt binders. The rutting potential of the paving mixes was studied using the wheel-tracking test. Moving loads were applied through wheels with solid rubber tires, which traveled with a reciprocating motion on two gyratory compacted cylindrical specimens that were paired together. Gyratory compaction was employed to compact the test mixes to achieve uniform density and air void distribution within individual specimens. The asphalt mixes were compacted using the same aggregate gradation, according to the Superpave mix design. The machine allowed rut tests to be conducted at different temperatures. The results of a test program are reported to demonstrate the effects of asphalt binders and the temperature on rut development in asphalt mixes.

Performance based binder type selection using mixed integer programming technique

The rationale behind an asphalt mix design is optimizing the binder content for the desired aggregate gradation to satisfy the specified volumetric and strength requirements. The designed asphalt mix should be durable and cost effective. The mechanical behavior of a designed asphalt mix is affected by the traffic loading and climatic variations. To improve the mechanical properties of asphalt mixes, additives are added to the base asphalt binder. These binders are called modified asphalt binders. The objectives of the present study are to compare the performance of asphalt mixes with different binders by two different mix design methods and to optimize the asphalt binder type to achieve the desired performance. Two methods of mix design namely, Marshall and Superpave mix design methods are considered. The performances of asphalt mixes viz., tensile strength, moisture damage, densification and rutting resistance were compared. The results indicated a statistically significant difference in the optimum asphalt binder content from the two mix design methods. The Marshall method of asphalt mix design is found to yield lower optimal asphalt binder content when compared to the Superpave method of mix design. The moisture susceptibility and construction densification index of asphalt mixes designed using Superpave method were found to be significantly lower than that of the mixes designed by Marshall method. Optimization using a Mixed Integer Linear Program (MILP) indicated that the polymer modified asphalt binder outperforms the requirements of engineering properties when compared to other commercial binders used in the study.