Superpave Mix Research Articles

Optimizing asphalt mix design through predicting effective asphalt content and absorbed asphalt content using machine learning

Superpave mix design procedure is still empirical. Random and lengthy trials in a laboratory during the design procedure can consume immense manpower and materials resources. To simplify and accelerate the Superpave mixture design procedure, this study explored the use of machine learning models to achieve an automated and timesaving mix design method through predicting effective asphalt content (Pbe) and absorbed asphalt content (Pba). Five different machine learning (ML) algorithms including Support vector regression (SVR), bagging with ridge regression, Random Forest, Adaptive boosting (AdaBoost), and Gradient boosting were trained. The inputs related to mixture design include aggregates gradation, the bulk specific gravity of aggregates, blend absorption, air void, PG grade of the asphalt binder, and the number of gyrations (Ndes). The kernel density estimation was used to detect outliers of the datasets. The effect of different methods used to encode PG grade, which is categorical variables, on the performance of ML models was analyzed. The performances of ML models were evaluated by calculating different performance scoring metrics, such as coefficient of determination (R2), root means square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE). The improved mix design procedure based on an ML model was proposed. The result showed that compared to other encoding methods, the ordinal encoding method used to encode the variables of PG grade can achieve the best performance of ML models. The Gradient boosting algorithm (R2 = 0.9479, 0.9459) was found as the best estimator to predict the Pbe, and Pba, respectively, compared with those obtained by other machine learning models. Furthermore, determining Pb through predicting Pbe and Pba indirectly with ML models was more accurate than predicting Pb directly with ML models. Therefore, the Gradient boosting model was used in the improved mix design procedure. A case study was implemented to verify the feasibility of the proposed mix design method. The gradation and the optimal asphalt content obtained from the proposed method with the Gradient boosting model was consistent with that obtained by the traditional Superpave method with laboratory tests.

Modelling and evaluating moisture susceptibility of laboratory prepared asphalt concrete mixtures

Moisture susceptibility, one of the key reasons of asphalt concrete (AC) pavement deterioration, lowers the durability of AC pavements. Analyzing and evaluating the combined effect of aggregate gradation and asphalt on moisture susceptibility is critical for avoiding and/or minimizing premature failures of AC mixtures; however, evidence of such combined effect is scant. As such, this paper examines the vulnerability to moisture in laboratory-prepared AC mixtures to establish the impact of differential aggregate gradations (both wearing and base) and bitumen grade. Superpave gyratory compacted mixtures are subjected to indirect tensile strength (ITS) test and are evaluated using tensile strength ratio (TSR). Four wearing course gradations, two base course gradations and two binder grades are considered in this study. The findings of the laboratory tests suggests that Asphalt Institute Manual Series (MS-2) wearing course mix and Superpave mix (SP-2) base course mix prepared with 40/50 binder grade result in higher TSR values, implying relatively better resistance to moisture damage of these AC mixtures compared to other tested mixtures. In addition, the study found that wearing mixtures prepared with 40/50 binder grade reveal 40% more tensile strength compared to the same mixtures prepared with 60/70 binder grade. To study the relationship of moisture susceptibility, a first order multiple linear regression model is developed as a function of percent sieve passing, nominal maximum aggregate size and binder grade. The model being proposed captures data variability with high degree of accuracy. The model is also validated and sensitivity analysis is carried out in order to determine changes in TSR with regard to the explanatory variables. The findings of this research will help in selecting the AC mixtures while considering their sensitivity to moisture damage and the developed model will contribute in evaluating moisture susceptibility of AC mixtures without performing hectic experimental tests.

Effect of Soft Clay on the Volumetric and Mechanical Properties of Hot Mix Asphalt

Abstract. To define the behaviour of asphalt mixture including various penetration grade bitumen has been a major subject of paving engineering. This search investigated the volumetric and mechanical properties of a hot-mix asphalt (HMA) mixture with the Superpave mix design. The mixture was added with powdered soft clay at five different percentages based on the bitumen weight (0%, 2%, 4%, 6%, and 8%). Performance tests were then conducted to determine the resilient modulus and volumetric properties of the mixture. Results show that bulk specific gravity increased after adding soft clay to the asphalt mixture. The amount of air and mineral aggregate voids also decreased with increasing SC contents. Furthermore, the addition of 4% SC improved mixture stiffness, as determined through indirect resilient modulus test under aging conditions. Therefore, soft clay can be added to asphalt mixtures to improve their volumetric and mechanical properties, such as strength and durability.

Comparative study on permanent deformation in asphalt mixtures from indirect tensile strength testing and laboratory wheel tracking

For an asphalt mixture to present rutting resistance, it must have a high shear strength. In an abbreviated protocol, the shear strength of an asphalt mixture can be estimated in the laboratory through the indirect tensile (IDT) strength test and the unconfined compression test, using the Mohr-Coulomb failure theory. So, taking advantage of the simplicity of the IDT test, this research investigated whether the other relationships between stress and strain, derived from the indirect tensile strength test, also demonstrated the potential to explain the shear strength of an asphalt mixture. The correlation between the mechanical properties observed in the stress–strain curve of the asphalt concrete under the indirect tensile strength test and parameters of accumulated permanent deformation with the French wheel tracker was analyzed. The research was conducted with two types of binders and three gradations of granitic aggregates (small, medium, and intermediate) within the same maximum nominal size range adopted by airport agencies, totaling six types of asphalt mixtures. After the Marshall mix design, the mixtures were mechanically tested with a wheel track device. A SUPERPAVE mix design was conducted with two of these mixtures to obtain the Flow Number parameters. Finally, a good relationship was established between the indirect tensile strength test and permanent deformation, using tensile yield modulus and the ratio between total dissipated tensile and compressive energies. The interaction between the two situations predicted by the biaxial stress test (tensile and compression), mainly by the relations between dissipated and recoverable energies and by the tensile parameters, allowed an inference about the shear strength of the material.

Influence of concentration and packing of filler particles on the stiffening effect and shearing behaviour of asphalt mastic

The experimental investigation of the effects of filler-bitumen interaction on the stiffening and shearing characteristics of asphalt mastic is presented in this paper. The role of filler particles in terms of particle dispersion, particle sedimentation rate, particle dissipation energy, and their shearing response as a function of their viscosities under different concentrations was analysed. Structural and geometrical morphological tests of the filler particles were also carried out using the Scanning Electron Microscope (SEM) analysis. A neat bitumen of 60/70 penetration grade and two alternative mineral fillers, namely lime kiln dust (LKD) and dolomite powder (DP), were used to produce asphalt mastic mixture at a filler- bitumen ratio (F/B) of 0.4, 0.8, and 1.2 in accordance with the Superpave mix design dust to binder ratio specification. The two individual fillers particle size gradations, was assessed using a laser diffraction technique. The delta ring and ball, as well as the penetration index tests were conducted to determine the physical properties of the asphalt mastic. The shearing response of the asphalt mastic was also determined using a rotational viscometer (RV) device for various shear values at mastic mixing temperature. The results of the study inferred that the stiffening ability of mineral fillers was more dependent on the physical filler properties, such as particle surface area, voids between the interstices of particles, the concentration of particles, and the crowding distance of the particles in the asphalt mastic. It also revealed that the resistance of a neat bitumen to shearing occurs in a shear-thinning response behaviour, while that of an asphalt mastic occurs more as a shear thickening resistance response. The morphological analysis of both the fillers highlighted the differences in voids, fines, surface area, and particle shape structure of the two fillers.

Development of Performance Grading Map of Nepal Based on Superpave System

The Performance of the bituminous binder plays important role in the overall performance of the pavement system. One of the major cause of pavement failure is the bitumen grade, i.e selection of suitable grade of bitumen. Therefore, performance grading of bituminous binder is inevitable for the specific temperature and climatic zones. This study is focused on the determination of performance grading of bituminous binder for various temperature zones in Nepal. In this study, twenty one years’ daily maximum and minimum secondary temperature data of 70 meteorological stations were collected and were analyzed for temperature zoning. Performance grading of bituminous binder was conducted with the help of Strategic Highway Research Program (SHRP) and Long-Term Pavement Performance Program (LTPP) prediction models. The concept of Superpave has been adopted for the analysis, which stands for superior performing asphalt pavement. The Superpave mix design includes a new analysis system based on performance characteristics of the pavement layer. The bituminous binder grades for Nepal have been determined on the basis of air temperature thereafter predicting the pavement temperatures. The study has determined seven different performance grade zones based on SHRP and four different performance grade zones based on LTPP model. The study synthesized the Performance Grade (PG) map of the country.

Influence of Compaction Method on Rutting Resistance of Hot Mix Asphalt

The main goal of the present investigation is the comparison between conventional Marshall and Superpave design methods for resistance to rutting if applied in the mix design of the wearing course layers in flexible pavements. Detailed work is completed to accomplish the goals of the study by implementing Marshall and Superpave specimens through utilizing aggregate from AL-Taji Quarry and asphalt cement with (40-50) grade from Dourah refinery plant and one sort of mineral filler. Specimens were fabricated by Marshall and Superpave methods and tested by creep tests to evaluate the strain for these mixes. The effect of compaction method and additives were investigated on the performance of these mixes. From the analysis results, it appears that; the Superpave blends are increasingly practical as compared to those with conventional Marshall blends. In addition, adding carbon fibers and lime to the blends decreases the strain mixture. It is additionally seen that the Superpave Gyratory compactor is equipped for accomplishing lower air void contents than the Marshall hammer. Furthermore, the Superpave mix reflects better resistance against permanent deformation. Finally, the present study recognizes the importance of using the Superpave system for design asphalt mix instead of the Marshall method in Iraq.

Design Process of Asphalt Mixture Incorporating Compaction-Effort Variable

AbstractThe Superpave mix design is a process of repeatedly optimizing the aggregate gradation and asphalt content in accordance with specified limits. As one of the important design parameters, th...

Evaluation of Aggregate Crushing Tests and Their Correlation with Superpave Mix Design Properties

AbstractThis paper evaluated alternative test methods to determine the crushing potential of aggregates and documented the influence of aggregate characteristics on the engineering properties of as...

Packing Theory and Volumetrics-Based Aggregate Gradation Design Method

AbstractCurrent gradation design in Superpave mix design method is an empirical-based trial-and-error method, which is costly and time-consuming. Moreover, few mechanical properties have been evalu...

Effect of Aggregate Gradation on Performance of Asphalt Concrete Mixtures

AbstractThis paper investigates the process of selecting the aggregate gradation according to the Superpave mix design specifications and evaluates the volumetric properties and mechanical performa...

Effect of Aggregate Gradation on Rutting of Thin Asphalt Overlay

Permanent deformation (rutting) of asphalt pavements has a major impact on the service life of pavements. Rutting reduces the performance of the pavement and produces serious hazards for highway users. Due to the axle loads incensement, and high local summer temperature, rutting became the major distress in flexible pavements for many countries. Recently, thin asphalt overlay (TAO) is recommended as a significant remedy technique for deteriorated pavements. Aggregates are one of the main structure materials asphalt paving mixtures, whereas, aggregate properties remarkably effected on the asphalt pavements performance. Aggregate gradation is representing the significant feature of aggregates that affecting permanent deformation of traditional hot mix asphalt (HMA) thick pavement layers. The aim of this study is to examine the influence of aggregate gradation differences on rutting features of modified TAO mixtures that comprising waste polymers. The evaluation process included the preparation of polymer modified asphalt (PMA) comprising two types of additives, namely, Crumb Rubber Modifier (CRM) and Low-Density Polyethylene (LDPE). CRM and LDPE in the form of fines that have a particle size under 250 um were used as additives to liquid neat asphalt, individually and collectively by weight of virgin asphalt; i.e., PMA included 15.0% of CRM and (2.5. %, 5.0%, 7.5% and 10.0% of LDPE. Three types of aggregate gradations were used, i.e. 12.5, 9.5 and 4.75mm, Nominal maximum aggregate size, (NMAS). The Superpave mix design system was adopted in volumetric proportioning of prepared mixtures, while Wheel Tracking (WT) test was used to determine the rut depth characteristics for prepared mixtures. about 30 asphalt concrete specimens were prepared to forecast the TAO behavior concerning permanent deformation for wearing course type III A and B according to State Corporation of Roads and Bridges in Iraq, while for 4.75mm, NMAS (sand asphalt layer) an abroad specification was used. Results demonstrated that the aggregate gradation plays a vital role in increasing permanent deformation for several type of TAO mixtures. Also, the addition of CRM by 15% to the neat asphalt led to an increase in the resistance of the mixture to permanent deformation. Moreover, PMA with LDPE became hardener (higher viscosity) which led to increase binder stiffness, whereas a consequent is stiffening the mixture. Therefore, optimizing aggregate gradation with PMA including waste polymers can limited the rutting occurrence distinguishably

Performance testing of asphalt paving mixtures for hot condition using tension–compression test

In this paper, laboratory experiments were conducted on two different asphalt mixes, one using the Marshall mix design method (MMD) and the second using modified Marshall mix design (3M) method. The 3M method is based on the incorporation of two factors, the new asphalt binders (performance grade) and the Superpave gyratory compactor (SGC) as in Superpave mix design method, into the traditional MMD method. All specimens had the same mixtures of aggregate gradation incorporated with two different compaction methods and two asphalt grades using two different classification methods: asphalt cement binder (B60-70) based on the penetration test (Pen system) and PG 70-10 based on performance grade system (PG). However, there were some errors at low temperature (− 25, − 10 °C) and high temperature (54 °C), so these values may be discarded. The tension–compression complex modulus test |E*| is dependent on temperature and loading frequency. Thus, the results of this test will give a more accurate representation of the absolute value of the tension–compression complex modulus test |E*| that defines the elastic properties of a linear viscoelastic material subjected to a sinusoidal loading. In addition, 2-complex modulus (E*) and phase angles (ΦE*) in the test have been measured at temperatures of − 25, − 10, − 5, 10, 25, 35 and 54 °C as well as frequencies of 25, 10, 5, 1, 0.5 and 0.1 Hz. The value of the dynamic modulus reflects the stiffness of the mixture and its resistance to deformation at a designated frequency and temperature. The results show an improvement in the |E*| in the modified 3M mix over the traditional MMD mix. The 3M method using asphalt binder PG 70-10 and gyratory compactor (SGC) as in Superpave mix design method, improves the |E*| of the asphalt mixture in HA climate. As well, intrinsic characteristics related to binder properties, aggregate gradation and compaction method in HA climate have the most significant effect on the predicted |E*|.

Evaluation of Workability and Mechanical Properties of Stone Matrix Asphalt Mixtures Made With and Without Stabilizing Additives

Stone matrix asphalt (SMA) is a gap-graded mixture which is the combination of higher concentration of coarse aggregate and binder mortar. The coarse aggregate skeleton provides the mixture with stone-on-stone contact, giving it strength, while the high binder content mortar adds durability. The mortar is typically composed of fine aggregate, mineral filler, binder, and a stabilizing additive. A stabilizing additive such as cellulose fibers, mineral fibers, or polymers is added to SMA mixtures to prevent draindown of the mastics. In addition, it has the potential of reinforcing and improving the tensile strength of SMA mixtures. This paper presents the findings of performance of SMA mixtures with and without stabilizing additive. Superpave mix design, draindown, fatigue, rutting, workability, and moisture-induced damage properties of the SMA mixtures was evaluated. Three types of stabilizing additives (B, S, and V), one nominal maximum aggregate size (NMAS) 13.0 mm, and an unmodified asphalt binder (VG-30) were used in the study. Results indicate that the addition of stabilizing additive controls binder draindown and mix design properties of SMA mixtures satisfies the IRC SP 79 requirements. Resistance to rutting, fatigue, and moisture-induced damage of SMA with stabilizing additives were higher than SMA mixture without stabilizing additive. Further, SMA mixture without stabilizing additive takes less energy for densification compared with SMA mixture with stabilizing additives.

Sensitivity of the Superpave mix design method to different methods for determining the maximum specific gravity

This study aimed to analyze the influence of different methodologies to determine the maximum specific gravity on the Superpave mix design method. The comparative analysis focused on the volumetric parameters, on the choice of the design particle size and, consequently, on the respective design asphalt binder contents of the studied asphalt mixtures. Regarding the particularities of the research, there were no significant differences in the design binder contents obtained using the two adopted methodologies for determining the maximum specific gravity. From a practical point of view, the adoption of any of the methods interfered little with the results of the application of the Superpave mix design method. This fact demonstrates a quality of this method since similar researches based on the Marshall design method evidences the sensitivity of the protocol for determining the asphalt binder content in relation to the used type of maximum specific gravity.

A Study on the Design Method for the Material Composition of Small Particle-Size Asphalt Mixture for Controlling Cracks in Asphalt Pavement

Generally, various kinds of cracks are the main type of distresses during the service period of asphalt pavements. To save maintenance costs and improve the crack resistance of asphalt pavements effectively, this paper presents a unique design method for the material composition of small particle-size (SPS) asphalt mixture for controlling cracks in asphalt pavement. First, Stone Mastic Asphalt (SMA)-II was designed as a basic gradation according to the A.N. Talbot curve and SMA-II-1, SMA-II-2 and SMA-II-3 were designed according to the Superpave mix design method, the Bailey method and the Particle interference theory, respectively. Second, based on Marshall test results, the optimal fiber content and optimal asphalt content of three gradations were determined. Then, the influence of the passing rate of 1.18-mm sieve and 0.075-mm sieve on the air voids of SMA-II and the influence of the filler-asphalt ratio on the performance of SMA-II were investigated, and an appropriate range of filler-asphalt ratio was obtained. Finally, a high-temperature performance test, a water stability test, and a skid resistance test demonstrate that the overall performance of SMA-II can satisfy the specifications. A low-temperature bend test and analysis of bending strain energy density show that SMA-II with a crumb rubber modifier and a polymer fiber has better crack resistance performance than SMA-I (SBS-modified mixture). Life-cycle cost analysis shows the economic advantage of SPS asphalt thin overlays over traditional AC-13 thin overlays.

Evaluation of the hot mix asphalt compactability utilizing the impact compaction method

This study investigates possibility of utilizing an accelerometer to evaluate compactability of hot mix asphalt compacted with an impact hammer. For over 50 years Marshall Asphalt Mix Design has been the principal choice for the asphalt mix designers around the world. Although the United States has almost entirely moved to Superpave Mix Design, the rest of the world nations still choose the Marshall Method. The investigation was conducted with the accelerometer placed on the falling mass of the Marshall Hammer and acceleration data was stored and analyzed. Data obtained from the accelerometer was filtered and the asphalt mix response after each blow was analyzed. Results from the study showed that during impact compaction, a so-called locking point exists. This point is defined as the first blow when the peak acceleration and the impact time become stable. When this point is reached, further compaction has a noticeably lower effect on decreasing air void content. A Superpave Gyratory Compactor was used to confirm the results obtained with the impact hammer, and a correlation was established.

SUPERPAVE VOLUMETRIC MIX DESIGN OF HOT MIX ASPHALT: CASE STUDY OF ISPARTA

The pavement design system that a generic method of designing mixtures custom to the unique performance requirements enforced by the heavy traffic volumes, maximum and minimum temperatures and structural part at specific pavement section is the SUperior PERforming Asphalt PAVEment (Superpave) Mix design. Accomplishing the needed grade of pavement performance Superpave Mix Design enables selecting and assembling asphalt binder, aggregate. Superpave system is practicable to raw and reclaimed, hot mix asphalt (HMA). Also, Superpave performance tests are practicable for defining a diversity of specialized mixtures. Superpave Mix Design thoroughly addresses the degradation and permanent deformation and low-temperature cracking discipline owing to material choice and mixture designing. Furthermore, it takes into consideration moisture sensitivity impacts for supporting or striking these distresses to improve. The objective of State of the Art is to present an overview of Superpave volumetric mix design procedure with a case study of Isparta region in accordance with literature.

Application of mechanistic empirical approach to predict rutting of superpave mixtures in Iraq

In Iraq rutting is considered as a real distress in flexible pavements as a result of high summer temperature, and increased axle loads. This distress majorly affects asphalt pavement performance, lessens the pavement useful service life and makes serious hazards for highway users. Performance of HMA mixtures against rutting using Mechanistic- Empirical approach is predicted by considering Wheel-Tracking test and employing the Superpave mix design requirements. Roller Wheel Compactor has been locally manufactured to prepare slab specimens. In view of study laboratory outcomes that are judged to be simulative of field loading conditions, models are developed for predicting permanent strain of compacted samples of local asphalt concrete mixtures after considering the stress level, properties of local material and environmental impacts variables. All in all, laboratory results were produced utilizing statistical analysis with the aid of SPSS software. Permanent strain models for asphalt concrete mixtures were developed as a function of: number of passes, temperature, asphalt content, viscosity, air voids and additive content. Mechanistic Empirical design approach through the MnPAVE software was applied to characterize rutting in HMA and to predict allowable number of loading repetitions of mixtures as a function of expected traffic loads, material properties, and environmental temperature.

Evaluation of Moisture and Ageing Effects on Calcium Carbonite Nanoparticles Modified Asphalt Mixtures

Flexible pavements deteriorate and crack with time due to the frequent traffic load imposed upon it. Many studies have been done to predict the effects of frequent traffic load and environmental conditions on pavements in the effort to find the best pavement design which resist deterioration and ensure longer pavement service time. This study investigates the effect of mixing asphalt with varying percentages of nano calcium carbonate (CaCO3), namely 0, 2, 4, and 6 %. The mixtures were designed based on the Superpave mix design criteria. Investigation was done using several tests, namely resilient modulus, indirect tensile strength, moisture susceptibility, and dynamic modulus tests. Samples were subjected to aging to determine their resilient modulus. The results of the investigation show that resilient modulus and indirect tensile strength increased when higher percentages of nanoparticles were added to asphalt mixture, with improvement of 138 and 48.18% respectively. Modified binders showed up to 17% improvement in moisture susceptibility comparison to base asphalt mixture, while the result of dynamic modulus test showed that the stiffness of modified asphalt increased 76.69%. The investigation also found that adding 6% CaCO3 nanoparticles to asphalt produced modified asphalt with the best performance. In addition, the results show that the modified asphalt with CaCO3 is suitable for hot and humid regions (tropical countries) in the field of highways construction, as the modifier was able to mitigate the influences of high-temperature rutting and moisture damage.