Superpave Mix Research Articles

Acceleration of Superpave Mix Design: Solving Multi-Objective Optimization Problems Using Machine Learning and the Non-Dominated Sorting Genetic Algorithm-II

Acceleration of Superpave Mix Design: Solving Multi-Objective Optimization Problems Using Machine Learning and the Non-Dominated Sorting Genetic Algorithm-II

Case Study on Using Warm Mix Asphalt at Reduced Production Temperatures for Balanced Mix Design

This study provides a case study to illustrate the feasibility of using warm mix asphalt (WMA) at lower production temperatures to design asphalt mixtures with balanced rutting and cracking resistance in a laboratory setting. Two balanced mix design (BMD) modification approaches were evaluated to modify an existing Superpave mix design with unbalanced performance because of inadequate cracking resistance: (1) adding asphalt binder and (2) using WMA with a surfactant-based chemical additive. The modified mix designs were tested with the indirect tensile asphalt cracking test and high-temperature indirect tensile strength test to determine compliance with the Alabama Department of Transportation’s (ALDOT’s) BMD performance requirements. The original and modified mix designs were then tested in the modified overlay test to characterize their reflective cracking resistance, and the results were input into the Texas Asphalt Concrete Overlay Design System (TxACOL) software for theoretical asphalt overlay design simulations. Finally, asphalt binder testing was conducted to determine the impact of BMD modifications on the rheological properties of extracted binders. Laboratory testing showed that both BMD modifications improved the cracking resistance of the mix design but through different mechanisms. All the modified mix designs met ALDOT’s BMD requirements with balanced rutting and cracking resistance at their corresponding optimum binder content (OBC), which was 0.4%–0.7% higher than the volumetric OBC, respectively. TxACOL simulations showed that BMD modifications significantly improved the predicted reflective cracking performance and service life of asphalt overlays, but the improvement varied depending on the underlying pavement and traffic conditions.

Performance Evaluation of Steel Slag on Hot Mix Asphalt Mixture

Researchers have been actively exploring alternative substances to modify asphalt mixtures and improve their qualities. While asphalt has been the traditional binder used in road construction due to its excellent adhesive and waterproofing properties. In this investigation, an assessment is conducted in a laboratory environment to evaluate the effectiveness of incorporating recycled steel slag as an addition in hot mix asphalt. The utilization of the Superpave mix design methodology was employed in this study to modify fine steel slag with a particle size of 300 m. Various percentages of steel slag modifier, namely 5%, 10%, 15%, and 20% of the total weight of the fine aggregate, were incorporated. The outcomes of this investigation revealed that the mixtures containing steel slag exhibited superior performance compared to those without any slag addition, serving as the control sample (0% (slag. The inclusion of steel slag in the asphalt mixes has demonstrated a significant enhancement in stability while concurrently reducing the levels of permanent deformation. The outcomes derived from the study indicate that asphalt mixtures containing steel slag additives at varying proportions (5%, 10%, 15%, and 20% by weight of the fine aggregates) exhibited superior performance in terms of the indirect tensile modulus test, static creep test, and dynamic creep test when compared to the control sample. Notably, the results highlight that the incorporation of 15% steel slag yielded the most favorable overall performance values among the tested asphalt mixes.

Evaluating and quantifying the variations and sensitivity in asphalt-filler interaction indices

The interaction within an asphalt-filler blend is usually defined by its volume filling and interfacial reciprocation tendencies. This interplay between a reinforcing solid filler within liquid asphalt thus ends up dictating the blend's transition point from a “diluted region” to a “concentrated region”, and the glass transitioning state of the asphalt itself. While prior studies focused on distinguishing asphalt-filler interactions based on composite reinforcement models, describing the definitive behaviour of its suffusing phase reciprocation has proved elusive. Hence, this study aims at redefining asphalt-filler interaction by evaluating and quantifying the varying distinctions in each established mastic composite model. Asphalt mastics composed of three distinct fillers of dolomite powder (DP), lime kiln dust (LKD), and ordinary Portland cement (OPC), along with a conventional PEN 60/70 binder, were blended together at 0.4, 0.8, and 1.2 filler to binder ratios (F/B) based on the Superpave mix dust to binder specification. The OPC mastic was regarded as the control mastic sample for all tests performed. A temperature sweep test was conducted on all prepared mastic test samples using dynamic shear rheometer equipment at varying temperatures of 46 °C, 52 °C, 58 °C, 64 °C, 70 °C, 76 °C, and 82 °C, for a controlled strain value of 5%, and an angular velocity of 10 rad/s. Asphalt-filler interaction was further analysed using evaluation index coefficients based on rheological performances, i.e., ΔG*, L-A-δ, K-B-δ, K-B-G*, and KE respectively. Variations in the evaluation coefficients obtained were also determined via statistical normality tests of skewness and kurtosis. Results obtained indicated a strong asphalt-filler interaction response for coefficients ΔG*, L-A-δ, K-B-G*, and KE, while K-B-δ exhibited inconsistent interaction responses. Similarly, the normality test results also inferred that ΔG*, L-A-δ, K-B-G*, and KE portrayed better skewness values compared to K-B-δ.

Use of Basic Oxygen Furnace Slag (BOFS) in Superpave Mix Design: BOFS Aggregate Properties

This research aims to evaluate the properties of basic oxygen furnace slag (BOFS) as aggregates used in Superior Performing Asphalt Pavements (Superpave) mix design. A total of five different aggregates, including one limestone and four BOFS aggregates with different ages, were evaluated by the following aggregate properties: specific gravity, water absorption, Los Angles abrasion, aggregate crushing value, angularity, flakiness, soundness (sulfate chemical and freeze-thaw resistance), and expansion characteristics. Then, the volume stability of the hot mix asphalt (HMA) mixture was also discussed based on the aging effect of BOFS aggregate. Test results indicated that aged BOFS aggregate performs better than unaged BOFS aggregate: Aged BOFS aggregate has lower water absorption, lower aggregate crushing value, higher abrasion resistance, and less expansion. The flakiness and angularity of BOFS aggregates were satisfied with Superpave criteria. However, if free-lime (f-CaO) and free magnesium (f-MgO) in BOFS aggregate exist, it may cause the volume stability of asphalt mixtures with BOFS aggregate. In conclusion, if BOFS is appropriately aged and weathered, BOFS can be an alternative to conventional aggregate.

Modified asphalt-rubber green pavement (MARGPave) mixtures: Product development and performance assessment

The major objective of this study was to develop “Modified Asphalt-Rubber Green Pavement (MARGPave)” mixtures with dense- and gap-graded aggregate structures to accomplish performance attributes superior to the conventional asphalt-rubber mixtures. The scope encompassed production of one conventional dense-graded, one dense-graded MARGPave, one gap-graded MARGPave, and one gap-graded asphalt-rubber mixtures using the Superpave mix design, conduct of stiffness modulus tests, moisture sensitivity, and fatigue evaluation at varying temperature-frequency combinations, which generated over 300 data points. The dense-graded MARGPave mix exhibited three times higher fatigue life and increased durability than the conventional dense-graded mix. The gap-graded MARGPave mix had lower modulus at all temperatures by more than 50% than the dense-graded MARGPave mix due to 2% higher asphalt content and rubber inclusions. Likewise, the modulus of gap-graded MARGPave mix was higher than gap-graded asphalt-rubber mix across all temperatures and frequencies, indicative of the elastic nature of the MARGPave mix due to higher rubber content. Higher modulus at higher temperatures and lower modulus at lower temperatures were concurrently displayed by dense-graded MARGPave mix, which indicated that the material would be resistant against rutting and low-temperature thermal cracking, thereby able to outperform conventional materials with insignificant rate of change of viscosity with increasing temperatures, and the presence of rubber particles that would render the mix the necessary additional resilience to endure the mix performance for the entire design life. It is noteworthy that the procedure of blending asphalt binder, aggregates, and the modified asphalt-rubber product that replaces some portions of fine aggregates helped create MARGPave mixtures that was found akin to the semi-dry process technology. It is envisioned that the indigenously developed MARGPave mixtures will be best suited as a roadway construction and maintenance strategy that supports the engineering use of end-of-life tires, encouraging the waste-to-wealth concept.

Stiffness evaluation of Forta Fibre Reinforced Asphalt Concrete (FRAC) mixture under different pulse repetition load

Pavement structure can be designed either as a flexible or a rigid pavement based on its structural behaviour, with flexible pavements being frequently favored due to its advantages. One of the major problems that normally occurred in road construction was pavement distresses due to the quality of the materials. Numerous studies were carried out to explore sustainable ways to improve the pavement performance especially on modification of the asphaltic concrete in construction phases. This paper investigates the effect of Forta-Fi fiber on stiffness performance of hot mix asphalt mixture (HMA). In this respect, conventional asphalt binder grade 60/70 and Nominal Maximum Aggregate Size (NMAS) 12.5mm were used in the preparation of asphalt mixture specimens as specified in Superpave mix design method. Performance of modified samples incorporating 0.3, 0.5 and 0.7% of total mixture were evaluated for resilient modulus accordance to ASTM D4123 using Universal Testing Machine (UTM). The samples were tested at 25°C and 40°C with pulse repetition period 1000ms, 2000ms and 3000ms to simulate low, medium and high volume of traffic. As a result, the resilient modulus values of modified asphalt mixture improved 38% with 0.3% additive of Forta-Fi at 25°C with 3000ms pulse repetition period, while at 40°C with 3000ms pulse repetition period improved 23% with 0.5% additive of Forta-Fi. Based on these studies, the addition of fibers reinforcement into the asphalt mixture has a significant effect on resilient modulus of fibers reinforced asphalt mixture.

The effect of mix design method on performance of asphalt mixtures containing reclaimed asphalt pavement and recycling agents: Superpave versus balanced mix design

The balanced mix design (BMD) is an alternative method to determine the Optimum Binder Content (OBC) of asphalt mixtures that considers both volumetric and performance properties. However, the feasibility of using this method for designing asphalt mixtures with high reclaimed asphalt pavement (RAP) materials (e.g., 25% and 50%) without and with different types of recycling agents (RAs) needs to be further investigated. To this end, the OBC of asphalt mixtures was first determined through Superpave Mix Design (SMD) by considering volumetric properties. Then mixtures using OBC and OBC ± 0.6% were prepared. Three mechanical tests, including Hamburg Wheel Tracking (HWT), Illinois Flexibility Index (I-FIT), and Indirect Tensile Strength (ITS) in dry and wet conditions, were utilized for high-temperature rutting, mid-temperature cracking, and moisture damage resistance characterization, respectively. The results showed that the RAP-blended mixtures with and without RAs prepared with the OBCs could pass rutting and moisture damage resistance criteria while the cracking resistance of these mixtures was lower than the accepted threshold, except control mixture (i.e., C). Although introducing the RAs to the RAP blended mixtures improved their cracking resistance, an increase in OBC is still needed in RAP mixtures in order to meet the cracking resistance requirement. It was concluded that the SMD might not be an appropriate method for designing the mixtures containing high-RAP materials with and without RAs and these mixtures need to be designed using the BMD method. Among the three RAs evaluated in this study, the aromatic extract RA had the most influence on the rutting performance regardless of the RAP content, while mixtures treated by the aromatic extract RA showed the best cracking resistance.

Evaluation the Usage of Local Materials in HMA Surface Layer

The importance of roads and all the facilities related to the mobility of people, goods, and vehicles in the world exceed the social and economic significance but play a main role in politics and government decisions. As a result of the increasing population in Iraq and the dramatical growth in heavy vehicles twenty years ago and due to the rising percentage of new construction projects in the country, the need appeared to assess and improve the hot mix asphalt layers used in the construction of flexible pavements. In this research, a hot mix asphalt surface layer was used with a 12.5 mm nominal maximum aggregate size from one aggregate source (Al Nibaie quarry) and one penetration grade type of asphalt binder (40 -50), also in this research work has been added one type of polymers by several percentages namely, Crumb Rubber Modifier (CRM) to enhance the properties of asphalt binder which in turn improves HMA. The evaluation process included the preparation of two types of mixtures (unmodified and modified mixtures) by using the Superpave mix design method and to estimate the ability of mixtures to resist the three main types of failure that may be flexible pavement exposed to, Wheel track test was used to simulate the permanent deformation resistance of mixtures, flexural beam fatigue test to determine the fatigue cracking resistance of mixtures and indirect Tensile Strength test was used to determine the strength to moisture damage for prepared mixtures. Results demonstrated that adding modified waste polymer to the asphalt cement with different percentages significantly improved mechanical and durability properties.

Climate change and asphalt binder selection across ontario: A quantitative analysis towards the end of the century

The climate across the world and especially across Canada is becoming warmer. Recent research suggests that, on average, past and projected warming in Canada are about twice those of global values. As part of the Superpave Mix design system, Performance Grade (PG) of the asphalt binder is selected based on historical climatic conditions in relation to the expected in-service temperature spectrum of the pavement surface. Given the effects of climate change, it is important to ascertain how projected ambient conditions may impact pavement surface temperatures and therefore the suitable PG towards more durable and resilient pavement construction in the future. In this study, new regression models, to predict pavement surface temperatures, were developed using air temperatures and latitude of a site. These models were developed to determine the relationships between asphalt pavement surface temperature and ambient weather data from weather stations within the Ontario Ministry of Transportation's Road Weather Information System (RWIS). The developed models were used to predict the pavement temperatures for future climate data from different Global Circulation Models (GCMs) and Representative Concentration Pathways (RCPs), and the results were compared with that of latest Long-Term Pavement Performance (LTPP) models. According to the results of this study, based on the scale of the expected warming, changes in the asphalt binder grades across Ontario are expected in the future. The results of this study also suggest that different types of PGs including 52–34, 58–28, 64–28and 70–22 may need to be adopted by the end-century. This study provides practical recommendations that road authorities and planners may use to adapt paving materials to changing temperature conditions.

Dynamic Creep Performance of Hot Mix Asphalt Mixture Incorporating Fibre

Permanent deformation is one of the distress that develops gradually as the number of load applications increases and appears as longitudinal depressions in the wheel paths and small upheavals to the sides. For this reason, numerous studies conducted on modification asphalt binder or mixture by various fibre. This paper presents the evaluation of creep modulus and permanent deformation of modified asphalt mixture with fibres. In order to envisage the modified asphalt mixture, Forta-fi, Kenaf and PET was blended to estimate the creep properties and rut depth value at different loading pattern. Superpave mix design method was employed with NMAS 12.5mm to obtain the optimum bitumen content established at 4% air void. In the respect, bitumen 60/70 penetration grade with 0.5% of Forta-Fi, 0.1% Kenaf fibre and 0.5% PET by weight of asphalt mixture were prepared. Dynamic Creep Test was performed in accordance withthe EN 12697-25:2005 guidelines using the Universal Testing Machine (UTM). As the result, the minimum value of permanent deformation was found at 0.5% of PET. Based on these studies, adding a minimum percent of PET in the asphalt mixture shows a better resistance to rutting deformation and enable a better understanding of the properties in modified asphalt mixtures.

Relationship between the physicochemical and electrostatic charge characteristics of filler materials on the morphological and adhesive Pull-Off tensile strength of asphalt mastics

• This paper assesses the viability of using mineral fillers from industrial by-products. • Lime kiln dust and dolomite powder were studied and compared to cement powder. • Changes in asphalt binder phases occur as a result of asphalt-filler interactions. • The pH conditions dictate mastics adhesive tendencies due to electrostatic ionic exchange. • Thus, impacting pull-off strengths within asphalt-aggregate interfaces. The influence of filler particle mineralogy, pH and electrostatic charge on the adhesive tensile strength and morphological structure of asphalt mastic composites were assessed in this study. Three different fillers i.e., dolomite powder (DP), lime kiln dust (LKD), and ordinary Portland cement (OPC) together with a conventional PEN 60/70 binder were used for the asphalt mastic preparation. The mastics were mixed at dosages of (0.4, 0.8, and 1.2) filler to binder concentration (F/B) by volume as per the dust to binder specifications of Superpave mix designs. OPC mastic was utilised as the control mastic sample for all conducted tests, while the DP and LKD mastics were tested as sustainable alternatives to the OPC. The impact of filler inclusions in asphalt liquid phases was investigated via optical microscope assessments. Similarly, physicochemical tests of the elemental and mineralogical composition of each filler were accounted for using x-ray diffraction tests. The surface charge characteristics of each test filler was analysed relative to its mastic pH conditions through the application of zeta potential tests. Adhesive pull-off tensile strengths of the mastics on granite and limestone interfaces were also assessed for both dry and moisture conditions. The incorporation of fillers in asphalt binders highlighted the effect of filler reactivity and inert tendency on binders’ morphological phase modification wherein the OPC and LKD were reactive with the asphaltene while the DP was less reactive and inert. Results obtained from both the x-ray diffraction and zeta potential tests also infer the calcium based OPC and LKD to exhibit better surface ionic attraction compatibility with the PEN 60/70 binder than the DP at high F/B. Meanwhile, the relationship between the filler surface charge and mastic pH condition was observed to be significant and reliant upon the mastics adhesive pull-off tensile characteristics.

Effect of Lime Stone & Cement on the Mechanical Properties of Hot Mix Asphalt (HMA)

Most of the roads in Iraq are paved using Hot Mix Asphalt (HMA) which is consisted of aggregates, asphalt cement and filler. In this study a laboratory investigation is conducted using two types of widely used fillers highly and locally available. Four different proportions of fillers are. Filler proportions used in this study are four proportion (i.e., 1.9%, 2.5%, 3.5%, and 4.5%) by total weight of aggregate for both types of fillers used. These proportions were blended using asphalt with penetration 40/50 and Performance Grade (PG70-10) using super-pave mix design methodology. The performance of bitumen binder with both types of filler was evaluated by: Penetration, Ductility, Softening Point, Penetration Index, Volumetric properties, Indirect Tensile Strength and Tensile Strength Ratio. The volumetric properties indicate that, the proportions of (1.9%, and 2.5%) for both type of filler are within the Super-pave criteria as the ITS increased with the increase of filler content and the highest TSR values for 2.5% Limestone dust is 90%, while for 3.5% Cement is 89.7%. Finally, it was concluded that the HMA is highly influenced by the amount and type of filler content.

Characterisation of asphalt concrete mixes with municipal solid waste incineration fly ash used as fine aggregates substitution

ABSTRACT Characteristics of dynamic modulus (|E*|) and phase angle are necessary to determine the response of bituminous mixtures. Limited regressions are available in the literature for phase angle prediction. This research focuses on the effect of using municipal solid waste incineration (MSWI) fly ash as fine aggregates substitution on the performance of HMA mixes. Therefore, (MSWI) fly ash was incorporated in bituminous mixtures in five substitution percentages (0%, 5%, 10%, 25% and 50%). Mix design was conducted according to Superpave mix design method to find the optimum binder content of the various mixes. Two predictive models were used to better fit the phase angle mastercurvesand reduce the deviation at higher and lower limits of the frequency loading. The results indicated that the absorption of binder increased with higher substitution percentages. Similarly, higher voids in mineral aggregates and voids filled with asphalt values were observed with higher replacement percentages. The incorporation of (MSWI) fly ash affected the mixture's stiffness. Lower (|E*|) values were observed for all mixes as compared to the control mix. Mixes with MSWI fly ash developed lower and higher phase angle values as compared to the conventional mix depending on the percentage of replacement and the frequency range.

Evaluation of Resilience Parameters of Soybean Oil-Modified and Unmodified Warm-Mix Asphalts—A Way Forward towards Sustainable Pavements

The sustainable design and construction of highways is indispensable for the economic growth and progress of any region. Highway pavements are one of the core transportation infrastructures that require energy efficient materials with durability and an optimized lifecycle. Recent research has proven that warm-mix asphalt pavements prepared with renewable bio-binders are less susceptible to distresses. This study aims to investigate the resilience characteristics (load time, deformation time) of soybean oil modified and unmodified warm-mix asphalts. Aggregates, asphalt binders and asphalt mixes were characterized in accordance with the Superpave Mix Design Criteria. The resilient modulus tests were performed as per ASTM D7369. The test results indicated that the soybean-modified warm asphalt mix samples showed a 20% to 32% reduction in load-carrying capacity than unmodified warm asphalt mixes. The values of the horizontal and vertical recoverable deformations observed in the soybean-modified mixes were found to be 3% to 7% more than in the unmodified mixes. A slight variability (up to 7%) was also observed in the time-response spectra, i.e., peak load, unload and rest periods, in the soybean-modified mixes compared with the unmodified mixes. The Pearson correlation coefficient showed a significant trend between the resilient modulus test parameters for the soybean-modified warm asphalt mixes, i.e., load deformation, load time and deformation time. Soybean oil showed sustainable behavior as a bio-binder, particularly in the deformation-time response for the warm asphalt mixes. However, the effect of soybean in terms of the reduction of the load-carrying capacity from a sustainability perspective needs to be investigated.

Selection of Durable, Environmentally Friendly, and Cost-Effective Asphalt Mixtures.

In recent years, due to the advent of several additives and innovations, asphalt mix design has become more complex. The mixes meeting the volumetric mix design requirements may still fail prematurely in the field. Thus, a transition from a simplistic volumetric-based mix design to a performance-based mix design is required, which was also envisioned in the Strategic Highway Research Program (SHRP) and Superpave mix design. In addition to performance verification, asphalt mix designs should also be evaluated for the life-cycle costs and environmental impact to encourage durable as well as sustainable and cost-effective alternatives. In this study, three asphalt mixtures with different reclaimed asphalt pavement (RAP) contents and additives were evaluated for cracking and rutting performance by using different performance thresholds for asphalt mixtures that are generally used in the construction of high-volume roads in Oregon. A balanced mix design process was followed to determine the required binder content for the three mixtures. Based on the life cycle cost and environmental impact analyses, the mixture with warm mix additive (WMA) was selected as the most economically and environmentally viable asphalt mixture to be used for construction in Oregon.

Influence of Balanced Mix Design Approaches on Pavement Design Making Through an Illustrative Example

Laboratory tests have been developed and used over many years to improve the performance-related predictions of volumetric-based asphalt mix designs. Volumetric property requirements were mainly set for improving field pavement performance. These requirements have been established based on specific material properties. However, with the increased use of innovative and recycled materials, these requirements have shifted from guidelines for achieving a better mix design to guidelines limiting innovation and potential improvements. Therefore, it is time to move toward a balanced mix design (BMD), the ultimate goal of Superpave mix design. According to AASHTO PP 105, four major BMD approaches are available providing different levels of freedom compared with the traditional volumetric-based mix design. In this study, BMD approaches are explored using typical northern Nevada materials. An array of performance tests for rutting and cracking were conducted to evaluate the impact of the test selection on BMD. Moreover, the influence of asphalt mixture components (e.g., binder content, reclaimed asphalt pavement [RAP], recycling agents, gradation) on BMD were investigated. The results show that BMD process conversion is influenced by asphalt mixture properties (e.g., mixtures with similar gradation require different BMD approaches to achieve a well-performing asphalt mixture). Binder content was found to significantly influence BMD performance. In addition, it was concluded that asphalt mixtures with higher RAP content do not necessarily imply worse cracking performance. Furthermore, a poor correlation was observed between asphalt mixture costs and performance, where a mixture with the highest cost did not necessarily yield the best overall performance.

The feasibility of recycled micro polyethylene terephthalate (PET) replacing natural sand in hot-mix asphalt

Microplastic pollution is contaminating the human food chain worldwide. At the same time, construction excessively exploits natural sand, requiring the incorporation of alternative materials to achieve sustainable development. From this scenario, the study evaluates the potential of recycled micro-PET replacing natural sand on hot-mix asphalt (HMA) mechanical behavior by weight and volume. The materials’ characterization occurred via XDR, XRF, TGA/DTG, FTIR, SEM, and AFM tests. The Superpave mix design, X-ray micro-tomography (μ-CT), indirect tensile strength (ITS), resilient modulus (RM), and moisture damage tests were performed in conventional and PET-incorporated mixtures, considering 2% (in wt.), 4% (in wt.), and 8% (in wt. and vol.) substitutions. The 8% PET replacing sand by volume showed no significant change in the mixture’s optimum asphalt content (OAC) due to the binder absorption equivalence between the materials’ surfaces. For the same binder content, the increase in PET content in weight decreased the binder film thickness and increased the volume of voids, visualized as non-permeable micropores in μ-CT. Although adding and incrementing PET reduced the mixtures’ ITS and RM values, its most significant contribution was enhancing the resistance to moisture damage, especially for regions where the pavement deterioration process is associated with an intensive rainfall regime, thus demonstrating this application’s practical feasibility in concrete asphalt paving.

Volumetric Mix Design Adjustments for Improving Asphalt Mixture Durability

State highway agencies (SHAs) are looking for guidance on how they can make changes to their Superpave volumetric mix design procedures to obtain higher design binder contents to improve the cracking resistance and durability of asphalt mixtures. To assist SHAs, this paper was prepared to: (a) synthesize most common adjustments made by SHAs to their Superpave volumetric mix design procedures to obtain higher design binder contents; and (b) verify the effectiveness of these adjustments through laboratory experiments. Based on a survey of SHAs, the three most common adjustments to the Superpave mix design system to obtain higher design binder contents include: lowered design gyrations (Ndesign), increased minimum requirements for voids in mineral aggregate (VMA), and lowered design air voids (including air voids regression). These adjustments were verified in a laboratory testing program which included a virgin fine-graded mixture and a 20% reclaimed asphalt pavement (RAP) coarse-graded mixture. The results suggest that lowering Ndesign may help increase the design binder content initially but mix designers can select design gradations to reduce VMA and binder content back to levels achieved with the higher Ndesign levels. The other common adjustments (i.e., increased minimum VMA and lowered design air voids) can yield higher design binder contents. However, these approaches may be ineffective if Gsb is not accurately measured during mix design or if VMA is not controlled during mix production.

Development of Cost-Effective High-Modulus Asphalt Concrete Mixtures Using Crumb Rubber and Local Construction Materials in Louisiana

One of the emerging solutions to enhance the durability of asphalt pavements is the use of a French asphalt mix known as “High-Modulus Asphalt Concrete (HMAC).” This mix uses a hard asphalt binder, high binder content (about 6%), and low air voids content as compared with Superpave mixtures. The key objective of this study was to develop a cost-effective HMAC mixture using crumb rubber and local materials in Louisiana. To achieve this objective, four HMAC mixtures were prepared using two asphalt binders (PG 82-22 and PG 76-22 plus 10% crumb rubber) and two Reclaimed Asphalt Pavement (RAP) contents (20% and 40%); additionally, a conventional Superpave mixture in Louisiana was prepared as a control mixture. The laboratory performance of these five mixtures was evaluated in relation to workability, dynamic modulus, rutting resistance, and cracking resistance. The AASHTOWare Pavement ME Design software was also used to estimate the long-term field performance of these mixtures. Results indicated that the HMAC mixture prepared with 10% crumb rubber and 20% RAP successfully met the French mix design specifications for HMAC and LaDOTD specifications. This HMAC mix outperformed the control Superpave mix in relation to dynamic modulus, rutting resistance, and cracking resistance. Additionally, this HMAC mixture can reduce the required asphalt thickness by 1.5 or 2 in. based on traffic level. The cost-effectiveness analysis indicated that this HMAC mixture was more cost-effective than conventional Superpave mixtures in Louisiana. In addition, this mixture is environmentally friendly as it can reduce the disposal of scrap tires in landfills.