Hot Mix Asphalt Mixtures Research Articles

Effect of adding glass fiber on the properties of asphalt mix

The continuing rapid growth in traffic, along with the rise in allowable axle loads, requires improvement of highway paving materials. In the recent decades, different types of fiber materials are utilized for improving the performance of asphalt mixture. A laboratory investigation was carried out into the effect of adding Glass Fiber (GF) on some properties of Hot Mix Asphalt (HMA) mixtures. Subsequently, five HMA specimens were prepared using the Marshall mix design method for wearing surface mix (mix 4C). Marshall Stability (MS) and flow tests were applied to the specimens. Also, MS and flow values were recorded. For the Optimum Asphalt Content (O.A.C) and different GF percentages, the Marshall parameters were calculated. Then, some special tests were conducted to measure the different mix properties, including loss of stability, wheel tracking and indirect tensile strength tests. Results of the study led to important conclusions regarding using of Glass Fiber (GF) to improve most of the properties of HMA mixtures. Finally, this study recommended a proposed mix with 0.25% GF by weight of the total mix.

Influence of Recycled Concrete Aggregate (RCA) towards the Performance of Hot-Mix Asphalt (HMA) Mixture

Influence of Recycled Concrete Aggregate (RCA) towards the Performance of Hot-Mix Asphalt (HMA) Mixture

Warm asphalt rubber: A sustainable way for waste tire rubber recycling

Recycling end-of-life tire rubber as asphalt modifier is known as a sustainable paving technology with merits including enhanced pavement durability, waste tire consumption and noise reduction. However, the criticisms on the high construction emissions of asphalt rubber (AR) have limited its application. Warm mix asphalt (WMA) effectively reduces the mixing and compaction temperatures of conventional hot mix asphalt mixtures. The combination of AR and WMA, called warm asphalt rubber (WAR), is a promising paving material which achieves pavement sustainability from principles to practices. Many studies have demonstrated that WMA technologies work effectively with AR pavement in different ways, alleviating the concerns of potential higher emissions of AR by decreasing mixing and paving temperatures. A comprehensive literature review about WAR brings a better understanding of this promising paving technology. The findings of 165 publications were summarized in this review. It summarized the recent developments of WAR in various aspects, including rheological properties, mix design, mixture mechanical performance, field application, construction emission, and asphalt-rubber-WMA additive interaction. It is expected that this review is able to provide extensive information to explore further research development and application of WAR.

The tailored traits of reclaimed asphalt pavement incorporating maltene: performance analyses

ABSTRACT Environmental issues and fluctuations in the price of asphalt binders have increased the demand in usage of reclaimed asphalt pavement (RAP) material for asphalt mixtures. The RAP binder, nevertheless, is often highly aged and has several drawbacks, for instance, low cracking resistance, low workability, and low fatigue in the resulting mixtures. These issues can be resolved by using rejuvenators. As such, this research work assessed the engineering properties of reclaimed hot-mix asphalt (HMA) mixture rejuvenated by maltene-derived asphalt. The tests examined Marshall properties, moisture damage, resilient modulus (MR), dynamic creep, Cantabro loss, and rutting resistance, including the stripping and coating tests. The results showed that maltene had been effective in mitigating the aging effect of RAP asphalt, while the rejuvenated mixture exhibited considerable enhancement, especially when compared to the virgin and RAP mixtures without maltene. A simple cost analysis revealed that maltene was cost-effective as it compensated for the adverse effects of RAP, hence can be used to raise the content of RAP in asphalt mixture.

Influence of recycled concrete aggregates from different sources in hot mix asphalt design

The waste generated by the construction industry generally has an undesired negative impact on both human and animal life as well as the environment. Among these wastes, recycled concrete aggregate (RCA), due to its good residual physical, mechanical, mineralogical, and chemical properties, has attracted promising potential for re-use and incorporation in the construction of new infrastructural elements. These infrastructure applications include construction of sidewalks, curb and gutters, subbase/base layers, and/or as a partial replacement of natural aggregates (NA) in the production of hot mix asphalt (HMA) mixtures. In this laboratory study, experimental research work was conducted to evaluate the influence of RCA on the mechanical properties and performance of RCA modified HMA mixtures against a control HMA mixture without any RCA. RCAs were obtained from two different concrete sources, namely: (a) one from the demolition of a building (RCAB), and (b) another one from the rehabilitation of a Portland cement concrete pavement (RCAP). Both NA and RCA were characterized taking into account physical and mechanical properties. HMA mixtures were produced using the Marshall mix-design method by replacing 0.0% (control), 15%, 30%, and 45%, respectively, of the coarse NA fraction with RCA. Thereafter, laboratory testing (i.e., Scanning Electron Microscopy [SEM], resilient modulus, indirect tensile strength, etc.) including material property characterization and performance evaluation were conducted on HMA samples. Overall, the laboratory test results showed that the RCA modified mixtures exhibited a similar behavior to conventional HMA mixtures, but with greater environmental benefits and potential cost savings through the recycling and reuse of waste concrete aggregates. However, it was observed that the laboratory performance of RCA modified mixtures is strongly dependent on the RCA source and dosage, with RCAP exhibiting superior performance over RCAB. HMA mixtures produced with RCA provided higher optimum asphalt-binder content (OAC) than that of mixes with NA.

Thermal-Insulation Effect and Evaluation Indices of Asphalt Mixture Mixed with Phase-Change Materials.

Under strong winds and at low temperatures, heat loss of hot-mix asphalt mixtures is likely to occur, which leads to temperature segregation. Temperature segregation affects the forming quality and the performance of asphalt pavements. In this study, a phase-change thermal-insulation agent (PCTIA) was prepared for reducing the temperature dissipation. A cooling simulation experiment was performed to test the temperature-dissipation process for an ordinary asphalt mixture and the asphalt mixture mixed with PCTIA (AM-PCTIA). The thermal-insulation effect was analyzed according to the temperature difference and the thermal-insulation extension time. Moreover, two indices—the thermal-insulation accumulated time difference value (IATDV) and thermal-insulation accumulated time difference index (IATDI)—were proposed for evaluating the thermal-insulation ability and efficiency. The results indicated that the temperature at the center of the AM-PATIA was 4 °C higher than that for the ordinary asphalt mixture. The insulation time was prolonged by 29.8 min at the ambient temperature of 15 °C. As the ambient temperature increased, the thermal-insulation effect of the PCTIA improved.

Suitability of Fiber Lengths for Hot Mix Asphalt with Different Nominal Maximum Aggregate Size: A Pilot Experimental Investigation.

Fiber length is a key parameter for the mixture design of basalt fiber-reinforced hot mix asphalt (HMA), which significantly affects the mix performance. To evaluate the suitability of fiber lengths for HMA with different nominal maximum aggregate size (NMAS), basalt fiber with the lengths of 3, 6, 9, 12, and 15 mm were selected for dense graded gradations with different NMASs (namely, SUP-13, SUP-20, and SUP-25), so as to prepare the fiber-reinforced HMA mixtures. Then, the mix performance was evaluated by an indirect tensile asphalt cracking test (IDEAL-CT), a four-point bending beam fatigue test, a wheel tracking test, a uniaxial penetration test, a low temperature bending beam test, and a freeze-thaw splitting test. Based on the performance results, the optimum fiber length for each mix gradation was proposed by the normalization method. The results showed that adding basalt fiber can enhance the comprehensive performance of all three types of HMA to a great extent. Furthermore, fiber length presented remarkable impact on the crack resistance, the fatigue resistance of the HMA, and the low temperature crack resistance, but it had limited influence on the high temperature deformation resistance, and water stability. The optimum fiber length for SUP-13, SUP-20, and SUP-25 was 6, 9, and 12 mm, respectively.

Improvement of thermal and optical responses of short-term aged thermochromic asphalt binder by warm-mix asphalt technology

Thermochromic asphalt materials, due to their dynamically reversible thermal and optical responses in accordance with ambient temperature, have the significant potential in prolonging the lifespan of pavement and improving the urban climatic environment. However, the traditional hot-mix asphalt mixture preparation method with high-temperature conditions can cause damage to durability of thermochromic microcapsules contained in asphalt matrix and hence compromise the temperature regulation functionality of thermochromic asphalt materials. Therefore, the effects of reduced aging temperature by warm-mix asphalt (WMA) technology on properties of short-term aged thermochromic asphalt binder were investigated in this research in terms of rheological property, fluorescent morphology, chemical structure, optical reflectance and temperature regulation effectiveness. In addition, environmental impacts of thermochromic asphalt mixture with warm-mix technology were also discussed. The results indicate that the mixing and compaction temperatures of thermochromic asphalt mixture can be reduced by 16 °C due to WMA technology. The reduced aging temperature by Sasobit can more efficiently maintain the morphology integrity of thermochromic microcapsules, mitigate the outflow of functional core materials and thus improve the optical reflectance of short-term aged thermochromic asphalt binder. When exposed to outdoor solar radiation in hot summer, the asphalt mixture prepared by thermochromic asphalt can achieve a 3 °C decrease in pavement temperature compared with pure asphalt mixture. In addition, the thermochromic asphalt mixture prepared by WMA technology can further reduce the pavement temperature by 2 °C when compared with traditional hot-mix thermochromic asphalt mixture. The reduced pavement surface temperature in hot summer can significantly reduce the amount of convection and irradiation heat from pavement to urban atmosphere, which is of great significance to the improvement of urban microclimate and the sustainable development of city.

Demarcation Study on Reclaimed Asphalt Pavement Contents in Recycled Hot Mix Asphalt Mixtures for Wearing Course in Asphalt Pavements

The present study evaluated reclaimed asphalt (RAP) containing hot mix asphalt (HMA) mixtures performance, to assess the effect of 5% RAP alteration on the marginal change in performance between 20%, 25%, and 30%. Then, the results from assessment were used to classify the RAP contents in HMA mixtures as low, moderate, and high by comparing the performance of the mixtures. The HMA specimen’s preparation followed the Marshall mix design procedure with a 12.5 mm nominal maximum aggregate size (NMAS). Rutting and stripping resistance were selected as the primary performance. The wheel tracking (WTT) and indirect tension strength (IDT) tests were done to assess rutting and stripping performance, respectively. The WTT results indicated that a mixture with 30% RAP performed well in rutting resistance, followed by 25% and 20% RAP mixtures. The results of the tensile strength ratio (TSR) from the IDT showed that mixtures with 0% RAP and 20% RAP were susceptible to stripping. On the other hand, mixture with the 25% RAP had good stripping resistance. From the test results, it was observed that RAP contents up to 20 % had similar performance as 0% RAP mixture. Mixtures containing 25% RAP and 30% RAP found better on rutting and stripping resistance. Based on the experiment results, the 5% variation in RAP content affects the performance of the mixtures significantly. The present study concluded that RAP content could be tiered as follows; up to 20 % is low content, above 20% to 30% as moderate, and above 30% is high content.

ANN-based dynamic modulus models of asphalt mixtures with similar input variables as Hirsch and Witczak models

ABSTRACT Artificial neural networks (ANNs) and Gb*-based regression models were used for the prediction of the dynamic modulus (|E*|) of South Carolina’s hot mix asphalt mixtures (HMAs) the majority of which contained recycled asphalt pavement (RAP). Models’ training and testing were done using a database that contained 1656 |E*| values from 93 HMA mixtures. Gb*-based models included the Hirsch, revised Hirsch, Bari-Witczak, revised Bari-Witczak, Al-Khateeb 1, Al-Khateeb 2, NCHRP 1-40D, and the simplified global models. The results showed that Gb*-based regression models had a significant bias in prediction; Coupling VMA and Gb* had the most influence on |E*|; four-layer ANNs generally had a better performance than three-layer ANNs on using Hirsch model’s related inputs; ANN 3-15-15-1 and ANN 8-15-15-1 (developed with similar input variables as the Hirsch and Witczak regression models respectively) showed very high performance of R 2 > 0.994 on testing. Therefore, ANNs could be considered to capture the influence of the binders’ rheological properties, mixture’s volumetric properties, and RAP on |E*| of HMA mixtures far better than regression-based models.

Improving Durability of Asphalt Pavements in Louisiana through Increased In-Place Field Density

The objective of this project was to evaluate the effects of increasing the initial in-place density of asphalt pavements on expected field performance and durability. This study was completed as part of the FHWA’s demonstration project on “Enhanced Durability through Increased In-Place Pavement Density.” Two approaches for increasing in-place density were explored: (i) the addition of an Evotherm warm-mix asphalt (WMA) additive at a dosage rate of 0.6% by the weight of mix; and (ii) the addition of 0.2% asphalt binder (Plus AC) to the design optimum asphalt binder content of standard dense-graded mixtures. The field component of the research involved three 4,000-ft long test sections representing control hot-mix asphalt (HMA) mixtures, Evotherm WMA mixtures, and the Plus AC HMA mixtures. Each test section included a binder and a wearing course for a total of six mixtures. Density measurements were determined in the laboratory from field cores taken at each test section. The high- and intermediate-temperature properties of field cores were evaluated using the Loaded Wheel Tracking and Semi-Circular Bending tests, respectively. Further, the Indirect Tensile Dynamic Modulus (IDT |E*|) test was conducted for full viscoelastic characterization of the asphalt mixtures. The two approaches considered in this study were successful in increasing field density, especially for the binder course mixtures. The two strategies for increasing in-place density also resulted in better than expected resistance to cracking and rutting, as well as an increase in mixture stiffness as measured by the IDT |E*|.

Field and simulated rutting behavior of hot mix and warm mix asphalt overlays

Research implementing new pavement technologies often focuses on material characterization; however, expanding the research to study and validate how new technologies influence pavement design is needed for continual improvement. Numerical analysis approaches use laboratory mixture data to predict field performance. This study compares predicted rutting by MEPDG design, estimated rutting from Finite Element (FE) simulations, and actual rutting performance in the field. Ten years ago, warm mix asphalt research was underway to measure the effect of warm mix asphalt (WMA) additives and lower production temperatures on performance. WMA benefits include reduced mixing/compaction temperatures, reduced fuel consumption, and improved compatibility. In 2009, three asphalt overlay projects were constructed in Iowa using both hot mix asphalt (HMA), and WMA mixes to compare their performance. A series of dynamic modulus tests were conducted to determine dynamic modulus and phase angles of HMA and WMA mixtures. The dynamic modulus results were used to develop FE viscoelastic simulations to predict the rutting of HMA/WMA pavement sections. Iowa’s pavement management system provided field rutting of WMA/HMA sections. Also, pavement sections were evaluated using mixture input parameters in the Mechanistic-Empirical Pavement Design Guide (MEPDG). The results showed MEPDG based on linear elastic theories might overestimate the rutting of asphalt pavements, especially overlays placed on Jointed Plain Concrete Pavement (JPCP). In contrast, the FEM based on viscoelastic theories more accurately predicted the rutting of pavements. Calibration coefficients are proposed by this study, which may be useful for design engineers and industrial applications to correct and modify MEPDG overlay design thicknesses for HMA/WMA mixes placed on HMA and JPCP surfaces.

Pre-trained deep learning for hot-mix asphalt dynamic modulus prediction with laboratory effort reduction

Evaluating the hot mix asphalt (HMA) expected performance is one of the significant aspects of highways research. Dynamic modulus (E*) presents itself as a fundamental mechanistic property that is one of the primary inputs for mechanistic-empirical models for pavements design. Unfortunately, E* testing is an expensive and complicated task that requires advanced testing equipment. Moreover, a significant source of difficulty in E* modeling is that many of the factors of variation in the HMA mixture components and testing conditions significantly influence the predicted values. For each laboratory practice, a vast number of mixes are required to estimate the E* accurately. This study aims to extend the knowledge/practice of other laboratories to a target one in order to reduce the laboratory effort required for E* determination while attaining accurate E* prediction. Therefore, the transfer learning solution using deep learning (DL) technology is adopted for the problem. By transfer learning, instead of starting the learning process from scratch, previous learnings that have been gained when solving a similar problem is used. A deep convolution neural networks (DCNNs) technique, which incorporates a stack of six convolution blocks, is newly adapted for that purpose. Pre-trained DCNNs are constructed using a large data set that comes from different sources to constitute cumulative learning. The constructed pre-trained DCNNs aim to dramatically reduce the effort elsewhere (target lab) when it comes to the E* prediction problem. Then, a laboratory effort reduction justification is investigated through fine toning the constructed pre-trained DCNNs using a limited amount of the target lab data. The performance of the proposed DCNNs is evaluated using representative statistical performance indicators and compared with well-known predictive models (e.g., η-based Witczak 1-37A, G,δ-based Witczak 1-40D and G-based Hirsch models). The proposed methodology proves itself as an excellent tool for the E* prediction compared with the other models. Moreover, it could preserve its accurate performance with less data input using the transferred learning from the previous phase of the solution.

Fracture resistance study for hot mix asphalt mixture under out of plane sliding mode

Cracked pavements can be subjected to out-of-plane sliding or mode III deformation due to movement of vehicles. In order to design suitable asphalt mixture for manufacturing high resistance pavements against mode III failure, it is necessary to determine a characteristic parameter called mode III fracture toughness (KIIIc) for these materials. In this research a comprehensive experimental study is performed to obtain the value of (KIIIc) for hot mix asphalt (HMA) mixtures under different geometrical and testing conditions. An edge notch disc bend specimen was utilized for conducting the mode III fracture toughness experiments on HMA mixture at low temperature conditions. Several discs with three thicknesses were cut from HMA mixtures made by gyratory compactor machine and with different air voids. The experiments showed that by increasing the size of test specimen, mode III fracture toughness can increase significantly. Furthermore, KIIIc value is increased by decreasing the test temperature from 0 °C to −24 °C and decreasing the air void content from 7% to 3%. A regression analysis was implemented on the test results and it was found that the thickness and air void have the maximum and minimum influences on KIIIc value, respectively. In addition, it was shown that the mode III fracture toughness of tested asphalt mixture is noticeably less than the corresponding value of the same mixture tested under mode I condition with the same testing conditions. The fracture toughness ratio (KIIIc/KIc) that was varied from 0.5 to 0.7 for different testing conditions and specimen sizes was predicted theoretically using some stress/strain based fracture criteria.

Two-Step Mixing Process Elaboration of the Hot-Mix Asphalt Mixture Based on Surface Energy Theory

AbstractHot-mix asphalt (HMA) is a multicomponent mixture composed of asphalt, coarse and fine aggregates, fillers, and other necessary additives. The bitumen–aggregate adhesion and performance of ...

Improved estimation of dynamic modulus for hot mix asphalt using deep learning

This study developed neural network models for the estimation of dynamic modulus (|E∗|) for hot mix asphalt (HMA) mixtures from binder properties, mixture volumetrics and aggregate gradation. The data used for training the networks were extracted from a report of the National Cooperative Highway Research Program (NCHRP) 9–19 [1]. Unlike previous parallel studies, the networks presented employed a logistic activation upon the output to ensure the positiveness and for improved accuracy of the predictions. Comparative analyses were conducted between the resulting networks and conventional predictive equations as well as networks in other previous studies. A total of 7400 records of modulus measurements were involved, among which 6700 were randomly chosen for training, 200 for validation and 500 for testing purposes. Overall, the resulting networks significantly outperformed the Witczak’s predictive equations and networks in previous studies. For the viscosity based inputs, the network achieved R2 values of 0.984 and 0.978 on the 500 testing examples at arithmetic and logarithmic scales, respectively. For the complex modulus based inputs, the network attained R2 values of 0.961 and 0.959 respectively for the arithmetic and logarithmic scales. An analysis of the impacts of different variables on |E∗| prediction revealed that the variables for aggregate gradation were not as critical as the binder properties (viscosity and complex modulus) and mixture volumetrics.

Analysis of Composite Skeleton Characteristics of Recycled Asphalt Mixture via Weight Analysis Method

The aggregate skeleton of hot-mix recycled asphalt mixture comprises reclaimed asphalt pavement (RAP) and new aggregate and is a complex skeleton system containing old and new aggregates. The RAP content in the mixture directly determines the mechanical response characteristics of the composite skeleton, thus affecting the road performance. In order to explore the effect of RAP content on the characteristics of composite skeleton, in this study, the contact points in the composite skeleton were classified into three types: new-new, new-old, and old-old. On the basis of digital image technology and weight analysis methods, the distribution characteristics of the contact type of AC-13 mixture skeletons with different RAP contents were investigated; the correlation between the weight parameters of the contact type and the macroscopic mechanical properties of the mixture was studied. The results indicate that grading is the main factor affecting the total number of contact points; with increasing RAP content, the overall trend of new-new contact points is decreasing; the old-old contact points increase monotonously and then rapidly after the RAP content reaching 40%; the new-old contact points increase first and then decrease with a peak corresponding to 30% RAP. With increasing number of new-old contact points, the mechanical indexes of the recycled asphalt mixture enhanced. The weight analysis method can more simply and clearly reflect the correlation between the contact type of coarse aggregate and the mechanical parameters of mixture. In the mixing ratio design of the recycled asphalt mixtures, choosing a mixture with more new-old contact points achieved better road performance; therefore, effectively increasing RAP content may be one of the potential ways to enhance road performance.

Evaluating the Rutting Resistance of Wearing Course Mixtures with Different Fine Aggregate Sources Using the Indirect Tensile Strength Test

Abstract The aim of this experimental study was to determine if the indirect tensile (IDT) strength test results for Marshall cylindrical specimens are associated with a laboratory evaluation parameter for the rutting resistance of wearing course hot mix asphalt (HMA) mixtures. We investigated a wide range of HMA mixtures with various aggregate gradations; the specimens consisted of seven Vietnamese and six Indonesian HMA mixtures with a 12.5-mm nominal maximum particle size. Three different fine aggregates from two sources (natural sand and manufactured screening) were used to fabricate these HMA specimens. Wheel tracking tests were also conducted to verify the validity of the IDT strength test as a potential indicator of rutting resistance in HMA mixtures. The experimental results showed that the IDT strength test using Marshall cylindrical specimens has potential applications for evaluating rutting resistance, regardless of aggregate source. The study also explored the effects of fine aggregate on the resistance of HMA mixtures to permanent deformation. Overall, fine aggregate significantly influenced the rutting resistance of mixtures when the aggregate gradations were controlled to achieve the same gradations. In contrast, fine aggregates with different gradations were not strongly associated with the rutting resistance of HMA mixtures.

Variation of Asphalt Requirement and Strength Properties among Hot Mix (HMA) and Warm Mix (WMA) Asphalt Concrete

Due to the restrictions for protecting the environment, and the requirements to reduce fuel consumption, research work was started globally for verifying the possibility of implementation of warm mix asphalt (WMA) in pavement construction. Warm mix asphalt enables the production and compaction of asphalt concrete mixtures at temperatures (20-30 °C) lower than that of traditional hot mix asphalt (HMA). In this investigation, two WMA mixtures have been prepared in the laboratory using medium curing cutback (MC-30) and Cationic emulsion. HMA mixture was also prepared for comparison. Marshall specimens of (101.6 mm) in diameter and (63.5 mm) in height were constructed form the mixtures and subjected to indirect tensile strength (ITS) test, Marshall Stability, flow and volumetric properties determination. Test results were analyzed and compared. It was concluded that the stability of WMA is higher than HMA by 17 % and 47.87 % for (cutback and emulsified asphalt) WMA respectively, while the WMA exhibit lower flow than HMA by 34.67 % and 1.33 % when using (cutback and emulsion) WMA respectively. The optimum asphalt content was (20.69 and 32.35) % higher for (cutback and emulsion) WMA than that of HMA. The (ITS) at 25 ⁰C decreases by (28.58 and 4.51) % when the asphalt content increased and decreased by 0.5 % from optimum asphalt content (OAC) for WMA- emulsion asphalt.

Evaluation of Existing Short-term Aging Procedure for Hot-mix Asphalt Mixtures and Related Suggestions

Evaluation of Existing Short-term Aging Procedure for Hot-mix Asphalt Mixtures and Related Suggestions