Hot Mix Asphalt Mixtures Research Articles

Laboratory Investigation of Microwave Healing Characteristic of Hot Mix Asphalt Incorporating Steel Slag and Fly Ash

Abstract: This research aims to analyze the usage of fly ash (FA) as filler and Steel slag as coarse aggregate in hot mix asphalt concrete to monitor its healing characteristic under microwave heat. Both fly ash and steel slag are the industrial by-products. Using Marshall, Hot mix asphalt (HMA) mixtures were prepared for control and three different modified specimens having 10%, 20% and 30% steel slag as coarse aggregate, and 75% optimum fly ash content (OFC) as filler. Then thermal distribution and optimum healing time of test specimens were recorded using infrared thermometer. A three-point bending (TPB) tests were applied to the samples before and after the microwave healing procedures. Test results demonstrated that adding steel slag and fly ash in asphalt concrete mixtures increases the heating rates and improve the healing performance of hot mix asphalt using microwave heat. The replacement of natural coarse aggregate by 30% steel aggregate is extremely promising since it has not only improved healing results but also enhance the load-displacement relationship of the HMA mixtures with more ductile behavior. Overall, the use of steel slag and fly ash in hot mix asphalt is a significant option that helps to the sustainable pavement construction as it improves healing and cracking resistance. Keywords: Fly ash, Steel slag, Hot mix asphalt, Microwave heating, Three-point Bending

Effect of RAP content on fatigue performance of hot-mixed recycled asphalt mixture

Although it was widely recognized that the addition of recycled asphalt pavement (RAP) would affect the fatigue performance of hot-mix recycled asphalt mixture (HRAM), a quantitative analysis of how it affected the fatigue performance so far still lacking. The purpose of this study was to identify the effect of RAP content on the fatigue performance of HRAM. For this, the self-developed rejuvenator was used to prepare specimens, then the pavement performance test and the four-point bending test were performed on the specimens to measure the fatigue performance of HRAM. In which, the specimens were prepared with RAP content of 0%, 30%, 40%, and 50% respectively, and the dosage of rejuvenator was 5%. Results suggested that with the addition of RAP, the dynamic stability of HRAM increased by 4.8% ∼ 34.5%, and the rutting deformation decreased by 5.22% ∼ 19.22%. The flexure-tension failure strength of HRAM decreased by 12.39% ∼ 35.66%, and the maximum failure strain decreased by 9.31% ∼ 27.02%. The splitting strength of HRAM decreased by 6.73% ∼ 17.45%, and the TSR decreased by 3.57% ∼ 4.36%. This indicated that the high-temperature performance of HRAM had a positive correlation with the content of RAP, while the low-temperature performance and water stability showed a decreasing trend. The principal component analysis model was established to quantify the influence of RAP content on pavement performance through related performance indexes. From the fatigue performance test, the fatigue life of HRAM was increased with the addition of RAP. The variance analysis under the interaction of multiple factors showed that the p-values for temperature and strain level were 8.14E-4 and 1.418E-20 respectively. The temperature and strain level had a significant effect on the fatigue performance of HRAM, and the strain level was the main factor affecting the fatigue performance, then the fatigue equation and fatigue limit equation based on the temperature factor was established. The effect of different factors on fatigue performance of HRAM was quantified by establishing the back propagation (BP) neural network model, it was found that the prediction value was very close to the test results, and the R2 was 0.98819, which indicated that the established model has good fitting accuracy. The effect of RAP content on pavement failure characteristics was studied by establishing the three-dimensional finite element model, it was found that the deformation depth in each direction had a good linear relationship with the RAP content, and the fitting accuracy was close to 1. A comparison study indicated that the fatigue equation and fatigue limit equation based on temperature factor can better describe the coupling effect between RAP content and fatigue performance, the principal component analysis model can better describe the correlation degree between RAP content and pavement performance, the finite element model can better describe the correlation degree between RAP content and pavement structure deformation.

Predicting fatigue service life reductions of asphalt pavements due to deficiency in design-level values of effective binder content

The focus of this study is the evaluation of the effects of deficiencies in design-level values of effective binder content (Δ Vbe) on the top-down (TD) and bottom-up (BU) fatigue cracking performance of hot-mix asphalt (HMA) mixtures using AASHTOWare Pavement ME Design structural simulation program. Using an analytical–mathematical-based methodology, this study also aims to predict the reduction in fatigue service life (i.e., TD, and BU fatigue cracking) of asphalt pavements that are most sensitive to the variation (Δ Vbe). Two types of mixes with varying levels of Vbe are used to simulate the fatigue cracking performance of a full-depth (FD) pavement structure. For each of the three studied cases, one asphalt course has a variable value of Vbe, while the two other courses have a fixed value of Vbe. Results indicate that the Δ Vbe of 3% reduced 50%–70% of fatigue cracking service life. Additionally, Pavement ME shows a limitation to account for the effect of Vbe in the intermediate course on the BU fatigue cracking.

Field calibration and validation of a pavement aging model

ABSTRACT A pavement aging model (PAM) is established by calibrating and validating the NCHRP 09–54 kinetics model's predictions against field core measurements. Field cores, laboratory-mixed loose mixtures, and binders from a wide range of pavement sections are used, including both conventional hot mix asphalt (HMA) mixtures and modern materials (i.e. reclaimed asphalt pavement (RAP), warm mix asphalt (WMA), and polymer modified asphalt (PMA)). Field aging levels are measured at different depths from binder extracted and recovered from in-service field cores. The original component materials of these pavement sections are aged in the laboratory and used to calibrate the kinetics model. The measured field aging levels are compared against those predicted from the kinetics model to inform a depth and time dependent field calibration function for the PAM. The validation of PAM using an independent set of field sections shows that, within the limited data used in this study, the calibrated PAM may be able to predict the aging of the conventional HMA, RAP, WMA, and PMA mixtures. The PAM predictions are lastly found to outmatch the predictions by the Global Aging System (GAS) model.

Performance of zeolite synthesized from sewage sludge ash as a warm mix asphalt additive

The disposal of sewage sludge ash (SSA) is a growing problem with both environmental and economic ramifications. This study aims to synthesize zeolite from SSA as a foaming-based warm mix asphalt (WMA) additive, and comprehensively characterize its performance. The SSA-derived zeolite was first characterized using X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), and Thermogravimetry-Differential Thermal Analyzer (TG-DTA) tests. Then, WMA mixtures with the SSA-derived zeolite and a commercial zeolite additive, and a conventional hot mix asphalt (HMA) mixture were produced in the laboratory for a wide range of engineering performance tests, including the indirect tensile stiffness modulus test, indirect tensile fatigue test, moisture susceptibility test, and Hamburg wheel-tracking test. The experimental results indicated that the SSA-derived zeolite was pure zeolite A which can release approximately 20% crystal water gradually from 70 oC to 200 oC. The overall performance of the WMA mixture with SSA-derived zeolite was better than that of the WMA mixture with commercial additive, and comparable to that of the HMA mixture except for rutting resistance, which is marginally lower but still satisfactory. Cost-benefit analysis was conducted in the end, which demonstrated that SSA-derived zeolite is eco-efficient. This study concluded that it is feasible to use the SSA-derived zeolite as an effective and sustainable WMA additive.

Pavement Properties and Predictive Durability Analysis of Asphalt Mixtures.

The actual lifetimes of many highways are lower than that expected based on the initial pavement design, which brings increasingly prohibitive costs of pavement maintenance and repair. Although many works have been done, the real service lifetimes are still disappointing, and the researchers are also trying their best to increase the projects’ life span. In this study, to comprehensively predict the durability and lifetime of newly designed asphalt mixture structures, an asphalt pavement project consisting of three hot mix asphalt (HMA) mixtures were evaluated. The mixtures were constructed in the pavement project of the Weiwu expressway in Gansu Province. Pavement properties of the asphalt mixtures, rutting and temperature fatigue factors of the dynamic modulus are discussed. The fatigue resistance is supposed to improve on increasing the vehicles’ speed below the freezing point, which may be more suitable for applications in expressways. Meanwhile, the lifetime is measured according to the number of fatigue axle loads calculated, which were corrected between the specimens in the lab and the field core samples. Durability analysis prediction can be obtained based on the fatigue lifetime predictive model accordingly, which can provide more information about the fatigue lifetime and the rehabilitation planning of existing pavements in the future accordingly.

Determining the maximum permissible content of recycled asphalt pavement stockpile in plant hot-mix recycled asphalt mixtures considering homogeneity: A case study in China

In engineering practice, recycled asphalt pavement (RAP) is often obtained from various sources and is mixed and stockpiled in a disorderly manner, which is defined as a hybrid RAP. Thus, the material component of hybrid RAP shows great variability, possibly preventing the plant hot-mix recycled asphalt mixture (RHMA) from achieving stable quality. To address this problem, the German TL Asphalt-StB 07 guideline introduced an approach for evaluating the variability of RAP stockpile characteristics and subsequently determined the maximum permissible content of RAP in RHMA for different pavement layers based on the variability of the RAP stockpile. This study adopted this method in the Fuzhou–Yinchuan expressway maintenance project, Jiangxi Province, and reported a homogenization treatment measure for hybrid RAP. The results show that the material composition of hybrid RAP is characterized by significant heterogeneity in gradation and asphalt content, effectively reducing the heterogeneity of hybrid RAP, and the maximum permissible content of RAP in the binder layer can be increased by approximately 10% in the mass of RHMA. The homogenization treatment scale should comprehensively consider indices such as efficiency, cost, and expected dosage. The results of this study can serve as a reference value for determining a reasonable content of hybrid RAP in RHMA and ensuring stable RHMA quality.

Moisture characteristics of warm mix asphalt containing reclaimed asphalt pavement (RAP) or steel slag

Issues like limitation of natural resources of aggregates, global warming, need for eco-friendly, cost-effective, and high performance and durable asphalt mixture, have made the Reclaimed Asphalt Pavements Warm Mix Asphalt (RAP-WMA) and Steel Slag Warm Mix Asphalt (SS-WMA) interesting substitutions for conventional Hot Mix Asphalt mixtures. Furthermore, presence of moisture initiates and accelerates the deterioration of both of these mixtures. In this way, the response of the RAP-WMA to the moisture damage was compared with the SS-WMA using experimental tests including Indirect Tensile fatigue failure, Resilient Modulus, Indirect Tensile Strength, Semi-circular Bending, and Dynamic Creep tests. The obtained results show that although the RAP-WMA and SS-WMA mixtures contain hydrophilic and moisture sensitive aggregates and aged binder, they had an appropriate performance against the effect of moisture. Also, the SS-WMA mixtures showed better performance against moisture than the RAP-WMA mixtures, and therefore, they can be recommended as a substitution for RAP-WMA in regions where moisture damage is prevailing.

Asphalt Mixture with Scrap Tire Rubber and Nylon Fiber from Waste Tires: Laboratory Performance and Preliminary M-E Design Analysis

Scrap tire rubber and nylon fiber are waste materials that could potentially be recycled and used to improve the mechanical properties of asphalt pavement. The objective of this research was to investigate the properties of scrap tire rubber and nylon fiber (R-F) modified warm mix asphalt mixture (WMA). The high-temperature performance was estimated by the Hamburg wheel-tracking testing (HWTT) device. The low-temperature cracking performance was evaluated by the disk-shaped compact tension (DCT) test and the indirect tensile strength (IDT) test. The stress and strain relationship was assessed by the dynamic modulus test at various temperatures and frequencies. The extracted asphalt binder was evaluated by the dynamic shear rheometer (DSR). Pavement distresses were predicted by pavement mechanistic-empirical (M-E) analysis. The test results showed that: (1) The R-F modified WMA had better high-temperature rutting performance. The dynamic modulus of conventional hot mix asphalt mixture (HMA) was 21.8%~103% lower than R-F modified WMA at high temperatures. The wheel passes and stripping point of R-F modified WMA were 2.17 and 5.8 times higher than those of conventional HMA, respectively. Moreover, the R-F modified warm mix asphalt had a higher rutting index than the original asphalt. (2) R-F modified WMA had better cracking resistance at a low temperature. The failure energy of the R-F modified WMA was 24.3% higher than the conventional HMA, and the fracture energy of the R-F modified WMA was 7.7% higher than the conventional HMA. (3) The pavement distress prediction results showed the same trend compared with the laboratory testing performance in that the R-F modified WMA helped to improve the IRI, AC cracking, and rutting performance compared with the conventional HMA. In summary, R-F modified WMA can be applied in pavement construction.

Učinak aditiva punilu na otpornost djelovanja vode u mješavinama splitmastiksasfalta (SMA)

SMA mixtures improve the permanent deformation resistance of hot-mixed asphalt mixtures. The effects of filler additives on moisture damage of SMA mixtures are investigated in this study. The class C and class F fly ashes and hydrated lime are used as filler additives. These are replaced with filler material at 0.5%, 1.0%, 2.0%, and 4% of the total weight of the mixture. Dry and wet (slurry) methods are used in mixing the filler additives. Class C fly ash significantly improved resistance to moisture damage. However, the effect of using liquid antistripping agent with filler additives is insignificant.

A Method for the Determination of Mixing Temperatures of Different Components of Recycled Hot Mix Asphalt Mixtures

A Method for the Determination of Mixing Temperatures of Different Components of Recycled Hot Mix Asphalt Mixtures

The Mechanical Resistance of Asphalt Mixture with Steel Slag to Deformation and Skid Degradation Based on Laboratory Accelerated Heavy Loading Test.

Steel slag is a main form of solid waste. Using this component to replace part of the aggregate in an asphalt mixture is an effectively way of treating solid waste. To study the performance degradation of asphalt mixture with various content of steel slag under heavy loading, some large-sized basalt hot mixed asphalt mixture (BHMA) and steel slag hot mixed asphalt mixture (SHMA) in a form of specimens were prepared and a heavy loading wheel tracking test was conducted. The aggregate characteristics of basalt and steel slag were measured. The deformation and skid resistance of the asphalt mixture with different content of steel slag was tested and analyzed. Due to the particle characteristics of steel slag aggregate, it was found that a low content of steel slag can effectively improve the resistance to deformation and skid resistance of the asphalt mixture under heavy loading. The response of SHMA can still meet the pavement technical requirement after long-term heavy loading service. The main change in the mixture under heavy loading is the crushing of the 9.5–16 mm aggregate, and the content of this part also significantly affects the deformation. This study explains the mechanism of degradation of SHMA under heavy loading: the large aggregate is crushed and forms a new aggregate skeleton structure.

Assessment of freezing and thawing cycle (FTC) effects on mixed mode I/III fracture toughness and work of fracture of HMA asphalt mixtures

Asphalt fracture due to initiation and propagation of cracks is a major failure mode especially at cold regions. Freezing and thawing phenomenon that is often seen at rainy environments can double the damage of overlays and pavement systems. Study of the crack resistance of asphalt concrete materials exposed to such environmental condition can provide good insights for the designers and engineers of pavement structures. Mixed mode I/III (combined opening-tearing mode) is a possible mode of fracture in overlays especially for edge cracks located in road bends. The effects of freeze/thaw mechanism on mixed mode I/III fracture characteristics of asphalt mixtures have not been studied till now. Hence, in this research using Edge Notch Disc Bend (ENDB) test configuration a series of mixed mode I/III fracture experiments are conducted on fixed hot mix asphalt (HMA) mixture exposed to different numbers of freeze/thaw cycles (FTCs). Each FTC cycle was consist of thawing inside the water at 25 °C for 12 h and then storing the ENDB sample inside a freezer at −25 °C for 12 h. The fracture experiments were done after exposing five FTCs of 1, 3, 5, 7 and 9 and the corresponding values of fracture toughness and work of fracture obtained from different cycles were compared with the fracture results of control HMA mixture (i.e. with no freeze/thaw cycles). The results showed that in general both fracture toughness and fracture energy values are reduced by increasing the number of FTCs showing the negative influence of freezing and thawing mechanism on the low temperature cracking resistance of HMA mixtures. However, the rate of cracking resistance reduction becomes smaller by increasing the number of FTCs and typically after applying seven freeze/thaw cycles a plateau form is seen for the curves of fracture toughness and work of fracture. Such endurance limit range that is approximately 0.4 times the corresponding fracture strength of the control HMA mixture can be used as a design input parameter for estimating the long term performance of pavements subjected to both traffic loads and freeze/thaw cycles in real situations.

Rheological and Chemical Evolution of HMA and WMA Binders Based on Ageing Kinetics.

It is fundamental to predict or estimate the rheological behavioural evolutions of binders and mixture to ensure a durability service life of the whole infrastructure. This study compared the long-term ageing kinetics of hot mix asphalt (HMA) and warm mix asphalt (WMA) produced with the same base bitumen. The difference in the component was that the WMA contained 1% of Cecabase warm agent and 5.5% of water by the weight of bitumen, to obtain a large expansion ratio (47 times). Rolling thin-film oven test (RTFOT) and pressure ageing vessel (PAV) laboratory ageing were carried out on the binder with or without the warm agent. The oven ageing procedure was conducted on the loose HMA and WMA mixtures for 0, 3, 6, and 9 days. Research results indicated that the dual effect of the studied warm agent and the foaming water sharply decreased the viscosity of the binder at a high temperature. Compared with the HMA, the warm agent improved the ageing resistance of the asphalt binder. However, higher content, such as 5.5 wt.%, of foaming water deteriorated viscosity due to a thinner bitumen film, which was more susceptible to oxidation. Therefore, less than 2 wt.% of warm agent and foaming water was recommended in the foamed WMA preparation.

Nano-Al2o3 Composite on Intermediate and High Temperature Properties of Neat and Modified Asphalt Binders and Their Effect on Hot Mix Asphalt Mixtures

Nano-Al2o3 Composite on Intermediate and High Temperature Properties of Neat and Modified Asphalt Binders and Their Effect on Hot Mix Asphalt Mixtures

The Influence of Coal Fly Ash on the Mechanical Properties of Hot Mix Asphalt Mixture

Coal is one of the most important sources of energy, providing for over 40% of global electricity generation. Coal fly ash (CFA) is the by-product of thermal generation of energy in coal-fired power plant. CFA has been widely employed in the construction of concrete; however, there are only a few cases in which asphalt pavements have employed coal fly ash. This paper aims to determine the performances of CFA as filler in hot mix asphalt (HMA) mixture. This study used four CFA contents as filler by weight of aggregate in the dry method, namely CFA-0, CFA-2, CFA-4, and CFA-6. The mixtures were tested for stability, flow, stiffness, moisture damage, and Cantabro loss test. The findings indicated that the stability values of asphalt mixtures containing CFA were higher than conventional mixture. In addition, incorporating CFA also improved resistance towards moisture damage and durability. As a result, it can be inferred that CFA can be employed as filler substitute in HMA mixtures.

Investigating Mechanical Performance of Ravelling in Hot Mix Asphalt Containing Plastic Waste

One of the road damages on the flexible pavement is ravelling. Ravelling caused by the release of aggregate grains from the asphalt mixture. The interaction between the wheels of the vehicle and the surface of the pavement causes friction that pushes the aggregate out. The plastic waste on road pavements has been widely used to improve the performance of road pavement structures. Most of previous study focused on Hot Mix Asphalt (HMA) ravelling using Cantabro test. The purpose of this study was to investigate the ravelling performance of plastic waste material in hot mix asphalt mixtures. In addition, the use of plastic waste can reduce the environmental impact due to the high volume of plastic waste. The test is carried out in the laboratory using a rotation abrasion device based on the principle of rotating wheel load with loading, speed, and testing time parameters. Furthermore, the ravelling resistance value of HMA was obtained in dry and wet conditions. The addition of plastic waste into asphalt can increase the ravelling resistance of HMA mixes. The results of the wet test have greater ravelling resistance than dry test.

Laboratory investigation of bituminous concrete using Reclaimed asphalt pavement and waste Engine oil

The conventional method of preparing bituminous mixes incorporating bitumen and virgin aggregates requires a huge amount of energy to produce along with environmental concerns. In pavement industry, the usage of Reclaimed Asphalt Pavement (RAP) material is growingup dueto financial considerations and the necessity of environmental conservatism. The effective utilisation of reclaimed asphalt pavement waste in bituminous pavement can overcome its disposal issue as well as it is cost effective too. Whereas replacing RAP with virgin aggregates have some drawbacks related to workability and overall quality of the pavement. Reclaimed Asphalt Pavement is subjected to environmental degradation hence affected due to aging. Long term aging effect is very prominent in reclaimed asphalt pavement materials. Hence, it becomes stiff and difficult to employ. To make it workable and its efficacious usage rejuvenators are needed. The addition of oil-containing additives can be useful as rejuvenators. For the present study, Waste Engine Oil (WEO) has been used as a rejuvenating agent. The main objective of this research is to evaluate the effect of RAP with or without rejuvenator in the Hot Mix Asphalt (HMA) mixtures. To assess the performance of the bituminous mixes Marshall properties, Tensile Strength Ratio (TSR) and Indirect Tensile Strength (ITS) for moisture susceptibility were performed. The HMA mixture with 20%, 30%, 40%, 50%, 60%, and 70% of RAP content were prepared and subsequently 1.5% of waste engine oil (by the weight of RAP content) was added to other HMA mixes containing the same RAP proportion. Corresponding result indicates that with the addition of RAP to the HMA mixes showed improved Marshall Properties, Tensile Strength and resistance against moisture susceptibility. Whereas, addition of WEO improves the Marshall Properties but decrement in Tensile Strength was observed.

Laboratory Performance Evaluation of Hot Mix Asphalt Mixture Using Belessa Kaolin as a Filler with Superpave Aggregate Gradation

Mineral fillers and different aggregate gradations have a great effect on the mechanical property of asphalt concrete pavements. In this research, the effect of nonconventional material so‐called Belessa kaolin and Superpave gradation on marshal properties, moisture susceptibilities, and permanent deformation in asphalt mixtures was investigated. The chemical composition of Belessa kaolin shows that the total content of silicon dioxide (SiO2), iron oxide (Fe2O3), and aluminum oxide (Al2O3) was 63%, 24.1%, and 2.84%, respectively. The physical properties of Belessa kaolin were conducted on specific gravity, and the plastic index was 2.62 and 3.24, respectively. Based on the study area characteristics and temperature, a bitumen grade of 60/70 penetration is selected. Hot mix asphalt (HMA) specimens were prepared from three different Superpave gradations with conventional filler crushed stone dust (CSD) of different proportions (5.0, 6.0, and 7.0%) and five different bitumen contents (4, 4.5, 5, 5.5 and 6%). A hot mix asphalt with 5.0% of CSD was selected as the control mix based on Ethiopian Road Authority (ERA) standard specifications. The conventional filler was replaced by Belessa kaolin at different replacement rates (0, 10, 20, 30, 40, and 50%) on the basis of the control mix with 5% CSD and 5.1% optimum bitumen content (OBC). The replacement rate of 30% of Belessa kaolin provides better marshal properties and resistance to moisture susceptibility. The results of the experiments indicated that the use of Belessa kaolin on HMA has fulfilled the criteria specified on the specification as a filler with Superpave aggregate gradation up to 30% replacement of conventional filler in HMA.

Rutting prediction of hot mix asphalt mixtures reinforced by ceramic fibers

One of the most severe problems with flexible asphalt pavements is permanent deformation in the form of rutting. Accordingly, the practice of adding fiber elements to asphalt mix to improve performance under dynamic loading has grown significantly in order to prevent rutting distress and ensure a safe and long-lasting road surface. This paper explores the effects of a combination of ceramic fiber (CF), a low-cost, easily available mineral fiber, and thermal insulator fiber reinforced to enhance the Marshall properties and increase the rutting resistance of asphalt mixes at high temperatures. Asphalt mixtures with 0%, 0.75%, 1.5%, and 2.25% CF content were prepared, and Marshall stability and wheel tracking tests were employed to study the effect of added CF on asphalt mixture performance. Scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) were also used to investigate the morphologies of CF and reinforced asphalt mixtures and to identify the mechanism of improvement .According to the study results, the ideal ceramic fiber content was 1.5%, which yielded an improve in Marshall stability and reduced rut depth by 22.05% and 27.71% at temperatures of 50°C and 60°C, respectively, when compared to asphalt mixtures without CF. Microscopic analyses clearly revealed the surface properties, particle diameter size, and fiber distribution of the reinforced mixture, including the network structure and strength mechanism, which improved the performance of the asphalt mixture by forming a three-dimensional network.