Wax-based Warm Mix Asphalt Research Articles

A novel method for determining the wax precipitation temperature in wax-based warm mix asphalt

ABSTRACT To accurately determine the wax precipitation temperature (WPT) of wax-based warm mix asphalt binder, a novel algorithm for WPT calculation was proposed, and the process of wax precipitation in asphalt, as well as the effects of aging, cooling rate, and shear rate on wax precipitation characteristics, were investigated through dynamic shear rheometer (DSR) tests and polarised light microscopy (PLM) experiments. The research findings reveal the following: The refined WPT algorithm exhibits heightened precision compared to the traditional viscosity method, showcasing superior reproducibility and mitigating human-induced errors. During the cooling process, wax molecules become oversaturated, leading to the precipitation of wax crystals and the transformation of asphalt into a solid–liquid two-phase system. The aging of asphalt causes changes in its composition, shifting the phase equilibrium towards favouring wax precipitation. The WPT of asphalt is also influenced by the cooling rate and shear rate, and a larger cooling rate and shear rate will reduce the WPT. Wax crystals are less numerous and more regular in shape at low cooling rates.

Thermal stress calculation of wax-based warm mix asphalt considering thermorheologically complex behavior

The warm mix asphalts which reduce the environmental pollution always show thermorheologically complex behavior under the realistic working conditions (the long-term loading at the low temperature) in the cold region. However, many scholars ignore the thermorheologically complex behavior when calculating thermal stresses. In this paper, the new thermal stresses calculation method considering thermorheological complexity of four wax-based warm mix additives (Fischer-Tropsch (F-T) based wax, fatty acid amides (FAA) based wax, polyethylene (PE)-based wax, and linear aliphatic hydrocarbon (LAH)-based wax) modified asphalt binders were proposed, which was the process of incremental iterative (Named as ‘the incremental method’). The results show that the warm mix asphalt exhibits the thermorheologically complex behavior under long-term loading condition at the low temperature through the tail of the master curve of stiffness modulus, and the thermal stresses considering thermorheologically complex characteristics calculated by the incremental method are greater than that calculated by the traditional Monismith method. Therefore, the incremental method should be used to calculate the thermal stress of asphalt binders under the long-term loading condition instead of the Monismith method, otherwise the cracking risk of the asphalt binder will be underestimated. The wax-based warm mix additives with longer chain molecules and cold storage time can increase the thermorheological complexity more evidently, and the thermal stresses of asphalts with thermorheologically complex characteristics are more sensitive to cooling rate. All in all, the proposed incremental method will provide a supplement to the calculation method of the thermal stresses in the asphalt binder.

Effect of warm mix additives and hydrated lime on viscosity and bonding–debonding behaviour of RET and PPA modified asphalt binder with aggregates

Higher energy requirement for asphaltic layer construction with asphalt binder containing reactive elastomeric terpolymer (RET) and poly phosphoric acid (PPA) can be addressed to a greater extent with the addition of warm mix asphalt (WMA) additives. However, moisture damage related problem is one of the concerns with such addition, which further aggravates with an increase in ageing level. The addition of lime may help in addressing moisture damage related problems in such cases. Previous research works show that based on the interaction between asphalt binder and particular WMA additive, the viscosity may undesirably increase also. So far, the influence of different WMA additives (wax, chemical surfactant (CS) and water-based (WB)) on the workability related properties of asphalt binder containing RET and PPA is not understood. It is also not clear if such warm mix additives with/without lime can help in improving long-term bonding with different aggregate types or not. Therefore, this research work aimed at identifying the appropriate WMA additive (with/without lime) which can help in (a) addressing the workability related problem and (b) improving long-term bonding with different aggregate types. To achieve this, different types of WMA additives (with/without lime) were added to RET and PPA modified binder. Viscosity-based measurement and chemical analysis using Fourier transform infrared spectroscopy were performed to understand workability and underlying chemical changes. Results indicated that although wax and CS-based warm mix additives can help in reducing energy demand, the addition of WB warm mix additive will have a negative impact from the workability perspective. Likewise, dynamic contact angle for different binder combinations was measured to evaluate the surface free energy components, which further helped to examine the long-term bonding with different aggregate types. Among different WMA additive types, the use of wax-based WMA additive was found to be most effective in improving compatibility with different aggregate types. Also, irrespective of the binder combination, the addition of lime improved the long-term bonding with considered aggregate types.

Investigation of Adhesion Performance of Wax Based Warm Mix Asphalt with Molecular Dynamics Simulation.

Compared with traditional hot mix asphalt (HMA), wax based warm mix asphalt (WWMA) can be mixed with the aggregate at a lower temperature and achieve the desired compaction. However, the adhesion performance of WWMA on aggregate is uncertain. To evaluate the adhesion performance of asphalt and aggregate, researchers used contact angle test, pull-off test, and ultrasonic washing experiments. However, these tests cannot adequately explain the microscopic mechanism of the interface between asphalt and aggregate. Molecular dynamics (MD) can better explain the adhesion mechanism of asphalt aggregates because they can be simulated at the molecular scale. So, the purpose of this research is to use the MD method to study the adhesion performance between WWMA and aggregate. Two aggregate oxides (CaCO3 and SiO2) models, the matrix asphalt model and WWMA models, were built in Materials Studio (MS) software. The adhesion work of asphalt and aggregate oxides was calculated. With the increase of wax modifier content, the adhesion work of asphalt and aggregate oxides (CaCO3 and SiO2) first increases and then decreases. When the wax modifier is increased to 3 wt%, the adhesion works of the WWMA-SiO2 and WWMA-CaCO3 increase by 31.2% and 14.0%, compared with that of matrix asphalt. In this study, the accuracy of the MD calculation result was verified by the pull-off experiments and the contact angle experiments. WWMA was prepared by a high-shear mixer emulsifier. In the pull-off experiments and the contact angle experiments, the tensile strength and the adhesion work between the aggregate and the asphalt containing 3% wax modifier reaches peak values. These values are 140.7% and 124.9%, compared with those between the aggregate and the matrix asphalt. In addition, the results of the pull-off experiments and the contact angle experiments are in good agreement with that of the MD simulation. Finally, Fourier transform infrared spectroscopy (FTIR) shows that the carbonyl content of WWMA is greater than that of matrix asphalt. It explains well that the wax modifier promotes the adhesion between asphalt and aggregate. This paper provides an important theoretical basis to understand the adhesion performance of WWMA and aggregate.

Laboratory investigation and statistical analysis of the rutting and fatigue resistance of asphalt mixtures containing crumb-rubber and wax-based warm mix asphalt additive

Recent studies show that using crumb rubber modifier (CRM) improves the mechanical and rheological properties of asphalt samples. However, the higher viscosity of rubberized binders increases the production temperatures of resulting mixtures. Using Warm Mix Asphalt (WMA) technology in combination with rubberized binders is a practical solution to alleviate this problem. However, mechanical characteristics of rubberized warm mixtures should be further analyzed to determine the effects of warm additives on the performance of asphalt mixtures. This study was performed to investigate the effects of an organic WMA additive, Slack wax (SW) (2%, 4%, and 6% by weight of binder), upon rutting and fatigue resistance of rubberized asphalt mixtures (15% and 20% CRM by binder weight). Further, a statistical analysis was conducted to define the possible relationships between fatigue life and three mechanical factors: toughness index (TI), resilient modulus, and indirect tensile strength (ITS). The results of the dynamic creep test indicated that both CRM and SW increased the flow number of asphalt samples yielding more resistant mixtures against rutting distress. The wheel tracking test results were consistent with the dynamic creep test. According to the indirect tensile fatigue test, the addition of SW was effective in improving the fatigue life of both control and rubberized asphalt specimens under two studied stress levels. TI values derived from the ITS test showed that rubberized warm mixtures can significantly increase the flexibility and energy absorptivity of asphalt mixtures. The results of bivariate correlation analysis indicated a direct relationship between the fatigue life-Mr and fatigue life-TI parameters. The significant values of correlation demonstrate that TI value derived from a cheap, easy, and fast ITS test is a practical parameter to predict the fatigue life of rubberized warm mixtures.

Decision support for selecting optimal method of recycling waste tire rubber into wax-based warm mix asphalt based on fuzzy comprehensive evaluation

Recycling crumb rubber (CR) derived from waste vehicle tire as asphalt modifier is an effective waste management approach with both engineering and environmental merits. However, the high viscous asphalt rubber (AR) brings higher energy consumption and hazardous construction emission. Wax-based warm mix asphalt (WMA) additive has proven to be able to alleviate these concerns. Application of WMA additives enriches the methods of recycling CR into asphalt. Preliminary investigations documented the effects of CR recycling methods on the service performance of warm crumb rubber modified asphalt mixture (WCRMA). Therefore, making a decision on the optimal recycling method considering the overall service performance is necessary. Nevertheless, there are limited studies focusing on the recycling method assessment and decision-making approach. To fill this gap, WCRMAs with different crumb rubber recycling methods were prepared and tested in laboratory. The effect of the recycling method on the overall service performance of WCRMAs was characterized. A fuzzy comprehensive evaluation (FCE) method was employed to quantify the performance grade of asphalt mixtures according to fuzzy logic. The weight matrix of all the service properties was developed based on the Analytic Hierarchy Process (AHP) under the considering of the circumstance of southern China. The experimental work revealed the significant influence of the recycling method on the service performance of WCRMAs. By means of the FCE method, this study suggested that for southern China with hot and humid climate, the optimal method of recycling CR into wax-based WCRMA is mixing AR and Sasobit first followed by incorporating them into aggregate. In rainy regions, asphalt mixture produced by directly mixing AR, Sasobit, and aggregate at 160 °C may perform better because it showed the best moisture damage resistance and good overall performance.

Influence of thermal history on the intermediate and low-temperature reversible aging properties of asphalt binders

This paper aims to investigate the influence of thermal history on the intermediate and low-temperature characterisation of asphalt binders. First, various asphalt binder intermediate and low-temperature characterisation methods and the significance of thermal history on asphalt characterisation were reviewed. Second, regular Superpave performance grading (PG) test, extended bending beam rheometer (Ex-BBR) test, double edge-notched tension (DENT) test and torsion bar low-temperature frequency sweep test were performed on selected asphalt samples with different treated thermal history. In addition, black space diagrams were also drawn to show the phase separation properties of varying asphalt binder formulations. The results showed that grade loss of wax-based warm mix asphalt almost kept constant when a small amount of microcrystalline wax (1% by mass of binder) was added. However, grade loss increased obviously with adding more microcrystalline wax (higher than 2%). Prolonged isothermal conditioning had a different degree of influence on the small-strain rheological and large-strain damage properties of asphalt binder. Applying slower loading frequency in dynamic shear rheometer (DSR) caused more obvious decrease in phase angle due to prolonged conditioning time.

Permanent Deformation Characteristics of Warm Asphalt Binders under Reduced Aging Conditions

Warm Mix Asphalt (WMA) technologies allow a 20 to 40°C reduction in production temperatures of asphalt mixes. These technologies are often synergistically combined with modified asphalt binders to tackle the increased production temperature requirements with these binders. Because of lower production temperatures, the asphalt binders containing WMA additives undergo reduced short-term aging and thus need to be examined for permanent deformation behavior at different reductions in production temperatures. The present study evaluates permanent deformation characteristics of warm asphalt binders as function of short-term aging temperature, modified binder type, and various dosages of a wax-based WMA additive: Sasobit. Experimental variables included are: three short-term aging temperatures (163°C, 143°C, and 123°C), two modified asphalt binders (polymer, and crumb rubber modified), and three contents of WMA additive (1%, 2%, and 3%). Warm binders as well as control binders are characterized in terms of viscosity, failure temperature, temperature sweep, frequency sweep, and multiple stress creep and recovery tests. WMA additive compensates the reduced stiffness of binders on being aged at lower temperatures, as rheological parameters of warm binders aged at 143°C and 123°C compare well with control binders. Statistical models for the rheological parameters as function of the experimental variables are also developed.

Application of WMA Technology to Bituminous Base Course Mixes

Warm Mix Asphalt, due to lower mixing and compaction temperatures, provides some engineering benefits over conventional Hot Mix Asphalt. In this study, an attempt is made to assess the viability of using Warm Mix Asphalt technology in bituminous base courses. An organic wax-based Warm Mix Asphalt additive was used in this study to produce Dense Bituminous Macadam, a commonly used bituminous base course mix in India. Experimental variables included three additive contents and four mixing temperatures. Rheological properties of binder modified with different doses of additive were examined. In all, twelve Warm Mix Asphalt Dense Bituminous Macadam mix types were prepared, evaluated and compared with Hot Mix Asphalt Dense Bituminous Macadam (control) mix. Rheological test results showed the addition of wax-based additive improved stiffness and resistance against permanent deformation of the base binder. Tensile Strength Ratio and retained Marshall Stability results indicated that Warm Mix Asphalt Dense Bituminous Macadam mixes were resistant to moisture-induced damage.

Using a modified asphalt bond strength test to investigate the properties of asphalt binders with poly ethylene wax-based warm mix asphalt additive

This paper presents a feasibility of a modified Asphalt Bond Strength (ABS) test method for use with a new adhesion testing device with three different pullout stubs and its application for evaluating Polyethylene (PE) wax-based Warm Mix Asphalt (WMA) additive. Four different asphalt binders were used to evaluate the feasibility of applying the existing AASHTO ABS test method using a new ASTM-certified adhesion testing device and three different pullout stubs. The modified ABS test method was used to evaluate the loss of adhesion and cohesion in asphalt bond strength due to moisture-induced damage. The paper also discusses rheological properties of extracted asphalt binders from three different test sections in Minnesota, Ohio and Iowa constructed using PE wax-based WMA additive and different amounts of Reclaimed Asphalt Pavement (RAP) materials. Based on the modified ABS test results using the new adhesion testing device, it was found that the proposed pullout stub with 0.0mm thickness (no edge) exhibited consistent results. Based on the results from extracted asphalt performance grading and the multiple stress creep recovery (MSCR) test, it was found that the PE wax-based WMA additive, which was specially designed for asphalt mixtures with a high RAP content, significantly improved the rheological properties of aged asphalt binders from RAP materials.

Comprehensive Evaluation of Warm SMA Using Wax-Based WMA Additive in Korea

Abstract Conventional stone mastic asphalt (SMA) is being increasingly used in highways and expressways because it provides high rutting resistance, good skid resistance, and noise reduction for heavily trafficked roads. However, the conventional SMA mixture requires high mixing and compacting temperatures to create a suitable coating between the polymer-modified asphalt and large size of aggregate. Warm-mix asphalt (WMA) technology is being extended to provide significant economic benefits when applied to heat sensitive mixture, such as polymer-modified mixture, to reduce mixing and compacting temperatures. In this study, the performance characteristics of SMA–WMA mixture using new polyethylene wax-based WMA additive were evaluated against the conventional SMA mixture without additive, in terms of the moisture susceptibility, viscoelastic properties, rutting resistance at high temperature, fatigue resistance, and crack resistance at low temperature. The mix design was carried out in the laboratory for the conventional SMA mixture, and a similar composition was adopted for the SMA–WMA mixture (with the incorporation of 1.5 % WMA additive in the asphalt binder weight), in order to evaluate the influence of the performance characteristics of the resulting SMA mixture. Drain-Down and Cantabro test results of SMA–WMA mixture meet the requirement of the relevant criteria. Compared to the conventional SMA, the mixtures containing WMA additive show superior performance in moisture susceptibility, rutting resistance at high temperature, fatigue resistance at intermediate temperature, and crack resistance at low temperature. Therefore, this implies that the WMA additive is effective in reducing the production temperature, without compromising the performance of the SMA–WMA mixture.

Laboratory Evaluation and Field Implementation of Polyethylene Wax-Based Warm Mix Asphalt Additive in USA

The use of Warm Mix Asphalt (WMA) for the construction of roads around the world is growing rapidly. This paper presents a new organic WMA product that has been recently introduced to the US market, which is Polyethylene (PE) Wax-based WMA additive with crystal controller to increase the low temperature cracking resistance and anti-stripping agent to enhance moisture susceptibility. To determine the optimum dosage rate, the viscosities of the binder with varying amounts of additive were measured. Based on the Asphalt Binder Cracking Device (ABCD) test, it was found that the low-temperature cracking temperature of asphalt binder would not be affected by the amounts of the additive up to 3.0%. The new Polyethylene (PE) Wax-based WMA mixtures with Reclaimed Asphalt Pavement (RAP) materials were also tested using the Hamburg wheel tracking device and the wheel passes were significantly higher with WMA mixtures PG 64-28 binder, Minnesota aggregates and 25% RAP than the ones with 64-22 binder, Iowa aggregates and 10% RAP. The Hamburg test results seemed to be influenced by more on the characteristics of aggregates and RAP materials than the WMA additive. Two in-service roads in Iowa and Minnesota were successfully rehabilitated using the PE Wax-based WMA mixtures. The average void of 3.8-cm (1.5-inch) WMA overlay (9.0%) was higher than that of HMA overlay (7.0%) placed on an urban street in Iowa City. It was partly due to asphalt temperature that was lowered to match the lower aggregate temperature. However, it is interesting to note that the average air void of the cores obtained from the rehabilitation section of the same street using the same WMA was significantly lower (6.0%). In Minnesota's state highway, the average air voids of four WMA and HMA cores for quality control were 5.85% and 5.29%, respectively and those of four other WMA and HMA cores for quality assurance were 6.05% and 6.01%, respectively. The WMA pavements were easier to reach 94% density with fewer passes of a compactor than the HMA.

Laboratory investigation into the effects of working temperatures on wax-based warm mix asphalt

The comparative laboratory investigation described in this paper focuses on the effects of artificial wax as an additive for warm mix asphalts (WMAs). The investigation was performed in the Road Research Laboratory at the Politecnico di Milano, and it has been divided into two main phases to evaluate the working temperatures on: (i) compaction and volumetric parameters and (ii) the mechanical performance of two different asphalt mixtures for wearing courses. Results showed that mixtures containing wax are stiffer at low temperatures and produce greater deformations than traditional mixtures, whereas wax does not significantly influence fatigue resistance at 20°C.

EVALUATION OF WARM-MIX ASPHALT MIXTURES USING LEADCAP ADDITIVE

Warm-mix asphalt (WMA) is an emerging technology that can allow asphalt to flow at a lower temperature for mixing, placing and compaction. This technology can reduce energy consumption during asphalt production and reduce carbon dioxide emission and asphalt oxidation as well as extend asphalt paving season and delivery distance under enhanced working environment at the field. In Korea, an innovative wax-based WMA additive, which is named low energy and low carbon-dioxide asphalt pavement (LEADCAP), was developed to reduce mixing and paving temperatures applied in asphalt paving process. Since the first field trial project using the LEADCAP WMA technology in 2008, many LEADCAP WMA field trial projects have successfully been completed in Europe, United States and Asia. In this paper, the LEADCAP WMA mixtures along with the control hot-mix asphalt (HMA) mixtures were evaluated with respect to their crack resistance and rutting resistance based on the dynamic modulus test and full-scale accelerated pavement test (FSAPT). With the limited data carried out, it is concluded that LEADCAP additive can be effectively applied to WMA mixtures and LEADCAP WMA pavement is expected to perform comparable to HMA pavement.

Behavior of Selected Warm Mix Asphalt Additive Modified Binders and Prediction of Dynamic Modulus of the Mixes

Abstract This study evaluated the viscoelastic properties of a performance grade binder modified with different dosages of a selected wax-based warm mix asphalt (WMA) additive (WMA1). The effects of reduced rolling thin film oven (RTFO) aging on the stiffness of the WMA1-modified binder were also evaluated. The viscoelastic properties of the modified binders were then used to estimate the dynamic modulus (E*) values of the WMA mixes through time temperature superposition principles. Furthermore, the effects of a selected liquid anti-stripping agent (ASA), ASA1, on the properties of the WMA1-modified binder were investigated. It was observed that the linear viscoelastic limits of WMA1-modified binders decreased with an increasing dosage of WMA1. Reduced RTFO aging was found to have significant effects on the stiffness of the WMA1-modified binder. The Hirsch model was found to provide better approximations of the E* values than the Witczak model. The Witczak model, based on dynamic shear rheometer data, was found to significantly underestimate the E* values. Although ASA1 did not reduce the beneficial effects of WMA1, it was found to increase the E* values of the WMA mix. The findings of this study are expected to offer transportation professionals a better understanding of the evaluation of WMA binders and mixes.

Development of Warm-Mix Asphalt Additive and Evaluation of Performance

Several warm-mix asphalt (WMA) technologies have been developed and implemented worldwide. Because of the reduced production and compaction temperatures of WMA mixtures, WMA technology can reduce energy consumption, carbon dioxide emission, and asphalt oxidation as well as extend the paving season, increase hauling distance, and create a better working environment. A wax-based WMA additive called low-energy and low–carbon-dioxide asphalt pavement (LEADCAP), has been developed by the Korea Institute of Construction Technology and Kumho Petrochemical and is the first WMA additive developed in South Korea. This paper introduces the characteristics of this newly developed WMA additive and presents the performance evaluation of WMA with LEADCAP. To evaluate the performance of the WMA mixture with LEADCAP additive, the Superpave® mix design, moisture susceptibility test, and mechanical test were performed. Common hot-mix asphalt and a WMA mixture with Sasobit additive were also evaluated for comparison. Sasobit is also a wax-based additive and is well-known. Mechanical tests included the dynamic modulus test, the direct tension fatigue test, and the triaxial repeated loading permanent deformation test. From the limited data obtained in this study, it was concluded that LEADCAP could be effectively used in WMA mixtures and that the performance of WMA with LEADCAP could be expected to be comparable to that of hot-mix asphalt and WMA with Sasobit additive.

Performance Characteristics of Thin-Lift Overlay Mixtures

This study designed and evaluated the performance of thin-lift mixtures that incorporated a high reclaimed asphalt pavement (RAP) content, recycled asphalt shingles (RAS), and a warm-mix asphalt (WMA) technology, both individually and collectively. A Superpave® 9.5-mm mixture was designed with new materials and designated as the control mixture. The same control mixture was developed with 40% RAP, with 5% RAS, and with 35% RAP and 5% RAS. Each of the mixture designs was then repeated at a lower mixing and compaction temperature according to a wax-based WMA technology. The effect of the RAP, RAS, or both on the stiffness of each mixture was measured by using the dynamic modulus. The performance of each mixture was determined by measuring (a) its reflective cracking resistance with an overlay tester, (b) its low-temperature cracking resistance with an asphalt concrete cracking device, and (c) its moisture susceptibility with a Hamburg wheel tracking device. In addition, binder was extracted from each mixture and the performance grade determined. The mixtures that incorporated high RAP content, RAS, or both exhibited higher stiffness, which was confirmed with the extracted binder grading results. The use of RAP, RAS, or both reduced the reflective cracking resistance but did not have a negative impact on the low-temperature cracking resistance of the mixtures. Moisture susceptibility test results indicated that the addition of RAP, RAS, or both improved the mixtures' resistance to moisture failure. The addition of WMA technology to the mixtures provided similar or improved performance in most of the mixture tests.