Warm Mix Research Articles

Evaluation of Aging and Moisture Damage Potential of Warm Mix Asphalt Incorporating a Synthetic Wax Additive

This paper presents the effects of a warm mix additive on the moisture damage of warm mix asphalt (WMA). Asphalt mixtures were made using different WMA contents (0, 2 and 3%) at different compaction temperatures. Aging properties were studied from the effects of artificial long-term aging on resilient modulus (MR) and indirect tensile strength (ITS) of WMAs. Moisture damage was investigated in term of tensile strength ratio (TSR) of unaged and aged specimens conditioned in one and three cycles of freezing and thawing. The results showed that the aging significant affected the MR and ITS of WMA. The additive content increased with air voids but in contrary with the bulk density. Hence, the use of higher additive content can be more beneficial in terms of resilient modulus. Decreasing compaction temperature could significantly decrease the ITS while the TSR of WMA reduced as compaction temperature decreased. From moisture damage tests, the TSR of aged samples was found to be lower than that of unaged samples

An Evaluation of the Cracking Resistance of Steel- and Glass-Fiber-Reinforced Asphalt Mixtures Produced at Different Temperatures

This study focuses on the effects of the production temperatures, warm mix asphalt (WMA) additive, and fiber content on the cracking resistance of steel- and glass-fiber-reinforced asphalt mixtures. By using three different approaches, which included different mixing and compaction temperatures, along with the incorporation of a WMA additive, the samples were produced utilizing the Marshall mix design method. The low-temperature cracking resistance and bottom-up fatigue cracking resistance of the asphalt mixture samples were assessed through indirect tensile (IDT) tests performed at two different test temperatures: −10 °C and 20 °C, respectively. According to the fracture work density values, glass fibers significantly improve the low-temperature cracking performance of asphalt mixtures. Furthermore, it was found that the low-temperature cracking resistance of the hot mix asphalt (HMA) mixtures containing fibers was similar to that of the mixtures prepared using the WMA additive at 15 °C lower mixing and compaction temperatures than the HMA mixtures. To conclude, the WMA additive improved the compactability of the steel- and glass-fiber-reinforced asphalt mixtures without compromising the low temperature cracking performance, despite the low mixing and compaction temperatures.

Recycled Concrete Aggregates (RCA)-based asphalt mixtures: A performance-related evaluation with sustainability-criteria verification

This investigation aims to explore the feasibility of using Recycled Concrete Aggregate (RCA) as a partial replacement for Natural Aggregates (NAs) in the production of Hot Mix Asphalt (HMA) and Warm Mix Asphalt (WMA). As WMA technology, Iterlow T (a chemical additive) was selected. For both types of asphalt mixtures, the RCA dosages of 0, 15, 30 and 45% by weight of coarse aggregates were considered. Notably, four different RCA sources were assessed, and the alkali-silica reaction and attached mortar quantity were analyzed for each one. In order to examine the effect of the coarse RCA on the performance-related properties of the asphalt mixtures, a test protocol was conducted. This protocol comprised four tests, i.e., stiffness modulus, moisture susceptibility, rutting resistance, and fatigue life. Additionality, a sustainability-criteria verification was performed employing the Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) methodologies. Respectively, the LCA and LCCA estimate each alternative's environmental impacts and production costs. Consequently, the main finding obtained were: (i) as the coarse RCA content increases, asphalt mixtures exhibit a reduction in their mechanical performance; (ii) the performance-related properties of the HMAs and WMAs with a 15% RCA dosage are acceptable, but more elevated amounts generate highly noticeable deterioration; and (iii) 15% of coarse RCA minimizes the environmental burdens and maximizes the cost-effectiveness of the asphalt mixtures fabrication. Thus, the main contribution to the literature that achieves this research is to perform a comprehensive multi-criteria examination on the potential of the RCA as a recycled material to minimize the depletion of non-renewable resources.

Performance evaluation of WMA mixtures with RAP

Nowadays, asphalt industries are seeking for new methodologies in order to minimize global warming and emission of greenhouse gases. One of the solutions found out was the use of warm mix asphalt (WMA) technology which allows reduction in asphalt mixing, working and compaction temperature. WMA reduces the desired temperature in comparison with hot mix asphalt by 20–40°C. In addition to this issue, the lack of superior quality natural aggregate resources everywhere around the world, it is essential to use the available natural resources efficiently along with the available construction and demolition waste such as recycled asphalt pavement (RAP) if possible, without compromising in the performance of the mixtures. In this study, reclaimed asphalt pavement was used as partial replacement for conventional aggregates and binder. The RAP contents of 0%, 25% and 50% were considered. Zycotherm was used as warm mix additive which improves the pavement moisture resistance by serving as an anti-stripping agent. The mixtures were prepared with HMA @ 130°C, HMA @ 160°C, WMA @ 130°C and all these three mixtures with partial replacement with RAP. The RAP material with 0, 25 and 50% replacement was adopted for both HMA and WMA for DBM grade 2 course. Zycotherm was added by 0.1% by weight of binder in both HMA and WMA mixes. The prepared test specimens were tested for Marshall and indirect tensile strength (ITS) test. The test results indicated that the WMA blend prepared using 0.1% by the weight of binder content showed good results compared to the hot mix asphalt @ 130°C. The indirect tensile strength ratio (TSR) of mixes containing RAP is found to be higher when compared to the mixes without RAP indicating lower moisture susceptibility of the mixtures. This study demonstrated the possible use of RAP in WMA mixes with better performance than HMA.

Mechanical performance and statistical analysis of natural and synthetic zeolite-warm mix asphalt as a function of compaction efforts

The compaction effort of mixes should be studied with caution since it significantly influences the mixtures' performance. A laboratory evaluation of warm mix asphalt (WMA) including synthetic zeolite (SZ) and natural zeolite (NZ) was conducted in this study. Marshall properties, tensile strength ratio, indirect tensile strengths at 25 and 60 °C, resilient modulus at 25 °C, and creep compliances at 40 °C were all examined. The NZ and SZ binders were produced by mixing one base binder (40/50 penetration grade) with 5% NZ and SZ binder components by weight. The 90 specimens were produced using the Marshall compactor at three different compaction efforts (35, 50, and 75 blows/face). Statistical analysis was conducted to examine the behavior and outcomes of asphalt binders. The results showed that (1) Both NZWMA and SZWMA combinations require 35 blows/face compaction effort to meet the minimum criteria of 8 kN stability, 2–4 mm flow, 85% tensile strength ratio, 14% VMA, and 448 kPa unconditioned tensile strength; (2) The production of NZWMA mixtures saves more time and fuel in the field than SZWMA mixtures while meeting the Marshall properties, creep performance, and moisture susceptibility at 35 blows/face compaction effort; and (3) A general trend of the Marshall, creep compliance, tensile strength, and resilient modulus performance as a function of compaction effort was observed for the NZWMA and SZWMA mixes used in this study.

Aging Resistance of Bitumen Modifiers: A Comprehensive Review

Abstract The deterioration of physical and mechanical properties of bituminous materials that are attributable to the aging of bitumen is one of the major causes of reduction in service life of flexible pavements. Thermal-oxidation and photo-oxidation aging are the two major types of aging of bitumen. Heat and oxygen cause thermal-oxidative aging, whereas ultraviolet irradiation and oxygen causes ultraviolet photo-oxidative aging of bitumen. Aging of binder leads to significant changes in the chemical composition of bitumen resulting in reduction of cracking resistance of bituminous mixes because of hardening of bitumen. So, it is quintessential to reduce the rate of hardening of bitumen induced by aging for prevention of premature failure of flexible pavements. The type of bitumen used for production of bituminous mixes have a significant effect on aging resistance of bitumen. The bitumen can be modified by using different types of modifiers such as antioxidants, bio-oils, nanomaterials, polymers, rubber, and ultraviolet absorbers. In addition to this, the modifiers such as fillers, warm mix additives, and rejuvenators also affect the aging resistance of bitumen. However, the effectiveness of these modifiers in preventing the hardening of bitumen because of aging varies with type of aging. The modifiers that exhibit improvement in thermal-oxidative aging resistance of bitumen are found to be less effective in improvement in photo-oxidative aging resistance and vice-versa. So, it is imperative to understand the effectiveness of different types of bitumen modifiers for the prevention of thermal-oxidative and photo-oxidative aging of bitumen. This review documents the resistance of different types of modifiers to thermal-oxidative and photo-oxidative aging. Finally, the scope for future work based on the critical gaps identified from existing works is also provided to assist further research.

English

English

The Microscopic Mechanism and Rheological Properties of SBS-Modified Asphalt with Warm Mixing Fast-Melting.

To overcome the shortcomings of traditional wet styrene-butadiene-styrene (SBS) modification technology, such as its high energy consumption and thermal decomposition, a warm mix and fast-melting SBS modifier was developed. Based on the theory of rheology, a dynamic shear rheometer (DSR) was applied to investigate the viscoelastic properties of the warm mix and fast-melting SBS-modified asphalt using a frequency scanning test. Atomic force microscopy (AFM) was used to reveal the modification mechanism of the SBS-modified asphalt. An investigation of the thermal stability of the asphalt binder was conducted using a thermogravimetric test (TG). The results exhibited that the SBS-modified asphalt had good viscoelastic properties, as well as thermal stability. The "bee structure" of the SBS-modified asphalt was finer and more stable. In addition, the adhesion and the Derjaguin-Muller-Toporov (DMT) modulus of the SBS-modified asphalt at a warm mixing speed was higher than that of regular SBS-modified asphalt.

Feasibility assessment of palmitamide derived from waste edible oil as a warm mix asphalt additive

The disposal of waste edible oil (WEO) has become a global challenge with both environmental and economic issues. To provide a novel strategy for the refinement recycling of WEO, this work investigated the feasibility of palmitamide derived from WEO as a warm mix asphalt (WMA) additive. The molecular structure and thermodynamic characteristics of palmitamide were first determined. Following, WMA binders with different palmitamide contents were prepared and their temperature sensitivity and rheological properties were evaluated. Additionally, the engineering performance of WMA mixtures was explored and the environmental benefits of WEO-derived palmitamide were assessed using the gas chromatography-mass spectrometry. The results demonstrate that the phase transition temperature of WEO-derived palmitamide is 98.87 °C, which shows great potential as a WMA additive. Palmitamide provides asphalt workability suitable for construction at relatively low temperatures through reducing the flow activation energy of asphalt. In addition, the moisture damage resistance and deformation resistance of WMA is also improved due to the hydrophobicity and filling effect of palmitamide, respectively. While it is inevitable that palmitamide slightly weakens the fatigue and low-temperature performance of WMA. Moreover, the application of WEO-derived palmitamide can reduce the volatile organic compounds of asphalt in the mixing stage and compaction stage by 40.3% and 30.8%, respectively. The findings contribute to the sustainable development of road engineering and the circular of waste resources.

Eco-friendly warm mix asphalt mixtures incorporating electric arc furnace steel slag as substitute to conventional aggregates

Eco-friendly warm mix asphalt mixtures incorporating electric arc furnace steel slag as substitute to conventional aggregates

Effect of nano molybdenum disulfide (Nano-MoS2) on fracture behavior of Warm mix asphalt (WMA)

Warm mix asphalt (WMA) has been developed for producing cleaner products than other asphalt mixtures. However, fractures caused by structural factors (microcracks caused by insufficient mixing of bitumen and aggregates at lower construction temperature) and environmental factors (microcracks caused by freeze–thaw cycles (FTCs) and aging process (AP)) lead to the formation of low temperature cracking (LTC) and intermediate temperature cracking (ITC), which is intensified by the loading factor. The present study aimed to evaluate and compare the short and long-term fracture behavior of WMA (containing vertical and angular cracks) using semi-circular bend (SCB) geometries under mode I loading conditions at low and medium temperatures. In order to improve the fracture behavior of WMA, an eco-friendly additive called molybdenum disulfide nanoparticles (Nano-MoS2) was used. The results showed that the mixture reinforced with 0.3 and 0.6% nano-MoS2 had better fracture resistance (Fracture Energy (GF) and Fracture Toughness (KIC)), Fracture Flexibility (Flexibility Index (FI), Toughness Index (TI), and Cracking Resistance Index (CRI)), and fracture toughness (Tensile Stiffness Index (TSI) and Tensile Strength (TS)) than the sample without additives under short-term and long-term conditions at temperatures of −15 and + 15 °C. Under 3FTC, the reduction of three indices KIC, GF, and Pmax (in agreement with the hypothesis), decrease in stiffness (in agreement with the hypothesis), and increase in the flexibility of the mixtures (against the hypothesis) was achieved. In addition, the increase of the three indices KIC, GF, and Pmax (against the hypothesis), increase of stiffness (agree with the hypothesis), and decrease of flexibility of the mixtures (agree with the hypothesis) were obtained under 6AP. After the addition of nano-MoS2 to the WMA, a large part of the reduction in the fracture indices was compensated due to the application of FTD cycles. Therefore, the mixture reinforced with nano-MoS2 had better long-term performance under mode I at low and medium temperatures (compared to the sample without additives and at the beginning of the design year). On the other hand, the long-term performance results showed that SCB samples containing vertical and angular cracks were more affected by 3FTC than 6AP. This result indicated the use of FTD cycles to evaluate the long-term performance of WMA mixture to achieve a better design.

Evaluation of the impact of long-term aging on fracture properties of warm mix asphalt (WMA) with high RAP contents

This study aimed to investigate the effects of long-term aging on the fracture characteristics of Warm Mix Asphalt (WMA) containing Reclaimed Asphalt Pavement (RAP). To this end, various RAP contents (0, 50, 75, and 100%) and one WMA additive (Zycotherm) were used. The Semi-Circular Bending (SCB) fracture test was conducted at intermediate temperature and fracture parameters, including the fracture force, fracture toughness, strain energy, J-integral, stiffness, and flexibility index were measured to identify the impact of aging and RAP addition on different fracture properties of WMA mixtures. To remedy the problem concerning the amorphous trend of fracture properties over the service time and intersecting the curves of fracture parameters versus service time, the area beneath the fracture parameter was employed as a reliable index for comparing different mixes. Then, summations of the area of all fracture parameters versus service time for various mixtures with different RAP content were identified as the overall fracture resistance of each mixture. Finally, an analysis of variance (ANOVA) was determined to statistically assess the results of the SCB fracture test. This study highlights the importance of considering long-term aging effects on WMA mixtures containing RAP and the potential benefits of using high RAP content in flexible pavements. Overall, this research can help agencies make a more precise decision regarding the consequences of high RAP content on the long-term performance of asphalt pavements.

Rheological Properties of Warm Mixed Asphalt

Adding a warm mixing agent to asphalt can lower the working temperature of asphalt construction by 20–40 °C. It is difficult to evaluate the impact of the existing warm mixed agent on the quality and effect of asphalt due to its wide variety. In this study, 70 # asphalt and 3 kinds of surfactants were selected to prepare warm mix asphalt. The result of different warm mix agents on the rheological properties of asphalt was evaluated through a rheological experiment. The results explained that the warm mixing agent could lower the Brookfield viscosity of asphalt. With the increase in asphalt temperature, the viscosity difference of different types of asphalt binder becomes smaller and smaller. A warm mixing agent will also reduce the creep stiffness of asphalt. In the multiple stress creep recovery test, the average recovery rate of asphalt and the average value of irrecoverable creep compliance have obvious stress dependence.

Rheological Properties of Desulfurized Crumb Rubber Modified Warm Mix Asphalt

In order to study the rheological properties of warm mix asphalt modified by desulfurized rubber powder with different meshes, the desulfurized rubber powder was mixed with matrix asphalt at the best content. Dynamic shear rheological test (DSR) was used to study the high temperature rheological properties of asphalt modified by waste rubber powder. Multi-stress creep test (MSCR) was used to study the high temperature deformation resistance of asphalt modified with waste rubber powder. The low temperature rheological properties of Sasobit and crumb rubber modified asphalt with different mesh numbers were evaluated by bending beam rheological test (BBR). The test results show that compared with the base asphalt, the complex modulus and rutting factor of CRMA 60 are significantly improved, and the effect is more obvious than that of CRMA 40 and CRMA 80. With the addition of Sasobit, the high temperature performance of WCRMA first increased and then decreased. With the addition of Sasobit, the creep stiffness modulus of WCRMA decreases, the creep rate increases, and the low-temperature properties first increase and then decrease. From the atomic force microscope (AFM), it can be seen that Sasobit promotes the compatibility between rubber powder and asphalt, and the performance of asphalt modified by 60 mesh rubber powder is best. When the mass fraction of Sasobit is 2.5%, WCRMA has the best comprehensive performance.

Use of Cashew Nut Shell Oil as Warm Mix Additive in Bituminous Mixtures

Use of Cashew Nut Shell Oil as Warm Mix Additive in Bituminous Mixtures

Digital image processing of warm mix asphalt enriched with nanocolemanite and nanoulexite minerals

Digital image processing (DIP) is a method used to view the internal structure of hot mix asphalt. However, in this study, the DIP of warm mix asphalt (WMA), which reduces environmental emissions and saves energy, was been investigated. Firstly, colemanite and ulexite minerals, of which the global reserves are abundant, were ground in a ball mill and nano-sized particles were observed for the first time in TEM micrograph. Secondly, these minerals were added to the foamed WMA in varying amounts of micron/nano-size. Marshall stability and repeated creep tests were performed and the void ratios in the mixtures were analyzed. Thirdly, a DIP system was designed. The primary purpose of this method was to scrutinize the impacts of voids and bitumen ratios around aggregates and the adhesion effect between the bitumen and aggregate. Finally, the void ratios identified by these tests were utilized to compare with those specified by the DIP method. The best deformation resistance for the ulexite appeared to result in a 5 %U + 53 μ mixture, whereas the highest deformation resistance for the colemanite yielded in 5 %C − 25 μ and 10 %C − 25 μ mixtures, according to repeated creep test results. The samples' void ratios identified around the aggregates were the lowest (1.35%) in the 5 %U − 25 μ mixture and the highest (3.72%) in the 10 %U − 25 μ mixture. It was concluded that the designed DIP was quite good in the interpretation of WMA with nanocolemanite and nanoulexite additives.

A Comprehensive Overview of the Utilization of Recycled Waste Materials and Technologies in Asphalt Pavements: Towards Environmental and Sustainable Low-Carbon Roads

Given the prevailing concerns about greenhouse gas emissions, global warming, and the growing demand for renewable resources, the pavement industry, among others, is actively engaged in researching and exploring low-carbon materials and technologies. Despite the growing interest in low-carbon asphalt pavement, there is still a significant knowledge gap regarding the use of various waste materials and technologies to achieve this goal. This study aims to close this gap by conducting a systematic review and scientometric assessment of the existing studies on the use of waste materials and technologies for low-carbon asphalt pavement. The study spans the years 2008 to 2023, and the scientometric analysis was conducted using the VOS viewer application. The study identifies materials and technologies in this area by examining co-authored country studies, publication sources, and keyword co-occurrence. It should be noted that a limited number of waste materials that allow CO2 emissions reduction was analyzed in this study. However, other waste categories, such as bio-oils and polymers, which can provide positive either environmental or economic impacts on the production of paving materials, were not considered in the scope of the study. Based on the current review, it was found that integrating recycled waste materials like recycled asphalt pavement, biochar, or crumb rubber with alternative mixing technologies such as warm mix asphalt and cleaner energy can significantly reduce CO2 emissions. China and the United States were identified as key research contributors to the low-carbon pavement. Furthermore, biomass-based fuel and electric construction equipment lower carbon and greenhouse gas emissions by 36–90% and 67–95%, respectively. However, before various recycled waste materials and technologies can be widely used in the asphalt industry, various challenges need to be addressed, including cost concerns, performance and durability concerns, standardization and regulations, availability, integration with existing facilities, and insufficient field and long-term data. The review identified critical research gaps, such as the absence of a homogeneous and reliable standard method for low-carbon asphalt pavement, limited field performance data, and a life cycle assessment approach in analyzing the emission reduction effects. The reviews will aid in the paradigm shift to a more carbon-friendly pavement industry that uses recycled waste materials and technologies.

Balancing the sustainable component of ethylene-vinyl acetate for achieved better compatibility improvement of wax-based warm mix additives in bitumen

The ethylene-vinyl acetate (EVA) polymers are always doped into waxy bitumen to inhibit network of wax crystals in bitumen. However, the compatibility improvement behaviors between wax-based warm mix (WWM) additives and bitumen by EVA are not clear, and the sustainable components of EVA for corresponding WWM additives to achieve better compatibility improvement are also not determined. This paper investigated compatibility improvement behaviors between commonly used WWM additives and bitumen after the addition of EVA to obtain sustainable components of EVA through experimental method of activation energy of viscous flow (AEVF) and density function theory-molecular dynamic (DFT-MD) calculations. The results show that the repulsions between the end of main-chain with highest electronegativity in WWM additives and polar molecules of EVA can alleviate the aggregation behaviors of WWM additives and EVA displays the best and worst compatibility improvements for additives with shortest and longest carbon chains, respectively. The dispersed asphaltenes combined with EVA can form the composite wax inhibitors (WIs) systems to increase diffusion coefficient and reduce percentage increment values of cohesive energy density (CED) to further disrupt ordered degree of WWM additives. On this basis, the sustainable carbon numbers of main-chain for EVA that are slightly less than average carbon numbers of WWM additives will help to better improve the compatibility of WWM additives. This investigation can provide the inspiration on how to choose the sustainable components of EVA to achieve high-efficiency compatibility improvement for corresponding warm mix asphalts (WMAs) with different average carbon numbers.

Study on effect of various rejuvenators on virgin asphalt binders suffering various aging conditions and the unified evaluation index

Adding rejuvenator is a feasible method to restore the properties of aged asphalt. Due to the complex rejuvenation mechanism between different rejuvenators and aged asphalt, there is no unified standard to evaluate the rejuvenation effect of rejuvenator. Most of the current research on rejuvenator focus on the characterization of macro mechanical properties of rejuvenated asphalt binder. In order to explore the changes of chemical composition and micromechanical properties of asphalt during aging and rejuvenation, fifteen kinds of virgin asphalt samples at different aging and rejuvenation stages were prepared. A commercial rejuvenator, aromatic oil and warm mix agent were selected as rejuvenators. The fifteen asphalt samples involved various aging methods, including water-ultraviolet aging, water free ultraviolet aging, RTFOT and PAV. Through gel permeation chromatography (GPC), Fourier transform infrared spectrometer (FTIR) and atomic force microscope (AFM) test, the reversibility evaluation index Rw, RC=O, RS=O and RDMT were proposed. These indexes could be used to quantitatively evaluate the rejuvenation effects of rejuvenator on the specific properties of aged asphalt. Based on the linear fitting results among various indexes, micro reversibility index of virgin asphalt (IRIV) was proposed. The results showed that the commercial rejuvenator and warm mix agent had a limited effect on the recovery of chemical composition and molecular weight of aged asphalt. The commercial rejuvenator over restored the micro mechanical properties of aged asphalt. The effect of aromatic oil on micro mechanical properties of aged asphalt was between commercial rejuvenator and warm mix agent. This study provides a way to quantitatively evaluate the rejuvenation effect of rejuvenator on virgin asphalt binder. It is helpful to better understand the aging-rejuvenation process of virgin asphalt binder more comprehensively from chemical and micromechanical properties.

Investigation of the time-domain linear viscoelastic response of warm mix asphalt mixture via discrete and continuous spectrum

Asphalt mixture is a temperature-sensitive material, and its viscoelastic properties are essential for pavement design and performance evaluation. This paper presents a method for investigating the time domain linear viscoelastic parameter response of asphalt mixture after adding different warm mix agents. The approach utilizes the generalized Sigmoidal function to construct master curves of storage modulus and loss modulus in the frequency domain, and both discrete and continuous spectrum analyses are used to analyze the viscoelastic behavior of the asphalt mixture. The effects of varying Kelvin and Maxwell element numbers on the discrete spectrum are compared to the spectral intensity and master curve obtained from the continuous spectrum. Results show that the generalized Maxwell model with 10−3 or 10−2 as the center point and the generalized Kelvin model with 103 or 104 can obtain more accurate results. When used as input for simulation software, the number of 11 elements can balance computational efficiency and accuracy. The study evaluates the impact of different warm mix agents on the relaxation modulus and creep compliance of asphalt mixture and discusses the practical implications of these findings for engineering applications. Adding Foam warm mix agent significantly lowers the asphalt mixture's relaxation modulus by approximately 44%, while Sasobit and Evotherm marginally raise it by 14% and 22%, respectively. The Foam warm mix agent also increases the equilibrium modulus of creep compliance to 0.091 MPa, 80% higher than that of HMA. The findings of this paper provide guidance for selecting the appropriate warm mix agent to improve pavement performance.