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Polymers, rubber, carbon black, nanomaterials, and other substances are frequently used for producing modified asphalt binders, which strengthen their ability to withstand fluctuating temperatures and growing vehicular loads. In order to achieve the intended performance, crosslinking agents/additives are frequently utilized to enhance the compatibility of various modifiers with the asphalt binder. This literature review paper provides a discussion on the use of different crosslinking agents, such as sulfur, dithiodimorpholine (DTDM), tetraethyl thiuram disulfide (TETDS), polyphosphoric acid (PPA), trans-polyoctenamer rubber (TOR), and peroxide, in the formulation of modified asphalt binder with different polymers, such as styrene-butadiene-styrene (SBS), ethylene vinyl acetate (EVA), and polyethylene (PE), as well as different rubber modifiers, such as styrene-butadiene rubber (SBR), crumb rubber (CR), and ethylene-propylene-diene-monomer (EPDM) rubber. The fundamental concepts of the chemistry of modified asphalt binder are covered first, and then various crosslinking additives/agents and their effects on the storage stability/compatibility and chemical and rheological properties of modified asphalt binder are reviewed. The environmental effects of using these crosslinking agents with modified asphalt binders are also covered in the present work. The paper concludes with recommendations for future research studies using crosslinking agents with different types of modified asphalt binders. [ABSTRACT FROM AUTHOR]

South Asian Region (SAR) is not only home to about 25% of the global population but also the site of many disasters, making it one of the most disaster-prone regions on the planet. The vulnerability of most of the population in the SAR can be due to the poor critical infrastructure in the region. The network of essential infrastructures like power supply, transportation systems, financial services, and administration that are crucial for the functioning of a society is called the Critical Infrastructure (CI). Appropriate interconnectedness and coordinated interdependencies of CI are essential for the smooth functioning of society, and any disruption in one or more of them could cause improper functioning of society. The prime objective of this study was to evaluate the CI's requirement, condition and status in five countries, namely Bangladesh, Bhutan, India, Nepal, and Sri Lanka. Experts from these five countries conducted a semi-structured review of the past and existing risks and the existing CI to find the future requirements and advancements in the CIs. It was found that the backbone of the CI is advancement in technology and innovations that require collaborative and innovative research and sharing of information and data within and with other nations.

There is a growing concern over the depletion of naturally occurring construction materials for lower unbound pavement layers. Stabilization of locally available materials has attracted considerable research interest. Nanotechnological additives have a good potential in stabilizing materials that are incompatible for pavement construction. The main aim of this research is to evaluate the use of nano-chemical additives on the laboratory and field characteristics of cement treated subbase (CTSB) mixes prepared with locally available soil. Locally available soil, cement, and nano-chemicals were utilized to assess their effect on California bearing ratio (CBR) and unconfined compressive strength (UCS) of chemically treated subbase mixes. The UCS of the soil-aggregate mix treated with cement improved by 103.4% on the addition of nano-chemical additives. The soaked CBR of the mix treated with the optimum dosage of cement and nano-chemical was increased by 219%. The laboratory-based evaluation was followed by construction of field sections utilizing the control subbase (soil-aggregate only), cement-treated subbase, and cement+nano-chemical treated subbase mixes. Deflectometric investigations were performed on the field sections using a light weight deflectometer. X-ray diffraction and scanning electron microscopy tests were carried out to study the microstructure of subbase mixes. Stabilisation using nano chemicals resulted in additional phases of ettringite that caused densification of matrix compared to pristine soil-aggregate mix. Pavement analysis and economic analysis of the different subbase mixes were also performed. The subbase prepared with 3% cement and 1.2 kg/m3 dosage of nano-chemical additive was found to be the optimum considering laboratory and field performance. [ABSTRACT FROM AUTHOR]

Composite modification of an asphalt binder forms an interesting approach to enhance the properties over diverse performance regimes. Aging of asphalt binders during the production, construction, and service life of the asphalt mixtures in pavement increases its stiffness and may have a negative impact on their resistance toward fatigue and low-temperature cracking, thus generating the need to evaluate the aging behavior of a composite-modified asphalt binder. This study analyzed the aging characteristics of individual and composite asphalt binders produced with waste ethylene-propylene-diene-monomer (EPDM) rubber, derived from manufacturing units dealing with nontire automotive rubber products, and the tire pyrolysis oil (TPO) derived from the pyrolysis of scrap tires. Three different pathways were used to formulate composite-modified binders, namely, without pretreatment and with pretreatment through heat and microwave irradiation. The study focused on the evaluation of physical, rheological, chemical, and microstructural characteristics of the composite-modified binders produced in different manners after being subjected to both short-term and long-term aging. Results showed that the effect of aging was adverse on the base binder and the binder prepared with TPO alone. In contrast, the addition of EPDM rubber alone improved the binder's aging resistance. The composite-modified binder through the pretreatment yielded significantly improved performance against aging; thus, composite modification with pretreatment can be a useful approach to yield aging-resistant binders prepared by EPDM and TPO. [ABSTRACT FROM AUTHOR]

Evaluation of the pavement condition is expensive, time-consuming, and labor-intensive and becomes even more challenging in remote areas. Nondestructive remote-sensing techniques can enable pavement condition assessment over a large areal extent. Remote-sensing sensors, capable of acquiring the emitted and reflected energies of the target with respect to the wavelength, can help in the identification and characterization of various asphalt mixtures prepared at a laboratory or field scale. This study aims at studying the spectral signature of asphalt mixtures with respect to aggregate gradation, binder type, binder concentration, aging, moisture conditions, and distress. In addition, an attempt has been made to identify the correlation between spectral features and asphalt mixture properties utilizing spectral metrics such as the Visible (VIS2) index and Shortwave Infrared (SWIR) index in visible and shortwave infrared regions of the electromagnetic spectrum, respectively. Indian and US specifications were followed for the fabrication and simulation of various states/conditions of asphalt mixtures. It was found from the analysis of spectral signatures that characteristic absorption features present between 1,700 and 2,300 nm can be used to identify different asphalt mixtures with distinct binder types and aggregate gradations. Also, variations in the intensity of these features were detected following various conditioning and distress simulations. Moreover, the statistical analysis indicated that the distressed samples exhibit a higher magnitude of spectral metrics (VIS2/SWIR) compared with the undamaged samples. The spectral characteristics of asphalt mixtures under different material compositions identified in the study offer great potential for pavement surface condition assessment through hyperspectral remote sensing. [ABSTRACT FROM AUTHOR]

Automobile/industrial waste ethylene-propylene-diene monomer (EPDM) rubber has attracted considerable interest as a potential asphalt binder modifier. A rubberized asphalt binder must have adequate storage stability to assure homogeneity during storage and hauling and attain the desired performance after construction. This study focused on the application of tire pyrolytic oil (TPO) derived from the pyrolysis of scrap tires as an additive for composite modification to enhance the storage stability of the EPDM rubberized binder. Sequential and pretreatment were the two different approaches employed to produce the TPO-EPDM rubberized asphalt binders in this work. Furthermore, the effect of a crosslinking agent (sulfur) on the compatibility of the TPO-EPDM rubberized binder was investigated for both sequential and pretreatment approaches. In all total, 18 different combinations of rubberized binders with EPDM, TPO, and sulfur were fabricated for storage stability characterization. Various empirical, rheological, chemical, and microstructural analyses based separation parameters indicated that TPO usage enhanced the storage stability of rubberized asphalt binder. Both sequential and pretreatment approaches increased the storage stability of EPDM rubberized binders with an increase in TPO dosages; however, the pretreatment approach outperformed the sequential approach. The addition of sulfur further improved the compatibility of rubberized binders. The results of Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM)–based separation parameters were similar to those found using empirical and rheological tests. Grey relational analysis (GRA) was used to rank the binders according to their separation parameters. GRA showed the best results in both sequential and pretreatment approaches with and without sulfur for an optimal TPO dosage of 6%. The enhanced storage stability performance of rubberized binders with the incorporation of TPO in the pretreatment approach of binder preparation was attributed to the achieved preswelling of rubber particles during premixing and conditioning processes. [ABSTRACT FROM AUTHOR]

Composite asphalt binder has emerged as a potential solution for improving asphalt functionality at a wide spectrum of temperatures. Storage stability of modified binder remains a main concern to ensure homogeneity during various stages including its storage, pumping, transportation, and construction. The aim of this study was to assess the storage stability of composite asphalt binders fabricated using non-tire waste ethylene-propylene-diene-monomer (EPDM) rubber and waste plastic pyrolytic oil (PPO). The influence of addition of a crosslinking additive (sulfur) was also investigated. Two different approaches were employed in the fabrication of composite rubberized binders: (1) sequential introduction of PPO and rubber granules, and (2) inclusion of rubber granules pre-swelled with PPO at 90°C to the conventional binder. Based on the modified binder fabrication approaches and the addition of sulfur, four categories of modified binders were prepared, namely sequential (SA), sequential with sulfur (SA-S), pre-swelled (PA), and pre-swelled with sulfur (PA-S). For variable modifier dosages (EPDM:16%, PPO: 2, 4, 6, and 8%, and sulfur: 0.3%), a total of 17 combinations of rubberized asphalt were subjected to two durations of thermal storage (48 and 96 hours) and then characterized for their storage stability performance through various separation indices (SIs) based on conventional, chemical, microstructural, and rheological analyses. The optimal storage stability performance was achieved at a PPO dosage of 6% under the four candidate approaches. It was also observed that the SIs based on chemical analysis and rubber extraction test had a good correlation with rheology-based SIs compared to the conventionally used softening point difference. A composite modified binder with PPO and EPDM rubber having adequate storage stability is a promising step in the use of sustainable composite-modified binders in asphalt pavement construction. [ABSTRACT FROM AUTHOR]

Open-graded asphalt friction course (OGAFC) is an asphalt course constructed over a dense-graded and impermeable surface to allow quick drainage of surface water runoff and enable reduction of hydroplaning and splash and spray. OGAFC mixtures demand high-quality aggregates to perform the intended functions while transferring traffic loads to the underlying layer. Steel slag is a byproduct generated during steel production, and large quantities are unutilized in steel-producing countries, including India. This study evaluated the mechanical performance properties of OGAFC mixtures using basic oxygen furnace (BOF) steel slag as replacement for coarse aggregates at percentages of 0%, 25%, 50%, 75%, and 100%. OGAFC mixtures with two types of modified asphalt binders and five percentage replacements of coarse natural aggregates with BOF steel slag were fabricated. The mechanical performance of the OGAFC mixtures was evaluated in terms of rutting resistance (dynamic creep test and Hamburg wheel tracking device test), cracking potential (indirect tensile strength, cracking tolerance index, and semicircular bending test), fatigue life (indirect tensile fatigue test), and modulus properties (indirect tensile stiffness modulus and resilient modulus). The test results indicated that the use of BOF steel slag not only improved the performance of OGAFC mixtures in terms of rutting resistance, cracking potential, and modulus properties, but also increased the fatigue life of the OGAFC mixes. OGAFC mixes up to 100% BOF steel slag content exhibited superior performance compared with the mixtures with natural aggregates. [ABSTRACT FROM AUTHOR]

Waste ethylene-propylene-diene monomer (EPDM) rubber and tire pyrolytic oil (TPO) derived from waste tire pyrolysis have shown promising results for their use in asphalt binder modification. However, their incorporation has shown improvements mainly either on rutting or fatigue behavior of the resultant asphalt binders. Composite modification may be a viable option to achieve improved performance with these two materials. The aim of this study was to evaluate the rheological, morphological, and chemical properties of asphalt binders produced through both individual and composite modifications using waste EPDM rubber and TPO. For composite modification, two different blending schemes were used: (1) sequential addition of TPO and EPDM rubber to the heated base asphalt binder; and (2) premixing of TPO and EPDM rubber prior to addition to the heated base asphalt. In the latter case, before being added to the base asphalt, TPO premixed EPDM rubber was conditioned at two temperatures (25°C and 90°C) to see the effect of different conditioning temperatures in composite modification. Firstly, the conventional properties of all the binders in the unaged state were assessed, followed by the evaluation of short-term-aged binders for Superpave and Shenoy rutting parameters, frequency sweep, zero shear viscosity, multiple stress creep and recovery, and Burger's modeling. The long-term-aged binders were evaluated through the Superpave fatigue parameter, Glover-Rowe parameter, and linear amplitude sweep. Fourier transform infrared (FTIR) spectroscopy and optical microscopy were used for chemical and morphological analyses. The premixing of EPDM and TPO accompanied with conditioning at 90°C imparted a synergistic effect with improvements in both rutting and fatigue performance of binder. The improvement in performance attributes was ascribed to the preswelling of EPDM rubber with TPO, which was evident from the morphological analysis. FTIR provided evidence of chemical interaction between EPDM rubber and TPO during the conditioning and blending processes. [ABSTRACT FROM AUTHOR]

This study evaluated tire pyrolytic oil (TPO) derived from waste tire pyrolysis as a rejuvenating agent for three types of aged asphalt binders (unmodified, polymer-modified, and crumb rubber–modified). Gas chromatography–mass spectrometry (GC–MS) was performed to identify chemical compounds present in TPO. The rheological characteristics of all binders were examined through the complex viscosity–frequency profile, zero-shear viscosity, failure temperature, Black space diagrams, Cole–Cole plots, Superpave fatigue parameter, Glover–Rowe parameter, and linear amplitude sweep (LAS) tests. Mass loss was also determined for the rejuvenated binders. All binders were subjected to Fourier transform infrared (FTIR) analysis, and sulfoxide and carbonyl indices were computed. Atomic force microscopy (AFM) was conducted to study the effect of TPO on the micromorphology of the binders. The normalized Euclidean distance approach was used to rank the rejuvenated binders with respect to the proximity of their rheological and FTIR characteristics to that of the unaged binder. The use of TPO as a rejuvenating agent enabled the aged binders to achieve properties comparable to those of the unaged asphalt binder. The AFM-based rejuvenation index (RI) indicated a good potential of TPO as a rejuvenator. The results of the binder rheological parameters and the FTIR indicators investigated in the study indicated that a 9% dosage of TPO as a rejuvenating agent was the most effective. [ABSTRACT FROM AUTHOR]

Pyrolysis technology is receiving growing attention for managing postconsumer tire and plastic waste streams. Pyrolytic char is generated as a byproduct in the pyrolysis process and faces challenges regarding its stable and reliable reuse. The use of tire pyrolytic char (TPC) and plastic pyrolytic char (PPC) has recently gained interest in asphalt binder modification, which can be a feasible and attractive alternative for their utilization. The present study focused on a multifaceted investigation at three levels: (1) characterization of the pyrolytic chars (TPC and PPC), (2) characterization of asphalt binders modified with different dosages (0%, 5%, 10%, 15%, and 20%) of TPC and PPC focusing on conventional, rheological, microscopic, and thermochemical tests, and (3) mechanical characterization of asphalt mixtures fabricated with TPC- and PPC-modified binders in terms of rutting, moisture damage, and fatigue performance. Leachate toxicity was also evaluated to ensure that the use of TPC and PPC in asphalt mixtures is safe for the environment. Results showed that both TPC- and PPC-modified binders and mixtures showed better rutting resistance than the control binder and mixture up to 20% dosage. Fourier transform infrared (FTIR) spectroscopy showed that TPC and PPC interacted chemically with the base binder during modification. Leaching tests indicated that TPC and PPC could be safely used in asphalt mixtures for pavement construction. Comparing the fatigue and moisture damage results, it was found that the optimum performance was achieved at a 10% dosage of both TPC and PPC. This observation was consistent with fatigue tests on binders and asphalt mixtures. [ABSTRACT FROM AUTHOR]

Friction properties of open graded asphalt friction course (OGAFC) mixtures play an essential role in ensuring traffic safety, especially under wet weather conditions. This study evaluated the friction characteristics of basic oxygen furnace (BOF) and electric-arc furnace (EAF) steel slag aggregate incorporated OGAFC mixes. Nine sets of OGAFC mixes were fabricated using five percentage replacements (0%, 25%, 50%, 75%, and 100%) of the coarse natural aggregate fraction by BOF and EAF steel slags. The effect of modified binder type (polymer and crumb-rubber modified) on the frictional characteristics of OGAFC mixes was also examined. The principal friction test devices used were the British pendulum tester and dynamic friction tester. Multiple friction performance aspects were studied: (1) effect of surface condition (dry, wet, and ponding) on the measured friction coefficient; (2) separate evaluation of adhesion and hysteresis friction components; (3) variation of friction coefficient with varying slip speeds, and (4) friction performance later in the OGAFC service life using artificially polished aggregates, and comparison of the performance with unpolished aggregates. Results revealed that the use of steel slags in OGAFC mixes considerably enhanced the frictional characteristics and that the skid resistance of OGAFC-BOF mixes was better than that of OGAFC-EAF mixes. Frictional resistance of the mixes was found to increase with an increase in steel slag content. OGAFC mixes comprising polished steel slag aggregates also showed promising results with the increment in steel slag content. The findings also indicated that OGAFC-CRMB mixes perform better than OGAFC-PMB mixes. [ABSTRACT FROM AUTHOR]

Pyrolysis is being employed as a viable option for the disposal of different industrial and agricultural wastes, including end-of-life vehicle tires. Tire pyrolytic char (TPC), a solid fine carbonaceous material obtained as a by-product during the pyrolysis of waste tires, is gaining interest among pavement researchers for its use in asphalt binder modification. Good storage stability is essential to ensure that a modified binder retains the desired properties after its fabrication. Cross-linking agents are frequently used to enhance the storage stability of modified binders. This study characterized the storage stability performance of TPC-modified binders with and without the incorporation of cross-linking agents. Bituminous binders modified with TPC were analyzed for storage stability at multiple dosages of two widely used cross-linking agents: polyphosphoric acid (PPA) (0.5%, 1.0%, and 1.5%) and sulfur (0.15%, 0.3%, and 0.45%). In addition to softening point difference (SPD), separation indices (SIs) derived from frequency sweep, temperature sweep, and multiple stress creep and recovery (MSCR) tests were employed to characterize the storage stability. Compatibility evaluation was also done through Cole-Cole plots. Fourier transform infrared spectroscopy (FTIR) was used to study the storage stability through the changes in binder spectra. Remixing of the TPC-modified binders was also performed to assess the retrieval of homogeneity in a segregated TPC-modified binder. All the SIs were measured and compared for binder specimens before and after remixing. Binders were ranked based on the SIs, followed by sensitivity and correlation analyses of the SIs. TPC-modified binder showed a good storage stability performance with sulfur (at 0.3% optimum dosage) and PPA (at 1% optimum dosage). Remixing resulted in further enhancement in the storage stability performance of TPC-modified binders. The results of the study are quite useful considering the practical usage of TPC for a storage-stable modification of asphalt binder. [ABSTRACT FROM AUTHOR]

The open graded asphalt friction course (OGAFC) is a hot mix asphalt wearing course designed and constructed to mainly achieve the benefits of quick surface water drainage, high skid resistance, and low tire-pavement noise. OGAFC thus offers advantages of reduced hydroplaning, reduced splash and spray, reduced noise, and enhanced skid resistance and visibility (especially in wet weather). These mixes demand a uniform/open aggregate gradation for high permeability; establishment of proper stone-on-stone contact for good structural stability; and higher relatively stiff binder content for adequate resistance to moisture damage and binder draindown. Due to the lack of fines and higher binder content in OGAFC mixes, the asphalt binder tends to move down vertically under the influence of gravity when exposed to high temperatures during production (production-stage draindown) and over time at high pavement service temperatures (long-term draindown). This study evaluates long-term binder draindown of OGAFC mixes with both natural aggregates and basic oxygen furnace (BOF) steel slag, a waste/by-product of steel making, as a replacement for natural aggregates. OGAFC mixes with five replacement percentages (0%, 25%, 50%, 75%, and 100%) of BOF steel slag and two types of modified binders (polymer and modified crumb rubber) were subjected to different long-term binder draindown–conditioning protocols and then evaluated through determination of permeability characteristics, moisture susceptibility, raveling potential, and permanent deformation. The results revealed that aging in terms of temperature and duration has a significant effect on binder draindown. OGAFC mixes with higher BOF steel slag content showed better raveling, rutting, and moisture performance compared with a control mix after being subjected to long-term draindown. The inclusion of BOF steel slag up to 100% in OGAFC mixes produced encouraging results, with overall improvement in performance. [ABSTRACT FROM AUTHOR]

Globally, the growing volume of waste tires and plastics has posed significant concerns about their sustainable and economical disposal. Pyrolysis provides a way for effective treatment and management of these wastes, enabling recovery of energy and produces solid pyrolytic char as a by-product. The use of pyrolytic chars in asphalt binder modification has recently gained significant interest among researchers. As asphalt binder aging influences the cracking, rutting, and moisture damage performance of asphalt binder and the mixtures, evaluation of aging characteristics of char modified asphalt binders is quite important. The main objective of this study is the investigation of the aging characteristics of asphalt binders modified with waste tire pyrolytic char (TPC) and waste plastic pyrolytic char (PPC) through rheological and spectroscopic evaluations. To imitate short-term and long-term aging conditions, the asphalt binders were first treated in a rolling thin film oven (RTFO) and then in a pressure aging vessel (PAV). The aging characteristics were determined using four rheological aging indices based on complex modulus (G*), phase angle (δ), zero shear viscosity (ZSV), and non-recoverable creep compliance (Jnr) from multiple stress creep and recovery (MSCR) test. The fatigue cracking potential was then measured through binder yield energy test (BYET). These parameters were measured through a dynamic shear rheometer. Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H-NMR) spectroscopy analyses were then used to investigate changes in chemical composition due to aging in the char modified binders. Both TPC and PPC improved the high-temperature deformation resistance properties of asphalt binder. The TPC-modified binder showed better aging resistance than the control and PPC-modified binders, based on the different rheological and spectroscopic indices. The pyrolytic char modified binders also demonstrated good fatigue performance. [ABSTRACT FROM AUTHOR]

Pyrolysis has gained a strong interest in recent times for sustainable treatment and recovery of energy-rich products from different wastes including plastic. Waste plastic pyrolytic char (PPC) generated as a carbonaceous by-product in the pyrolysis process, is gaining attention as an asphalt binder modifier. Adequate thermal storage stability is an essential requirement for a modified asphalt binder to ensure that the composite offers integrity and homogeneous properties during its storage, handling and transportation in the field. The objective of this study was to evaluate and characterize the thermal storage stability properties of PPC modified binders. PPC modified asphalt binders were fabricated and evaluated at multiple dosages of sulfur as a cross-linking agent. In addition to the conventionally used softening point difference (SPD), characterization of thermal storage stability was attempted using rheology-based separation indices (SIs) derived through temperature sweep, frequency sweep, and multiple stress creep and recovery (MSCR) tests. These rheological SIs were based on complex modulus (G*), Superpave rutting parameter (G*/sin δ), Shenoy rutting parameter (SRP), zero shear viscosity (ZSV), and MSCR Jnr (at three stress levels 0.1, 3.2 and 10 kPa). Two formulations of each rheology-based separation index were studied: (1) ratio, and (2) maximum-average difference formulations. The temperature and frequency dependencies of rheological SIs were also evaluated. Further, the Fourier transform infrared spectroscopy (FTIR) was used to characterize storage stability by comparing the chemical functionalities of the PPC modified binders. A 0.3% dosage of sulfur was found to produce the best results considering all SPD, rheology-based SIs and FTIR. Principal component analysis showed that the ratio and maximum-average formulations had similar contributions to the first principal component accounting for more than 99% of the variability. [ABSTRACT FROM AUTHOR]

In hilly and high-rainfall regions, very sharp curves, lack of skid resistance, and poor visibility form a major cause for road-traffic accidents in India and other similar parts of the world. The construction of pavements with open-graded friction course (OGFC) wearing surfaces in such regions will help enhance road safety due to increased skid resistance, reduced hydroplaning, reduced splash and spray, and better visibility. OGFC mixes demand a high percentage (>90%) of good quality coarse aggregates for adequate stability and load transfer. India is the second-largest producer of steel, and about 12 million t of steel slag (as a byproduct) is generated every year and mainly lies unutilized in open areas, leading to environmental concerns. This study aimed to investigate the design and performance characteristics of OGFC mixes with basic oxygen furnace (BOF) steel slag as the coarse aggregate. Properties of OGFC mixes were evaluated by replacing 0%, 25%, 50%, 75%, and 100% of coarse natural aggregates by BOF steel slag. OGFC mixes were first evaluated for design parameters, including air void content, stone-on-stone contact, Cantabro abrasion loss (unaged and aged), and binder draindown. OGFC mixes with the different percentages of BOF slag were then evaluated for performance through the determination of indirect tensile strength, moisture damage resistance, porosity, and permeability. In addition, the benefits of OGFC mixes in terms of improved skid resistance were found under both dry and wet conditions at different contents of BOF slag. Results showed that steel slag used as coarse aggregate improved the frictional resistance of OGFC mixes. Steel slag-OGFC mixes also showed improved design and moisture resistance parameters compared to the values of these parameters for the control mixes (without slag). A replacement of coarse aggregate with BOF steel slag by 50% on a weight basis is recommended in OGFC mixes for enhanced safety in hilly and high-rainfall regions. [ABSTRACT FROM AUTHOR]

Management and disposal of waste polyethylene terephthalate (PET) bottles is an ever-growing challenge. The present study investigated the effect of incorporation of shredded waste PET bottles on properties of asphalt mixes in terms of: (i) process of PET addition, (ii) PET content, and (iii) PET size. Experimental design included three variables: two processes (dry process, and modified dry process), three PET contents (2.5%, 5.0%, and 7.5% by weight of binder), and two PET sizes (2.36-1.18 mm, and 0.30-0.15 mm). Volumetric properties, Marshall parameters, and moisture susceptibility characteristics of PET modified mixes were evaluated and compared with control mix (without PET). Analysis of variance (ANOVA) was performed to evaluate main and interaction effects of the variables. Results indicated that all the three variables had significant influence on the measured properties. Further, mixes prepared using modified dry process outperformed other mixes and showed highest resistance towards moisture induced damage. [ABSTRACT FROM AUTHOR]

Moisture-induced damage has been a major concern associated with warm mix asphalt (WMA). This study focused on the evaluation of moisture susceptibility characteristics of WMA mixes with different WMA additives and modified bituminous binders through the tensile strength ratio (TSR) and retained Marshall stability (RMS) tests. Experimental design included two binders (polymer and crumb rubber modified), four production temperatures, and two additives (Evotherm and Sasobit), each with a different dosage. Results indicated that (i) WMA additive type and its dosage had significant effect on moisture performance of warm mixes, and (ii) Evotherm mixes exhibited higher TSR and RMS values compared to Sasobit. The results were also analyzed statistically. [ABSTRACT FROM PUBLISHER]

Use of warm mix asphalt (WMA) technology to reduce construction temperatures of asphalt mix has gained strong interest worldwide. However, the technology is still in its inception stage in India. Present study evaluated the rheological properties of polymer- and crumb rubber-modified bitumen with various doses of WMA additive Sasobit (1%, 2%, and 3% by binder weight). Frequency sweep and temperature sweep results showed that increase in Sasobit content improved elastic properties of binders. Creep, repeated creep recovery, and multiple stress creep recovery results showed better resistance toward permanent deformation for Sasobit-modified binders in comparison to control binders. [ABSTRACT FROM PUBLISHER]

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With growing global concerns related to energy security and sustainability, interest in bio-fuels has increased significantly. Production of biofuel mostly begins with pyrolysis, a process that converts the biomass to liquid biooil, solid biochar and gases. A large amount of carbonaceous biochar is generated as a by-product during the pyrolysis. However, no major effort has been made in the past decade to utilize the biochar in pavement applications, especially as a bio-modifier to asphalt binders. In this study, an attempt was made to evaluate the carbonaceous biochar, obtained during bio-fuel production through pyrolysis of Mesua ferrea seed cover waste, as an asphalt modifier/extender to obtain bio-asphalts. Physical and chemical characterizations of biochar were carried out using scanning electron microscopy, Fourier transform infrared spectroscopy and energy dispersive X-ray analysis. This was followed by rheological characterization of asphalt binders (from two sources) modified with various concentrations of biochar (0, 5, 10, 15, and 20% by weight of binder). Flow behaviour, permanent deformation, and fatigue characteristics of bio-asphalts were evaluated and compared with control binders (no biochar). Aging susceptibility of biochar modified binders was also evaluated and compared for biochar contents and binder sources. Permanent deformation behaviour evaluated through multiple stress creep and recovery (MSCR) test indicated that the use of biochar improved the rutting resistance of binders. Improved binder performance against the effects of aging and deformation with the use of biochar makes it a promising asphalt modifier, especially for the warm tropical climatic conditions prevalent in India. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes (CNTs) printed into thin films have been shown to yield high mobility, thermal conductivity, mechanical flexibility, and chemical stability as semiconducting channels in field-effect, thin-film transistors (TFTs). Printed CNT-TFTs of many varieties have been studied; however, there has been limited effort toward improving overall CNT-TFT performance. In particular, contact resistance plays a dominant role in determining the performance and degree of variability in the TFTs, especially in fully printed devices where the contacts and channel are both printed. In this work, we have systematically investigated the contact resistance and overall performance of fully printed CNT-TFTs employing three different printed contact materials-Ag nanoparticles, Au nanoparticles, and metallic CNTs-each in the following distinct contact geometries: top, bottom, and double. The active channel for each device was printed from the dispersion of high-purity (>99%) semiconducting CNTs, and all printing was carried out using an aerosol jet printer. Hundreds of devices with different channel lengths (from 20 to 500 μm) were fabricated for extracting contact resistance and determining related contact effects. Printed bottom contacts are shown to be advantageous compared to the more common top contacts, regardless of contact material. Further, compared to single (top or bottom) contacts, double contacts offer a significant decrease (>35%) in contact resistance for all types of contact materials, with the metallic CNTs yielding the best overall performance. These findings underscore the impact of printed contact materials and structures when interfacing with CNT thin films, providing key guidance for the further development of printed nanomaterial electronics.