Low-temperature Cracking Research Articles

Interaction state and element leaching of waste incineration fly ash-asphalt mortar based on fillerization

Fly ash from diverse sources had various physical and chemical properties, resulting in different modified asphalt properties. Therefore, this paper aimed to investigate the interaction between fly ash and asphalt from different sources and the performance of fly ash-asphalt mortar and further sought the best-replaced amount of fly ash. The fillers included limestone, Dongguan fly ash, and Guangzhou fly ash. First, the filler's physical and chemical properties and microstructure were evaluated. Secondly, asphalt mortar was prepared according to the replaced amount (0%, 25%, 50%, 75%, 100%) and powder binder ratio (0.7). Then, the basic performance test, micro test, high-temperature rheological test, and low-temperature rheological test were conducted on asphalt mortar to investigate the interaction between fly ash and asphalt, as well as the high-temperature performance, elastic recovery ability, and low-temperature crack resistance of asphalt mortar. Finally, the segregation and heavy metal leaching of fly ash-asphalt mortar (FA-AM) were evaluated by the segregation and ICP test. The results indicate that fly ash had a small particle size, a rugged surface, well-developed porosity, abundant mineral components including potassium salt, sodium salt, and calcium carbonate, strong interaction with bitumen, and excellent compatibility. Adding fly ash and increasing the replacement amount improved the high-temperature performance of asphalt and enhanced the elastic recovery ability, but the low-temperature performance was weakened. The enhancement of Dongguan fly ash's high-temperature performance was more significant, while the low-temperature performance of Guangzhou fly ash was marginally superior to that of Dongguan fly ash. However, there was no discernible difference between the two types of fly ash in terms of elastic recovery ability. Segregation had no noticeable effect on the heavy metal absorption concentration of FA-AM, and the storage stability was excellent. Asphalt had the best stabilization effect on Zn, Cu, and Pb in FA-AM (Dongguan) and Pb and Cr in FA-AM (Guangzhou). The recommended replacement amount of Dongguan fly ash and Guangzhou fly ash was 25%∼50%.

Experimental Study of Permeable Asphalt Mixture Containing Reclaimed Asphalt Pavement

The current focus of research attention on reclaimed asphalt pavement (RAP) utilization is expanding the applications of RAP. This study aims to analyze the road performance of recycled permeable asphalt mixtures (RPAMs), which represents a novel direction for utilizing RAP. Firstly, the Marshall design method was used to carry out the material composition design of the RPAM with varying RAP contents (10%, 20%, and 30%). Subsequently, the performance of the RPAM with different RAP contents (10%, 20%, and 30%) and preheating temperatures (120 °C, 130 °C, 140 °C, 150 °C, and 160 °C) was tested with a permeable asphalt mixture containing 12% high-viscosity asphalt as the control group. The mixture’s performance included high-temperature stability, low-temperature crack resistance, water stability, anti-raveling performance, and dynamic mechanical properties. The results indicate that the higher the RAP content, the better the high-temperature performance of the RPAM, while the low-temperature performance, water stability, and anti-raveling performance deteriorate. At 30% RAP content, its pavement performance is comparable to that of the control group mixture. However, increasing RAP preheating temperature can improve low-temperature and water stability but may reduce high-temperature performance. The optimal RAP preheating temperature for pavement performance is between 140 and 150 °C. The dynamic modulus test showed that the higher the RAP content, the greater the dynamic modulus of the RPAM, leading to better high-temperature stability but reduced low-temperature crack resistance. The influence of RAP preheating temperature is the opposite. These test results demonstrate the feasibility of utilizing RAP for paving permeable asphalt pavement under controlled RAP content and preheating temperature conditions.

Another look at the semi-circular bend test for the performance ranking of hot mix asphalt

Semi-circular bend (SCB) testing has been widely used to evaluate the cracking resistance of asphalt mixtures. However, it remains unresolved which of the various SCB protocols can provide the most sensitive and precise ranking of different asphalt mixtures. This study aims to improve the current SCB protocol, emphasizing mixture preparation, testing condition and evaluation indices. The effect of aging methods in terms of reversible aging and irreversible aging and loading rates on the intermediate and low temperature cracking resistance of asphalt mixtures was analyzed. Subsequently, the response of different cracking evaluation indices was analyzed. Finally, the repeatability of different cracking evaluation indices was discussed. The results show that higher loading rates are slightly more sensitive to mix composition, possibly due to the toughening effect of polymer modifiers. However, whether higher or lower rates are more accurate remains to be investigated with ongoing field studies. Cracking initiation and resistance indices (CII and CRI) were superior from a repeatability and dynamic range perspective in comparison to flexibility and balanced cracking indices (FI and BCI). Thermoreversible aging over three days of cold conditioning at − 20 °C was found to significantly affect binder properties in selected samples. However, none of the SCB parameters after testing appropriately cold conditioned samples at room temperature reflected this deterioration. Hence, it remains to be investigated whether mixture testing at ambient temperatures properly ranks superior quality Alberta, Canada and Venezuelan sourced materials that are low in wax.

Performance Improvement of Asphalt Mastics Using Bamboo Fiber Reinforcement

Integrating fibers into asphalt mixtures improves their crack resistance and permanent deformation. Previous studies have found the effect of various fibers on asphalt mixtures, but bamboo fibers were not included. In addition to providing strength and toughness, bamboo fiber’s recycled nature saves resources and protects the environment. This study investigates the reinforcement effect by different particle sizes and contents of bamboo fiber on asphalt mastic. Three sizes (100 mesh, 200 mesh, and 400 mesh) and three contents (3%, 6%, and 9%) of bamboo fibers were selected to modify the asphalt mastic. The frequency sweep (FS), linear amplitude sweep (LAS), multiple stress creep recovery (MSCR), and bending beam rheometer (BBR) test were used to evaluate the linear viscoelastic properties, fatigue performance, rutting resistance, and cracking resistance of fiber-modified asphalt mastics, respectively. Results demonstrate that bamboo fibers have excellent stiffness-reinforced characteristics, increase the elasticity of the asphalt, and enhance the high-temperature stability and low-temperature crack resistance of the asphalt mastic but adversely affect the fatigue properties of the asphalt mastic. In addition, asphalt mastics exhibited the same crack initiation stage and different crack expansion behavior, and the fiber incorporation prevented further crack propagation. Burgers model was used to represent the rheological behaviors of the asphalt mastic with bamboo fiber, and the model parameters are estimated. Furthermore, the Burgers model results indicated that the fiber addition reduced the proportion of elastic compliance and viscous compliance but increased the proportion of delayed elastic compliance of the asphalt mastic. Finally, the statistical model obtained based on the statistical approach can appropriately fit the values of rheological parameters with different fiber contents and lengths. The optimal design solution is 200 mesh with 9% content.

Experimental Analysis to Evaluate the Impact of Styrene-Butadiene-Styrene and Crumb Rubber on the Rutting and Moisture Resistance of Asphalt Mixtures

The most severe distresses in asphalt pavement are rutting, fatigue, and low-temperature cracking; therefore, to solve these problems, it is essential to modify asphalt binders in asphalt concrete mixtures. In this study, a comparison between using styrene-butadiene-styrene (SBS) and crumb rubber (CR) as modifiers for asphalt binders to overcome distress issues was conducted. Base and SBS or CR-modified binders were subjected to all conventional and Superpave binder tests. Engineering tests such as the Hamburg wheel tracker and indirect tensile strength ratio were also run to evaluate the engineering properties. The used SBS percentages were 1, 2, 3, 4, and 5%, while CR percentages were 3, 6, 9, 12, and 15% by total weight. The results showed lower penetration, higher softening point, viscosity, and elastic recovery for both additives. In addition, dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests showed increasing values of both high and low temperatures of modified asphalt performance grade (PG) with increasing SBS or CR percent. The tensile strength ratio and Hamburg wheel tracker results showed the best engineering properties at 3% SBS or 9% CR, the optimum percent. A triple percentage of CR is needed to get the same effect of SBS for the asphalt mixture.

Influence of bitumen grade and air voids on low-temperature cracking of asphalt

Low-temperature cracking is one of the main causes of pavement distress in colder areas with below-freezing temperatures. Resistance of asphalt to this cracking depends on a number of factors. A complex knowledge about this phenomena is a key factor during the design process, the building and the use stage of roads. Among the leading drivers are the type of bitumen and air voids in the bituminous mixture. In this research project, both the bituminous binders and mixtures were tested to determine the influence of these components on the low-temperature performance of asphalt pavements. A wide range of bituminous binders were tested, including 20/30, 35/50, 50/70, 70/100 and 100/150 grades. This approach allowed for an in-depth evaluation of the impact of bitumen type and air voids on the low-thermal susceptibility of asphalt mixture. The basic tests for bitumen were performed such as the penetration value at 25 °C (EN 1426), the softening point with the Ring & Ball method (EN 1427) and the group composition with SARA analysis using the Thin Layer Chromatography with Flame Ionization Detector (TLC/FID) method. Both neat bitumen and bitumen after Rotating Thin Film Oven Test (RTFOT) short-term simulated ageing (EN 12607–1) were tested. Next, bituminous mixtures based on mentioned bitumen with 2.2%, 3.5% and 6.5% air voids were prepared and subjected to uniaxial tension in Thermal Stress Restrained Specimen Test (TSRST) to determine their low-temperature performance. The test results point to the binder type as the key determinant of the low-temperature performance of asphalt. Softer bitumens of a higher penetration have a better low-temperature performance and the group composition is the determinant of the TSRST failure temperature. The effect of air voids were of secondary importance in this respect.

Laboratory evaluation of the performance of reclaimed asphalt mixed with composite crumb rubber-modified asphalt: reconciling relatively high content of RAP and virgin asphalt

ABSTRACT Reclaimed asphalt pavement (RAP) applications are largely limited by the insufficient performance of reclaimed asphalt (RA). To address this challenge, the composite crumb rubber-modified asphalt (CCRMA) with SBS and SBR modifiers was mixed with RA to prepare reconciling and reclaimed modified asphalt (RRMA) and evaluate its performance in laboratory tests. Experimental groups of RRMA included five RA contents (30%, 40%, 50%, 60%, and 70%) and three aging degrees. Results showed that RRMA’s high-temperature and fatigue resistance performances improved by adding CCRMA, while this improvement was weakened with increasing RA content and aging degree. This was because the addition of CCRMA reduced the morphology of ‘bee-like structures’ and improved resistance to deformation. CCRMA slightly reduced moderate-temperature crack resistance but still improved low-temperature crack resistance because adding CCRMA reduced the internal adhesion of asphalt. The moderate-temperature crack resistance was below the threshold. However, it is necessary to consider adding other technical means when RRMA was aged for more than 20 hours with more than 60% RA content. Furthermore, the reliability of excellent performance was 85% for RRMA with 30% RA content under a short-term aging state, which provided a reference for the design of reclaimed asphalt binder.

Characterization of Sustainable Asphalt Binders Modified with Styrene–Isoprene–Styrene (SIS) and Processed Oil

The current study aims to evaluate the viscosity and rheological properties of PG 64-22 modified with Styrene–Isoprene–Styrene (SIS) and Processed Oil (PO) to enhance asphalt binder properties. Performance properties were measured at high, intermediate, and low temperatures. PG 64-22 was blended with SIS and Processed Oil at three levels (5%, 10%, and 15% by weight of binder) and two concentrations (6% and 12% by weight of binder), respectively. Modified binders underwent two short and long artificial aging processes, through the spinning of the thin film in an RTFO oven and a pressure aging vessel (PAV). The Superpave binder evaluations were carried out using a rotational viscometer (RV), dynamic shear rheometer (DSR), and bending beam rheometer (BBR). According to the findings of the research, the addition of SIS caused higher values of viscosity, but when co-modified with processed oil, there was a substantial decrease in viscosity values. As a result, workability was improved. (1) It was observed that a greater reduction in viscosity was achieved when the processed oil was present at a higher concentration at 135 °C compared to a lower concentration. (2) The study showed that the incorporation of processed oil led to a reduction in rutting performance of the asphalt binder. However, the addition of SIS resulted in a notable enhancement of rutting resistance. (3) The role of processed oil as co-modifier at concentrations of 6% and 12% caused significant decreases in G*sin δ, based on the susceptibility of asphalt molecules to accept oil molecules in their network links. (4) The extracted measurements from the BBR tests indicated that modification with SIS and PO improved the low-temperature cracking resistance significantly. Comparison of asphalt binders modified with 6% and 12% PO and the same SIS content showed significant changes in modification with 12% PO rather than 6%.

Performance and cost evaluations of 100% recycled hot asphalt mixtures for pothole patching applications in flexible pavements

Fixing the potholes using bituminous patching mixtures is a critical and costly pavement maintenance activity. The patching mixture's quality significantly affects patch durability and performance; always using the best material available is advisable. This study investigated the feasibility of using 100% hot recycled asphalt pavements (RAP) as a possible patching material by comparing the performance results with cold patching mixtures (CPM) as well as Superpave hot mix asphalt (SHMA) mixtures. Four different RAP mixtures, two fine-graded and two coarse-graded, from two distinct sources, are obtained. RAP mixtures were handled in a laboratory environment to obtain the hot recycled patching materials. Three different rejuvenators were incorporated into hot-recycled pavement material (HRPM) at manufacturer-recommended dosages to determine the best rejuvenator type. Performances of the mixtures are evaluated in terms of linear viscoelastic characterization, permanent deformation, and low-temperature thermal cracking potentials using dynamic modulus, flow number, and indirect tensile strength tests, respectively. The results show that RAP mixtures with any RAP source, gradation, and rejuvenator type outperformed CPM in performance tests and behaved similarly to SHMA mixtures.

Rheological Properties of Composite Inorganic Micropowder Asphalt Mastic

Graphene Tourmaline Composite Micropowder (hereinafter referred to as GTCM) modified asphalt was prepared by the ball milling method. The effects of different temperatures and different frequencies on the high-temperature performance of composite-modified asphalt were evaluated by dynamic shear rheological test, and the viscoelastic properties of composite-modified asphalt under different stresses and different temperatures were analyzed. The low-temperature rheological properties of GTCM-modified asphalt were analyzed by bending beam rheological test, and its mechanism was analyzed by Fourier transform infrared spectroscopy (FTIR) test. The results show that the temperature sensitivity and anti-aging resistance of GTCM-modified asphalt are significantly higher than that of tourmaline-modified asphalt. The improvement effect gradually increases with the increase in graphene powder content, and its addition does not change the viscoelastic properties of asphalt. The complex shear modulus and phase angle of GTCM-modified asphalt at appropriate temperatures are more conducive to tourmaline-modified asphalt and matrix asphalt, which can improve the rutting resistance of asphalt. In the same type, with the increase in composite modified micropowder content, the rutting resistance of modified asphalt is better. The improvement of rutting resistance of GTCM-0.5, GTCM-1.0 and GTCM-1.5-modified asphalt can reach 12.95%, 10.12% and 24.25%, respectively; the improvement range is more complicated due to temperature and frequency changes. The GTCM-modified asphalt has good low-temperature crack resistance. The creep stiffness modulus of GTCM-modified asphalt decreases with the increase in load time under different types and dosages, and its stiffness modulus is smaller than that of tourmaline-modified asphalt and mineral powder asphalt mastic. The creep rate increases with the extension of load time, which is greater than that of tourmaline-modified asphalt and mineral powder asphalt mastic. When the load was 60 s, the creep stiffness modulus of GTCM-0.5, GTCM-1.0 and GTCM-1.5-modified asphalt decreased by 5.75%, 6.97% and 13.73%, respectively, and the creep rate increased by 1.37%, 2.52% and 4.35%, respectively. After adding GTCM or tourmaline to the matrix asphalt, no new functional groups were produced due to the chemical reaction with the asphalt.

Use of the Iron Chloride Type of Lewis Acid Catalyst in High Reclaimed Asphalt Pavement Content Asphalt Mixtures

The use of reclaimed asphalt pavement (RAP) as a partial replacement for virgin aggregates and asphalt binders has received considerable attention recently. This approach is one of many promising methods for improving sustainability. However, many state Departments of Transportation are cautious in adopting high RAP content into their designs because of cracking and durability issues resulting from the aged RAP binder. A Lewis acid catalyst has been used to modify the asphalt binder’s chemical composition and disrupt the associated molecules formed in the aged RAP binder. The objective of this study is to assess the effectiveness of the use of a Lewis acid catalyst in improving the cracking resistance of an asphalt mixture containing high RAP contents. A suite of laboratory mechanical tests was performed, namely, the dynamic modulus test for linear viscoelastic properties; the semi-circular bend, Illinois flexible index, ideal cracking tolerance, and simplified viscoelastic continuum damage tests for fracture and fatigue resistance; the loaded wheel tracking test for rutting resistance and moisture susceptibility; indirect tensile creep compliance and strength tests for low-temperature cracking resistance; and the Cantabro abrasion test for durability. Further, AASHTOWare Pavement ME software was used to predict the long-term performance of asphalt pavements containing mixtures with high RAP contents and a Lewis acid catalyst. Results showed that the use of the Lewis acid catalyst can disrupt associated molecules formed in the aged RAP binder. Thus, asphalt mixtures containing high RAP contents (recycled binder ratio > 0.20) and a Lewis acid catalyst exhibited similar performances to conventional mixtures. Further, Pavement ME predicted fatigue cracking was lower for a structure containing a FeCl3-modified mixture as compared to a similar one with no FeCl3, illustrating the effectiveness of FeCl3.

Field Validation on the Use of Poker-Chip Test to Predict Cracking in Flexible Pavements

Cracking in flexible pavements is one of the most prevalent forms of distress. Two types of cracking ubiquitous to most regions are fatigue or alligator cracking, and thermal or low-temperature cracking. Cracking characteristics of a flexible pavement depend on a combination of factors that include the structural design of the pavement, asphalt mixture properties, component material properties, and construction quality. The cracking resistance of asphalt mixtures used in flexible pavements may be improved by use of asphalt binders with properties that are suitable to the application. Asphalt binder relies on its stiffness, tensile strength, ductility, and ability to relax to resist cracking due to repeated loading or changes in temperature. In current performance grade specifications of asphalt binders, cracking resistance is primarily characterized by asphalt rheology. Over the years, several researchers have considered this to be a gap. Several studies have been conducted to close this gap by considering various properties including strength and ductility. This study focuses on ductility of asphalt binders as measured by the poker-chip test to resist cracking. Field performance data measured on several pavement sections in Texas were compared with ductility of asphalt binders recovered from field cores. This study finds the poker-chip test to be a promising means of measuring ductility as well as characterizing ability of asphalt binders to resist fatigue and thermal cracking.

Optimization and analysis of biomass carbon loaded metal catalyst for catalytic cracking of toluene

The technology of hydrogen production from biomass pyrolysis is on the way, but the biomass tar produced in the process of pyrolysis seriously affects its practical application. The key to catalytic cracking technology was to develop highly low-temperature active and stable catalysts. In view of that, a new anti-sintering carbon-based nanocatalyst with distinct micro-mesoporous structure was synthesized by carbothermic reduction of the catalyst under mixed gas (H2/N2) atmosphere using cigarette stalks as raw material. The results showed that at a relatively low temperature of 700 °C, the catalyst had a high toluene conversion of 100 %, a stable lifetime of 250 min, a maximum hydrogen yield of 12,250 ppm and a desirable hydrogen selectivity of 77 %. The addition of hydrogen during the catalyst synthesis enabled a stronger interaction between the metal and the carbon support, which maintained a high metal distribution, resulting in a more interesting anti-sintering phenomenon of nickel nanoparticles at high temperatures. In particular, hydrogen etching of the support avoided collapse of the pores at high temperatures. At the same time, the etching enriched the pore structure of the support, thus increasing the specific surface area and pore volume of the support. This study provided a simple treatment of a carbon loaded nickel catalyst in the synthesis process and reported a novel low-temperature catalytic cracking catalyst with good toluene cracking activity and hydrogen generation.

Experimental investigation of usability of modified asphalt binder with waste expanded polystyrene (EPS)

EPS (Expanded polystyrene) is widely used in construction and packaging industries. Unfortunately, EPS is not mostly recyclable because it might not be economically feasible to store, transport, and process EPS so that it becomes recyclable. Therefore, alternative waste management strategies are urgently needed. The main objective of this study is to experimentally investigate the potential use of waste EPS in asphalt binder modification. As part of this study, a base asphalt binder with a Penetration grade of 70/100 was modified with waste EPS in four different ratios (0%, 1.5%, 3% and 4.5%, by weight of asphalt binder). The modified asphalt binder specimens were tested based on several physical (penetration, ductility, softening points and viscosity) as well as rheological/Superpave binder grading system tests including Rolling Thin Film Oven (RTFO), Pressure Aging Vessel (PAV), Dynamic Shear Rheometer (DSR), and Bending Beam Rheometer (BBR). Based on the tests results, rheological and engineering properties of the modified asphalt binders were compared with the ones of the base binder so that effect of waste EPS addition on the properties of the base binder was evaluated; and how the Superpave binder grades of the modified binders were changed with the additions of waste EPS was discussed. It was found out that modifying asphalt binders with EPS provided them with a better rutting resistance at the expense of lowering their fatigue and low temperature cracking resistance. Overall, it could be concluded that waste EPS can be potentially used in the asphalt binder modification by paying special attention to these factors, and it should be noted that using waste EPS in the asphalt binder modification has many economic and environmental benefits.

Low-Temperature Crack Resistance of Basalt Fiber-Reinforced Phase-Change Asphalt Mixture Based on Digital-Image Correlation Technology

DaoLu Tiaowen Cailiao (DTC) phase-change materials are important materials for improving the temperature adaptation of asphalt pavements. In order to improve the low-temperature crack resistance of asphalt pavements after adding DTC phase-change materials, basalt fiber-reinforced DTC phase-change asphalt mixtures with different basalt fiber dosages were prepared, and their mechanical properties, horizontal strain, and crack characteristics were analyzed using semicircular bending tests combined with digital-image correlation technology. The study showed that the basalt fiber increased the fracture strength of the phase-change asphalt mixture, delayed its damage time, improved its deformation capacity, reduced the crack development rate and damage degree of the interface, and enhanced its low-temperature crack resistance. The enhancement of low-temperature crack resistance of phase-change asphalt mixtures increased and then decreased, and the best effect was achieved when the dosage of basalt fiber was 3‰, which delayed the damage time of phase-change asphalt mixtures by 42.53 s, slowed down the crack expansion rate by 54.23%, and reduced the fractal dimension (D) and damage factor (Df) by 4.32% and 29.83%, respectively. In conclusion, basalt fibers can enhance the low-temperature crack resistance of phase-change asphalt mixtures, and the optimal dosage of basalt fiber is 3‰. Also, both D and Df showed a positive correlation pattern with KIC, but Df was more closely related to KIC, which shows that the new index Df based on the image analysis method and MATLAB software is reliable.

Investigation of road performances of rejuvenated styrene-butadiene-styrene modified asphalt mixture

Exploring the effective recycling of waste styrene-butadiene-styrene block copolymer (SBS) modified asphalt mixture is the difficulty and hotspot in the field of road materials research. Common rejuvenation method and reactive rejuvenation method were used to recover the road performances of aged SBS modified asphalt mixture (ASMBM) in this paper. The recovery effect of high- and low-temperature performance, fatigue resistance and water stability for ASMBM after rejuvenation was studied, and the road performance development of ASMBM after reactive rejuvenation in the early stage was also investigated. The results show that reactive rejuvenation method could significantly enhance the Marshall stability and rutting resistance of rejuvenated ASMBM, and further improve its low-temperature cracking resistance as compared with common rejuvenation method, which attributes to the reconstruction of aged SBS cross-linking structure and its improvement on the interface stability of rejuvenated mixture. Meanwhile, the fatigue life of reactive rejuvenated ASMBM under strain level of 400 με is 26.6 % higher than that of common rejuvenated mixture. Water stability test results show that reactive rejuvenation is more beneficial to restore the water-immersed Marshall stability and Hamburger rutting resistance of ASMBM. Furthermore, the road performances of reactive rejuvenated ASMBM have a further improvement with the extension of time in the early stage after rejuvenation, its Marshall stability, the freeze-thaw splitting strength ratio and water-immersed Marshall stability could restore to the initial level of fresh mixture. Thus, reactive rejuvenation method is more conducive to realizing the high-performance recycling of waste SBS modified asphalt mixture and enhance its recycling value.

Development and performance of pouring self-luminescent asphalt mixture

The application of long afterglow-based materials to the self-luminescent pavement could significantly reduce the power consumption of lighting at night and improve the traffic safety. This study designs a pouring self-luminescent asphalt mixture (PSAM) through pouring a grouting material including the long afterglow luminescent material (SrAl2O4:Eu, Dy) and epoxy resin into the porous pavement void configuration. First, the mechanical and afterglow properties of the epoxy resin-based long afterglow grouting material were systematically tested to determine the optimal composition ratio of raw materials. Then, the influence of time and viscosity on the grouting was studied by obtaining the luminous images of the cross and longitudinal sections of self-luminous asphalt mixture specimens. According to the volume characteristics of the grouting material and the mixture, the relationship between the theoretical grouting consumption and the actual grouting consumption was analyzed. Finally, the influence of porous mixture air void on afterglow characteristics and road performance of the PSAM was analyzed. From the acquired results, it was demonstrated that the optimum proportion of each component of the epoxy resin long afterglow grouting material was the following: epoxy resin: curing agent: toughener: long afterglow material = 100:18:15:14. Moreover, it was found that the temperature and pre-curing time have remarkable effects on the viscosity of grouting materials. In order to ensure a good grouting effect, the viscosity of the grouting material should be controlled within 1.7 Pa s. There was a good linear relationship between the actual grouting amount and the connected air void, although the actual grouting consumption was less than the theoretical grouting consumption. Furthermore, PSAM exhibited good afterglow performance and road performance. The afterglow brightness and water stability had no obvious relationship with the air void. In contrast, with the further increase of the air void, both the low-temperature crack resistance and the skid resistance were improved, and the high-temperature stability was reduced.

Thermal-mechanical coupled XFEM simulation of low temperature cracking behavior in asphalt concrete waterproofing layer

Asphalt concrete waterproofing layer (ACWL), which is used to reduce the moisture impact on high-speed railway structure, tends to crack at low temperatures and thus reduces its durability. Therefore, understanding the low-temperature cracking behavior of ACWL from both the material and structure perspectives is of great significance. In this study, thermal-mechanical coupled simulation based on extended finite element method (XFEM) was employed for research on this aspect, with the experimental and numerical monotonic-loading overlay test (ML-OT) to determine the fracture parameters of railway asphalt concrete materials and full-scale model to characterize the thermal cracking behaviors of ACWL. The results firstly showed that both the ML-OT and thermo-mechanical simulation on ACWL structure presented a four-stage fracture process, i.e. elastic response, crack initiation, crack propagation and final failure stage, at the temperature of −20 °C. Secondly, the effects of material formulation and structure design on the low-temperature cracking resistance was investigated: 1) In terms of material formulation, the binder B and gradation AC-13 was superior to their counterparts; 2) In terms of structure design, the ACWL layer thickness of 8 cm was the most unfavorable in the range of 6–16 cm, and the increased temperature difference accelerated the thermal cracking propagation in ACWL at the average temperature of −20 °C. In addition, two thermal stress mitigation strategies, namely laying the geotextile at base joints and setting expansion joints, were found to effectively prevent and delay the emergence of thermal cracks in ACWL at low temperatures. For recommendation, the developed thermal-mechanical coupled simulation framework, the custom-designed railway asphalt concretes, and the recommended ACWL thickness of 12 cm were applicable in future studies and engineering projects.

Effect of nano-reduced graphene oxide (NRGO) on long-term fracture behavior of Warm Mix Asphalt (WMA)

Recent studies have shown that in addition to ambient temperature, time-dependent factors such as temperature cycles and freeze–thaw cycles (FTCs) affect the speed of creation and growth of low-temperature cracks (LTCs) and intermediate-temperature cracks (ITCs) by creating the aging process in the asphalt mixture. Therefore, it is necessary to study the cracking behavior of asphalt mixtures by considering these factors. In the present study, an attempt was made to evaluate the long-term fracture behavior of Warm Mix Asphalt (WMA) modified with nano-reduced graphene oxide (NRGO) containing vertical and angular cracks under mode I loading conditions at low and intermediate temperatures using Semi-circular bend (SCB) geometry. In order to simulate long-term performance, two conditions of 3 FTC and aging process (for 6 days) were applied to the mixtures with and without NRGO, and the results were compared with samples subjected to 0 FTC (short-term performance). The results showed that adding 0.3% and 0.6% NRGO to the WMA mixture increased fracture toughness (KIC), fracture energy (GF), and stiffness under mode I at low and intermediate temperatures. At +15 °C and for the geometry containing the vertical crack, the NRGO-modified WMA mixture had better flexibility under 3 FTC than 0 FTC; while, the flexibility of the NRGO-modified WMA mixture decreased under aging process. For geometry containing angular crack, flexibility indices improved for NRGO-containing mixtures under 3 FTC and aging process (at +15 °C temperature). On the other hand, the results showed that the addition of NRGO to the WMA mixture, while increasing the maximum load at the moment of fracture, caused a decrease in the displacement at the fractured moment at low and intermediate temperatures. This result was obtained for the mixtures that were conditioned under aging process. However, the results showed that applying 3 FTCs decreased the maximum load at the moment of fracture and increased the displacement at the fractured moment. Finally, the results showed that the reduction of fracture indices was higher for WMA and NRGO-modified WMA mixtures under 3 FTCs (at temperatures ±15 °C); therefore, applying 3 FTC instead of aging process can be used to evaluate the long-term performance of asphalt mixtures.

Optimizing the Effective Use of Reclaimed Asphalt Pavement in Local Roadways

This study involved the construction of eight test sections in the City of Columbus, Ohio, to evaluate the effects of using different reclaimed asphalt pavement (RAP) contents and types of rejuvenator on the performance and properties of asphalt mixes used for local roads. The first section (control section) had a mix with 20% RAP and PG 64-22 binder. While three sections had mixes with 30%, 40%, 50% RAP, PG 64-22 binder, and Sylvaroad rejuvenator (tall oil), three other sections had mixes with the same RAP percentages and binder but used Hydrolene (aromatic extract) as the rejuvenator. Finally, the last test section was constructed using a mix with a 30% RAP and PG 64-28 binder (softer binder). Specimens were compacted in the laboratory from loose mixes that were obtained during the construction of each test section. Laboratory tests were conducted to evaluate the resistance of the prepared samples to moderate-temperature cracking, low-temperature cracking, rutting, and moisture damage. The test results showed that Hydrolene was more effective than Sylvaroad in improving the moderate-temperature cracking resistance of RAP mixes with more than 30% RAP. In addition, the tests results showed that the 30% RAP, 40% RAP, and 50% RAP mixes had similar low-temperature cracking resistance to that of the control. The laboratory test results also showed that mixes with 30% and 40% RAP had acceptable resistance to moisture damage. Furthermore, all mixes had acceptable rutting resistance. Finally, preliminary field evaluation showed that there were no observed distresses in the test sections after 7 months of construction.