Moisture Damage Resistance Research Articles

Adhesion Characteristics of Graphene-Modified Asphalt Using Surface-Free Energy Method

Graphene is an auspicious nanomodified material for asphalt pavements. This study aims to evaluate the effect of graphene composites (GCs) on the adhesion characteristics of asphalt based on surface-free energy (SFE) theory. The surface-free energy of graphene-modified asphalt was measured by the sessile drop method. The work of adhesion and stripping between asphalts and two kinds of aggregates were calculated through using their surface-free energy components. The macroadhesion property between asphalts and aggregates was obtained by the improved boiling method. Immersion Marshall test and freeze–thaw splitting test were conducted to verify the effectiveness of surface-free energy indexes. The results demonstrated that GC significantly increased total surface-free energy and dispersion components of asphalt but reduced the polarity components. The adhesion work between asphalt and both aggregates increased after modification, whereas the stripping work decreased after modification. GC can substantially improve the adhesion and resistance to moisture damage at the asphalt–aggregate interface, and the effect on asphalt-limestone is more obvious. There are strong correlations between macro evaluation indicators and surface-free energy calculated indexes, where the macro indicators are more strongly correlated with stripping work. Limestone is generally better at resisting moisture damage than granite. GC remarkably improved the water stability of the mixture, which further indicates that energy indexes are a good method to quantize the moisture damage resistance of hot mix asphalt (HMA). The high dosage of graphene-modified asphalt is potentially applicable to porous asphalt concrete (PAC) pavement with extra-large voids.

Recycled polyethylene waste as binder stabilizer for SMA mix in gulf environment

Each year, millions of tons of household and industrial waste, including plastic, are responsible for harming the environment through burning, landfilling, or going to dump in open water. Waste plastic disposal is a critical issue faced by municipalities in modern cities. In addition, the development of hundreds of kilometers of roads worldwide leads to the consumption of vast quantities of raw materials and the depletion of valuable natural resources. The high expense of virgin polymers and rising plastic waste have shifted the research focus toward green pavements that utilize waste plastics. Therefore, this research aims to investigate the use of recycled plastic waste as a binder modifier for Stone Mastic Asphalt mix (SMA). The high-temperature performance of the Recycled Polyethylene Modified Binder (RPMB) has been evaluated with various percentage dosages to satisfy the environment of the Gulf region. In addition, the impact of RPMB on the SMA mix was studied through three performance tests, drain down resistance, moisture damage resistance, and rutting performance. The results showed continuous improvement in rheological properties with increased recycled polyethylene (RP) content by up to 6%. The RP enhances the binder properties such as the rutting parameter, non-recoverable compliance, and viscosity to meet the high-temperature performance requirement for heavy traffic (UPG 76 H) of most roads in the gulf environment. However, the results showed that RPMB could not meet the recovery requirement set by AASHTO TP 70. That is due to RP's plastomer nature. Therefore, it is necessary to supplement some proportion of the RP with an elastomeric polymer. Further, the results of SMA mix properties with RPMB showed remarkable improvement over than control mixture in terms of resistance to drain down, moisture damage, and rutting by 55.1%, 52.6%, and 96.4, respectively.

Laboratory and field performances of grave emulsion manufactured using nanocellulose crystals as an asphalt-emulsion emulsifier

This research examines the feasibility of substituting commercial emulsifiers made by the chemical and petrochemical industries with nanocellulose. To achieve this, various bitumen emulsions are created using nanocellulose fibers and crystals as emulsifying agents. A grave-emulsion type GE-1 manufactured using bitumen emulsion produced with nanocellulose is studied. A control GE-1 is also tested. Modified proctor tests are employed to obtain the optimal fluid content; the optimum bitumen emulsion content is determined using an immersion-compression test. The compactability of GE-1 is analysed using a gyratory compactor. Finally, the moisture damage resistance (tensile strength ratio), stiffness (resilient modulus), and permanent deformation (repeated load axial test) are studied. A trial section constructed on a real scale. The cores are collected after one year and the stiffness is analysed. The results indicate that conventional emulsifying agents can be partially replaced with nanocellulose crystals in the manufacture of cationic slow-setting bituminous emulsions for grave emulsions.

Materials Optimization and Service Performance Evaluation of a Novel Steel Bridge Deck Pavement Structure: A Case Study

Although the double-layer pavement structure with a top layer of stone mastic asphalt concrete (SMAC) and a bottom layer of epoxy asphalt concrete (EAC) has been confirmed to have excellent overall performance in the laboratory, there is a lack of comparison and verification in practical projects. Hence, the utilization of the SMAC + EAC structure in this steel bridge deck pavement (SBDP) practical project and the clarification of its service performance are of significant importance for facilitating the promotion and application of this novel structure. This study relied on an SBDP reconstruction project in Ningbo, China. Indoor performance tests were used to determine the appropriate material compositions for SMAC and EAC. Subsequently, both ERS and SMAC + EAC pavement structures were paved in the project, and the service conditions of the different pavements after one year of operation were tested and compared. The results indicated that the epoxy SBS asphalt (ESA) binder prepared by substituting SBS-modified asphalt binder for the base binder, exhibited improved mechanical strength and toughness. The variation of modifier content significantly affected the high-temperature stability, low-temperature crack resistance, and moisture damage resistance of epoxy SBS asphalt concrete (ESAC) and high-viscosity SBS asphalt concrete (HSAC), while the gradation mainly influenced the skid resistance. The optimal contents of modifiers in ESA and HAS binders were finalized at 45 wt% and 11 wt%. After one year of operation on the trial road, the pavement performance of the SMAC + EAC structure had significant advantages over the ERS system, with all lanes having an SBDP quality index (SDPQI) above 90 and an excellent service condition. The successful application of the SMAC + EAC structure validated its applicability and feasibility in SBDP, which provided strong evidence for the further promotion of this structure.

Evaluating the Effect of Curing Time and Resting Time on Moisture Damage Resistance of Asphalt Mixtures Using the Pull-Off Tensile Strength (POTS) Test

This article explores the effectiveness of the Pull-off Tensile Strength (POTS) test as a tool for evaluating the moisture damage resistance of asphalt mixtures. Currently, indirect tensile strength (ITS) and the Hamburg Wheel Tracking (HWT) test are used, but they have limitations such as expensive equipment and being heavy. The POTS test is a low-cost and portable alternative. This study investigated the effect of curing time and resting time on the POTS of asphalt-aggregate systems by subjecting samples to different curing times and resting times before testing their tensile strength under dry and wet conditions. The results show that the tensile strength decreases with increasing curing time or exposure to water, indicating that the debonding process between asphalt and aggregates occurs more rapidly with aging. The tensile strength ratio (TSR) of the POTS test for all three asphalt binder types increases with resting time and curing time, with the highest values observed at a curing time of 2 h and a resting time of 5–15 min. Additionally, this study found a strong linear relationship between the tensile strength ratios of ITS and POTS tests, regardless of curing time and resting time. Overall, the POTS test is a promising alternative for evaluating moisture damage resistance in asphalt mixtures.

Effect of dynamic water pressure on the adhesion behavior of recycled asphalt-aggregate interface by molecular dynamics method

The integrity of the asphalt-aggregate interface is challenged by the dynamic water pressure under traffic loads, especially for recycled asphalt mixtures that represent lower moisture damage resistance by comparing with virgin asphalt mixtures. The effect of dynamic water pressure on the microscale interfacial adhesion properties between the waste-oil recycled asphalt and aggregate was comprehensively investigated based on the molecular dynamic simulation. The molecular models of recycled asphalt and aggregate were calibrated based on the chemical and physical analysis in experiments. The interfacial contact models between recycled asphalt with different regenerants (waste cooking oil-WCO, waste vegetable oil-WVO, and waste engine oil-WEO) and basalt aggregate were established, which also incorporated the thermodynamic process of water intrusion into the interface. The interface behaviors were studied by analyzing the cohesion energy of asphalt, the adhesion energy of interface, and the distribution of asphalt and water concentration on the aggregate surface. The results demonstrated that the dynamic water pressure can accelerate the water to penetrate the asphalt film. The recycled asphalt was pushed away from the basalt aggregate surface after the water film was formed at the interface, where the four components of asphalt leave the interface at different rates. Compared with the other two kinds of waste-oil recycled asphalt and conventional recycled asphalt, the WEO recycled asphalt-aggregate interface represented the optimum moisture damage resistance. The decrease of interface adhesion energy is about 55.7 % subjected to the coupling effects of the high-temperature and dynamic water pressure at 0.5 MPa.

Prediction and evaluation the moisture damage resistance of rejuvenated asphalt mixtures based on neural network

The aim of this paper is to establish a model for predicting the moisture damage resistance of the rejuvenated asphalt mixture. Based on the surface free energy theory, the contact angels between asphalt and aggregate were measured with known reagents using the sessile drop method. The adhesion work, spalling work and moisture damage resistance index of the asphalt-aggregate interface system were then calculated. Secondly, the tensile strength ratio of the rejuvenated asphalt mixture was determined, and the influence of six indices, including RAP content, rejuvenator content, adhesion work, spalling work, per cent air voids in bituminous mixtures (VV) and freeze–thaw cycle on the performance of the moisture damage resistance of rejuvenated asphalt mixture was analyzed using the gray correlation entropy method. Finally, a three-layer neural network was used to predict the moisture damage resistance of the rejuvenated asphalt mixture. The results show that as the content of aged asphalt increases, the adhesion work of the asphalt- aggregate interface system decreases. Furthermore, for the system of the same rejuvenated asphalt and different aggregates, the rank of adhesion and water resistance from strong to weak is asphalt-limestone＞asphalt- granite, and the rank of the gray entropy correlation between six indices and moisture damage resistance from strong to weak is adhesion work＞spalling work＞VV＞rejuvenator content＞RAP content＞freeze-thaw cycles. Finally, the accuracy of the neural network predicting the moisture damage resistance of rejuvenated asphalt mix reaches 96.188%, which provides a new method to predict the moisture damage resistance of rejuvenated asphalt mixture.

Moisture damage susceptibility of a wood-based bio-binder for total replacement of asphalt binders

There is limited information on the characteristics and performance of paving mixtures made with 100% bio-binders. Moisture damage resistance of this type of mixture is a concern since the components of the bio-binder may have a higher affinity with water than asphalt binders. In this context, this paper presents a moisture damage susceptibility evaluation of wood-based bio-binder-aggregate interfaces in terms of energy parameters calculated from surface free energy components. The bio-binder was used as a total replacement for asphalt binders, and the responses were compared to a neat- and a highly modified-asphalt binder, considering different aggregate sources. Results suggest the bio-binder has similar moisture damage resistance to the neat asphalt binder and higher resistance than the highly modified asphalt binder, providing a first indication for the potential use of this bio-binder as 100% asphalt binder replacement. However, additional research is still required to validate these findings at the mixture level.

Moisture Susceptibility of Asphalt Mixtures: Conditioning and Testing Protocols

Moisture damage is a common distress in asphalt pavements caused by infiltrated moisture, which degrades mixture strength and affects pavement durability. Loaded wheel tracking (LWT) and modified Lottman (ML) tests are the two commonly used mechanical tests for assessing the moisture susceptibility of asphalt mixtures, but they have been reported to show limitations in consistently ascertaining the moisture sensitivity of different asphalt mixtures under field conditions. This study evaluated the effectiveness of different laboratory mechanical tests (LWT, ML, and semi-circular bend [SCB]) in ascertaining moisture sensitivity of asphalt mixtures. LWT, ML, and SCB tests were conducted on asphalt mixtures prepared with two asphalt binders (an unmodified PG 67-22 and a styrene-butadiene-styrene polymer-modified PG 70-22) and three aggregate types (limestone, crushed gravel, and semi-crushed gravel). Before testing, asphalt binder and mixture samples were exposed to five moisture conditioning levels: (1) unconditioned (dry), (2) single freeze-thaw cycle, (3) triple freeze-thaw cycle, (4) moisture induced stress tester (MiST) 3,500 cycles, and (5) MiST 7,000 cycles. A multiple stress creep recovery test was conducted on asphalt binders subjected to the five moisture conditioning levels. Results showed that the stress sensitivity of asphalt binders decreased after freeze-thaw and MiST conditioning. LWT rut depth and a new parameter which was developed as part of the study, SCB Jd ratio, were found to capture the progressive moisture damage in asphalt mixtures associated with different moisture conditioning levels. Mixtures containing PG 70-22 asphalt binder exhibited better moisture damage resistance compared with mixtures containing PG 67-22 asphalt binder.

The effect of mix design method on performance of asphalt mixtures containing reclaimed asphalt pavement and recycling agents: Superpave versus balanced mix design

The balanced mix design (BMD) is an alternative method to determine the Optimum Binder Content (OBC) of asphalt mixtures that considers both volumetric and performance properties. However, the feasibility of using this method for designing asphalt mixtures with high reclaimed asphalt pavement (RAP) materials (e.g., 25% and 50%) without and with different types of recycling agents (RAs) needs to be further investigated. To this end, the OBC of asphalt mixtures was first determined through Superpave Mix Design (SMD) by considering volumetric properties. Then mixtures using OBC and OBC ± 0.6% were prepared. Three mechanical tests, including Hamburg Wheel Tracking (HWT), Illinois Flexibility Index (I-FIT), and Indirect Tensile Strength (ITS) in dry and wet conditions, were utilized for high-temperature rutting, mid-temperature cracking, and moisture damage resistance characterization, respectively. The results showed that the RAP-blended mixtures with and without RAs prepared with the OBCs could pass rutting and moisture damage resistance criteria while the cracking resistance of these mixtures was lower than the accepted threshold, except control mixture (i.e., C). Although introducing the RAs to the RAP blended mixtures improved their cracking resistance, an increase in OBC is still needed in RAP mixtures in order to meet the cracking resistance requirement. It was concluded that the SMD might not be an appropriate method for designing the mixtures containing high-RAP materials with and without RAs and these mixtures need to be designed using the BMD method. Among the three RAs evaluated in this study, the aromatic extract RA had the most influence on the rutting performance regardless of the RAP content, while mixtures treated by the aromatic extract RA showed the best cracking resistance.

Temperature and Aging Effects on the Rheological Properties and Performance of Geopolymer-Modified Asphalt Binder and Mixtures.

Using geopolymer as a modifier for asphalt binders and mixtures gained momentum for investigation in recent decades. Limited research investigations attempted to link the effect of temperature and traffic loading on the rheological properties and performance of geopolymer-modified asphalt binders. The primary objective of this study is to evaluate the effect of fly ash-based geopolymer (GF), styrene-butadiene-styrene (SBS), and the combination of GF with SBS on the rheological properties and performance of asphalt binders at low and intermediate temperatures. The rheological properties and performance of neat and modified asphalt binders (4%GF, 8%GF,12%GF, 2%SBS, and hybrid (2%SBS+8%GF)) were evaluated utilizing dynamic shear rheometer (DSR) and bending beam rheometer (BBR) devices. To evaluate the fatigue resistance of asphalt binders, the linear amplitude sweep (LAS) and viscoelastic continuum damage (VECD) models were applied. The dynamic or complex modulus and moisture damage resistance were measured to investigate the influence of modifiers on the performance of asphalt mixtures. The findings demonstrated that for both unaged and RTFO-aged asphalt binders, additives reduced the temperature sensitivity of both G' and G″. When the binders were exposed to long-term aging using a pressure aging vessel (PAV), it was noticed that the 8%GF binder became more susceptible to temperature changes. The 2%SBS binder had the lowest creep stiffness compared with the neat and other modifiers, while the hybrid binder exhibited the highest resistance to fatigue distress at different temperatures compared with the other binders. The modified asphalt mixes (8%GF, 2%SBS, and hybrid) achieved the maximum tensile strength (St) compared with the neat asphalt binder, with an increase of more than 80%. The St increased from 580.4 kPa to 740.4 kPa, 884.8 kPa, and 917.4 kPa by utilising the 8%GF, 2%SBS, and hybrid binders, respectively. Furthermore, the modified asphalt mixture exhibited more ability to resist cracking, attaining the highest fracture energy in dry and freeze-thaw conditions.

Structural optimization of steel bridge deck pavement based on mixture performance and mechanical simulation

The upper layer of modified SMA mixture (SMAM) and the lower layer of epoxy asphalt mixture (EAM) is a steel bridge deck pavement (SBDP) structure with application potential, but there is a lack of systematic research on it. In this study, the pavement material and structure of SMAM + EAM were optimized using mixture performance tests and finite element analysis, which provided guidance to facilitate its promotion and application. Firstly, the pavement performance and dynamic properties of SMAMs and EAMs prepared with different binders were compared to preferably select the appropriate SBDP material. Secondly, the dynamic modulus master curves of the mixtures were established to provide material parameters for pavement structure design. Finally, the FEA method was applied to comparatively analyze the dynamic mechanical response of the pavement structure for different structures, thickness combinations, and temperatures to optimize the SBDP structure purposefully. The results demonstrated that EAM had better high-temperature rutting resistance than SMAM, while SMAM had superior moisture damage and skid resistance. The modifier contents in the asphalt binder used for SMAM and EAM were recommended to be 12 wt% and 40 wt%, respectively. From the FEA results, the SMAM + EAM structure met the performance requirements of SBDP. Compared with double-layered EAM, the deformation resistance of the SMAM + EAM structure was reduced, but it was beneficial to avoid the occurrence of crack defects and interlayer shear damage. Furthermore, the recommended pavement thickness combination was 4.5 + 3.5 cm.

Potential of Cashew Nut Shell Liquid as S Sustainable Organic Additive to Improve the Moisture Damage Resistance of Warm Mix Asphalt

Potential of Cashew Nut Shell Liquid as S Sustainable Organic Additive to Improve the Moisture Damage Resistance of Warm Mix Asphalt

Investigation on moisture damage resistance of asphalt pavement in salt and acid erosion environments based on Multi-scale analysis

The existing research on the moisture damage resistance of asphalt pavement in salt and acid erosion environments is mostly indirect tensile tests based on asphalt mixture scale. There is little comprehensive analysis based on multi-scale. However, for the study of moisture damage resistance of asphalt pavement, different scales have their own advantages and disadvantages. In view of this, this paper comprehensively analyzes the moisture damage resistance of asphalt pavement in salt and acid erosion environments based on three scales namely asphalt binder scale, asphalt-aggregate scale and asphalt mixture scale, and draws the following main conclusions: 1) On the whole, the deterioration tendency of salt and acid solution on the water stability mechanical strength of asphalt pavement is basically the same, and the specific order is acid rain (pH = 3) > 16 % seawater > 16 % NaCl > 8 % seawater > 8 % NaCl > distilled water > drying, indicating that salt and acid solution will aggravate the moisture damage of asphalt pavement, especially the acid rain with stronger corrosion effects. 2) The moisture damage resistance of asphalt-aggregate scale is weaker than that of asphalt binder scale and asphalt mixture scale. 3) The difference of moisture damage resistance test results between asphalt-aggregate scale and asphalt mixture scale in salt solution environments is smaller than that of other non-salt solutions. 4) The BBS test of asphalt-aggregate scale can effectively evaluate the self-healing performance of asphalt pavement. The self-healing ratio increased as the acid solution concentration increased, but the initial bond strength of BBS after high-concentration acid erosion was too small, so the bond strength after healing was still smaller than that of low-concentration acid solution. 5) The rotational viscosity of asphalt binder at 135 °C correlates well with the self-healing performance of asphalt pavement.

Effect of carbon nanotubes on fatigue cracking of asphalt mixtures modified by styrene-ethylene/propylene-styrene

ABSTRACT Fatigue cracking is a significant cause of failure in flexible pavements at moderate temperatures. Neat bitumen cannot properly perform at all temperatures and environmental conditions due to the increasing traffic volume. Consequently, this study examined the simultaneous usage of carbon nanotubes (CNTs) and the styrene-ethylene/propylene-styrene (SEPS) polymer as bitumen modifiers. The linear amplitude sweep (LAS) test and surface free energy (SFE) theory were used to determine the rheological characteristics and thermodynamic parameters of neat and modified bitumens, respectively. Using the SEPS nanocomposite up to 6% increased the fatigue life and moisture damage resistance of the asphalt mixtures by improving thermodynamic parameters such as adhesive free energy in dry and wet conditions. According to the LAS results, the modified bitumen outperformed the neat bitumen in terms of fatigue life under different strain levels. The fatigue life of the asphalt mixtures also decreased as the temperature increased from 10 to 20°C. However, for the mixtures containing the SEPS nanocomposite, the reduction in fatigue life was less noticeable due to the lower temperature sensitivity of the modified bitumen. The mixtures containing 6% SEPS nanocomposite demonstrated the highest performance.

Towards the sustainable utilization of steel slag in asphalt pavements: A case study of moisture resistance and life cycle assessment

The large-scale promotion of steel slag (SS) in pavement construction remains challenging due to the concern of swelling potential. This study combined molecular dynamics simulations, surface free energy theory, and X-ray computed tomography to characterize the moisture damage resistance of asphalt mixtures incorporating SS. A case study of the life cycle assessment of SS asphalt pavement under different application strategies (two gradation types and three volume contents) was conducted, including global warming and human-related health impacts. The results indicate the higher polarity and abundant alkaline components of SS contribute to the bonding strength and tend to reduce the moisture susceptibility. The adhesion of steel slag to asphalt is 137.58 %, 120.39 % and 37.06 % higher than that of granite, basalt, and limestone, respectively. The susceptibility index (Energy ratio) is reduced by 108.72 %, 107.90 % and 39.10 %, respectively. Moreover, the incorporation of SS improves the compactness of the structure and delays the penetration and the interconnection between large voids. While the number of micro-voids increases geometrically after steel slag incorporation, ranging from 250 % to 981 % during FT cycles. The proliferation of microdefects has the potential to develop into macro cracks under a long-term freeze-thaw environment, meanwhile the risk of swelling-induced cracks is exacerbated with the high use of SS. The increased consumption of asphalt and transport mass of SS during mixture production are detrimental to the overall environmental impacts. However, the use of SS avoids the damage of exploitation and eliminates the huge risks of landfill accumulation. These two benefits are enormous and cannot be accurately estimated.

Effect of low dosage crumbed rubber on the mechanical properties of a dense graded asphalt mixture

The benefits of crumb rubber modification of bituminous binder for asphalt mixture production is well established. Although most research has used high (20–30% by mass of the bitumen) crumb rubber dosages, there is now interest in low (5–15%) dosages for use in local road surfacing, where mechanical properties are less important. This paper quantifies the effects of low-dosage crumb rubber on the mechanical properties of a typical dense graded local road surface mixture. It was concluded that 5–10% crumb rubber dosage significantly increased the deformation (rutting) resistance and crack (fatigue) resistance of the asphalt. The effect of crumb rubber on mixture stiffness (modulus), moisture damage (stripping) resistance and workability (compactability) was mixed but was unlikely to present any practically important benefit or detriment. Consequently, 5–10% was concluded to be the preferred range of crumb rubber dosage for dense graded asphalt for local road surfacing.

Comparison of accelerated laboratory curing and maturation under uncontrolled conditions of gravel emulsions using a nonlinear weighted least-squares predictive model

ABSTRACT Cold-asphalt mixtures (CAMs) are evolved materials whose mechanical strength increases with their maturation. The relationship between CAM field maturation and laboratory-accelerated cure procedures is not well understood. Furthermore, there is controversy on the recommended methodology for laboratory-accelerated cure. So, in this work, the accelerated curing protocol for a CAM-type gravel emulsion was examined, and its uncontrolled maturation and performance were contrasted. For this, the mixture was subjected to either accelerated curing (from 0 to 7 days in a 50 °C oven) or natural curing (from 0 days to 6 months at 20 3 °C in the laboratory and at an unfixed temperature outside the laboratory). We analysed, as functions of time, the moisture, indirect tensile stiffness modulus (ITSM), and moisture damage resistance. A curing protocol of 2 days at 50 °C yielded ITSM values closer to those obtained under uncontrolled conditions. Nevertheless, total maturation of the mixture was achieved after 3.5 days of curing. The nonlinear weighted least-squares method yielded an expression that better predicted the performance of the gravel emulsion for the first six months of life. The model parameters were easily fitted using ITSM measurements derived from samples cured for 2 days in a 50 °C oven.

Effects of Fiber Type on the Mechanical Properties of the Open-Graded Friction Course Mixture.

The open-graded friction courses (OGFCs) have a large number of interconnected voids, which may cause serious water damage to the pavement. Hence, the road performance needs to be investigated. In this study, the mechanical properties of OGFCs containing two different fibers (lignin and mineral fiber) were investigated. Based on the procedure proposed by the Chinese specification JTG F40-2004, OGFCs were designed with the asphalt content between 4.1 and 4.7 wt % to find the optimal asphalt content (OAC). The mesh-basket draindown test was used to check the fiber's stabilization and absorption of bitumen. OGFCs containing the lignin/mineral fiber with OAC would be preferred in terms of the bulk specific gravity. These results indicate that the fiber can bring higher air voids to the OGFCs, and the different specific gravities of fibers may primarily account for the result. Both the lignin and mineral fibers can bring much more asphalts padded in the pores of mineral aggregates and subsequently larger OAC in OGFCs due to their higher asphalt absorption. Performance experiments were carried out to check the dynamic stability and moisture susceptibility of OGFCs containing the lignin/mineral fiber. The study suggests that the lignin and mineral fiber can be used to adjust the internal environment of OGFCs, enhancing the moisture damage resistance and improving the rutting resistance of OGFCs at high temperatures.

Characterization of Residual Moisture Distribution in Cold-Recycled Mixtures with Foamed Asphalt Using Hyperspectral Technology

Cold-recycling technology with foamed asphalt is used widely because it has the incomparable advantages of environmental protection and resource conservation. In this study, cold-recycled mixtures with foamed asphalt were prepared with different gradation types, mixing water contents, and curing times to study the distribution characteristics of residual moisture. An optimum foaming water content of 2.5% and foaming temperature of 165°C were determined for producing the foamed asphalt that was used for the cold-recycled asphalt mixtures. Hyperspectral imaging tests and spectral processing technology were used to obtain the image information and spectral information of residual moisture from 44 specimens; the moisture content of all specimens ranged from 0.25% to 4.70%. Pseudocolor-coding technology was utilized to realize visualization of moisture distribution. In addition, the residual moisture content prediction model was established based on the partial least-squares regression (PLSR) model. Correlations of the residual moisture distribution characteristics and moisture damage resistance evaluation indicators were developed. The residual moisture distribution characteristics and moisture damage resistance are affected significantly by aggregate gradations, mixed water content, and curing time. After 3 days of curing, the strength of the recycled mixture tends to be stable, and the moisture damage resistance can reach the specification requirements, and is suitable for open traffic. It was confirmed that there is a certain correlation between the internal residual moisture content value distribution range and the moisture damage resistance of the cold-recycled mixtures with foamed asphalt. This study could contribute to a better application of cold-recycled asphalt pavement for environmental protection and carbon stabilization.