Freeze-thaw Splitting Test Research Articles

Temperature Field Characterization of Iron Tailings Based on Microwave Maintenance Technology.

Microwave maintenance technology, as a new development trend, can realize the environmentally noninvasive and rapid repair of asphalt pavement and gradually replace traditional maintenance methods. Iron tailings were used as a self-healing material in this study to investigate the temperature response matching of microwave maintenance technology. Firstly, the physical properties and the mechanism of iron tailings were elaborated through macroscopic physical index testing and microscopic X-ray diffraction (XRD) analysis. Secondly, the applicability of aggregates to microwave heating was demonstrated by analyzing the temperature rise characteristics of the granules using infrared imaging. Then, the temperature field variation rules of the iron tailing asphalt mixture were summarized by microwave heating Marshall specimens. Finally, the road performance was assessed by conducting high-temperature dynamic stability, low-temperature tensile, water immersion Marshall, and freeze-thaw splitting tests. The experimental results showed that the iron tailings can be used as an aggregate for high-grade asphalt pavement and as the preferred aggregate for microwave maintenance technology. The iron tailings temperature field was radial from the inside out to provide different temperature response states for different pavement diseases, so the asphalt was dissolved and precipitated in a short time. The particle size of iron tailings was inversely proportional to the wave-absorbing heating rate, and the heating efficiency of the small particle size (0-4.75 mm) was the highest. The specimens doped with 4.75-13.2 mm iron tailings showed the best heating performance and road performance, with the average surface temperature of the specimens reaching 126.0 °C within 2 min. In summary, according to different disease types and construction needs, iron tailings can be used as an aggregate for asphalt pavement, providing an appropriate temperature field and improving the efficiency of the microwave maintenance of asphalt pavements.

Evaluation of cooling effect and road performance of warm mixed high viscosity porous asphalt mixture.

In order to study the effect of different warm mixing agents on the cooling and road performance of porous mixture bonded with High Viscosity Asphalt (HVA), the Superpave Gyratory Compactor (SGC) was proposed to conduct variable temperature compaction test on the warm mixed porous asphalt mixture. The relationship between the compaction difficulty coefficient and the temperature of the mixture was obtained by regression, and the mixing and compacting temperature and cooling effect of the warm mixed porous asphalt mixture were determined. Then, the influence of Evotherm M1 and EC120 warm mix agents on the performance of porous asphalt mixture was compared by rutting tests, beam bending tests, immersion Marshall tests, freeze-thaw splitting tests, and penetration strength tests. The results show that two types of warm mixing agents can reduce the mixing and rolling temperatures of the mixture by more than 10°C. The addition of warm mix agents will increase the high temperature stability, water stability, and shear resistance of porous asphalt mixtures. For the improvement effect of high temperature stability, EC120 warm mixing agent is greater than Evotherm M1 warm mixing agent, and for the improvement effect of water stability, Evotherm M1 warm mixing agent is greater than EC120 warm mixing agent. For shear resistance, the improvement effect of both is equivalent, with a penetration strength increase of about 3% to 4%. For low temperature performance, Evotherm M1 warm mixing agent improved the low temperature performance, while EC120 warm mixing agent showed the opposite effect.

Enhancing high-content recycled asphalt pavement regeneration: A laboratory separation and treatment approach

The escalating costs of aggregates and stringent sustainable development policies have emphasized the significance of effective high-content recycled asphalt pavement (RAP) regeneration technology. This study aims to present a novel laboratory separation and treatment approach for RAP materials, ensuring optimal performance of high-content RAP recycled asphalt mixtures. The proposed method is compared against factory-separated RAP materials in terms of agglomeration evaluation and mixture performance comparison. High- and low-temperature performance of the recycled asphalt mixture were evaluated through wheel tracking and trabecular bending tests. Furthermore, the moisture sensitivity of the recycled mixture was studied through immersion Marshall and freeze-thaw splitting tests. The uniformity and fusion between aggregates and asphalt in the recycled asphalt mixtures were meticulously analyzed using advanced techniques such as Scanning Electron Microscope and industrial Computed Tomography scans. The laboratory separation method encompasses flexible separation for 5–10 mm RAP materials and rigid separation for 10–20 mm RAP materials. Notably, the laboratory separation methods proved more effective in removing aged asphalt from the surface of 10–20 mm RAP materials compared to factory separation, thereby enhancing the adhesion between aggregates and asphalt and ensuring a more uniform recycled mixture. Although the dynamic stability of recycled asphalt mixture was reduced using laboratory separation, it still meets the requirements of relevant specifications. Moreover, the low-temperature maximum flexural tensile strain of the recycled asphalt mixture increased by 16%, with the residual stability and tensile strength ratio rising by 1.33% and 2.69%, respectively. Compared with the factory separation method, the laboratory separation method reduces the porosity percentage of the recycled asphalt mixture cross-section by 3.47%. Overall, the laboratory separation method for RAP materials provides valuable insights for enhancing the factory processing of RAP materials, contributing to the successful application of high RAP content regeneration technology in the pursuit of sustainable and cost-effective road construction practices.

Exploring the short-term water damage characteristics of asphalt mixtures: The combined effect of salt erosion and dynamic water scouring

In icy or snowy conditions, improper application and uneven dispersion of deicing salts on roadways can lead to saltwater accumulation, subsequently causing roadway scouring when vehicles transit. This study aims to assess the combined influence of salt erosion and dynamic water scouring on short-term water damage of asphalt mixtures. A custom-designed dynamic water scouring simulation apparatus is used, employing three diverse deicing salt solutions as agents for dynamic water scouring. Numerous iterations of dynamic water scouring tests are conducted on two types of graded asphalt mixtures. Post-scouring, alterations in air void content and water stability are evaluated through void content tests, Marshall water immersion tests, and freeze-thaw splitting tests. Additionally, the GM (1,N) damage prediction model from gray theory is applied for data modeling and prediction. The results reveal a significant impact of the combined effects of salt erosion and dynamic water scouring on the short-term performance of asphalt mixtures. In the early phase, dynamic water scouring primarily influences the asphalt composite, augmenting micro-cracks and causing aggregate disintegration. The intermediate phase sees the disintegration of the asphalt membrane by deicing salts, disrupting adhesion between asphalt and aggregate, and progressively leading to the emergence of new micro-cracks. During later stages, dynamic water scouring continues to deteriorate the asphalt composite, building on the erosion instigated by deicing salts, resulting in the expansion of newly formed micro-cracks and further aggregate disintegration. Among the three deicing salts, CH4N2O exhibits the most pronounced impact on short-term water damage, followed by NaCl, while CH2CH3OH has the least effect. Increasing the fine aggregate proportion in the asphalt mixture enhances water damage resistance. The GM (1,N) damage prediction model effectively anticipates air void content and water stability of asphalt mixtures. The research outcomes offer theoretical and technical support for understanding the durability and service lifespan of asphalt pavements in cold regions.

Preparation and Road Performance Study of Rubber–Diatomite Composite-Modified Asphalt Mixture

To examine the effect mechanism of rubber and diatomite on asphalt as well as the performance of asphalt mixtures for road applications, various composite-modified asphalts are prepared using rubber and diatomite. The performance of modified asphalts with various proportions is analyzed, and the optimal dosage ratio of modifiers is determined via the response surface approach. The microstructure of rubber–diatomite composite-modified asphalt is methodically examined using Fourier transform infrared spectroscopy and scanning electron microscopy. The road performance, aging resistance, and long-term stability of asphalt mixtures are evaluated through Marshall tests, wheel tracking tests, aging wheel tracking tests, freeze–thaw splitting tests, and cyclic freeze–thaw drying aging splitting tests. The obtained results reveal that asphalt with 22% rubber and 4% diatomite exhibits the best overall performance. The composite-modified asphalt essentially demonstrates the physical blending between rubber powder, diatomite, and base asphalt. The asphalt built from them formed a uniform and stable overall structure. Compared with rubber asphalt and rubber–SBS composite-modified asphalt, rubber–diatomite composite-modified asphalt exhibits superior road performance, including better aging resistance and long-term water stability in asphalt mixtures. This study can promote the further extensive application of rubber–diatomite-modified asphalt in road engineering, while providing new ideas for cost-saving and environmentally friendly asphalt modification.

Effect of alkali-treated bamboo fibers on the properties of asphalt mixture

ABSTRACT Bamboo fiber is a natural fiber that is ecologically beneficial and one of the best materials to replace lignin fiber for roads, which is still difficult to utilize properly in asphalt mixtures owing to its poor adherence, dispersion, and hydrophilicity. Previous research has discovered that alkali treatment, as an effective treatment approach, may effectively lower the hydrophilicity of plant fibers and improve their compatibility with the matrix. As a result, it is vital to investigate the effect of alkali treatment on bamboo fibers used in asphalt mixtures. The composition and microstructure of bamboo fibers treated with alkali were investigated using SEM and FTIR methods, while the adhesion between the bamboo fiber and asphalt before and after alkali treatment was tested using the fiber pull-out test. In addition, the dispersion rate of bamboo fibers in asphalt mixture was determined by developing a connection equation using the Schellenberg binder drainage test. The performance of bamboo fiber asphalt mixtures was then evaluated using rutting tests, beam bending tests, immersion Marshall tests, freeze-thaw splitting tests, and cyclic fatigue testing. The results showed that the alkali treatment successfully eliminated impurities in the outer layer of the bamboo fibers and reduced their hydrophilicity, which enhanced the asphalt-bamboo fiber interactions as well as the asphalt mixture’s water damage resistance, specifically manifested as the residual stability of ABM was enhanced by 7.8% and the splitting tensile strength of ABM was raised by 12.2%. Furthermore, the surface polarity of the bamboo fibers was reduced, which weakened the agglomeration phenomenon and increases the dispersion rate of bamboo fibers in the mixture by 9%, efficiently improving the low-temperature cracking resistance and fatigue performance of asphalt mixtures.

Adhesion property of municipal solid waste incinerator bottom ash and limestone with asphalt based on surface energy theory

ABSTRACT The aim of this paper is to investigate the adhesion of municipal solid waste incinerator bottom ash (MSWIBA) and limestone to asphalt using the principles of surface energy theory. MSWIBA asphalt mixes are known for their satisfactory water stability, with adhesion being a crucial factor, as demonstrated in previous freeze-thaw splitting tests. Contact angles of ground MSWIBA and limestone were measured using a capillary rise test, eliminating the influence of material surface structure. Subsequently, adhesion work and spalling work were calculated to correlate with water-induced damage. The results showed that the sequence of adhesion work was fine MSWIBA > limestone > coarse MSWIBA, while the sequence of spalling work was coarse MSWIBA > limestone > fine MSWIBA. The adhesion of MSWIBA asphalt mixes was evaluated using the water boiling test image method to validate the findings of surface energy theory. In both asphalt tests, the spalling rate followed this sequence: coarse MSWIBA > limestone > fine MSWIBA. The Adhesion index ER ranked as follows: ER Fine MSWIBA > ER limestone > ER coarse MSWIBA. These results suggest that the water stability of MSWIBA asphalt mixes is influenced by the surface energy of the components. Consequently, indices derived from surface energy theory can be applied in formulating and predicting the properties of MSWIBA asphalt mixes.

Effects of freeze–thaw cycles on micro and meso-structural characteristics and mechanical properties of porous asphalt mixtures

Abstract Porous asphalt concrete (PAC) have a typical big void-skeleton structure, and porous asphalt mixtures with large voids are more prone to freeze–thaw damage. As a result, research on the influence of freeze–thaw cycles on the micro-structure and mechanical characteristics of porous asphalt mixes offers a theoretical framework for overcoming water stability concerns in porous asphalt mixtures in practice, as well as for further popularization and application. In this study, styrene–butadiene–styrene (SBS)-modified asphalt and high viscosity modified asphalt were constructed on the basis of the original asphalt, and the mix proportions of asphalt mixes PAC-13, AC-13, and SMA-13 were designed. To begin, molecular dynamics simulations were used to look into the effects of freeze–thaw cycles on asphalt–aggregate interface adhesion and mixture micro-mechanical properties. Second, the effects of freeze–thaw cycles on the void characteristics of porous asphalt mixtures were explored utilizing digital image processing technologies. Finally, the freeze–thaw split test was utilized to evaluate the macroscopic mechanical properties of a porous asphalt mixture after freezing and thawing cycles. According to the study findings, high viscosity modified asphalt made with 4% SBS/8% TPS has the greatest performance. The application of SBS/TPS-modified asphalt can considerably improve the damage resistance of porous asphalt mixes. The micro-structure and mechanical qualities of porous asphalt mixtures are damaged by freeze–thaw cycles, and the damage gets worse as the number of cycles rises. The study’s conclusions provide a theoretical justification for the application of porous asphalt pavement.

Influence of Deicer on Water Stability of Asphalt Mixture under Freeze–Thaw Cycle

In seasonal frozen soil areas, the repeated freeze–thaw cycle of internal moisture in asphalt mixture in winter and spring will accelerate the peeling of asphalt film and aggravate the water damage of asphalt pavement. It is of great significance to carry out the attenuation law of mechanical properties of asphalt mixture under freeze–thaw cycles to prevent and reduce the economic losses caused by water damage to asphalt pavement. This study will investigate the impact of deicer application on the water stability of asphalt mixtures within the climatic conditions prevalent in Northwest China. Specifically, freeze–thaw cycle tests were administered to two types of dense-graded asphalt mixtures under three distinct deicer solutions and three disparate low-temperature environments. The Marshall water immersion test and freeze–thaw splitting test were employed to evaluate the water stability of asphalt mixtures subject to multiple factors, and the relative importance of each factor was statistically analyzed using the acquired data. Results demonstrated that AC-13 and AC-16 asphalt mixtures (AC is asphalt-concrete, which is asphalt concrete, and 13 or 16 represents the maximum particle size of aggregate (13 mm or 16 mm)), saturated in 15% CH4N2O, 20% NaCl, and 20% CH2CH3OH solutions, underwent a varying number of freezing–thawing cycles (0, 5, 10, 15, 20, 25, and 30) at temperatures of −5 °C, −15 °C, and −25 °C, respectively, displayed a discernible decline in their residual stability MS0 and freeze–thaw splitting tensile strength ratio TSR. This decline was particularly marked when temperatures dropped below the solution’s freezing point. Disregarding the fixed factors of weather variation (different low-temperature environments) and road service duration (number of freezing–thawing cycles), the aggregate grading imposed a more pronounced influence on asphalt mixture water stability than the presence of deicers.

Effect of deicing agents on the performance of airport asphalt pavement

Deicing agents are widely used to remove ice and snow on airport pavement, ensuring air traffic operation and safety. However, excessive spraying may affect the performance of airport pavement. The effects of different chloride deicing agents on the performance of airport asphalt and mixture have been assessed by previous studies. The three deicing agents (NaCl, KHF-1A, and NW056) were selected. Conducting various tests to examine their influence on the performance of asphalt and asphalt mixture. The tests include the DSR test, BBR test, indirect tensile test, bending test of small beam, and freeze-thaw splitting test. The results indicate that the asphalt anti-rutting factor G*/sinδ varies by 25%–45%, the asphalt creep stiffness increases by 15%–50%, and the anti-fatigue factor (G* sinδ) increases by 10%–40% under the effect of the deicing agents. The splitting strength of the mixture decreases by 10%–40%, the bending stiffness modulus increases by 6%–20%, and the freeze-thaw splitting strength ratio does not change significantly under the effect of the deicing agents. NW056 deicing agent has minimal effect on the performance of airport pavement and has optimal performance. The replacement of traditional chloride deicing agents helps to prolong the service life of airport asphalt pavement.

Experimental study of epoxy asphalt binder and porous epoxy asphalt concrete

Epoxy asphalt binder offers a promising solution for road material due to its low environmental impact and potential to reduce carbon emissions. In this paper, hot-mix epoxy asphalt binder (HEAB) and warm-mix epoxy asphalt binder (WEAB) were prepared firstly. The curing conditions of the binders were determined through viscosity and tensile tests, and their low-temperature properties were evaluated through bend creep stiffness tests. Furthermore, hot-mix porous epoxy asphalt concrete (HPEC) was designed with target void ratios ranging from 16% to 24%. Control groups included warm-mix porous epoxy asphalt concrete (WPEC) and high-viscosity modified porous asphalt concrete (HPAC) with a 20% target void ratio. The road performance of these various porous asphalt concrete was evaluated through multiple tests, including wheel tracking, low-temperature beam bending, dynamic modulus, four-point bending fatigue, freeze-thaw splitting, and Cantabro loss tests. The results indicate that HEAB follows a two-stage curing method of “160 °C, 2 h + 60 °C, 4 d”, while WEAB adopts a one-stage curing method of “120 °C, 5 h”, both of which demonstrate favorable properties. Moreover, HEAB exhibits better low-temperature properties compared to WEAB. The study also found that increasing the void ratio can reduce the high-temperature performance, freeze-thaw resistance, hydrothermal resistance, and dynamic modulus of HPEC. The low-temperature performance of HPEC reaches an inflection point at a target void ratio of 20%. Under the same target void ratio, HPEC exhibits the best high-temperature performance, dynamic modulus, fatigue resistance, freeze-thaw resistance, and hydrothermal resistance, followed by WPEC and HPAC. However, the low-temperature performance of both the HPEC and WPEC is lower than that of the HPAC. Overall, the use of epoxy asphalt binder in the preparation of porous asphalt concretes shows great potential for enhancing road performance.

Evaluation of the microscale structure and performance of asphalt mixtures under different design methods

Asphalt mixture design methods have an important influence on both the microscale structure formed and the corresponding properties. This research compared the performance of asphalt mixtures with the Balanced design method, Marshall design method, and Superpave design method. CT scans were performed on the mixture specimens under different design methods to analyze the mixtures' void distribution law and skeleton structure stability. Then, the water stability of asphalt mixtures with different skeleton structures was evaluated by the water immersion Marshall test and freeze–thaw splitting test, and the effects of temperature and loading frequency on the dynamic modulus of asphalt mixtures under different skeleton structures were assessed by uniaxial compression dynamic modulus test. Finally, based on the time–temperature equivalence principle and Sigmoid model, the master curves of the dynamic modulus of asphalt mixtures under different design methods were constructed. The results showed that the number of coarse aggregate contact points and the average coordination number of asphalt mixtures were relatively larger under the Balanced design method, and the residual strength ratio of asphalt mixture under the Marshall design method was 1.4% larger than that of the Balanced design method, and the residual strength ratio of specimens under Superpave design method was 6.1% larger than that of the Balanced design method. At the same time, based on the differences in the air void of the specimens under different design methods and the different skeleton structures, the dynamic modulus laws under the action of different frequencies were obtained, and the mechanism of the influence of the skeleton structure on the dynamic modulus of the mixture was revealed. This research has important implications for the durability improvement of asphalt mixtures.

Laboratory evaluation on performance of Polyurethane Porous Elastic Mixture

Poroelastic road surface (PERS)has high rubber particle content and air void, and its noise reduction performance is excellent. However, the performance of Polyurethane Porous Elastic Mixture (PUPEM) prepared with different contents of rubber particles and different types of polyurethane (PU) are rarely studied. This study aims to evaluate the comprehensive and functional performance of PUPEM and to analyze the influence of rubber particle content and PU type on PUPEM. PUPEM was prepared using different types of PU and different rubber particle content. The high-temperature performance, low-temperature bending performance, water stability performance, and skid resistance performance of PUPEM were evaluated by rutting test, low-temperature bending test, freeze–thaw splitting test, immersion Cantabro loss test, pendulum friction coefficient tester and sand patch method. The effects of air void content, rubber particle content, and thickness on the noise reduction performance of PUPEM were also studied by impedance tube test and dynamic modulus test. The results indicate that the PUPEM has excellent high-temperature performance, favorable low-temperature bending performance and skid resistance, and its water stability can meet the specification requirements. PUPEM also has favorable sound absorption and noise reduction performance through voids and noise reduction performance through elastic damping. In addition, the maximum sound absorption coefficient of PUPEM corresponds to a frequency that is influenced by the thickness. In order to balance the road performance and noise reduction of PUPEM mixture, it is recommended that the rubber particle content is 10%, and the polyurethane PU-Ⅰ with larger isocyanate index is used.

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.

Study of Factors Influencing Moisture Susceptibility of Warm-Mix Asphalt Using the Surface Free Energy Approach.

The application of warm-mixing technology brings considerable economical and environment benefits by decreasing the mixing temperature during warm asphalt mixture (WMA) production. However, the possible water residue also generates concerns for moisture susceptibility. For deep investigation on the influencing factors and mechanisms of the moisture susceptibility of WMA, surface free energy (SFE) tests and laboratory tests are applied in this research. A novel indicator based on SFE, namely, effective adhesion work, is proposed to assess the asphalt-aggregate adhesion with different moisture contents. Then, given the mixing procedure of the dry-mixing method, an advanced three-phase model as a form of asphalt-aggregate-warm mixing additive is introduced, improving the conventional two-phase asphalt-aggregate model for better reflecting the separate addition of warm-mixing additives during mixing. Afterwards, the influence of aggregate type, asphalt type, aggregate moisture content, warm-mixing agent type, and the warm-mixing process on the moisture susceptibility of WMA is analyzed utilizing the models and indicators proposed. Finally, the validity of the SFE indicator is verified by comparing the calculation of effective adhesion work with freeze-thaw splitting test results. The results show that all of the above factors impact the moisture susceptibility of WMA by influencing the interfacial adhesion, with the effect of moisture content being the most significant. Meanwhile, effective adhesion work and the three-phase model brought out in this research are proven to be feasible to characterize the adhesion properties of WMA, offering theoretical support to the research on warm-mixing technology.

Analysis of Asphalt Mixtures Modified with Steel Slag Surface Texture Using 3D Scanning Technology.

This paper investigates the use of steel slag in the place of basalt coarse aggregate in Stone Mastic Asphalt-13 (SMA-13) gradings in the early forming of an experimental pavement and evaluates the test performance of the mixes, combined with 3D scanning techniques to analyse the initial textural structure of the pavement. Laboratory tests were carried out to design the gradation of the two asphalt mixtures and to assess the strength, chipping and cracking resistance of the asphalt mixtures using water immersion Marshall tests, freeze-thaw splitting tests, rutting tests and for comparison with laboratory tests, while surface texture collection and analysis of the height parameters (i.e., Sp, Sv, Sz, Sq, Ssk) and morphological parameters (i.e., Spc) of the pavement were performed to assess the skid resistance of the two asphalt mixtures. Firstly, the results show that a substitution of steel slag for basalt in pavements is a good alternative for efficient resource utilization. Secondly, when steel slag was used in place of basalt coarse aggregate, the water immersion Marshall residual stability improved by approximately 28.8% and the dynamic stability by approximately 15.8%; the friction values decayed at a significantly lower rate, and the MTD did not change significantly. Thirdly, in the early stages of pavement formation, Sp, Sv, Sz, Sq and Spc showed a good linear relationship with BPN values, and these texture parameters can be used as parameters to describe steel slag asphalt pavements. Finally, this study also found that the standard deviation of peak height was higher for steel slag-asphalt mixes than for basalt-asphalt mixes, with little difference in texture depth, while the former formed more peak tips than the latter.

Adhesion of Nano-ZnO Modified Asphalt and Its Influence on Moisture-Sensitive Properties of Mixtures

This study investigates the effect of nano-ZnO on modified asphalt’s adhesion characteristics by preparing various mixtures with 0%, 1%, 2%, and 3% nano-ZnO contents. Within the study context, the adhesion characteristics of asphalt mixtures with different nano-ZnO to limestone, basalt, and granite contents are studied using a boiling test. The surface-free energy (SFE) parameters of four asphalt and three aggregate types are evaluated using a theoretical approach and then verified by performing pull-off tests, and the adhesion work between different asphalt and aggregates is calculated. In addition, the effect of nano-ZnO on moisture-sensitive properties of the asphalt mixture is assessed using a freeze-thaw split test and semicircle bending (SCB) test. The study results have shown that nano-ZnO can enhance adhesion characteristics of the asphalt. The surface energy of modified asphalt with high ZnO content is relatively larger, and the adhesion between asphalt and limestone is better than the basalt and granite. The aggregates’ chemical composition and the SFE’s parameters significantly affect the adhesion between asphalt and aggregates. Furthermore, the correlation between the surface-free energy theory and the pull-off test results is better than the boiling test ones. Nano-ZnO enhances the asphalt mixture’s moisture sensitivity before and after freeze-thaw cycles and impacts the initial state’s tensile strength and cracks resistance, especially after freeze-thaw cycles where the improvement is obvious.

Preparation and Properties of Composite Graphene/Carbon Fiber Pouring Conductive Asphalt Concrete.

To solve the problem of snow on steel bridge areas endangering traffic safety and low road traffic efficiency in winter, conductive gussasphait concrete (CGA) was prepared by mixing conductive phase materials (graphene and carbon fiber) into Gussasphalt (GA). First, through high-temperature rutting test, low-temperature bending test, immersion Marshall test, freeze-thaw splitting test and fatigue test, the high-temperature stability, low-temperature crack resistance, water stability and fatigue performance of CGA with different conductive phase materials were systematically studied. Second, the influence of different content of conductive phase materials on the conductivity of CGA was studied through the electrical resistance test, and the microstructure characteristics were analyzed via SEM. Finally, the electrothermal properties of CGA with different conductive phase materials were studied via heating test and simulated ice-snow melting test. The results showed that the addition of graphene/carbon fiber can significantly improve the high-temperature stability, low-temperature crack resistance, water stability and fatigue performance of CGA. The contact resistance between electrode and specimen can be effectively reduced when the graphite distribution is 600 g/m2. The resistivity of 0.3% carbon fiber + 0.5% graphene rutting plate specimen can reach 4.70 Ω·m. Graphene and carbon fiber in asphalt mortar construct a complete conductive network. The heating efficiency of 0.3% carbon fiber + 0.5% graphene rutting plate specimen is 71.4%, and the ice-snow melting efficiency is 28.73%, demonstrating good electrothermal performance and ice-snow melting effect.

Effect of increasing preheating temperature on the activation and aging of asphalt binder in reclaimed asphalt pavement (RAP)

During preheating, the activation and aging of RAP binders occur simultaneously, and both of them are closely related to the preheating temperature. The objective of this study was to investigate the effect of increasing preheating temperature on the activation and aging of RAP binder, and to find out the appropriate preheating temperature. Three sources of RAP and nine preheating temperatures (110 °C–190 °C) were included in this study. An activation test, producing 100% RAP specimens, was conducted to evaluate the binder activation. The gel permeation chromatography (GPC) test was carried out to estimate the aging level of RAP binder. In addition, the performance of hot-recycled asphalt mixture containing 30% RAP was analyzed by low-temperature splitting test, freeze-thaw splitting test, and rutting test. Ultimately, a parameter called activation-aging index (IAA) was proposed to reflect the coupling effect of activation and aging. The results indicated that increasing preheating temperature had a significant effect on the improvement of binder activation regardless of the RAP source. In addition, there was a critical temperature, beyond which the activation was difficult to be further improved. However, the increase rate of binder aging became more significant with increasing temperature, contrary to the change law of activation. As for the coupling effect, the results of recycled asphalt mixtures showed that increasing preheating temperature improved the rutting resistance, but may damage the moisture susceptibility. The low-temperature performance, however, exhibited a non-monotonic trend and had a good correlation with IAA. It is recommended to take IAA as a reference for finding the optimal preheating temperature.

Research on Recycling of Phosphorus Tailings Powder in Open-Graded Friction Course Asphalt Concrete

The reuse in high-value materials is one of the important resource utilization approaches of phosphorus tailings. At present, a mature technical system has been formed on the reuse of phosphorus slag in building materials, and silicon fertilizers in the extraction of yellow phosphorus. But there is a lack of research on the high-value reuse of phosphorus tailings. In order to make safe and effective utilization of phosphorus tailing resources, this research concentrated on how to solve easy agglomeration and difficult dispersion of phosphorus tailing micro-powder, when it was recycled in road asphalt. In the experimental procedure, phosphorus tailing micro-powder is treated in two methods. One method is to directly add it with different contents in asphalt to form a mortar. Dynamic shear tests were used to explore the effect of phosphorus tailing micro-powder on the high-temperature rheological properties of asphalt influence mechanism of material service behavior. The other method is to replace the mineral powder in asphalt mixture. The effect of phosphate tailing micro-powder on the water damage resistance in open-graded friction course (OGFC) asphalt mixtures was illustrated, based on the Marshall stability test and the freeze-thaw split test. The research results show that the performance indicators of the modified phosphorus tailing micro-powder meet the requirements for mineral powder in road engineering. Compared with standard OGFC asphalt mixtures, the residual stability of immersion and freeze-thaw splitting strength were improved when replace the mineral powder. The residual stability of immersion increased from 84.70% to 88.31%, and freeze-thaw splitting strength increased from 79.07% to 82.61%. The results indicate that phosphate tailing micro-powder has a certain positive effect on the water damage resistance. These performance improvements can be attributed to the larger specific surface area for phosphate tailing micro-powder than ordinary mineral powder, which can effectively adsorb asphalt and form structural asphalt. The research results are expected to support the large-scale reuse of phosphorus tailing powder in road engineering.