Freeze-thaw Splitting Research Articles

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.

Pavement performance of previous pavement materials based on CAVF design

Based on the coarse aggregate void filling method (CAVF), four kinds of permeable asphalt mixtures (PAC) with target voids of 18%, 20%, 22%, and 25% respectively were designed, and their road performance was comprehensively evaluated by a series of laboratory tests, such as permeability tests, immersion Marshalls, freeze-thaw splitting, rutting, low-temperature bending, four-point fatigue bending, and so on. The experimental results show that the CAVF method is more accurate and PAC designed by the CAVF method has more connected voids and better pavement performance. The optimal design void ratio of the PAC is 22%.

Engineering properties and air void characteristics of cold recycled mixtures with different compaction methods

Cold recycled mixtures (CRM) offer advantages in terms of resource conservation and reduced CO2 emissions. This paper utilizes the vertical vibration testing method (VVTM), Marshall compaction (MC), Superpave Gyratory Compactor (SGC), and field core samples to analyze the effects of different compaction methods on the engineering properties of CRM. The study begins by discussing the volumetric and mechanical parameters of CRM with different compaction methods, followed by an analysis of fatigue performance. Additionally, CT scanning technology is used to study the effect of different compaction methods on the void characteristics of CRM. The results demonstrate that VVTM specimens offer better mechanical properties compared to MC and SGC specimens. Furthermore, the RT (splitting tensile strength), MS (dry-wet tensile strength ratio), and TSR (freeze-thaw splitting strength ratio) of VVTM specimens exhibit the highest correlation with field core samples, reaching 97%, 97%, and 95%, respectively. The VVTM specimens also exhibit the biggest fatigue, which is similar to that of the field core sample. The Weibull distribution model is utilized to predict the fatigue life of CRM with different compaction methods, with the fatigue equation indicating that VVTM specimens have better fatigue performance. In addition, the number of voids, diameter of voids, and fractal dimension of VVTM specimens along the longitudinal direction are closer to those of field cores. The fractal dimension of CRM specimens with different compaction methods is between 1.2 and 1.4, indicating that the complex shape of voids may alter stress concentration and impact the performance of CRM.

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.

Research on pavement performance of recycled asphalt mixture based on separation technology of asphalt and aggregate in RAP

Asphalt-aggregates separation of reclaimed asphalt pavement (RAP) with bio-oil as solvent is an economical, simple, and efficient method to recycle RAP materials. The byproducts of asphalt-aggregates separation of RAP are recycled aggregates and blends of bio-oil and old asphalt (BBOA). In this paper, to improve the recycling rate of BBOA and recycled aggregate after asphalt aggregate separation, Buton Rock Asphalt (BRA) is used as a high-temperature property modifier to compensate for the aging resistance and high-temperature of BBOA. The physical properties of rock asphalt modified bio-oil asphalt (RMBA) with different amounts of BBOA were studied by viscosity, frequency scanning, multiple stress creep, bending beam rheology, and aging tests. At the same time, recycled aggregates of different particle sizes and RMBA were used to prepare asphalt mixture with diverse mix design methods. The pavement properties of the recycled asphalt mixture were evaluated by rutting resistance, low-temperature bending beam, freeze–thaw splitting, and fatigue tests. The results show that RMBA realizes the complementary advantages of BRA as a high-temperature modifier and BBOA as a low-temperature performance modifier. The recommended dosage of RMBA is 20 %rock asphalt and 7 %BBOA. Under different preparation methods, the pavement performance of rock asphalt modified bio-oil asphalt mixture, asphalt mixture containing coarse recycled aggregate, and asphalt mixture containing oil sand meet the requirements of asphalt pavement design specifications, the preliminary realization of 100% recycling of RAP.

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.

Preparation Scheme Optimization of Thermosetting Polyurethane Modified Asphalt.

To solve the issue of the poor temperature stability of conventional modified asphalt, polyurethane (PU) was used as a modifier with its corresponding curing agent (CA) to prepare thermosetting PU asphalt. First, the modifying effects of the different types of PU modifiers were evaluated, and the optimal PU modifier was then selected. Second, a three-factor and three-level L9 (33) orthogonal experiment table was designed based on the preparation technology, PU dosage, and CA dosage to prepare the thermosetting PU asphalt and asphalt mixture. Further, the effect of PU dosage, CA dosage, and preparation technology on the 3d, 5d, and 7d splitting tensile strength, freeze-thaw splitting strength, and tensile strength ratio (TSR) of the PU asphalt mixture was analyzed, and a PU-modified asphalt preparation plan was recommended. Finally, a tension test was conducted on the PU-modified asphalt and a split tensile test was performed on the PU asphalt mixture to analyze their mechanical properties. The results show that the content of PU has a significant effect on the splitting tensile strength of PU asphalt mixtures. When the content of the PU modifier is 56.64% and the content of CA is 3.58%, the performance of the PU-modified asphalt and mixture is better when prepared by the prefabricated method. The PU-modified asphalt and mixture have high strength and plastic deformation ability. The modified asphalt mixture has excellent tensile performance, low-temperature performance, and water stability, which meets the requirements of epoxy asphalt and the mixture standards.

Feasibility of high titanium heavy slag used as aggregates for asphalt mixtures

High titanium heavy slag (HTHS) is a typical solid waste produced in the iron production process of vanadium titanomagnetite. The feasibility of using the HTHS as coarse aggregates in the two gradations of AC-13 and AC-20 asphalt mixtures mixed with base asphalt and SBS modified asphalt binders was discussed in this paper. Firstly, the physical and chemical properties of HTHS were tested. Then, asphalt mixtures with limestone coarse aggregate were replaced by HTHS at five rates of 0% (control), 25%, 50%, 75% and 100% were designed and made by Marshall method. Twenty types of asphalt mixtures was discussed by their different volume properties, and the volume properties of asphalt mixtures under the optimal asphalt content (OAC) were further verified. Finally, selected properties of asphalt mixtures under the optimum asphalt content were tested. Results showed that 1) HTHS had low activity and good stability, the mechanical properties met the requirements of coarse aggregates for asphalt mixtures; 2) With the increased replacing rate of HTHS, the OAC and asphalt absorbed by aggregate (Pba) of 20 asphalt mixtures increased simply due to the porous structure of HTHS; 3) The rough, hard surface of HTHS improved the mechanical anchoring force between aggregates and increased the Marshall stability and rutting resistance of asphalt mixtures. However, with the increased replacing rate of HTHS, the Marshall residual stability, freeze-thaw splitting strength ratio and maximum tensile strain at low temperature decreased.

Modified ground calcium carbonate mineral powder using in asphalt concrete: modification mechanism characterization at macro and micro levels

The study investigated the modification mechanism of modified ground calcium carbonate (GCC) mineral powder using in asphalt concrete. Two types of Titanate coupling agents, namely, K38S (TCA-K38S) and 201 (TCA-201), as well as sodium stearate coupling agent, were adopted to prepare modified GCC. The optimized preparation process was obtained through the orthogonal test. Two kinds of modified GCC were preferably selected to prepare asphalt concrete according to modification mechanism characterization, their performance was analyzed and evaluated at macro and micro levels. The study results show that, the optimal scheme of sodium stearate modified GCC is modification temperature of 80°C, modification time of 50 min, modifying agent dosage of 2.0%. The crystal structure of GCC remains unchanged after modification, with the original lattice structure being maintained. TCA-201 and sodium stearate exhibit better coating properties than that of TCA-K38S. The contact angles of TCA-201 and sodium stearate modified GCC are larger than that of TCA-K38S modified GCC. The in-service performance of AC-13C asphalt concrete modified with sodium stearate is found to be superior to that of TCA-201 modified AC-13C asphalt concrete. Compared with the unmodified AC-13C asphalt concrete, the Marshall modulus, residual stability, freeze-thaw splitting strength ratio, and maximum flexural tensile strain of sodium stearate modified AC-13C asphalt concrete are increased by 54.55%, 2.73%, 10.47%, and 26.41% respectively. This paper provides theoretical guidance for the application of GCC mineral powder in asphalt concrete.

Study on Road Performance of Polyurethane Cold-Recycled Mixture.

To give full play to the advantages of polyurethane as a binder, such as mixing at room temperature, short curing time, and high curing strength, polyurethane was used as the binder of a waste asphalt mixture, and the pavement performance of PCRM (Polyurethane Cold-Recycled Mixture) was analyzed. Firstly, the adhesion performance of polyurethane binder with new and old aggregates was evaluated using the adhesion test. Then, the mix proportion was designed according to the material characteristics, and the reasonable molding process, maintenance conditions, design indexes, and the optimal binder ratio were proposed. Secondly, the high-temperature stability, low-temperature crack resistance, water stability, and compressive resilient modulus of the mixture were evaluated through laboratory tests. Finally, the pore structure and microscopic morphology of polyurethane cold-recycled mixture were analyzed by industrial CT (Computerized Tomography) scanning, and the failure mechanism of polyurethane cold-recycled mixture was revealed. The test results show that the adhesion between polyurethane and RAP (Reclaimed Asphalt Pavement) is good, and the splitting strength of the mixture increases greatly when the ratio of glue to stone reaches 9%. Polyurethane binder has low sensitivity to temperature and poor water stability. With the increase of RAP content, the high-temperature stability, low-temperature crack resistance, and compressive resilient modulus of PCRM showed a decreasing trend. When the RAP content was less than 40%, the freeze-thaw splitting strength ratio of the mixture was improved. After the incorporation of RAP, the interface was more complex and there were many micron-scale holes, cracks, and other defects; after high-temperature immersion, the polyurethane binder appeared to show a certain degree of peeling at the holes of the RAP surface. After freeze-thaw, the polyurethane binder on the surface of the mixture produced many cracks. The study of polyurethane cold-recycled mixture is of great significance to realize green construction.

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.

Analysis on factors affecting moisture stability of steel slag asphalt concrete using grey correlation method

The moisture sensitivity of steel slag asphalt concrete has been receiving close attention from the road construction industry. Although researchers have conducted numerous studies on the water damage resistance of steel slag asphalt concrete, the evaluations are inconsistent, and it is difficult to distinguish the weighting ratios of the factors influencing the moisture sensitivity of asphalt concrete in the current study. Based on the water immersion Marshall test, freeze-thaw splitting test, and Hamburg rutting test, this study tested the water stability of asphalt concrete prepared from steel slag by different processes, aiming to illustrate the influence of the preparation process of aggregates on the water sensitivity of asphalt concrete. The results showed that the water stability of asphalt concrete prepared from steel slag obtained by the roller method and the hot smothering method was better than that of limestone asphalt concrete, while the water stability of asphalt concrete prepared from steel slag was inferior to that of limestone concrete. Subsequently, the adhesion between the three steel slag and limestone respectively and asphalt was compared in the modified boiling method, and the surface morphology structure of the four aggregates was characterized by scanning electron microscopy (SEM), and the results showed that the adhesion between the aggregates and asphalt was consistent with the moisture sensitivity of asphalt concrete. Finally, the comprehensive analysis concluded that the main factors affecting the water stability of steel slag asphalt concrete were asphalt, aggregate, gradation, and particle size, in that order.