There is still controversy over whether the mechanical properties of steel slag concrete are superior to those of ordinary crushed-stone concrete and which method of substituting steel slag for aggregates yields better mechanical performance. Four groups of specimens were designed in this study, namely ordinary crushed-stone concrete, coarse steel-slag natural-sand concrete, crushed-stone fine steel-slag concrete, and all-steel slag concrete. The compressive strength, flexural strength, splitting tensile strength and failure morphology of the four groups of specimens were tested. Meanwhile, microhardness, scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy tests were conducted to analyze the differences in their mechanical properties from a microscopic perspective. The corresponding test results indicated that: (a) Under the test conditions of this study, the order of compressive strength, flexural strength, and splitting tensile strength of concrete is ordinary crushed-stone concrete < coarse steel-slag natural-sand concrete <crushed-stone fine steel-slag concrete < all-steel slag concrete. (b) Steel slag fine aggregates are superior to steel slag coarse aggregates in enhancing the mechanical properties of concrete. Crushing steel slag coarse aggregate into steel slag fine aggregate to replace ordinary fine aggregates is more effective in enhancing mechanical strength than directly using coarse steel slag to replace coarse aggregates. When steel slag simultaneously substitutes for both coarse and fine aggregates, the concrete strength is the highest. Despite limitations of this study, the above conclusions, if further validated by future studies, will provide valuable references for further research on steel slag concrete.

To eliminate macroscopic cracks in cement stabilized base and ensure sufficient mechanical performance while enhancing its anti-cracking performance, this study focused on cement stabilized steel-slag macadam (CTSM) with an aggregate framework of limestone (particle size 15 30 mm) and steel-slag (particle size 0 15 mm). By exploiting the micro-expansion property of steel-slag and incorporating nano anti-crack reinforcing agent (NARA) together with fly ash as composite anti-cracking measure, an anti-cracking CTSM (ACTSM) was developed. In the study, the performance of CTSM was investigated via mechanical and shrinkage tests. Furthermore, the anti-cracking mechanism of ACTSM was researched through microscopy analysis. Finally, ACTSM exhibited excellent mechanical and anti-cracking performance, and the following conclusions were reached: (1) replacing part of the coarse aggregate and all fine aggregate with steel-slag while utilizing its micro-expansion property can enhance the anti-cracking performance of CTSM; (2) NARA dosage at 0 0.3

Cement stabilized materials are extensively utilized in base due to superior properties. However, one notable drawback of a cement cementitious system is its propensity for shrinkage cracking. Furthermore, a substantial volume of steel slag has been generated and accumulated by industrial production, which exhibits microexpansion characteristics. In this study, steel slag was employed as a complete substitute for sand in the preparation of full steel slag cement-fly ash mortar (FSCFM), maximizing the dry shrinkage compensation effect of steel slag. Nano anticrack reinforcing agents were incorporated to exert enhancing and fiber connecting effects. By studying the mechanical properties and crack resistance of FSCFM, the feasibility of using steel slag and nano anticrack reinforcing agents in cement stabilized materials to mitigate shrinkage cracking was explored. The conclusions are as follows: (1) steel slag was proven to be an effective substitute for materials in cement-based cementitious systems, (2) at an optimal dosage of 0.1-0.2%, the nano anticrack reinforcing agent was observed to potentially enhance the mechanical properties of the cement-fly ash cementitious system, and (3) the triad application of steel slag aggregates, nano anticrack reinforcing agent, and fly ash indicated potential to significantly improve the internal microstructure of the cementitious system, exhibiting a good synergistic effect on the development of the crack resistance and strength evolution in the system.

This study was conducted to investigate the hydrostatic stability of a steel slag porous asphalt mixture (SSPA) under freeze-thaw cycles in seasonal frozen soil areas and thereafter, compare its (SSPA) characteristic properties and advantages with a traditional porous asphalt pavement. In the study, the freeze-thaw stability of SSPA was tested through multiple freeze-thaw cycle splitting, scattering loss, and trabecular bending tests under various cyclic temperature water immersion conditions including quantitatively analyzing the SSPA volumetric changes. In addition, the scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) tests were used to analyze the microscopic damage mechanism of SSPA after being subjected to various cyclic temperature water immersion conditions. The corresponding test results indicated that: (a) the long-term freeze-thaw cycles had significant adverse effects on the hydrostatic stability, physical/mechanical properties, and volume stability of SSPA; and (b) when the melting temperature was increased, both the hydrostatic stability and mass gain/loss ratio of SSPA decreased whilst the void ratio increased. On the other hand, the SEM and EDS results showed that an increase in the number of freeze-thaw cycles or melting temperature led to a corresponding increase in the width of the steel slag-asphalt transition zone. This resulted in a weakening of the mechanical connection and anchorage between steel slag and asphalt, as well as the destruction of their adhesion bond. However, the short-term freeze-thaw cycles had little effect on the hydrostatic stability of SSPA because the steel slag-asphalt interfacial strength was enhanced by short-term freeze-thaw cycles.

A steel slag porous asphalt (SSPA) mixture, as the surfacing layer of permeable asphalt pavements, not only ensures the pavement surface drainage and noise reduction functions, but also improves the comprehensive utilization of steel slag resources and the inherent protection of the ecological environment. However, compared with ordinary asphalt mixtures, SSPA is more susceptible to water damage, such as scouring and frost swelling caused by external rainwater intrusion, resulting in the deterioration of the pavement performance. Therefore, it is of good practical imperative to study the water stability and moisture damage mechanism of SSPAs. In this study, the water stability of SSPA, that was subjected to a series of time–temperature H2O-immersion schemes, was investigated using the pull-out and H2O-immersion Marshall tests, whilst the microscopic mechanism of moisture damage was studied using the scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), and X-ray diffraction (XRD) tests. The corresponding results showed that: (a) with the increase in the H2O immersion time, the water stability of SSPA first increased and then decreased; and (b) the water stability of SSPA was strong under medium-temperature H2O-immersion or short-term high-temperature H2O-immersion. SEM, on the other hand, showed that the transition zone spacing was closely related to the chemical adhesion mechanism between the asphalt and steel slag aggregate. Additionally, the FTIR analysis further showed that the steel slag asphalt mastic spectra had new absorption peaks at 3200~3750 cm−1, inherently indicating the existence of chemical bonding between the asphalt and steel slag, with the XRD results showing that CaSO4·2H2O had a beneficial effect on the water stability of SSPA.

To study the effect of flame retardant on the physical properties and flame-retarded and smokesuppression properties of SBS modified asphalt, flameretardant modified asphalt with different flame retardant dosages（10% ～ 50%） was prepared to analysis the performance change law of flame-retarded modified asphalt by physical property tests, toughness and tenacity tests, oxygen index test and smoke density test. The results show that the flame retardant can enhance the high temperature performance of SBS modified asphalt, and reduce its low temperature performance and temperature sensitivity. Flame retardant can improve the toughness and tenacity of SBS modified asphalt, but excessive dosage of flame retardant may reduce the fracture resistance of asphalt. The dosage of flame retardants should be more than 40 %, which make the flame-retarded asphalt have good flame-retardant and smoke-suppression performances.

利用有限元分析软件ABAQUS建立了沥青路面结构在纵坡路段的计算模型,研究了重载交通与纵坡坡度同时作用对沥青路面结构的影响,修正了现有的沥青路面疲劳开裂与永久变形病害预估模型.结果表明:沥青层纵向剪应力、沥青层表面拉应力和拉应变均随纵坡坡度的增加而增加;上面层和中面层所受剪应力远大于下面层,各面层所受剪应力差别很大;通过回归得到了疲劳开裂纵坡修正系数和沥青层永久变形纵坡修正系数,从而使病害预估模型可适用于纵坡路段.

采用水煮法测定TAFPACK-Super(TPS)改性沥青与凝灰岩集料之间的黏附性等级,并通过原子力显微镜(AFM)测定基质沥青及三种TPS掺量(3％、6％、12％)改性沥青的纳观黏附特性.结果表明:TPS改性剂可以提高沥青与集料间的黏附性等级,而凝灰岩集料表面水分和尘土减小了沥青与集料间黏附作用.TPS改性剂改善了基质沥青表面的纳观黏附力与黏附功,增强了沥青的黏附性能.

To study the effect of flame retardant on the rheological properties of SBS modified asphalt,flame retardant modified asphalt with different flame retardant dosages（10% ～ 50%） was prepared to test the rheological properties of flame retardant asphalt by Dynamic Shear Rheology test（DSR） and Bending Beam Rheometer test（BBR）. The results show that the flame retardant can improve the rutting factor of flame retardant asphalt and enhance the high-temperature rheological properties of flame retardant asphalt. With the increase of flame retardant dosage, the fatigue factor of flame retardant asphalt increases continuously. The addition of 20% ～ 30% flame retardant can maintain the fatigue performance of the original asphalt. Flame retardants can increase the creep stiffness of flame retardant asphalt and reduce the relaxation rate, which improve the lowtemperature rheological properties of flame retardant asphalt.

Asphalt binder is a complex mixture of dark brown polymers composed of hydrocarbons with generally poor fire resistance. To improve its flame retardancy when used in tunnel asphalt pavements, a new inorganic flame-retardant filler (FR) containing magnesium hydroxide, aluminum hydroxide, inorganic phosphate, and melamine salt was explored. Thereafter, limiting oxygen index (LOI) and smoke suppression tests for the flame-retarded asphalt binder (FRA) mastics mixed with FR and styrene-butadiene-styrene (SBS) copolymer asphalt binder were conducted. Thermogravimetric (TG) and differential scanning calorimetry (DSC) curves for the FRA were correspondingly generated. Based on the TG data, the reaction function g(α), apparent activation energy Ea, and pre-exponential factor A were quantitatively evaluated using kinetic analysis. In addition, a Fourier transform infrared spectrometry (FTIR) test was utilized to assess the effects of the presence of FR on the chemical composition of the asphalt binder. Dynamic shear rheometer (DSR) tests were also performed to evaluate the rheological behavior of FRA. Results show that the presence of the FR significantly reduced the LOI and improved the smoke suppression during combustion of the asphalt binder mastics. The presence of FR was found to increase the Ea and the complexity of the combustion reaction, thereby improving the flame retardancy of the asphalt binder. FTIR analysis indicated that the presence of FR did not induce any strong chemical reactions to significantly impact or alter the functional groups of the asphalt binder. Furthermore, it was also observed that the rutting parameter and critical failure temperature of FRA increased with the addition of FR due to the stiffening effect of the solid FR particles.

Steel slag pervious concrete (SSPC) is a novel sustainable and ecofriendly pavement material. The constituent elements making up SSPC are typically cement, steel slag, superplasticizer, sand, and water. To improve its strength and cracking resistance, an optimum amount of anticrack additives (ACA) was added to SSPC. In this paper, the relationships between the mechanical properties and the microscopic characteristics of SSPC with ACA were studied using the universal testing machine (UTM), X-ray diffractometer (XRD), Fourier infrared spectrometer (FfIR), and scanning electron microscope (SEM)s. The test results indicated best strength and cracking resistance performance for the SSPC with 0.3% ACA. From XRD and FTIR analysis, the main hydration products were found to mostly contain calcium-silicate-hydrate (C-S-H) gel and Ca(OH)(2). However, with an increase in the ACA content, the SSPC strength decreased progressively. Overall, the study indicated that 0.3% was the optimum ACA dosage to maximize the SSPC performance in terms of mechanical strength and cracking resistance. (C) 2022 American Society of Civil Engineers.

To explore the applicability of steel slag porous asphalt mixture, the interaction capability and microscopic interfacial mechanism between asphalt-binder and steel slag aggregate-filler were investigated in this laboratory study. These objectives were accomplished by comparing and analyzing the differences between steel slag and basalt aggregates in interacting with the asphalt-binder. The study methodology involved preparing basalt and steel slag asphalt mortar to evaluate the penetration, ductility, softening point, toughness, and tenacity. Thereafter, the interaction capability between the asphalt-binder and aggregates was characterized using the interaction parameters of the asphalt mortar obtained from dynamic shear rheometer (DSR) testing. For studying the functional groups and chemical bonding of the asphalt mortar, the Fourier Transform infrared (FTIR) spectrometer was used, whilst the interfacial bonding between the asphalt-binder and aggregates was analyzed using the scanning electron microscope (SEM). The corresponding test results indicated that the physical and rheological properties of the two asphalt mortars were similar. However, whilst the FTIR analysis indicated domination through chemical reactions, the interaction capability and interfacial bonding between the asphalt-binder and steel slag aggregates exhibited superiority over that between the asphalt-binder and basalt aggregates, with pronounced adsorption peaks appearing in the steel slag asphalt mortar spectrum. On the other hand, the SEM test revealed that, compared with the basalt, the micro-interfacial phases between the steel slag and asphalt-binder were more continuous and uniform, which could potentially enhance the interfacial bond strength between the asphalt-binder and aggregates (filler).

Steel slag is increasingly applied during road construction and maintenance processes due to its superior surface and mechanical properties such as hardness, rough surface, and wear resistance. In this paper, the effects of steel slag on mechanical performances in varied skeleton structures of asphalt mixtures are evaluated. The Marshall mix design method is modified, and a concept of nominal asphalt-aggregate ratio is proposed to match the asphalt mix design that includes steel slag. The aforementioned methods are then applied to the asphalt concrete (AC) and stone matrix asphalt (SMA) gradations. The performance tests are carried out to further evaluate the influence of the modified method on the mechanical properties for both AC and SMA gradations. Results show that the performance indexes of the steel slag mixture can satisfy specification requirements by using the modified Marshall mix design method; then, its effectiveness is verified. In contrast to the mixtures without using steel slag, the asphalt mixtures with steel slag show better rutting resistance of SMA gradation due to the characteristics of strong internal friction resistance and higher strength; the low-temperature crack resistance can also be improved, especially for the SMA gradation. The steel slag mixture does not show strong volume expansion and has good water stability. The skid resistance performance of the steel slag mixture is improved at a small level for both skeleton structures. The overall results indicate that the performance improvement effects of steel slag for asphalt mixture are obvious, and the modified Marshall design method can be used to guide the mix design for the application of steel slag in the asphalt mixture, which can significantly reduce the engineering cost and environmental effect for producing the asphalt mixture, promoting the sustainability of asphalt pavement.

为了研究凝灰岩沥青混合料的水稳定性,以外掺的方式加入TPS改性剂,制备密级配AC-16型沥青混合料,进行浸水马歇尔试验和冻融劈裂试验,分析TPS掺量对凝灰岩沥青混合料水稳定性能的影响规律,并借助原子力显微镜(AFM)测试沥青的微观表面形貌.结果表明:TPS改性剂改变了沥青表面微观形貌与"蜂状结构"分布状态,提高了沥青自身的黏聚力.TPS改性剂能增强沥青和凝灰岩集料之间的黏附作用,改善凝灰岩沥青混合料的水稳定性.

To investigate the influence of multiple cycles of aging and rejuvenation on the rheological, chemical, and morphological properties of styrene–butadiene–styrene (SBS)-modified asphalt-binders, the asphalt-binders were aged using two laboratory simulation methods, namely a rolling thin film oven (RTFO) test for short-term aging and pressure aging vessel (PAV) for long-term aging. The asphalt-binders were then rejuvenated with three types of rejuvenators (Type I, II, and III) with different dosages (i.e., 6%, 10%, and 14% for the first, second, and third rejuvenation, respectively). A dynamic shear rheometer (DSR) was then used to analyze the effect of rejuvenators on the rheological properties of all the asphalt-binders. The changes in the functional groups and microscopic morphology in the process of multiple aging and rejuvenation cycles were studied using Fourier transform infrared (FTIR) and atomic force microscopy (AFM). The results indicated that the three rejuvenators could soften the stiffness and restore the microstructures of the aged asphalt-binders in the process of repeated aging and rejuvenation from DSR and AFM testing. Considering the rutting and fatigue properties, the Type I rejuvenator exhibited the potential to achieve the desired rejuvenation effects under multiple rejuvenation cycles. During the multiple aging and rejuvenation cycles, the aging resistance of SBSMA decreased gradually from the FTIR results. This inherently limited the number of repeated rejuvenation cycles. This research is conducive to promoting the application of repeated penetrating rejuvenation.

Since asphalt mortar is highly heterogeneous and occurs as an interfacial bonding material between the asphalt-binder and aggregate, it is very important to have a detailed and adequate understanding of its mechanical properties at a multi-scale (micro and macro) level analysis. In this study, the fundamental properties of the asphalt mortar were evaluated and quantified using molecular dynamic simulations. The tensile strength, stress-separation responses, and adhesive-bonding strength were numerically measured and characterised from a micro perspective. Other mechanical properties such as the complex modulus, low-temperature stiffness modulus, hardness, and elastic modulus were also experimentally measured to verify the dynamic simulations and modelling results. In comparison to the macro experimental test results, it was found that the micro-simulated results were superior in terms of characterising the mechanical properties of the asphalt mortar. Whilst the tensile strength, adhesive-bond strength, and hardness of the asphalt mortar changed significantly as a function of aging, the stress-separation responses and elastic modulus were hardly affected. Overall, the study findings indicated that multi-scale characterisation of the mechanical properties of asphalt mortar is a potentially promising methodology for quantitatively evaluating and understanding the mechanical properties.

Aging has a detrimental impact on the interfacial interaction and bonding between asphalt-binder and aggregates, which influence ultimately on the performance of asphalt mixtures and pavements. Evaluation of the mechanical properties of the interface between the asphalt-binder and aggregates has thus become a hot research topic, particularly as a function of aging. In this study, the interfacial tensile strength, compressive strength, elastic modulus, and interfacial recovery energy were measured and quantified using molecular dynamic simulation. Whilst the free volume of the asphalt mixtures exhibited sensitivity to aging, the interfacial tensile strength decreased with an increase in the degree of aging. In general, the mechanical properties of the asphalt-binder-aggregate interface were found to be significantly dependent on the aggregate type. Furthermore, the study results indicated that interfacial recovery energy is a key characteristic property for characterizing the interfacial adhesive force within asphalt mixtures. Overall, the study of mechanical properties of the asphalt-binder and aggregate interface, as presented in this paper, contributes to quantifying the adhesive properties and improving the performance of asphalt mixtures.

Aging is responsible for the irreversible asphalt-binder stiffening and brittleness. However, various rejuvenators can recycle the aged asphalt-binder. In this study, molecular models of rejuvenators for aged asphalt-binders were constructed using molecular dynamic (MD) simulations. The diffusion coefficients of the rejuvenator, aged asphalt-binder, and four components of the aged asphalt-binder were calculated. The solubility parameters, storage stability, and morphology of rejuvenated aged asphalt-binder were analyzed using MD, softening point tests, and fluorescence microscope, respectively. The results showed that the rejuvenator exhibited excellent regeneration performance and a high diffusion coefficient in the aged asphalt-binder, significantly improving the diffusion of the aged asphalt-binder, especially the diffusion of the saturated and aromatic components in the aged asphalt-binder. The blended mixture of the rejuvenator and the aged asphalt-binder had good storage stability with less than 1.0 degrees C softening point difference after 48 h. The micro-morphology results showed that the rejuvenator could be evenly distributed in the aged asphalt-binder and form the cross-linking network structures blend with good consistency and compatibility. Overall, this novel organic rejuvenator (namely Soybean-oil) exhibited promising potential for rejuvenating aged asphalt-binders, especially the long-term and extremely aged asphalt-binders.

This paper presents an efficient method utilizing user-defined computer functional codes to determine the reliability of an embankment slope with spatially varying soil properties in real time. The soils' mechanical properties varied with the soil layers that had different degrees of compaction and moisture content levels. The Latin Hypercube Sampling (LHS) for the degree of compaction and Kriging simulation of moisture content variation were adopted and programmed to predict their spatial distributions, respectively, that were subsequently used to characterize the spatial distribution of the soil shear strengths. The shear strength parameters were then integrated into the Geostudio command file to determine the safety factor of the embankment slope. An explicit metamodal for the performance function, using the Kriging method, was established and coded to efficiently compute the failure probability of slope with varying moisture contents. Sensitivity analysis showed that the proposed method significantly reduced the computational time compared to Monte Carlo simulation. About 300 times LHS Geostudio computations were needed to optimize precision and efficiency in determining the failure probability. The results also revealed that an embankment slope is prone to high failure risk if the degree of compaction is low and the moisture content is high.

To evaluate the physical and rheological properties of rejuvenated styrene-butadiene-styrene-modified asphalt (SBSMA) binders designed for rapid in-place pavement recycling, an aged SBSMA binder was rejuvenated with three rejuvenators (i.e., Types I, II, and III) in different dosages. The physical properties of rejuvenated SBSMA were obtained to determine the optimal type and dosage of rejuvenators for the first and second rejuvenation. Performance grade (PG) tests, multiple stress creep recovery (MSCR) tests, and linear amplitude sweep (LAS) tests were conducted to measure the rheological properties using the dynamic shear rheometer (DSR) and bending beam rheometer (BBR). The results exhibited that the rejuvenators could soften the multiple aged binder and enhance its high- and low-temperature performance. The rejuvenation effect of rejuvenator Type I with the optimal dosage of 6∼8% was the most appropriate for the first rejuvenation. The optimal dosage of the second rejuvenation was 10∼12%. The addition of rejuvenators decreased the rutting factor G∗/sin δ, creep stiffness (S), delta Tc (ΔTc) parameter, recovery response (R), and yield stress of rejuvenated SBSMA. On the other hand, an increase in the rate of relaxation (m-value), nonrecoverable creep compliance (Jnr), and yield strain of rejuvenated SBSMA was recorded. Overall, the study findings indicated an improvement in the elastic properties of rejuvenated SBSMA, which contributes to improving the rutting, thermal, and fatigue cracking resistance of asphalt binder and ultimately the response of asphalt pavements.