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The present article deals with the optimization of additives used to improve penetration resistance of Himalayan soil and designing the pavement thickness. Eggshell powder, polypropylene fiber and sodium chloride were used as additives in a fine-grained soil for improvement in soil properties as a subgrade material. Optimization of additives was done using Taguchi method and MINITAB 21 software was employed for the analytical analysis of the responses obtained from the laboratory tests. The test results showed that the additives have potential for improvement in penetration resistance of fine-grained soil by 2.26 and 2.0 times that of untreated soil under unsoaked and soaked conditions respectively leading to considerable reduction in pavement thickness. The correlations given by the US Army Corps of Engineers and Indian Road Congress were used for determining the pavement thickness. Pavement thickness offered by US Army Corps of Engineers method is less and misleading to consider for pavement construction, whereas Indian Road Congress method has proved far better by offering rational lateral dimension for designing Indian rural hilly roads. [ABSTRACT FROM AUTHOR]

In road engineering, road construction requires a large amount of natural aggregate; its substitution with recycled construction-solid-waste aggregate not only saves resources but also reduces the burden on the environment. The main components of construction solid waste are concrete blocks and brick slag; the breakability of the latter can affect the performance of mixed recycled aggregate, which hinders the use of construction solid waste in road engineering applications. To analyze the applicability of recycled construction-solid-waste aggregate containing brick slag aggregate in the subgrade layer, the effect of brick aggregate content on the CBR (California bearing ratio) and crushing value of mixed recycled aggregates was evaluated based on laboratory tests, and the field compaction quality of the recycled aggregates was analyzed. The results show that the 9.5–19 mm mixed recycled aggregate samples were crushed to a higher degree during the compaction process. A brick aggregate content less than 40% had little effect on the performance of mixed recycled construction-solid-waste aggregate. It is recommended to use a 22 t road roller for five passes (two weak vibrations + two strong vibrations + one weak vibration) at a speed of 3 km/h in the main compaction stage of the subgrade filling. [ABSTRACT FROM AUTHOR]

This article presents a systematic review of the most cutting-edge research on precast pavement technology for the first time. Firstly, precast pavement is divided into two categories, precast cement concrete pavement and precast carpeted flexible pavement, according to the application of precast technology in pavement engineering. Subsequently, the structural characteristics, advantages, and disadvantages of various precast pavement systems are compared and analyzed; technical problems in precast pavement systems are explained; and future development directions are identified. In addition, the text specifically mentions the great contribution of precast carpeted flexible pavement technology in reducing the harmful effects of asphalt fumes on humans and the environment. This work will promote the application of prefabrication in road engineering and provide suggestions and references for subsequent research. [ABSTRACT FROM AUTHOR]

The objective of this research is to enhance the high-temperature antirutting and antiaging characteristics of bioasphalt. In this study, silica fume (SF) was selected to modify bioasphalt. The dosage of bio-oil in bioasphalt was 5%, and the dosage of SF was 2%, 4%, 6%, 8%, and 10% of bioasphalt. The high- and low-temperature characteristics, aging resistance, and temperature sensitivity of Bio + SF were evaluated by temperature sweep (TS), the multiple stress creep recovery (MSCR) test, the bending beam rheology (BBR) test, and the viscosity test. Meanwhile, the road behavior of the Bio + SF mixture was evaluated using the rutting test, low-temperature bending beam test, freeze–thaw splitting test, and fatigue test. The experimental results showed that the dosage of SF could enhance the high-temperature rutting resistance, aging resistance, and temperature stability of bioasphalt. The higher the dosage of SF, the more significant the enhancement effect. However, incorporating SF weakened bioasphalt's low-temperature cracking resistance properties. When the SF dosage was less than 8%, the low-temperature cracking resistance of Bio + SF was still superior to that of matrix asphalt. Compared with matrix asphalt mixtures, the dynamic stability, destructive strain, freeze–thaw splitting strength ratio, and fatigue life of 5%Bio + 8%SF mixtures increased by 38.4%, 49.1%, 5.9%, and 68.9%, respectively. This study demonstrates that the development of SF-modified bioasphalt could meet the technical requirements of highway engineering. Using SF and bio-oil could decrease the consumption of natural resources and positively reduce environmental pollution. [ABSTRACT FROM AUTHOR]

Growing concern over the combustion cost and environment has made road engineers and scientists to explore the possible use of locally available materials for the construction of roads. The present study evaluated the strength and durability characteristics of five sites having locally available silty soils using lime and cement–sand stabilization technique. The test results showed that the cement–sand stabilization technique using 6% cement and 5% local sand resulted in higher strength and durability as compared to lime stabilization. There is also a significant increase in the value of the soaked California bearing ratio (CBR). As unconfined compressive strength (UCS) attained the threshold strength as prescribed by IRC SP 72 2015 for the granular sub-base (GSB) layer, by the use of sand cement stabilization, this technique of stabilization for local silty soils could be used for GSB for low volume road (LVR) construction. As observed from microstructural results which were performed by analysing SEM images, sand cement stabilisation leads to CSH gel and agglomerate formation thereby increasing strength and durability properties. The cost analysis for the replaced stabilized GSB layer showed that using sand–cement stabilization, the estimated cost can be reduced by 56% of the total cost as compared to the conventional method. [ABSTRACT FROM AUTHOR]

To comprehensively and objectively evaluate the actual safety condition in road and bridge engineering construction, the road and bridge engineering construction safety risk evaluation index system is constructed combined with the factors induced by emergencies in the road and bridge engineering construction process. Aiming at the dynamic uncertainty of road and bridge construction safety risk, using Fuzzy Set Theory and an improved similar aggregation method to determine the prior probabilities and conditional probabilities of network nodes, and then selecting the transition probabilities of nodes through expert opinions and incident reports, leading to the development of a dynamic evaluation model for safety risks in road and bridge engineering construction based on Fuzzy Dynamic Bayesian Network, this model can make the construction safety risk prediction result accurately. Taking the Hebi City Provincial Highway 304 reconstruction project as an example for analysis, the results indicate that the model can accurately predict the probability of changes in safety risks in road and bridge engineering construction. Additionally, it can identify critical risk factors and provide crucial supporting information for decision-makers to optimize risk management strategies. [ABSTRACT FROM AUTHOR]

The huge demand for sand and gravel resources in road engineering construction leads to excessive consumption of resources and environmental damage. Recycling waste concrete and industrial solid waste as a road material is a promising alternative. In order to explore the application of these solid wastes in the road base, this paper studies the effect of adding lithium slag activated by an alkaline activator, fly ash (FA) and a combination of the two on the compressive strength, splitting strength and shrinkage performance of recycled cement-stabilized macadam mixture (RCSM). The optimum content of recycled aggregate (RA), alkali-activated lithium slag (AALS) and FA in composite-improved RCSM was optimized using a response surface method (Box–Behnken), and the microscopic characteristics of the mixture were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the optimum dosage of AALS, FA and RA determined by the response surface method is 15%, 10% and 40%, respectively. Compared with the cement-stabilized macadam mixture (CSM) with 40% RA, the 28 d compressive strength and 28 d splitting strength of the composite-improved RCSM are increased by 26.8% and 22.9%, respectively, and the dry shrinkage coefficient and average temperature shrinkage coefficient are decreased by 25.8% and 14.8%, respectively. Microscopic tests show that AALS and FA participate in the hydration reaction, generate more hydrated silicate (C-S-H) and ettringite (AFt), refine pores, effectively improve the performance of the internal interface transition zone of the mixture, make the microstructure of the mixture denser, and improve the strength and shrinkage performance of RCSM. This study provides technical support for the reuse of resources and the sustainable development of road construction. [ABSTRACT FROM AUTHOR]

Aggregate particles migrate and rearrange their spatial positions during the compaction process. To analyze the migration law, an accurate method to track migration of particles is proposed using discrete-element simulation and experimental verification. First, the coarse aggregates were generated based on realistic aggregate shapes using a three-dimensional (3D) Blu-Ray scanner. Subsequently, the fine aggregates, ranging from 0.075 to 2.36 mm, and asphalt mastic were replaced with balls with a radius of 0.7 mm. Then the three-dimensional dynamic compaction models of asphalt mixture were established using the Superpave gyratory compaction method and Marshall impact compaction method. Next, the migration tracking test of particles was developed adopting particle marking, step-by-step compaction, and CT scanning. Finally, the accuracy and efficiency of the virtual models were validated using the experimental data from the migration tracking test. The results indicate that the established compaction models can accurately track the aggregates particles and measure the migration indexes. The compaction methods have a great influence on the migration behavior. The displacement of the particles for the Superpave gyratory compaction method is greater than that for the Marshall method, and the displacement is multidirectional, whereas the displacement of particles for the Marshall impact compaction method mainly are vertical. [ABSTRACT FROM AUTHOR]

The use of natural river silt treated as a 'waste material' has become the focus of research in the Yellow River flooded area, especially in the field of highway engineering. It is therefore of great significance to study the deformation and stiffness degradation of Yellow River silt (YRS) under long-term cyclic loads. To this end, a series of undrained cyclic triaxial tests on YRS for a large number of cycles (10 000) was carried out using a triaxial apparatus and the effects of confining pressure and cyclic stress ratio on the resilient strain of the YRS were explored. The critical cyclic stress and the critical cyclic stress ratio between the plastic shakedown state and incremental collapse state of the YRS were determined, and the modulus-softening behaviour of the YRS was assessed. The results of this study not only provide theoretical support for the long-term engineering performance of YRS, but also provide theoretical guidance for the cyclic response of all similar types of subgrade soils. [ABSTRACT FROM AUTHOR]

The as-built roughness, or smoothness obtained during pavement construction, plays an important role in road engineering since it serves as an indicator for both the level of service provided to users and the overall standard of construction quality. Being able to predict as-built roughness is therefore important for supporting pavement design and management decision making. An as-built IRI prediction model for asphalt overlays based on profile transformation was proposed in a previous study. The model, used as basis for this work, was developed for the case of wheeled pavers without automatic screed levelling. This study presents further development of the base prediction model, including the use of an automatic screed control system through a long-distance averaging mobile reference. Formulation of linear systems that constitute the model are presented for the case of a wheeled paver using contactless acoustic sensors set-up over a floating levelling beam attached to the paver. To calibrate the model, longitudinal profile data from the Long-Term Pavement Performance SPS-5 experiment was used, obtaining a mean error of 0.17 m/km for the predicted IRI. The results obtained demonstrate the potential of the proposed approach as a modelling alternative. [ABSTRACT FROM AUTHOR]

In this study, the variation of shear strength behavior and particle breakage (after shearing), as a function of moisture state and compaction level, is investigated for recycled concrete aggregate blended with recycled clay masonry. Recycled masonry was blended with concrete aggregate in percentages ranging from 0% to 30% by total weight. Tests include; basic engineering characteristics (particle size, modified compaction, hydraulic conductivity, and California Bearing Ratio, CBR) as well as unconsolidated undrained static triaxial testing. In triaxial tests, moisture levels ranged from 60% to 100% of optimum moisture content, but compaction levels ranged from 90% to 98% of maximum dry density. The hydraulic conductivity for blends is approximately 2x10-6 cm/s, which indicates a relatively low hydraulic conductivity. Results show a proportional linear relationship between the shear strength of blends and the level of compaction. Despite this, both apparent cohesion and shear strength exhibited reverse linear trends. As expected, more compaction effort resulted in more particle breakage. Strict control should be performed over the compaction process to achieve the required compaction level which resulting in pavement materials being stiffer. [ABSTRACT FROM AUTHOR]

There have been immense research studies conducted on asphalt mixture design and the corresponding pavement performances. However, the flowability and workability of asphalt mixtures have not been well understood, which has a significant effect on the subsequent mixture performances. To quantitatively evaluate the mixing flowability of asphalt mixture and deepen the understanding of evolution mechanism of its strength composition, six types of asphalt binders were tested for their viscosities and the corresponding asphalt mixtures were prepared in this study. Their flowing behavior during the mixing process was tested at different mixing rates and temperatures using a modified Marshall mixing equipment. It was found that the higher the mixing temperature and the smaller the mixing rate, the less mixing power was consumed and the easier asphalt mixture was to mix. Moreover, the flowing behavior of asphalt mixtures can be well described by the Bingham model. Further, a new parameter termed as mixing workability index was introduced to evaluate the mixing difficulty of asphalt mixtures, and it was found that the asphalt binder types have a significant effect on mixture workability. [ABSTRACT FROM AUTHOR]

To establish the rutting prediction model of asphalt pavement under layered variable modulus, the deviation of permanent deformation prediction of asphalt pavement caused by dynamic modulus change was corrected. Based on the asphalt mixture dynamic modulus test and laboratory triaxial dynamic creep test, the correlation between the asphalt mixture dynamic modulus ( | E ∗ | ) and its high-temperature deformation resistance was verified. Abaqus finite element software was used to analyze the dynamic modulus and vertical compressive stress of asphalt pavement with depth and temperature at different times, and the correction factor (m) of vertical compressive stress of each sub layer under different dynamic modulus was proposed. According to the idea of `sub layer deformation superposition', a rutting prediction model of layered variable modulus asphalt pavement was established by using SPSS software regression analysis, which included temperature, asphalt layer thickness, vertical compressive stress, correction factor, load action times and other factors. The results showed that the established rutting prediction model can more accurately predict the permanent deformation of asphalt pavement, improve the rutting prediction accuracy of middle and lower layers by 6. 03% and 10. 34%, respectively, and improve the overall asphalt layer by 5. 19%. [ABSTRACT FROM AUTHOR]

The gussasphalt mixture has excellent water tightness, coordinated deformation ability and durability, while the epoxy asphalt mixture has extremely outstanding strength and heavy load on high temperature resistance. In order to realize the integration of the advantages of the two mixtures, the epoxy gussas-phalt mixture is proposed. The mechanical properties and 170 °C viscosity tests of epoxy resin and hot mixed epoxy asphalt from three sources were carried out; based on the mix proportion design of hot mixed epoxy gussasphalt mixture, the fluidity, Marshall, penetration, rutting, bending and fatigue performance tests of the mixture with mixing time of 45 min and 135 min were carried out. The results show that the mechanical properties of the three epoxy resins and the hot mixed epoxy asphalt are basically the same, and the viscosity is up to 1 Pa ⋅ s at 170 °C for more than 3 h; the performance of mixture attenuates greatly with the increase of mixing time; the type of epoxy asphalt has no significant effect on the performance indexes except flow value and ultimate flexural strain. When mixing for 45 min, the performance of XB epoxy gussasphalt mixture is the best, the fluidity is less than 5 s, and the constructability fluidity maintenance time is more than 135 min. The Marshall stability exceeds 48 kN, the rutting dynamic stability reaches 18 945 times/mm, the penetration increment is only 0.1 mm, and the ultimate flexural strain at - 10 °C exceeds 3 000 µε. The impact toughness of fatigue performance index reached 3 517 N ⋅ mm, and its performance was far higher than that of conventional gussasphalt mixture, and many indexes were also higher than that of epoxy asphalt mixture, and the cost is also relatively low. The hot mixed epoxy gussasphalt mixture has the advantages of both the gussasphalt mixture and the hot mixed epoxy asphalt, which can effectively improve the high-temperature strength of the gussasphalt mixture, and is of great significance to improve the quality and durability of steel bridge pavement in China. [ABSTRACT FROM AUTHOR]

In order to explore the applicability of environment -friendly polyurethane (EPU) in modified asphalt, the EPU modified asphalt was prepared by in - situ polymerization with polycarbonate diol ( PCDL ) as the soft segment and diphenylmethane diisocyanate (MDI) and butanediol (BDO) as the hard segment. FTIR test was used to analyze the chemical composition of EPU modified asphalt. The penetration, softening point, ductility, and viscosity were used to evaluate the physical properties of the modified asphalt. The compatibility of modified asphalt was evaluated by softening point difference. Dynamic shear rheological test was used to investigate the high temperature rheological properties of modified asphalt. Differential scanning calorimetry and bending rheometer experiments were used to investigate the creep mechanism of modified asphalt at low temperature. The results show that EPU molecules react with asphalt molecules in asphalt to form transaction structures. The addition of EPU can effectively improve the physical properties and high temperature properties of asphalt, and the compatibility is good. EPU has a lower glass transition temperature, so EPU also shows excellent improvement effect on the low-temperature performance of asphalt. This study can provide a new idea for the production of EPU modified asphalt. [ABSTRACT FROM AUTHOR]

To effectively utilize waste mask materials in road engineering and minimize resource waste, the melt-blown fabric (MBF) of waste masks was utilized to modify the virgin bitumen. The preparation process of MBF-modified bitumen was investigated, and the physical and rheological properties of bitumen were measured. Subsequently, the blending mechanism during preparation and the dispersion morphology of the modifier were explored. Finally, the pavement performance of the mixture was investigated, and a radar chart analysis was performed to quantitatively assess the effects of MBF modification. Results suggested that the recommended preparation process of shear time, shear rate, and shear temperature was 170 °C, 4000 r/min, and 15 min, respectively. MBF enhanced the high-temperature stability of the binder and weakened the temperature susceptibility. The modification was primarily a physical process. No network structure and agglomeration formed in the bitumen after modification. The addition of MBF significantly improved the resistance of the asphalt mixture to a high-temperature deformation and water damage but harmed its low-temperature crack resistance. The comprehensive assessment results of 0% ( f 1 ), 1% ( f 2 ), 3% ( f 3 ), and 5% ( f 4 ) MBF to improve the properties of the mixture were in the following order: f 3 > f 4 > f 2 > f 1 , where the impact of 3% MBF was the most significant, followed by 5% and 1% MBF. [ABSTRACT FROM AUTHOR]

Appropriate design in linear construction depends on many factors, including detailed geological conditions. One of the biggest problems are unrecognized erosion forms, in particular karst ones, which have a huge impact on the design and subsequent operation of roads. For this purpose, in addition to conventional methods such as drilling or geotechnical probing, which are point-based, non-invasive spatial geophysical methods are used. This article presents an example of the use of geoelectrical surveys, Electrical Resistivity Tomography (ERT) for the recognition of karst zones for linear investments. The article describes ERT investigations, which to some extent allows to identify dangerous karst phenomena occurring in the Lublin Upland (Poland), which are of great importance at the design stage of roads and in their further safe operation. Non-invasive geophysical research has been verified and confirmed by traditional geotechnical research, which confirms the effectiveness of their use. The Electrical Resistivity Tomography was used as a method providing a broader spectrum of knowledge on the spatial arrangement of soil layers in the subgrade of the planned road investments. It also enabled a more accurate, more detailed interpretation of geotechnical studies. The described geophysical investigations opens wide possibilities for their application to researchers. In the future, non-invasive methods have a chance to become as reliable as geotechnical methods, but this requires a lot of research to improve the effectiveness and accuracy of the interpretation of the obtained results. [ABSTRACT FROM AUTHOR]

For achieving the better modifying effect of polyurethane on asphalt pavement materials, the PUA powder modifier was prepared with fine grinding at the glass transition temperature, and polyurethane-modified asphalt (PUA-MA) with different dosages of modifier was prepared. The impact of the PUA on the physical properties of asphalt binder was studied. The modifying mechanism of PUA on asphalt was explored by investigating the thermal performance and chemical composition of asphalt (thermogravimetric analysis, differential scanning calorimetry test, and Fourier transform infrared spectroscopy). The micrograph of the interactive interface was characterized by scanning an electron microscope. Furthermore, the rheological properties of PUA-MA were also investigated and analyzed. The results indicated that the PUA had a dense structure with few pores on the surface. After mixing with asphalt, it altered the asphalt's internal structure via physical fusion and chemical reaction (carbamate formation). PUA improved the thermal stability of asphalt, enhanced the asphalt's thermal decomposition temperature, and further reduced the thermal mass loss while decreasing the glass transition temperature. The addition and dosage increase in the PUA modifier significantly improved the softening point, viscosity, complex shear modulus, and rutting factor of asphalt. Also, the PUA could improve the elastic recovery ability of asphalt and enhance the rutting resistance of asphalt at high temperatures. However, the crack resistance at low temperatures was not effectively improved (ductility and penetration decreased). When the dosage was 6–9%, PUA-MA had the best high-temperature performance, but asphalt showed poor low-temperature performance at this dosage. This study provides a theoretical reference for popularizing and applying polyurethane as an asphalt modifier in road engineering. [ABSTRACT FROM AUTHOR]

Part-fill and part-cut subgrade is widely distributed in mountainous highway engineering, and their resilient modulus and settlement exhibit significant transversal non-uniformity, which has an important effect on the performance of cement concrete pavement structure. A numerical model, focusing on a two-slab system on part-fill and part-cut subgrade, was developed by the finite element computer programme taking into account non-uniform settlement (a large range of partial contact) simultaneously with non-uniform modulus. Cement concrete pavement structure responses, including the load stress, vertical displacement and joint load transfer capacity were comprehensively investigated considering the two part-fill and part-cut subgrade characteristics. The results indicate that the non-uniform settlement has a higher impact on the concrete pavement structure than that of the non-uniform modulus in more cases. When the resilient modulus of the fill part is close to that of the cut part, the additional stress (relative stress increment) caused by the combination of the two factors is approximately the sum of the additional stress caused by the two factors individually. [ABSTRACT FROM AUTHOR]

The smoothness achieved in pavement construction, or as-built roughness, has great importance in road engineering. Traditionally, as-built roughness has been studied in the literature from an empirical approach, based on the statistical correlation between the roughness IRI observed before and after the execution of paving works. In the case of asphalt overlays, this article highlight interactions in the construction process that limit the predictive capacity of the traditional empirical approach; demonstrating, through the frequency response of the paver screed and the IRI model, that fitting a before-after IRI type regression is insufficient to explain the variability observed in as-built roughness. From the preliminary analysis carried out an original approach to as-built IRI prediction is proposed, based on the modelling of the asphalt paver and its levelling response to surface roughness during the paving process. Formulation of linear systems that constitute the model are presented for the case of a wheeled paver without using of automatic levelling. Longitudinal profile data from the Long-Term Pavement Performance SPS-5 experiment was used to calibrate the model, obtaining a mean error of 0.22 m/km for the predicted IRI. The results obtained demonstrate the potential of the proposed approach as a modelling alternative. [ABSTRACT FROM AUTHOR]

For the particular engineering-geological conditions and natural environment in permafrost regions, the highway has a high damage ratio during the operation. In warm and ice-rich permafrost regions, highway pavement and embankment have poor serviceability, which threatens driving the vehicle and safe operation. Traditional field surveys on highway damage cannot entirely, rapidly and precisely obtain the distress information along the whole road. In this paper, the Qinghai-Tibet Highway (QTH) pavement distress was investigated in 550-km-long permafrost regions based on the field surveys in 2014 and 2019 and the unmanned aerial vehicle (UAV) imagery. The type and damage ratio of distress were extracted by the remote sensing image classification method. The pavement roughness and embankment height were acquired by the spatial analysis of geographical information system. This paper provides a novel insight and efficient method for the distress investigation and exploration of distress formation in permafrost region, which can be applied in other similar engineering projects in the cold and inclement permafrost region. Furthermore, this paper also presents valuable and first-hand field data for evaluating highway serviceability and prevention of road damage during operation and maintenance stages. [ABSTRACT FROM AUTHOR]

To further improve the application quality of the waterborne epoxy resin (WER) in road engineering, a variety of WER and polyurethane-modified WER were prepared. The WER was treated by acid solution immersion, alkali solution immersion, salt solution immersion, oil immersion or artificial-accelerated aging. The mechanical properties of the WER before and after the treatment by various methods were tested. Based on the ideal point method of entropy weight, the influence degree of each treatment method on the mechanical properties of the WER was analysed, and the mechanical properties decay and residual mechanical properties of the WER were evaluated. The bonding durability of the WER was analysed. The results show that after the xenon lamp aging treatment, the mechanical properties of the WER decreased most significantly. The mechanical durability of the WER modified by polyurethane is improved to a certain extent, and the retention rates of their mechanical properties are >85%. After treatment by various corrosion or aging methods, the retention rates of mechanical properties of the PUE-E44 WER are >89.29%, showing an improved corrosion and aging resistance. The residual mechanical and bonding properties of the PUD-E51 WER are at a high level, and still show improved mechanical and bonding properties. [ABSTRACT FROM AUTHOR]

Accurate judgement of devoid damage information by 3D-Radar is an effective way of repairing damage in nondestructive pavements. In order to systematically analyse the characteristics of devoid damage under nondestructive pavements in 3D-Radar response. In this study, the 3D-Radar response to devoid damage of different sizes, locations and moisture contents was quantified by FDTD orthorectified simulations. Data acquisition of the pre-buried devoid damage on site was carried out using 3D-Radar, compared with the orthorectified simulation results and numerical analysis. The detection effect was also verified by relying on the project. The results show that the radar wave characteristics of the devoid damage are obvious. Different colour and waveform image characteristics in B-Scan in the presence and absence of water at the location; the size of the devoid also has an impact on the image characteristics. It depends on the footprints and size of the devoid. It creates "upward-convex", "down-concave" and straight features; the presence of the devoid characteristics in the 3D-Radar mapping will enhance the confidence of the devoid identification through field tests and engineering verification. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In cold regions, the mechanical performance of cement-stabilised macadam (CSM) deteriorates significantly due to freeze–thaw (F-T) actions. This paper attempts to investigate the F-T attenuation mechanism of mechanical performance of CSM from the perspective of the evolution of voids structure. To this end, multiple groups performance tests were conducted to study the effect of cement content, freezing temperature, and humidity conditions on the mechanical performance of CSM. Then the size distribution and evolution process of internal voids of CSM after F-T actions were investigated by computed tomography (CT) test. The results indicate that the resilient modulus (RM) and compressive strength (CS) of CSM decrease when F-T cycles increase until 15, and then stabilise gradually with a reduction of less than 5% in the last 5 cycles. It is presumbly attributed to the generation and melt of ice lenses in voids, distorting original matrix of particles. Additionally, increasing cement content can reduce the deterioration of mechanical performance, while increasing moisture content and decreasing freezing temperature promote the deterioration of mechanical performance. The F-T actions cause volume expansion of the larger voids (>100 mm3) before 5 cycles and then mainly result in more small voids (<1 mm3) during 5∼15 cycles. There is an apparent linear relationship between average voids ratio and RM and CS for CSM. The correlation coefficient R2 is higher than 0.92 and 0.73, respectively. [ABSTRACT FROM AUTHOR]

One of the most prevalent ailments of the road is crack. When it does, the standard of road engineering will be significantly lower and may even result in road collapse. Early detection of the cracks will result in significant maintenance cost savings if timely maintenance is performed. Although direct detection is highly challenging, the range of image cracks on the actual pavement is too large, the image quality is insufficient, the composition is complicated and the image range is too wide. Traditional manual detection methods have a number of drawbacks, including a lack of precision, a significant danger of detecting operation and a lengthy processing time. Therefore, in this research, we employed a novel technique based on image processing for the pavement detection method based on the features of pavement cracks. In order to avoid those difficulties Pre-processing (Median Filter), feature extraction (ResNet-50) and feature selection (Adaptive Salp Swarm Algorithm) techniques are also included in order to produce a clear image. With this proposed method, a variety of crack types including longitudinal, transverse, alligator and block can be identified. [ABSTRACT FROM AUTHOR]

Asphalt pavements absorb more than 90% of the incident solar radiation, which induces not only high-temperature degradation but also the urban heat island (UHI) effect. In this study, a novel nanoscale non-stoichiometric compound containing tungsten (MxWO3) was used for the first time to prepare thermal shielding coatings to reduce the temperature of pavements and mitigate the UHI effect. Coatings with good shielding characteristics were selected for outdoor thermal insulation tests to evaluate their properties. MxWO3 (M = K, Na, Cs) exhibited significant thermal shielding, especially CsxWO3. Outdoor thermal insulation tests were performed for the CsxWO3 coatings, and it was found that the greater the doping, the more significant the thermal shielding effect. Compared with untreated pavements, the surface-coated pavement exhibited significant cooling at 5 cm and 15 cm depth-wise, which reduced the overall pavement temperature by 1–2 °C, and the coating thickness affected the cooling effect. [ABSTRACT FROM AUTHOR]

Aiming at the problems of limited search area and inadequate evaluation methods for automatic highway alignment selection junction, based on genetic algorithm, the highway alignment constraint model, automatic highway alignment optimization model and operation speed prediction model were constructed to realize automatic highway three-dimensional spatial alignment solution search and safety evaluation. The results show that the automatic alignment selection and safety evaluation method based on genetic algorithm can overcome the deficiency that alignment junction can only be searched for in a given section under the given design area, proposed technical, economic and safety conditions, and achieve the automatic convergence and optimization of the design scheme. Under the condition of alignment safety, the alignment junction can be guaranteed to be searched automatically in the proposed alignment selection area globally, which verifies the feasibility of the automatic highway alignment selection method based on genetic algorithm and improves the efficiency of the alignment selection work. The method can realize the evaluation of road alignment safety with speed consistency as the index, and improve the safety design level of the alignment selection scheme. The study can provide reference for improving the theoretical basis of automatic road alignment selection and continuing the research on automatic road alignment selection methods. [ABSTRACT FROM AUTHOR]

To break through the limitations of two-dimensional plane in the optimization of highway route design in cold regions, a new framework is proposed that effectively combines the spatial data analysis of GIS with the 3D visualization function of BIM to achieve 3D route design optimization. This paper relies on the cold zone freeway He-Yi, firstly obtaining high precision geographic data model through GIS data collection and normalization processing, then integrating it into the BIM platform to obtain 3D geographic information model, and finally using BIM technology for sub-regional route selection application to achieve scientific and efficient cold zone route planning. The research results show that the deep excavation roadbed and tunnel models generated by using GIS geographic data and BIM technology are compared and analyzed from both safety and economic aspects of the scheme, and the comprehensive results are consistent with the designer's opinion. The comparison with the simulation results of water tank experiments verifies that BIM technology can evaluate the rationality of different schemes of water-related projects through flood simulation analysis. The traffic simulation analysis of complex intersections using this framework and the traffic data obtained can provide reference data for the determination of road construction indexes. The research on the application of GIS+BIM information technology to the three-dimensional design of HeYi freeway route can form exemplary results to provide reference for the optimization of the subsequent cold region project selection. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of graphite tailing sand blending on the water stability performance of asphalt mixes, this work used graphite tailing sand to replace traditional fine aggregate in the preparation of asphalt mixes, and designed asphalt mixes with graphite tailing sand blending 10% to 80% by volume of mechanized sand, and two interface modifiers were added, with a mass fraction of 0. 6% anti-spalling agent and 0. 4% silane coupling agent to improve the adhesion of graphite tailings to asphalt. The adhesion of fine aggregates to asphalt and the effect of interface modifiers on adhesion enhancement were evaluated by water elution method. Finally, the effect of graphite tailings with different volume admixture on the water stability of asphalt mixture was analyzed by water immersion Marshall test and freeze-thaw splitting test, and the improvement effect of different types of interface modifiers was evaluated. The test results showed that the flaking rate of graphite tailing sand was 82. 23%, which was lower than that of 59. 93% of the mechanism sand; the water stability of asphalt mixture gradually decreased with the increase of graphite tailing sand admixture; Marshall stability increased and then decreased with the increase of graphite tailing sand admixture. Both interface modifiers can effectively improve the adhesion of graphite tailing sand to asphalt. The maximum admixture of graphite tailing sand was 30% without the use of interface modifier, and the maximum admixture of graphite tailing sand was increased to 40% with the addition of anti-exfoliation agent, and to 50% with the addition of silane coupling agent. The results of this study indicate that graphite tailings sand can be used as an aggregate for asphalt mixes instead of mechanized sand. [ABSTRACT FROM AUTHOR]

In cold regions, the mechanical performance of cement-stabilised macadam (CSM) deteriorates significantly due to freeze–thaw (F-T) actions. This paper attempts to investigate the F-T attenuation mechanism of mechanical performance of CSM from the perspective of the evolution of voids structure. To this end, multiple groups performance tests were conducted to study the effect of cement content, freezing temperature, and humidity conditions on the mechanical performance of CSM. Then the size distribution and evolution process of internal voids of CSM after F-T actions were investigated by computed tomography (CT) test. The results indicate that the resilient modulus (RM) and compressive strength (CS) of CSM decrease when F-T cycles increase until 15, and then stabilise gradually with a reduction of less than 5% in the last 5 cycles. It is presumbly attributed to the generation and melt of ice lenses in voids, distorting original matrix of particles. Additionally, increasing cement content can reduce the deterioration of mechanical performance, while increasing moisture content and decreasing freezing temperature promote the deterioration of mechanical performance. The F-T actions cause volume expansion of the larger voids (>100 mm3) before 5 cycles and then mainly result in more small voids (<1 mm3) during 5∼15 cycles. There is an apparent linear relationship between average voids ratio and RM and CS for CSM. The correlation coefficient R2 is higher than 0.92 and 0.73, respectively. [ABSTRACT FROM AUTHOR]

One of the most prevalent ailments of the road is crack. When it does, the standard of road engineering will be significantly lower and may even result in road collapse. Early detection of the cracks will result in significant maintenance cost savings if timely maintenance is performed. Although direct detection is highly challenging, the range of image cracks on the actual pavement is too large, the image quality is insufficient, the composition is complicated and the image range is too wide. Traditional manual detection methods have a number of drawbacks, including a lack of precision, a significant danger of detecting operation and a lengthy processing time. Therefore, in this research, we employed a novel technique based on image processing for the pavement detection method based on the features of pavement cracks. In order to avoid those difficulties Pre-processing (Median Filter), feature extraction (ResNet-50) and feature selection (Adaptive Salp Swarm Algorithm) techniques are also included in order to produce a clear image. With this proposed method, a variety of crack types including longitudinal, transverse, alligator and block can be identified. [ABSTRACT FROM AUTHOR]

Highway engineering itself is a large-scale project with high construction safety requirements, involving multiple construction safety factors. In order to better ensure the orderly development of highway tunnel construction, it is necessary to strengthen construction safety evaluation. The construction safety management evaluation of highway engineering is viewed as the multiple-attribute decision-making (MADM) issue. In this paper, an extended probabilistic neutrosophic number TOPSIS (PNN-TOPSIS) method is established for construction safety management evaluation of highway engineering. The PNN-TOPSIS method integrated with CRITIC method in probabilistic neutrosophic sets (PNSs) circumstance is applied to rank the optional alternatives and a numerical example for construction safety management evaluation of highway engineering is used to proof the newly proposed method's practicability along with the comparison with other methods. The results display that the approach is uncomplicated, valid and simple to compute. [ABSTRACT FROM AUTHOR]

Adhesion is easily affected by moisture erosion, thus reducing pavement performance. SBS modified asphalt is widely used in road engineering due to its excellent performance. For analyzing the adhesion properties between SBS modified asphalt and aggregates under moisture damage, the macro-scale SBS modified asphalt-coated aggregates and micro-scale asphalt-aggregate adhesion models were prepared first. The moisture damage was applied to the coated aggregates and adhesion models subsequently. After that, the quantitative boiling tests and molecular dynamics (MD) simulations were carried out. Finally, the multi-scale adhesion results were analyzed using Pearson correlation analysis. The macro-scale results imply that as the degree of moisture damage increases, the stripping area of the asphalt-aggregate interface rises. The micro-scale results reveal the moisture damage mechanism that is the penetrated moisture into asphalt-aggregate interface disrupt the adhesion force by the action of hydrogen bonds and Van der Waals forces. The Pearson correlation coefficient is 0.996, which indicates that the multi-scale adhesion results present an extremely strong linear relationship. This research contributes to the analysis of moisture damage in asphalt pavements in pluvial as well as seasonal frozen regions, and also provides a reference for correlation analysis between the multi-scale results. [ABSTRACT FROM AUTHOR]

Road construction in karst areas is a challenging task. Combining the advantages of geosynthetics and fiber Bragg grating (FBG), this paper creatively presents a new type of FBG-3D printed geogrid, which allows reinforcement and accurate deformation monitoring. A series of model tests were carried out to investigate the mechanical and deformation characteristics of the subgrade with underlying karst cave reinforced by FBG-3D printed geogrid. The experimental results indicated that the fully coordinated deformation between FBG sensor and geogrid was successfully achieved by 3D printing technology, and the relationship between fiber wavelength and strain was obtained. The existence of cave had an adverse effect on the subgrade, but the FBG-3D printed geogrids effectively improved the bearing capacity and footing settlement, and the reinforcement effect increased with the decrease of geogrid spacing. In the cyclic loading experiments, the earth pressure inside the subgrade reinforced by geogrid changed as a half-sine wave in each cycle. The FBG sensors accurately measured the strain change inside the subgrade, and the data showed that the deformation of measuring point above the cave model was the largest. The research conclusions provide important basic data for the construction and monitoring of highway and geotechnical engineering projects. • FBG-3D printed geogrid has both reinforcement and strain monitoring capabilities. • Relationship between fiber wavelength and strain was determined by calibration experiment. • Effects of the subgrade with an underlying earth cave reinforced by FBG-3D printed geogrid were analyzed. • Earth pressure inside the subgrade changed as a half-sine wave in each cycle. [ABSTRACT FROM AUTHOR]

Safety is an important aspect of road design. In highway geometric design, road engineers use a two-stage design method due to its convenience, but the available two-dimensional design tools on the market are believed to impose limitations. Horizontal and vertical alignment parameters are considered and determined at the designer's discretion, potentially downplaying the three-dimensional characters of spatial curves. This study focuses on the three-dimensional characteristics of highway alignments and investigates a safety evaluation method to establish the relationship between crash rate and spatial curve properties. This will necessitate an analytical investigation into the effects of higher-order properties, such as curvature and torsion, on the geometry of spatial Cartesian curves. First, these combinations of horizontal and vertical alignments were categorized into six classifications, each with its own spatial expression in mathematical form. After manipulating the curvature and torsion of the spatial curve algebraically, the correlation between geometric design variables and crash rate was ultimately established. A few cases involving geometric design data and crash facts were utilized for verification. The results revealed a considerable positive correlation between curvature or torsion variance and crashes per million vehicles kilometers, as a slight difference between curvature and torsion could also be spotted. And curvature distribution is correlated with collision frequency more closely than torsion spatial variation. [ABSTRACT FROM AUTHOR]

Mitigation of GHG emission is increasing concerned in the research field of road engineering. The quantitative assessments of integral road structural designs in different countries would shed light on the implementation of sustainable road development and global warming controlling. The study referred to the European E6 and the Yanqing-Chongli expressway to quantify the GHG emissions for Norwegian and Chinese roads, and investigate the critical procedures and factors in resulting in the differences of GHG emissions. The data inventory and research framework for life cycle assessment (LCA) were established according to their applied materials, structural design and construction techniques. Moreover, the quantification of GHG emission was conducted as considering the surface layers, base layers, subbase and frost protection layer. The comparative results indicate that the Norwegian road generated extra 1.43 t equivalent CO 2 more than Chinese road during the 20-year service life, and the surface layers are the most source of GHG emission in road structure, which occupied 65.75% for Chinese road and 43.19% for Norwegian road. Additionally, the materials extraction phase caused the largest proportion of GHG emission in Chinese road case, while the road construction phase was verified as the capital GHG contributor in Norwegian road case with 108.27 t equivalent CO 2 emitted. The obtained results in the comparative study could provide the practical references for low-carbon road construction and promising strategies for globalization development. [Display omitted] [ABSTRACT FROM AUTHOR]

This study reveals the thermal control mechanism of a ventilated–closed block layer composite embankment structure by analyzing the heat transfer and temperature change based on the measured data of the high-grade highway experimental engineering in the Beiluhe area of the Qinghai–Tibet Plateau. During the cold season, natural convection occurred in the block layer when the upper boundary temperature was approximately 2 °C lower than that of the bottom boundary. In addition, heat from the foundation was transferred upwards through the block layer via heat convection. During the warm season, air inside the block layer was almost static, and external heat was transferred downwards through the block layer via heat conduction. The equivalent thermal conductivity of the block layer in the cold season was approximately 17.4 times that of the warm season, and heat release through the block layer was 9.65 times that of heat absorption, exhibiting a thermal semiconductor effect. The results show that the frozen soil foundation was in net exothermic state, the permafrost table continuously rose, and the mean annual soil temperature continuously decreased above 14 m depth. This research can contribute to thermal control technology development and construction scheme selection of expressway in permafrost regions. [ABSTRACT FROM AUTHOR]

Using fiber and cement to modify waste slurry and apply it to roads is an effective way to recycle waste slurry. A new type of road material, fiber–cement-modified waste slurry (FRCS), was prepared in this study. The static and dynamic characteristics of the cement soil were studied using an unconfined compressive strength test and dynamic triaxial test. The results show that the optimum fiber content of FRCS is 0.75%. In the unconfined compressive strength test, under this fiber content, the unconfined compressive strength (UCS) of the FRCS is the largest, and the elastic modulus and modulus strength ratio are both the smallest, indicating that the tensile properties of the cement slurry have been enhanced. In the dynamic triaxial test, the hysteretic curve of the FRCS tends to be stable with the increase in the number of cycles, the dynamic elastic modulus of the FRCS decreases first and then increases with the increase in the dosage, while the damping ratio becomes stable after a rapid decline, and the fiber incorporation increases the cumulative strain of the soil–cement under low-stress cycles, indicating that the ductility of the FRCS is improved. In addition, a cumulative strain prediction model of the FRCS is established in this paper, which can provide a reference for the resource application of waste slurry in road engineering. [ABSTRACT FROM AUTHOR]

For the life calculation of pavement under the combined action of aircraft load and temperature coupling field, the recommended values of the maximum temperature gradient of pavement with different thicknesses are obtained through the accurate measurement of the temperature distribution based on the pavement depth. The loading parameters of the simulated temperature field are determined. Based on the analysis of a large number of simulation tests, the sensitivity of soil modulus, pavement slab thickness, and temperature difference factors to the stress on the pavement slab is analyzed. The correlation model between temperature stress and the temperature difference is established, and its effectiveness is verified through examples. The simulation load test analysis of aircraft and the temperature coupling is conducted at the critical load level of the pavement. The results show that the coupling stress generated under the combined action of temperature gradient and aircraft load is less than the sum of temperature warping stress and load stress, with a difference of 4.93%. Based on the principle of stress damage accumulation under the coupling action of load and temperature, the residual allowable number of actions of pavement is calculated, the pavement residual life evaluation model under the coupling field is constructed, and an example is applied to provide a theoretical reference for improving the relevant research in the field of pavement structure design. [ABSTRACT FROM AUTHOR]

Roundabouts are a superior solution to traffic operation issues at intersections with complex geometry, such as skewed and offset approaches where there are property constraints or where realigning approaches is costly. Although roundabouts with offset, skewed approaches are unavoidable, the current design standards are typically established based on standard roundabouts having radial approach alignments and perpendicular approaches. This work aimed to (1) examine the geometric characteristics of roundabouts with offset or skewed approaches or both, (2) establish the relationships of the design parameters with the approach offset and angle, (3) develop geometric optimization models, and (4) recommend geometric design guidelines for inscribed circle radius, entry curve radius, and exit curve radius. The approach or intersection angle ranges are also recommended for single-lane and two-lane roundabouts under urban and rural conditions. Design graphs and tables of the minimum required radii were developed. They not only help highway designers and engineers to select the appropriate parameters and reduce trial-and-error efforts during design, but also offer a guide to property needs during the planning stage. [ABSTRACT FROM AUTHOR]

Considering the characteristics of steel slag, the effective relative density of steel slag was measured by the impregnation method. By the volume substitution method, the asphalt mixtures with different steel slag content were prepared for replacing the coarse aggregates. According to the technical requirements of the ultra-thin friction course, the road performance and the function characteristics of the steel slag asphalt mixture were evaluated. The test results show that with the increasing of steel slag content, the performance indexes of dynamic stability, maximum tensile strain and tensile strength ratio of asphalt mixture are increased with latter decreasing. When the steel slag content is 50%, the comprehensive performance of asphalt mixture is the best. With the increasing of the placement time of test specimens, the high temperature performance index of the steel slag asphalt mixture is increased slightly, while the low temperature crack resistance index and water stability index are decreased. The skid resistance and abrasion resistance of asphalt mixture are significantly improved with the addition of steel slag. The impermeability of the mixture is reduced, while the water seepage coefficient values of several steel slag asphalt mixtures can still meet the requirements of the standard test methods of bitumen and bituminous mixtures for highway engineering (JTG E20—2011). [ABSTRACT FROM AUTHOR]

The strength-formation mechanism for industrial-construction residue cement stabilization of crushed aggregate (IRCSCA) is not clear. To expand the application range for recycled micro-powders in road engineering, the dosages of eco-friendly hybrid recycled powders (HRPs) with different proportions of RBP and RCP affecting the strengths of cement-fly ash mortar at different ages, and the strength-formation mechanism, were studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the early strength of the mortar was 2.62 times higher than that of the reference specimen when a 3/2 mass ratio of brick powder and concrete powder was mixed to form the HRP and replace some of the cement. With increasing HRP content substituted for fly ash, the strength of the cement mortar first increased and then decreased. When the HRP content was 35%, the compressive strength of the mortar was 1.56 times higher than that of the reference specimen, and the flexural strength was 1.51 times higher; XRD and SEM studies of the hydrated cement mixed with HRP showed that the amount of CH in the cement paste was reduced by the pozzolanic reaction of HRP at later hydration ages, and it was very useful in improving the compactness of the mortar. The XRD spectrum of the cement paste made with HRP indicated that the CH crystal plane orientation index R, with a diffraction angle peak of approximately 34.0, was consistent with the cement slurry strength evolution law, and this research provides a reference for the application of HRP to produce IRCSCA. [ABSTRACT FROM AUTHOR]

Upon detecting a crash impact, the vehicle restraint system locks the driver in place. However, external factors such as speeding, crash mechanisms, roadway attributes, vehicle type, and the surrounding environment typically contribute to the driver being jostled within the vehicle. As a result, it is crucial to model unrestrained and restrained drivers separately to reveal the true impact of the restraint system and other factors on driver injury severities. This paper aims to explore the differences in factors affecting injury severity for seatbelt-restrained and unrestrained drivers involved in speeding-related crashes while accounting for temporal instability in the investigation. Utilizing crash data from Thailand between 2012 and 2017, mixed logit models with heterogeneity in means and variances were employed to account for multi-layered unobserved heterogeneity. For restrained drivers, the risk of fatal or severe crashes was positively associated with factors such as male drivers, alcohol influence, flush/barrier median roadways, sloped roadways, vans, running off the roadway without roadside guardrails, and nighttime on unlit or lit roads. For unrestrained drivers, the likelihood of fatal or severe injuries increased in crashes involving older drivers, alcohol influence, raised or depressed median roadways, four-lane roadways, passenger cars, running off the roadway without roadside guardrails, and crashes occurring in rainy conditions. The out-of-sample prediction simulation results are particularly significant, as they show the maximum safety benefits achievable solely by using a vehicle's seatbelt system. Likelihood ratio test and predictive comparison findings highlight the considerable combined impact of temporal instability and the non-transferability of restrained and unrestrained driver injury severities across the periods studied. This finding also demonstrates a potential reduction in severe and fatal injury rates by simply replicating restrained driver conditions. The findings should be of value to policymakers, decision-makers, and highway engineers when developing potential countermeasures to improve driver safety and reduce the frequency of severe and fatal speeding-related single-vehicle crashes. [ABSTRACT FROM AUTHOR]

The cracking behavior of subgrade filling is crucial for the stability of road embankments. Slag-modified soil (SMS), which is commonly used as a reinforcing material for construction in highway and railway engineering, has special mechanical and microstructural characteristics that are easily altered under external disturbances. Although the macroscopic deformation of SMS has been widely examined, research on its cracking behavior at the mesoscale under an external load has received insufficient attention thus far. This study uses real-time X-ray computed tomography (X-CT) as a nondestructive tool for characterizing the microstructure of a SMS specimen subjected to uniaxial compression. Rules for the dynamic propagation of cracks in the specimen during deformation are identified based on two-dimensional (2D) and three-dimensional (3D) visualization and quantitative characterization. The results showed that the SMS can be divided into three components—cracks, soil, and steel slag—based on the density gradients from X-ray CT images. The preprocessed X-ray CT images and reconstructed crack models dynamically demonstrated the expanding and connecting patterns of internal cracks during the entire process of deformation. Values of the crack ratio and the degree of connectivity were positively correlated with the axial strain as expressed by a cubic spline function and a linear function, respectively. Curves of the distribution of the volumes of the cracks suggest that cracks in SMS can be divided into four groups: minicracks, mesocracks, medium cracks, and macroscopic cracks. From quantitative and visual perspectives, a large number of original cracks with small volume and low connectivity were gradually transformed into a main fracture under uniaxial loading. The localized shear band, which existed in the zone adjacent to the main fracture, was generated and obliquely distributed in an irregular, flat strip shape in the middle of the SMS specimen. This study suggests that the real-time X-ray CT scanning technique has broad application prospects for detecting the mesostructure in subgrade filling. [ABSTRACT FROM AUTHOR]