Permanent Deformation Behavior Research Articles

Enhanced understanding on permanent deformation behaviour of subgrade compacted clay under long-term cyclic loading

The long-term performance of pavement structures is heavily reliant on the sustained load-carrying capacity of the subgrade soil. Under repetitive traffic loads, permanent deformation (PD) gradually accumulates in the subgrade due to plastic yielding and soil particle rearrangement, which can compromise the serviceability and durability of overlying pavement layers. This study aimed to enhance the understanding of compacted clay response under long-term cyclic loads through a systematic repeated load triaxial (RLT) testing approach. The proposed approach considered depth-dependent static and dynamic stresses exerted on compacted clay beneath pavement structures and traffic loads. A series of RLT tests were conducted to investigate the impact of key factors, including soil properties (moisture content and compaction degree), stress conditions (confining pressure and deviator stress), and load characteristics (load duration and rest period), on the PD behaviour of compacted clay subgrade. Stress-strain hysteresis loops and damping ratios were analyzed to enhance the fundamental understanding of subgrade PD evolution. The results showed that higher moisture content and lower compaction degree significantly increased PD, with the PD response transitioning from plastic shakedown to plastic creep. Greater deviator stress also exacerbated PD accumulation. Variations in loading duration and rest period influenced the PD behaviour, demonstrating the importance of accurately simulating the stress history experienced by subgrade soil elements under traffic loading. The findings provide valuable insights to optimize subgrade design and implement performance-based management of pavements.

Effect of morphology and structure of MXene Ti3C2Tx on mechanical, thermal properties of PEEK nanocomposite

As a new type of 2D nanomaterials, MXene can improve the thermal, mechanical, and tribological performance of polymers as a reinforcing additive. However, there is a lack of systematic research on the impact of the morphology and structure of MXene on the performance of nanocomposite. In this study, MXene Ti3C2Tx with different morphologies was prepared and the effect of morphologies on the mechanical, thermal and creep properties was explored. Mechanical test results illustrate that the addition of MXene Ti3C2Tx fillers contributes to the improvement of mechanical properties. Among the three fillers, d-Ti3C2Tx exhibit a better reinforcement effect in PEEK than m-Ti3C2Tx and f-Ti3C2Tx, which are greatly related to the morphology of the MXene Ti3C2Tx, the interface and defects between the PEEK and the MXene Ti3C2Tx. After adding MXene to the PEEK matrix, the internal friction of PEEK molecule segment motion would aggrandize and the composites would deform and take longer relaxation times. Due to the larger interface between d-Ti3C2Tx and the matrix, the composite material exhibits the smallest creep strain magnitude and permanent deformation behavior after recovery. However, the high activity of 2D MXene nanomaterials resulted in a decrease in the thermal stability of PEEK.

Investigation of Permanent Deformation Behaviour of Subbase Layer Mixed with Non-Plastic Stone Dust of the Pavement

Investigation of Permanent Deformation Behaviour of Subbase Layer Mixed with Non-Plastic Stone Dust of the Pavement

Permanent deformation characteristics of unsaturated subgrade soils under cyclic loading

Excess permanent deformation of subgrade may cause critical rutting in pavements, and subsurface water significantly affects the accumulation of permanent deformation. This study aims to reveal the permanent deformation behaviour of unsaturated subgrade soils. Subgrade box tests were performed at varying moisture content, stress levels and loading frequency, respectively. The test results show that the permanent deformation significantly increased with moisture content. The concept of a permitted moisture content-applied dynamic load envelope was proposed. Based on curve fitting, a prediction model of permanent deformation of subgrade soils was developed, and the effects of moisture content and loading cycles were included. The validation results show that the model exhibited reasonably good performance in modelling the deformation. This study may provide an alternative way for predicting the permanent deformation of unsaturated subgrade soils.

Fatigue Cracking Behaviour and Characteristics of Flexible Pavement Subjected to Freight Coal-Truck Loading

Fatigue cracking is one of the varieties of flexible pavement distress caused by frequent traffic loads, and it is also a sign of structural collapse. Using finite element methods, numerical simulations were conducted to evaluate the strain changes that occur throughout the process of flexible pavement cracking. Several flexible pavement configurations with various thickness and different material properties of AC layer were developed, and several loading conditions in terms of the axle load, the speed, and the loading cycles of the freight truck were modelled. The numerical modelling showed that the greatest horizontal tensile strain in the 1stAC layer (surface course) is at the surface-centre of the pavement structure, which is predicted to be prone to top-down cracks. In other side, the greatest horizontal tensile strain in the 2ndAC layer (base course) is at the bottom-below of the tire tread, which is predicted to be vulnerable to bottom-up cracks. The outcomes of this study added to the knowledge gathered from previous studies, especially regarding the critical locations within the AC layer with the greatest magnitude of horizontal tensilestrain and their potency to experience either the top-down cracking or bottom-up cracking, as well as related to the effect of slowing the truck speed and increasing both the truck’s hauling load and loading cycles on the fatigue life of asphalt concrete layer. Future research needs to be done to evaluate the balance between both permanent deformation behaviour of the AC layer and to determine the optimum flexible pavement configurations.

Rutting Performance Evaluation of BMD Surface Mixtures with Conventional and High RAP Contents under Full-Scale Accelerated Testing.

The balanced mix design (BMD) constitutes a significant step forward in the pursuit of better-performing asphalt mixtures. This approach/framework offers increased innovative opportunities for the proper design and production of engineered asphalt mixtures without the need to strictly adhere to traditional volumetric requirements. The primary objective of this paper is to conduct a comprehensive investigation of the permanent deformation (rutting) behavior of surface mixtures (SMs) with conventional and high reclaimed asphalt pavement (HRAP) contents through full-scale accelerated testing under incremental loading conditions while accounting for the environmental aging effect. HRAP SMs were designed in this study, marking the initial application of Virginia Department of Transportation (VDOT) BMD special provisions, with attempts to incorporate 45% and even 60% RAP. Results showed that all BMD HRAP mixtures exhibited higher rut depths compared to the control mixture, which can be attributed to the inclusion of high binder contents aimed at enhancing cracking resistance. The asphalt pavement analyzer (APA) rut test and the stress sweep rutting tests were performed on mixtures sampled during production. Correlation analysis revealed significant and strong positive correlations between accelerated pavement testing (APT) and the multilevel laboratory rutting performance tests considered in this study. Finally, while acknowledging the limitations and all the assumptions considered in this study, the correlation analysis recommended refining the VDOT BMD APA rut depth threshold by lowering the current limit of 8 mm to 7 mm to ensure good performing mixtures from a rutting point of view.

Effect of truck and train loading on permanent deformation and fatigue cracking behavior of asphalt concrete in flexible pavement highway and asphaltic overlayment track

Abstract This research investigated the largest magnitude of displacement and horizontal tensile strain in several critical locations within the asphalt concrete (AC) layer in both the flexible pavement highway (FPH) and asphaltic overlayment track (AOT) structure using the numerical modeling method. The role of the hauling loads, speed, and loading cycles of freight truck’s dumps and freight train’s wagons on the mechanical behavior of FPH and AOT in terms of the permanent deformation and fatigue cracking was examined. Furthermore, the performance of the FPH and AOT in terms of permanent deformation and fatigue cracking characteristics due to various magnitudes of hauling loads, speed, and loading cycles of freight truck’s dumps and freight train’s wagons was compared to determine the optimum infrastructure for the freight coal transportation, based on the hauling capacity as well as the magnitude of permanent deformation and the horizontal tensile strain of the AC layer. According to the findings of this study, it is suggested to choose the AOT structure with fourth or sixth loading systems to run the freight coal transportation with the highest magnitude of the hauling capacity of 360,000 tons, since it produces the minimum magnitude of the permanent deformation and fatigue cracking of the AC layer. Future research should be conducted to examine the potential and the characteristics of fatigue cracking due to the contact between the edge of the sleeper and the surface of the AC layer in AOT.

Impact of Rest Period and Stress Paths on Asphalt Concrete Permanent Deformation Behavior

Impact of Rest Period and Stress Paths on Asphalt Concrete Permanent Deformation Behavior

Study on optimal preparation and rheological characteristics of waste low density polyethylene (LDPE)/styrene butadiene styrene (SBS) composite modified asphalt binder

The sustainable utilization of waste low density polyethylene (LDPE) in asphalt pavements has enormous environmental and economic benefits. To enhance and benefit more from LDPE, this study deals with use of LDPE and styrene butadiene styrene (SBS) collectively for composite modification of asphalt binder. The study intends to identify the optimal blending parameters of LDPE/SBS composite modified asphalt binder by using the orthogonal experiment. The paper deals with the investigation of conventional properties and rheological properties such as Penetration, softening point, ductility, Superpave rutting parameter (G*/sinδ), failing temperature, rotational viscosity and multiple stress creep and recovery (MSCR) test parameters of the binder. Moreover, the dispersion of modifiers in asphalt binder is studied by optical microscopy. The test results point out that the optimal blending parameter for preparing LDPE/SBS composite modified asphalt is 90 min of blending at 180 °C maintaining a rate of 2500 rpm. The blending time parameter has the highest influence on the properties, with the blending temperature and blending rate having a relatively lower impact. Although, both the LDPE and SBS individually have a good impact on high temperature characteristics of asphalt binder but together as a composite, in addition to showing improved high temperature properties, they also reveal high resistance towards permanent deformation and better elastic behaviour. It is concluded that the LDPE/SBS composite modified asphalt binder performs well and is recommended better for high temperature climates. Furthermore, it is good way to enhance the application of LDPE in pavement industry and promote environmental sustainability.

Investigation on permanent deformation in steel-concrete composite beam bridge deck pavement under temperature-load coupling effect

Rutting is one of the common distresses observed in asphalt pavement, influenced by temperature and load conditions. To clarify the permanent deformation behavior of steel-concrete composite beam (SCCB) bridge deck pavement under temperature-load coupling effect and provide references for the distress cause analysis, five typical SCCB bridge deck pavements were selected. The temperature distribution and the temperature stress of the pavement structures were analyzed by numerical simulation under periodic temperature variations. In addition, considering the daily variation in traffic volume, the permanent deformation of the five pavement structures were calculated under temperature-load coupling effect. Finally, the influence of heavy load on the development of rutting distress was also investigated. The results show that the temperature field and temperature stresses within the SCCB bridge deck pavement exhibit periodic variations under periodic temperature variations. Additionally, after 500,000 times of standard axle load application, “EA + SMA” exhibits the smallest permanent deformation and the best resistance to rutting distress under temperature-load coupling effect. Finally, heavy load conditions have a great influence on the permanent deformation of SCCB bridge deck pavement. In areas with severe rutting distresses, it is recommended to use “EA + SMA” pavement structure in SCCB bridge.

Modeling the Dynamic Behavior of Recycled Concrete Aggregate-Virgin Aggregates Blend Using Artificial Neural Network

Construction and demolition waste (CDW) aggregates have increased as a result of the rise in construction activities. Current research focuses on recycling of CDW to replace dwindling natural aggregates but pays little attention to permanent deformation behavior due to the anisotropic nature of the blended CDW aggregates. Accordingly, this study performs repeated load triaxial tests to evaluate the permanent deformation mechanism of the blended materials under various shear stress ratios and moisture conditions. An artificial neural network (ANN) deformation prediction model that accounts for the complex nature of the blended CDW and natural aggregate was developed. Moreover, a sensitivity analysis was performed to determine the relative importance of each input variable on the deformation. The results indicated that the shear stress ratio and confining pressure profoundly influence the deformation. It was demonstrated that the proposed prediction model is more robust than the conventional one. The sensitivity analysis revealed that the number of loading cycles, confining pressure, and shear stress ratios are the principal factors influencing the permanent deformation of the blended aggregates with sensitivity coefficients of 31%, 25%, and 21%, respectively, followed by the CDW and moisture contents. This model can assist practitioners and policymakers in predicting the permanent deformation of CDW materials for unbound pavement base/subbase construction.

Energy-based insight into characterization of shakedown behavior of fully weathered red mudstone

Weathered Red mudstone is widely distributed in Sichuan basin. The compacted weathered red mudstone has been used as subgrade fill materials of high-speed railway in southwestern of China. Dynamic responses of such materials under cyclic loading are critical to long-term stability of subgrade. Shakedown concept is widely employed in characterizing the permanent deformation behavior of soils. According to the evolution of axial strain (Werkmeister’s theory) or unit dissipated energy (Tao’s theory) with loading cycles, the behavior of unbound granular materials can be classified into three categories: plastic shakedown, plastic creep and incremental collapse. However, both theories are more suitable for the unbound granular materials with some limitations when used to separate the plastic creep and incremental collapse behavior. To overcome the limitations of the current theories, 26 cyclic triaxial tests were conducted on a saturated fully weathered red mudstone (SFWRM) to study the evolution of axial strain and unit dissipated energy during cyclic loading. A clear dependency of axial strain, axial strain rate on the unit dissipated energy level under various cyclic stress states were observed. A new criterion which is based on the responses of unit dissipated energy with cyclic stress ratio, was proposed to determine the limit between plastic creep and incremental collapse. Comparing with Werkmeister’s criterion and Tao’s criterion, the proposed criterion showed a better performance in identifying the incremental collapse behavior of the SFWRM.

Cold recycling mix design approach targeting permanent deformation resistance

Cold recycling technology offers a sustainable construction pathway for pavements with a potential of recycling up to 100% of the existing in-situ materials. This study introduces a new approach to design emulsion-based cold recycling mixtures. The proposed mix design approach channels the design efforts to optimize the mixture’s components and evaluate its long-term performance. The elements of the proposed design include altering aggregate gradation to achieve optimum packing; a method to selecting an optimum moisture content that is derived from both liquid components in the mixture; and selecting the residual asphalt content based on the mixture’s resistance to permanent deformation. To evaluate the reliability of the proposed mix design method, an optimum mixing water content was derived for an optimum RAP gradation. The effect of varying the emulsion content while keeping the mixing water content constant was evaluated on the mixture’s volumetrics, strength, and permanent deformation behavior. A conventional triaxial compression stress path was applied on samples compacted with several residual asphalt contents. The triaxial test results were compared with results obtained from Hamburg Wheel Tracking Test and Asphalt Pavement Analyzer rutting device. The increase in residual asphalt content at optimum mixing water content led to a systematic increase in strength and reduction in voids that stabilizes as the content increases. The permanent deformation experiments showed the importance of imposing a deformation criterion to select the residual asphalt content in the mix design stage. Additionally, the triaxial repeated load tests demonstrated the importance of using anticipated stress states to characterize permanent deformation resistance which cannot be captured by simple performance tests. Representative stress states in the CR layer should be taken into account during the mix design stage where higher stresses are anticipated in the recycled layer.

Permanent deformation characteristics of expandable foam grout under cyclic loading

Expandable foam grout (EFG) is a novel flowable cementitious material for filling underground cavities. This study evaluates the permanent deformation behavior of EFGs under cyclic loading. EFG consists of cement, water, and admixture. EFG samples are mixed at a water–cement ratio of 100% and an admixture content of 5.6% to prepare cylindrical specimens cured at four different times. Sinusoidal loads with different maximum axial stresses are vertically applied. The permanent deformation of EFG increases with the number of load cycles but at a decreasing rate. A power function model is used to represent the relation between the permanent deformation and number of load cycles. The model generally matches the measured values but can overestimate the deformation at specific strain levels and curing times. The accumulated permanent deformation increases with the applied axial stress and decreases with longer curing times. The final permanent deformation decreases with the increase in the curing time, and the rate of final permanent deformation also decreases. A linear relationship is found between the final permanent deformation and unconfined compressive strength. These findings can help estimate the damage and durability of underground structures backfilled with highly flowable and expandable cementitious materials under cyclic loads.

Effect of self-cementing properties on the mechanical behaviour of recycled concrete aggregates in unbound pavement layers

Recycled concrete aggregates (RCA) are increasingly being used in unbound pavement base and subbase layers, while the influence of their self-cementing properties on the mechanical behaviour has not been thoroughly studied. In this paper, the self-cementing properties, permanent deformation and resilient deformation behaviour of two RCA, NRCA (New RCA, crushed recently) and ORCA (Old RCA, crushed long time ago), showing significantly different self-cementing properties, after curing for different times (1, 180, 360 and 720 days), were investigated by pH value measurements, calorimeter tests and repeated load triaxial tests (RLTT). The results show that the self-cementing properties can significantly improve the mechanical behaviour of RCA, which is comparable to that of lightly treated materials. The permanent strains of NRCA, showing strong self-cementing properties, decrease to a very low value quickly after curing for 180 days, and then stabilize. While the resilient modulus of NRCA increases continuously with curing time, up to the studied curing time (720 days), 4.3 times larger than that curing for 1 day. It was also found that the traffic loads can damage the bonds between particles formed due to the self-cementing properties. On the contrary, for ORCA, showing negligible self-cementing properties, curing has no influence on the mechanical behaviour.

Road Pavement, Road Pollution, and Sustainability under Climate Change Increased Temperature

This paper presents a multidisciplinary approach to understand the impacts of temperature increase on the retention of particulate pollutants, such as heavy metals and microplastics, by the road pavement material. A soil with a particle size distribution similar to road dust was selected. A Wheel Tracking device was used to assess the permanent deformation behavior of prismatic specimens and the retention of the dust, at controlled temperatures of 40 °C and 60 °C, likely to occur on pavement in the future. The soil representing road pollutants was placed at the top of the slabs prior to the Wheel Tracking Test (WTT), based on the European Standard EN 12697-22:2020. After the WTT, two common methods were used, in order to evaluate the soil retention (pollution accumulation) on road pavement. The results confirm that the viscoelastic behavior of bituminous mixtures under increased temperatures can contribute to particle retention at the pavement. Future studies are needed to understand the phenomena, the retention characteristics by different bituminous mixtures, and the efficiency of pollutants capture. The work opens the opportunity to develop innovative road pavement bituminous mixtures that can reduce the discharge of road particulate pollutants, and have increased resilience and sustainability in extreme weather conditions.

Development of a generalised creep-recovery test and a back-calculation method for determining the permanent deformation of asphalt mixtures in the time domain

The measured strain during a creep-recovery (CR) test comprises both reversible and irreversible strains; therefore, adequate treatment is required to accurately separate them. In this paper, a generalised version of the CR test was proposed to investigate the permanent deformation behaviour of asphalt mixtures exerted by a variety of loading patterns in the time domain. The companion back-calculation algorithm was also proposed to separate with improved accuracy and repeatability the pure viscoelastic (VE) and viscoplastic (VP) strains. First, the creep compliance (CC) was back-calculated based only on the recovery data by using an approximate analytical creep compliance function of the Huet-Sayegh model as the solution function in the optimisation process. Then, the pure VE and VP strains were determined. The results show that the proposed method attains a good level of reliability although relatively short durations of the recovery period have been used.

A statistical analysis of the effect of confining pressure on deformation characteristics of HMA mixtures in the modified wheel track testing

Permanent deformation in the form of rutting is a critical mode of failure observed in flexible pavements. While several research have been conducted to develop multiple tests for the characterisation of permanent deformation, little information is obtainable from the existing literature on how the factors or the interaction of the factors from these tests affect the permanent deformation behaviour in a simulative test, such as the wheel tracker. This research focuses on statistical analysis and ruggedness testing of the factors affecting the permanent deformation behaviour of asphalt mixes tested in the Modified Wheel Tracker (MWT). The analysis involved five factors in total, each at two levels. These factors are binder type, voids in total mix (VTM %), nominal maximum aggregate size, temperature, and confining pressure. The study utilised half-fractional factorial design in accordance with ASTM E1169-20. Significant parameters were determined through statistical analysis and regression models were proposed. The contour plots provided various combinations of the most significant factors for the corresponding responses. Based on the statistical analysis of the experiments conducted without any confinement, temperature, amongst all other factors, was found to impose the greatest effect on the permanent deformation behaviour based on vertical and horizontal FN Indices. Experiments with controlled confinement show that “confining pressure” is the most significant factor for the rutting parameters. The sensitivity analysis points out that to maintain the vertical deformation at 2000 cycles to be in the range ± 25% from the model, the confining pressure and temperature should be controlled within the range ± 25% and ± 5%. The use of the MWT shows that long-term rutting development can well be predicted from rutting at 2000 cycles using linear and exponential models.

Permanent deformation response of demolition wastes stabilised with bitumen emulsion as pavement base/subbase

The stabilisation of the granular base course using binders has been adopted for many years; however, the use of bitumen emulsions has been emerging in recent times. Nevertheless, there is limited knowledge on the deformation behaviour of bitumen emulsion-stabilised recycled demolition wastes, particularly in pavement base and subbase applications. In this study, the effect of bitumen emulsion on the permanent deformation behaviour of two types of recycled demolition wastes, recycled concrete aggregate (RCA) and crushed brick (CB) is evaluated. The aggregate samples were blended with an anionic slow-set bitumen emulsion at different contents of 0, 1, 2, and 3 % by dry weight of aggregates. Compacted specimens were partially dried to achieve target values of 70 and 90 % of their optimum moisture contents to investigate the effect of in-service moisture content. Specimens were next subjected to repeated loading triaxial tests that comprised of multiple stages at varying stress levels to simulate moving loads of vehicles. The shakedown theory was adopted to characterise the blends based on their permanent deformation responses. Most of the proposed blends exhibited a Range B behaviour, i.e., plastic creep responses. Also, CB samples generally experienced higher permanent strain accumulations and hence, inferior permanent deformation responses compared to RCA. The inclusion of bitumen emulsion to the aggregates generally caused a decrease in resilient strains, showing that emulsion-stabilised RCA and CB could provide increased resistance under repeated traffic loading. It was also concluded that higher moisture contents led to higher permanent strains and permanent strain rates.

Development of Artificial-Neural-Network-Based Permanent Deformation Prediction Model of Unbound Granular Materials Subjected to Moving Wheel Loading.

The majority of existing regression models for unbound granular materials (UGMs) consider only the effects of the number of loading cycles and stress levels on the permanent deformation characteristics and are thus unable to account for the complexity of plastic deformation accumulation behavior influenced by other factors, such as dry density, moisture content and gradation. In this study, research efforts were made to develop artificial-neural-network (ANN)-based prediction models for the permanent deformation of UGMs. A series of laboratory repeated load triaxial tests were conducted on UGM specimens with varying gradations to simulate realistic stress paths exerted by moving wheel loads and study permanent deformation characteristics. On the basis of the laboratory testing database, the ANN prediction models were established. Parametric sensitivity analyses were then performed to evaluate and rank the relative importance of each factor on permanent deformation behavior. The results indicated that the developed ANN prediction model is more accurate and reliable as compared to previously published regression models. The two major factors influencing the magnitude of accumulated plastic deformation of UGMs are the shear stress ratio (SSR) and the number of loading cycles, of which the calculated influence coefficients are 38% and 41%, respectively, while the degree of influence of gradation is twice that of the confining pressure.