Accumulation Of Permanent Deformation Research Articles

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.

The Effect of a Liquified Wood Heavy Fraction on the Rheological Behaviour and Performance of Paving-Grade Bitumen

Biomass is one the most abundant renewable energy sources, and it can be processed through different thermochemical methods to obtain oils that can replace the petroleum bitumen used in road construction. For the construction industry to accept the bitumen replacement with bio-oil, it is necessary to know its properties and determine the applicability of conventional testing methods. This research utilized a liquified wood heavy fraction (bio-oil) obtained from waste wood through an innovative thermochemical liquefaction process. The aim was to investigate a kind of bio-bitumen produced by blending this bio-oil with paving-grade bitumen. The rheological behaviour in a wide temperature range, the performance relative to fatigue cracking and permanent deformation sensitivity, and the evolution with oxidative ageing were evaluated for the bio-bitumen and paving-grade bitumens. The bio-oil significantly affected the rheological behaviour of bitumen through an overall decrease in the phase angle and by failing the time–temperature superposition principle. The strong elastic response of the bio-bitumen improved resistance to fatigue and permanent deformation accumulation; however, resistance to oxidative ageing declined. Linear viscoelastic rheological indicators proposed in the literature to assess the material’s performance showed a similar trend of variation with oxidative ageing for bio-bitumen and paving-grade bitumen, though the indicators’ values could not be directly compared.

Numerical simulation for vibration-induced settlement and permanent deformation accumulation in permafrost subgrades of the Qinghai-Tibet Railway

Train-induced vibrations critically influence permafrost subgrade deformation. This study used ABAQUS secondary development to establish a finite element model of vibration-induced settlement for permafrost subgrades in the Qinghai-Tibet Railway (QTR) based on a cumulative plastic strain model. A numerical simulation method for cumulative vibration-induced settlement prediction considering seasonality, vibration frequency, train types, and global warming was proposed. The scientificity of the simulation was verified by monitoring data. Then, the influences of embankment height, ice-rich permafrost thickness, and initial mean annual ground temperature (MAGT) of the site on cumulative vibration-induced settlement and permanent deformation accumulation in permafrost subgrades were analysed. The study further quantitatively evaluated cumulative dynamic and static deformation in the DK1136 section under various global warming conditions. The results indicate that cumulative vibration-induced settlement primarily occurs near the ice-rich permafrost layer and is significantly influenced by ground temperature. Permanent deformation accumulation increases with increasing embankment height, ice-rich permafrost thickness and initial MAGT of the site. Permanent deformation accumulation primarily results from thaw consolidation of the permafrost layer, with vibration-induced settlement contributing approximately 20 %. For permafrost regions, an optimal railway embankment height of 3–3.5 m and effective mitigation of settlement issues involve lowering the ground temperature and the embankment weight. These findings provide essential insights for subgrade challenges in permafrost regions.

Dynamic mechanical performance of geogrid–waste tyre-reinforced railway ballast under cyclic loading

The accumulation of permanent deformation under cyclic loading in the granular bed is the main source of ballast track settlement. Therefore, studying the dynamic mechanical behaviour of reinforced railway track beds under cyclic loading is crucial. To reduce the accumulated of permanent deformation of railway track bed, geogrids–waste-tyre reinforced railway track bed was used to study in order to effectively control the permanent deformation of ballasted railway track bed. The test was conducted to investigate the mechanism of permanent deformation of geogrid–waste tyre-reinforced railway track bed through the evolution of cumulative plastic strain, permanent strain rate and dynamic elastic modulus of railway track bed under different confining pressures, dynamic stress amplitude, and amount of reinforcement. Results show that geogrid and waste tyre reinforcement have significant effects on the accumulated permanent deformation of the railway ballast. Geogrid reinforcement is better than waste tyres in improving the performance of the ballast fill. Reinforcement with geogrid significantly reduces the permanent strain rate, although the impact on this rate varies depending on the position and amount of reinforcement used. Notably, reinforcing the middle three layers of the track bed sample with waste tyres substantially decreases the permanent deformation rate. In contrast, the application of reinforcement across all five layers with waste tyres increases the permanent deformation rate. The dynamic elastic modulus of the track bed sample not only increases significantly but also rises with the dynamic stress amplitude due to the reinforcement of the geogrid and the waste tyre. The dynamic elastic modulus gradually stabilises with the increase in cyclic loading, indicating a stable accumulated deformation in the railway track bed.

A numerical framework for modelling settlements of railway ballast layers

Permanent deformation in ballast layers is a major contributing factor to the railway track geometry deterioration. In spite of a considerable amount of research on understanding and predicting performance of ballast layers, accurately capturing their settlements remains a challenge. In order to contribute to solving this important issue, a new numerical method for predicting ballast settlements is presented in this paper. This method is based on the finite element (FE) method combined with a constitutive model that captures permanent deformation accumulation in unbound materials under cyclic loading. This allows predicting permanent deformations of large structures and at large number of load cycles in a computationally efficient manner.The developed constitutive model is validated based on triaxial test measurements over wide range of loading conditions. Stress state in ballast layers has been examined with a 3D FE model, for several embankment structures and traffic load magnitudes. The determined stress distributions and loading frequencies were used as an input of the constitutive model to evaluate permanent strains and settlements of ballast layer. The influence of embankment structural designs and traffic loading magnitudes on the ballast layers settlements is examined and the results obtained are compared with the existing empirical performance models.

Deciphering Permanent Uplift Along the Pacific Coast of South America Through Signal Analysis of Various Tectonic Processes

AbstractThe tectonically active South American margin is characterized by the accumulation of deformation contributing to uplift of the Andean forearc at millennial time scales. However, the mechanisms responsible for permanent coastal uplift are debated, mainly because methodologically consistent, continental‐scale analyses of uplifted terraces have not yet been carried out for South America. Uplifted marine terraces are generally used to infer permanent coastal deformation and uplift; we used almost 2,000 measurements of last‐interglacial marine terraces to calculate an uplift‐rate signal on which we performed a wavelength analysis. The same spectral analysis was applied to tectonic and subduction parameters associated with accumulation of permanent deformation to detect possible links with the uplift‐rate signal. The uplift‐rate signal displays a constant background‐uplift rate along the margin, perturbed by changes at variable wavelengths. Similarities between its wavelength spectrum and the spectra of tectonic parameters suggest potential correlations pointing toward underlying processes. For example, crustal faulting is mainly responsible for short‐wavelength deformation; intermediate‐wavelength to long‐wavelength tectonic features indicate various extents of locked areas on the megathrust that relate to its long‐term seismotectonic segmentation. We suggest that moderate, long‐term background uplift is caused by major, deep earthquakes near the Moho, although records of such events are sparse. Due to their disparate occurrence, we infer accumulation of permanent deformation over millennial time scales through multiple, distinct uplift phases that are spatially and temporally distributed. Our study highlights the application and utility of a signal‐analysis approach to elucidate the mechanisms driving surface deformation in subduction zones at a continental scale.

Modeling Lifetime Performance of Monopile Foundations for Offshore Wind Applications

This paper explores the application of a numerical method for modeling pseudorandom cyclic loading, at very large cycle numbers, to the design of offshore wind turbine foundations. The work expands the development of a novel constitutive modeling framework, the hyper-plastic accelerated ratcheting model (HARM), for which the key constitutive equations and the calibration method are presented. HARM captures both the nonlinear hysteretic behavior during cycling and the accumulation of permanent deformation (ratcheting) with large cycle numbers in a rigorous, yet computationally efficient manner, enabling the computation of foundation response over a lifetime of loading. This paper demonstrates how the approach can be applied to the cyclic pile field testing from the pile soil analysis (PISA) project. Following calibration, the model is used to assess pile response to three load signals representative of operational and extreme loads throughout the lifetime of a full-scale wind turbine foundation: (1) a short storm, (2) a 35-h storm, and (3) lifetime loading. The paper discusses how computational efficiency can be achieved while maintaining a high level of calculation accuracy.

A new method for the analysis of foundation behavior in sand under drained high‐cycle loading

AbstractIn offshore technology, especially in offshore wind energy converters, permanent deformations of the structures must be limited. For that purpose, the accumulation of permanent deformation due to cyclic loading must be predicted as accurately as possible. To account for this accumulation in non‐cohesive soils, different approaches such as semi‐empirical methods, p‐y curve methods and numerical methods are available. Among the numerical approaches, the Stiffness Degradation Method (SDM) has the advantage of practical feasibility. However, it is only compatible with a relatively simple constitutive law and does not consider the influence of un‐ and reloading stress paths in the soil. With the basic concept of SDM, a new method termed Cyclic Strain Accumulation Method (CSAM) is proposed. In CSAM, the weaknesses of SDM, especially its incompatibility with advanced constitutive laws, are overcome, while retaining the practical feasibility as the main advantage of SDM. Through numerical calculations of a monopile, it is found that the CSAM is able to reproduce SDM results if the same material law is applied. The results of SDM and CSAM for the case of a vertical loaded strip footing have been presented. The comparison shows that the CSAM results are more realistic than the SDM results. Besides, CSAM is computationally more efficient and open for further optimisation. The effects of sophisticated material law and the consideration of un‐ and reloading are investigated. Results show that CSAM is a promising new approach to account for the deformation of foundations under cyclic loading in non‐cohesive soils.

Properties and Characterization Techniques of Graphene Modified Asphalt Binders.

Graphene is a carbon-based nanomaterial used in various industries to improve the performance of hundreds of materials. For instance, graphene-like materials have been employed as asphalt binder modifying agents in pavement engineering. In the literature, it has been reported that (in comparison to an unmodified binder) the Graphene Modified Asphalt Binders (GMABs) exhibit an enhanced performance grade, a lower thermal susceptibility, a higher fatigue life, and a decreased accumulation of permanent deformations. Nonetheless, although GMABs stand out significantly from traditional alternatives, there is still no consensus on their behavior regarding chemical, rheological, microstructural, morphological, thermogravimetric, and surface topography properties. Therefore, this research conducted a literature review on the properties and advanced characterization techniques of GMABs. Thus, the laboratory protocols covered by this manuscript are atomic force microscopy, differential scanning calorimetry, dynamic shear rheometer, elemental analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Consequently, the main contribution of this investigation to the state-of-the-art is the identification of the prominent trends and gaps in the current state of knowledge.

Railway formation design by elasto-plastic FEM mechanistic-empirical approach

A design method for conventional railway track formations to limit deformations in fine-grained subgrades is proposed. It is based on previous performance-based design methods with the important distinction that two-dimensional mechanisms are considered. Advanced hardening plasticity constitutive models are used for the subgrade to predict permanent deformation under a single loading directly, rather than by elastic analysis and approximate empirical transfer functions, before using empirical relationships to predict permanent deformation accumulation of the subgrade under successive loadings. The approach was validated by back-analysis of a laboratory test and full-scale trial. A parametric study identified a strong correlation between mobilised subgrade shear strength and permanent strain and between mobilised track bearing capacity and permanent subgrade deformation – correlations that could streamline design significantly. A strain rather than stress-based criterion for subgrade failure was found to be more appropriate since it takes account of the contribution of ballast strength at resisting permanent strain in the subgrade. The benefits of geogrids in granular layers on subgrade strains can be directly assessed using this method. Simple, approximate equations to determine permanent subgrade strain and deformation are derived that could be used for rapid non-FEM based optioneering prior to more rigorous, time consuming, analysis being performed.

Use of raw sugarcane molasses as a partial replacement of asphalt binder: An experimental investigation

Bio-bitumen is becoming 'talk in the air' within the pavement community due to its sustainable advantages. While it is not easy to replace the conventional bitumen, which is one of the oldest engineering material, increasing environmental concerns and oil crisis demands at least partial, if not complete, replacement of bitumen. In this study, raw sugarcane molasses (SM), a by-product obtained from the sugarcane industry, was used as a partial replacement of asphalt binder. Several tests on binders and mixtures were carried out to assess its suitability for asphalt pavement. The optimum dosage of SM was found to be 25% by weight of bitumen. VG30 modified with 25% SM had rutting and fatigue performance similar to, or improved, compared to the control binder. Irrespective of the aggregate source, SM modified mixes showed satisfactory performance in terms of moisture resistance, fatigue resistance, and accumulation of permanent deformation. Statistical analysis showed that there is no significant impact of binder type (VG30 and 25SM) on the performance of asphalt mixtures. Therefore, 25% molasses can be successfully used to partially replace the conventional bitumen, which in addition to being a sustainable technology, will reduce the cost of binder in the mix by approximately 21%.

Evaluation of the effects of textile fibre derived from end-of-life tyres (TFELT) on the rheological behaviour of asphalt binders

End-of-Life Tyres (ELT) consist of rubber, steel and textile fibre (TFELT). Unlike rubber and steel, the possibilities for the re-use of TFELT are limited, and its final disposal is an environmental problem. This article explores an alternative re-use of TFELT as an additive for asphalt binder (AB). The TFELT was characterised using scanning electron microscope (SEM), polarized microscopy and thermogravimetric analysis. Two Asphalt Binders (AB14 and AB24) and three addition percentages (0.1%, 0.3% and 0.5%) were evaluated. The effects on the physical properties at high, intermediate and low temperature were studied by determining the softening point, penetration and FRAASS breaking point. We also evaluated the effects on the rheological properties, by determining the rutting and fatigue parameters at different states of ageing (short and long term). Resistance to the accumulation of deformations was measured by applying the Multiple Stress Creep Recovery test (MSCR), and resistance to fatigue by the Linear Amplitude Sweep test (LAS). The results showed significant effects in reducing the accumulation of permanent deformation, by up to 40% for the addition of 0.5% TFELT, without any reduction in properties of resistance to thermal cracking.

A 3D-FE Model for the Rutting Prediction in Geogrid Reinforced Flexible Pavements

Permanent deformation (rutting) is an important disturbing failure on flexible road pavements. This phenomenon appears on the flexible pavement as longitudinal depressions, and it is a consequence of the degradation of materials under high traffic loading based on consolidation/densification, surface wear, plastic/shear flow, and mechanical deformation. Hence, the rutting phenomenon depends on the accumulation of permanent deformations on pavement surfaces subjected to repeated wheel loads. In recent years, several studies have confirmed that the service life of asphalt pavements can be increased by using geosynthetics between or within layers because of the improved mechanical properties. The aim of this paper is to present the results of the 3D-finite element (FE) simulations and the development of the rutting phenomenon in a traditional flexible pavement and a reinforced one, both subjected to a cyclic load. Through Abaqus/CAE software, a road section reinforced by a geogrid was analyzed and compared with a traditional road section to investigate the advantages given by the geosynthetic completely embedded at two-thirds of the asphalt concrete layer (AC) in terms of permanent deformations. The results show the capability of the proposed FE study, that uses the plasticity model of Drucker-Prager for unbound materials combined with the simple creep law to model HMA layers to predict the permanent deformation distribution.

Plasticity-Based Method for the Design and Analysis of Cold Recycled Pavement Layers

Abstract Asphalt cold recycling technologies allow the use of up to 100 % reclaimed asphalt pavement (RAP) from an existing asphalt pavement to construct new base layers and new subbase layers. Bituminous stabilized materials (BSM), obtained from cold recycling technologies, are susceptible to traffic-induced accumulation of permanent deformation. In the current design methods, BSM pavement layers are typically assumed to have a linear elastic response under traffic loading application, and this does not account for plasticity initiation and accumulation in the material. This research study provides insight on how to integrate plasticity behavior in numerical simulations of rehabilitated pavement structures with BSM. A BSM mixture prepared with 1.5 % cement by weight of total mixture and 1.5 % foamed asphalt binder content by weight of dry aggregates is characterized in the laboratory. Subsequently, a three-dimensional elastic-perfectly plastic finite element model is developed for the simulation of triaxial shear strength tests. Lab measured force-displacement curves are matched with the numerical simulations at different confining pressures. The calibrated mechanical properties are then used as input parameters in multilayer pavement models for pavement evaluation. Different pavement structures with and without BSM layers are compared in terms of a maximum allowable number of loading repetitions before reaching a 20-mm rut depth on the surface of the pavement. The results indicate that structures with BSM and traditional granular base layers yield comparable results in terms of rutting potential. In addition, the study presents a framework for the design and analysis of cold recycled pavement layers and a method to integrate the plasticity behavior of partially-bonded and unbounded layers for pavement evaluation.

DEPENDENCE OF THE PROPERTIES OF SULFUR AND PEROXIDE VOLCANISES BASED ON A MIXTURE OF ISOPRENE WITH POLYVINYL ACETATE ON THE STRUCTURE OF THE VOLCANIZATION NETWORK

The effect on the crosslinking process of modified isoprene rubber (SKI-3-PVA) with the participation of sulfur and dicumyl peroxide (PD) in the presence of hexachloroparaxylene (HCPA) and 2,4-dichloro-6-dimethyl-amino sym triazine was studied. It was found that, depending on the length of time, the number of crosslinks in these systems (SKN-3-PVA + sulfur + GHPK + ZnO; SKI-3-PVA + PD + GHPK) is 2.5x105 and 1.9x105 mol / cm³, respectively, per Based on the observed changes in the parameter of the spatial grid of the crosslinked samples, the yield of effective crosslinks was calculated. It was shown that in the presence of dicumyl peroxide in filled systems, the number of crosslinks decreases, and a decrease in crosslinks is also observed. Comparative tests of elastomeric materials based on SKI-3 - PVA copolymers in liquid aggressive media were carried out. Sol-gel analysis found that with an increase in the content of the copolymer in isoprene, the concentration of the number of cross-linked molecules in the copolymer increases. It is shown that the physical and mechanical properties of filled vulcanizates are inferior to sulfuric ones in strength properties, but surpass peroxide ones in thermal aging and the action of solvents. It was found that an increase in aging with an increase in the heating time of the samples indicates the formation of additional cross-links. The role of zinc oxide in the peroxide crosslinking of the SKI-3 - PVA copolymer has been studied. It was found that the introduction of zinc oxide has a noticeable effect on the rate of sulfur and peroxide crosslinking of mixtures based on SKI-3 - PVA copolymers, an increase in the structuring time of mixtures, destructive processes are observed, and the number of crosslinks and crosslinks decreases. It was found that the physical and mechanical properties of peroxide vulcanizates are inferior to sulfuric ones in strength properties, but they are superior to peroxide ones in thermal aging. It is shown that an increase in the resistance to aging with an increase in the heating time of the samples indicates the formation of additional cross-links. As a result of the reaction with oxygen and the accumulation of interacting polar groups. A decrease in the degree of swelling is associated with the formation of C-C chemical bonds in elastomers, it effectively participates in the formation of cross-links during peroxide vulcanization. The nature of the interaction of sulfur PD, HCPC, and DCDEAST with elastomers was judged by the change in the conditional number of crosslinks (n´c) and the number of crosslinked molecules (1 \ Ms) in unfilled sulfur and peroxide vulcanizates. It is shown that in sulfur peroxide mixtures based on SKI-3-PVA with the proposed agents at room temperature it causes the formation of effective crosslinks, and with an increase in the duration of heating in systems 1, 2, the number of crosslinked molecules increases. An increase in resistance to aging with an increase in the heating time of the samples indicates the formation of additional cross-links as a result of the reaction with oxygen and the accumulation of interacting polar groups. A decrease in the degree of swelling is associated with the formation of C - C chemical bonds in elastomers, effectively participating in the formation of a network of crosslinks during peroxide vulcanization. Thus, the analysis of the results of the studies performed allows us to conclude that elastomers based on the isoprene copolymer SKI-3-PVA obtained with the participation of vulcanizing agents of sulfur and peroxide (PD) in the presence of hexachloroparaxylene (HCP) and triazine compounds are superior to those known in terms of thermal stability. aging in strength and accumulation of permanent deformation in aggressive environments. Keywords: isoprene, polyvinyl acetate, hexachloroparaxylene, peroxide dicumil, vulcanization, modification

A study on the behaviour of offshore suction bucket foundations under cyclic axial compressive loading

ABSTRACT Suction bucket foundations of offshore wind turbines (OWTs) are subjected to cyclic loads induced by wind and waves. The behaviour of buckets embedded in saturated sandy soil subjected to cyclic axial compression was studied using a finite element (FE) model. Accumulation of permanent soil deformations and excess pore water pressure in saturated sandy soil due to cyclic axial compression were taken into account by a fully coupled two-phase model combined with a hypoplastic constitutive model with intergranular strain. The Kozeny–Carman relationship was adopted for porosity–permeability dependence. The main focus was dedicated to the changes in load transfer via components of bucket with increasing number of load cycles. Loads that led to progressive failure, attenuation and shakedown behaviour were described. Effects of soil permeability and density, load frequency and amplitude, the bucket aspect ratio on the load transfer and bearing mechanism of the bucket were presented.

Influence of Temperature on Mechanical Properties of Asphalt Concrete Mixture

Asphalt binder is a thermoplastic material that conducts as an elastic solid at lower service temperatures or throughout fast loading rate. At a high temperature or slow rate of loading, asphalt binder conducts as a different liquid. The classical duplication generates a required to assess the mechanical properties of asphalt concrete at the anticipated service temperature to reduce the stress cracking, which happens at lower temperatures, fatigue, and the plastic deformation at higher temperatures (rutting). In this study, an achievement was made to assess the effect of temperature on the mechanical characteristics of asphalt concrete mixes. A total of 132 asphalt concrete samples were attended utilizing two asphalt cement grades (40-50) and (60-70), and one aggregate gradation (type III A for wearing course) SCRB (R/9, 2003). The specimens were then tested at five different temperatures represented by 5, 15, 25, 40, and 60 °C to estimate their mechanical characteristics, including resilient modulus (Mr), permanent deformation, and fatigue features as Marshall features. The average resilient modulus (Mr), which belongs to a temperature of 5°C, was 328036 psi revealing an approximate loss of 88% of its strength in resilient modulus when there is an increase in temperature over 60°C. Meanwhile, there is an increase in the permanent deformation accumulation rate (slope value) of about three folds as the temperature changes from (5-60) °C whereas the fatigue life reduces 32 % with the rise in temperature from (5-25) °C.

Mechanical Response of Granite Residual Soil Subjected to Impact Loading

When constructing subway tunnels, blasting is commonly used to deal with granite boulders in weathered granite formations. It is, therefore, crucial to evaluate how the blasting-induced impact loading affects surrounding granite residual soil. By means of laboratory impact tests at different conditions, this paper presents the mechanical responses of granite residual soil. High-speed impact loading affects the soil in two ways, namely, (1) increasing the shear resistance; and (2) damaging the soil structure. Cyclic impact tests reveal the critical peak stress Acr, which approaches soil apparent preconsolidation pressure. When the peak stress exceeds Acr, the soil is severely damaged and the accumulative deformation increases sharply, indicating that the cementation of soil is destroyed. Besides, the soil is most resistant to impact loading at a threshold value of the loading frequency fth and exhibits better resistance under high confining pressures. A framework was proposed that reflects soil structural damage and within which the failure mechanism under impact loading is explained. The damage to the soil structure generated with energy dissipation is the decisive factor in soil failure, and the accumulation of permanent deformation is the direct reason why soil fails. Three response modes were proposed for studied soil under impact loading. This research provides parameters for subway tunnel construction and enhances the understanding of granite residual soil under impact loading.

Permanent deformation modelling of large-size unbound pavement materials tested in a heavy vehicle simulator under different moisture conditions

ABSTRACT Climate changes alter the environmental conditions which pavement design is based on, invalidating empirical design methods. Transition to mechanistic design requires the ability to model the behaviour of pavement materials under relevant environmental conditions. An accelerated pavement test (APT) is designed to test two instrumented pavement structures under moisture conditions which are altered by raising the groundwater table (GWT). Open-graded and well-graded subbase materials are used to investigate the effect of gradation on moisture dependency. Pavement response behaviour is modelled using a non-linear elastic (NLE) approach. Accumulation of permanent deformation under different moisture conditions is calculated by two models and compared to measured surface rutting. Moisture transport through the structures differs due to the subbase gradation. Increased GWT accelerates the accumulation of permanent deformations in both structures, identified by both models. One model provides a significantly better fit to the subgrade deformations and the width of the rutting profile.

Effect of Rubber Incorporation on the Behavior of Pavement Cemented Mixtures under Cyclic Flexural Loading: A Preliminary Study

Abstract The main purpose of this study is to investigate the effect of replacing natural aggregate with crumb rubber on the behavior of cement-stabilized crushed aggregate mixtures subjected to cyclic flexural loading. This behavior is evaluated in terms of fatigue life and resilient flexural modulus. The damage to the modified mixtures was also examined utilizing permanent deformation accumulation and degradation of resilient flexural modulus during a fatigue test. To ensure the same packing of aggregate mixture, the natural aggregate was replaced by waste tire rubber particles of similar gradation. Four volumetric replacement percentages (0 %, 15 %, 30 %, and 45 %) of the 6-mm fraction size were utilized. The results revealed that the inclusion of rubber improves the fatigue life of cement-stabilized aggregate mixtures and reduces the resilient flexural modulus. Damage investigation showed that the rubber has little effect on the degradability of the modulus during fatigue. However, more permanent deformation was accumulated after modification with crumb rubber. It was observed that the applied stress ratio affected the different phases of permanent deformation accumulation. It is suggested that the mechanism of fatigue improvement of rubberized mixtures occurs by delaying crack propagation and absorbing the energy during the microcracking stage.