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The soils across Lake Texcoco (LT) basin are notorious for the presence of highly compressible salt-affected lacustrine clays. The geological formation of the area accompanied by the unmonitored flow of water from Mexico City region has resulted in a unique sodium-rich clay that is highly plastic (plasticity index~200), and impermeable ( k~1.5 × 10−9 m/s) and possesses low compressive strength (unconfined compressive strength

The prediction of vertical movement in expansive soil is important primarily for the purpose of designing foundations and other horizontal structural elements such as pavements. Most of the existing approaches to predict vertical movement are conservative and over-predict soil movement and are based on field measurements from localised soil data sets. Therefore, a suction-based approach is adopted in this study, which has the advantage of considering the effects of both moisture energy (suction) and mechanical stresses that surround the soil. A simplified Excel spreadsheet is programmed to facilitate estimation of potential vertical movement (PVM) in subgrade soils using physical properties of the soil along with local climatic indices. The soil database from the Natural Resource Conservation Service (NRCS) is used to develop prediction models of suction compressibility index ([Formula: see text]) and diffusivity coefficient ([Formula: see text]) and is subsequently used in the spreadsheet. A contour map of the maximum PVM values for the entire continental USA is generated using the geographic information system platform and the estimated results from the spreadsheet. Finally, measured international roughness index values collected from the massive long-term pavement performance database are used to validate the calculated PVM values.

Lime stabilization is a common technique used to improve the engineering properties of clayey soils. The process of lime stabilization can be split into two parts. First, the mobilization and crowding of [Formula: see text] ions or [Formula: see text]molecules from hydrated lime at net negative surface charge sites on expansive clay colloids. Second, the formation of pozzolanic products including calcium-silicate-hydrate (C-S-H) because of reactions within lime-soil mixtures. The pozzolanic reaction is generally considered to be more durable, while the [Formula: see text] adsorption has been associated with more easily reversible consistency changes. This study offers a protocol to assess whether the stabilization process is dominated by durable C-S-H (pozzolanic) reactions or a combination of cation exchange and pozzolanic reactions. Expansive clays with plasticity indices >45% from a major highway project in Texas are the focus of lime treatment in this study. The protocol consists of subjecting lime-soil mixtures to a reasonable curing period followed by a rigorous but realistic durability test and investigating the quality and quantity of the pozzolanic reaction product. Mineralogical analyses using quantitative X-ray diffraction (XRD) and thermogravimetric analysis (TGA) indicates the formation of different forms of C-S-H. In addition, geochemical modeling is used to simulate the lime-soil reactions and evaluate the effect of pH on the stability of C-S-H. The results indicate C-S-H with Ca/Si ratio of 0.66 as most the stable form of C-S-H among other forms with Ca/Si ratio ranging from 0.66 to 2.25. The effect of reducing equilibrium pH on C-S-H is also evaluated. A reduction in pH favored dissolution of all forms of C-S-H indicating the need to maintain a pH ≥ 10.

Hydrated lime is widely used as a mineral filler to improve several properties of bituminous materials such as reducing the susceptibility of the composite to moisture-induced damage. Although experimental evidence supports the efficacy of using hydrated lime as a mineral filler, the molecular scale mechanism of reactivity of hydrated lime within the bitumen to reduce moisture damage is not understood. This is important when considering the durability of structural applications of bituminous materials such as asphalt concrete pavements subjected to both environmental and loading extremes. In this study, the interaction between hydrated lime and the key molecular building blocks of bitumen is modeled using density functional theory and compared against analogues of other common fillers such as calcite and quartz. Free energies of dissociation (ΔGdissoc) are calculated, and the nature of the bonds is characterized with contour maps of the Laplacian of the electron density. Hydrated lime is capable of reacting with specific functional groups in bitumen moieties and developing strong, water-resistant complexes. Among the functional groups investigated, carboxylic acids are the preferential reaction sites between hydrated lime and the bitumen moieties. Values as high as ΔGdissoc = +49.42 kcal/mol are reported for hydrated lime with water as the surrounding solvent. In contrast, analogues of calcite (ΔGdissoc = +15.84 kcal/mol) and quartz (ΔGdissoc = +4.76 kcal/mol) are unable to chemically react as strongly as hydrated lime in the presence of water. Contour maps of the Laplacian of the electron density indicate that the bonds between hydrated lime and model asphalt moieties are of an ionic nature. The atomistic modeling results correlate with thermodynamic calculations derived from experimental constants and are consistent with infrared spectrometric data.

This study is to characterise rheological properties of sulfur-extended asphalts with/without crumb rubber at high, intermediate, and low temperatures using standard asphalt binder tests. Four dosa...

The slopes along the Friant-Kern Canal were last treated in the 1970s with 4% quick lime to mitigate issues related to slope failure caused by expansive Porterville soils. The immediate benefits of lime treatment were well documented by the Bureau of Reclamation. However, questions remain over the long-term durability of lime-treated materials. In this study, we compare the engineering properties and changes in the soil mineralogy of treated and untreated sections to establish the effectiveness of lime after more than 40 years of performance. A geochemical model was developed using the GEM-Selektor program to simulate the geochemical reactions in the soil-lime system and predict stable pozzolanic products. The experimental results show a reduction in the plasticity index from 23 to 6 after lime treatment together with a tenfold increase in strength. Lime addition lowers the risk of volumetric expansion and erosion in soils from moderately high to very low. Further, a pH increase from 6.30 to 8.90 in lime-treated sections indicates that lime treatment continues to be effective. X-ray fluorescence analysis shows the presence of Ca2+ ions in quantities similar to the initial treatment dosage indicating negligible leaching of lime. The geochemical model provides evidence of the formation of pozzolanic products in the soil-lime system which was validated using thermogravimetry analysis. The performance history of the Friant-Kern Canal together with the findings of this study affirm the long-term durability of lime treatment on this project and strengthens the case for using lime in the repair of hydraulic structures.

The prediction of stress, strain, and permanent deformation (rutting) in granular layers is a challenging task and requires sophisticated constitutive relationships. This paper uses a mechanistic-based model to predict the rutting of granular layers in airfield pavements when subjected to different tire pressures. This model incorporates Drucker–Prager (D-P) plasticity and includes an evolving hardening function that accounts for the changes in the hardening function in cyclic loading. The developed model is implemented in Pavement Analysis Using the Nonlinear Damage Approach—Airfield Pavements software developed for performance prediction of airfield pavements. Using this model, it was possible to predict the permanent deformation of airfield pavements when subjected to C-17 and C-130 aircraft wheels. The model was validated against the test sections tested at the Engineering Research and Development Center for two different wheel loads.

Suction in subgrade layer reaches an equilibrium condition several years after construction of the pavement. The equilibrium suction has a direct influence on the resilient modulus of subgrade soil. In the current mechanistic-empirical pavement design guide, equilibrium suction is determined based on the empirical relationship with water table depth. However studies have shown that other critical factors also influence equilibrium suction. In this study, a new mechanistic-empirical model is presented to predict equilibrium suction considering the effects of physical properties of the soil and climatic factors. A simple regression model is also generated to predict the equilibrium suction from readily available parameters i.e., Thornthwaite moisture index (TMI), plasticity index (PI), and dry suction value at surface ( u dry ). In the final section of this paper, the effects of TMI and vegetation on equilibrium suction are evaluated for various soil classes and TMI ranges, respectively. A contour map of the equilibrium suction values for the entire continental United States has been generated using the geographic information system (GIS) platform and followed by the model predictions.

This paper presents a systematic and straightforward analysis procedure to extract the material parameters associated with a coupled nonlinear viscoelastic (VE), viscoplastic (VP), and hardening-relaxation (HR) constitutive model for asphalt mixtures. The recoverable and irrecoverable strain are represented by Schapery nonlinear VE model and Perzyna-type VP theory, respectively. A HR model is proposed to consider the relaxation of hardening. Dynamic moduli and repeated creep-recovery tests are used to calibrate the coupled VE-VP-HR model. The model is then validated against independent experimental data. Results show that the VE-VP-HR model has the ability to capture the response of asphalt mixtures subjected to various loading paths.

This study aims at employing the benchmarking strategy for assessing the state of the practice of the pavement industry in regions that have limited access to or lack the prerequisites for effectiv...

Cohesive zone modelling (CZM) has been used to model complex fracture process of various materials including bituminous materials. Among various CZM methods, this study used an extrinsic nonlinear viscoelastic cohesive zone (NVCZ) model implemented in a finite element method to efficiently predict nonlinear-inelastic fracture behavior of bituminous materials from crack nucleation, initiation, and propagation to complete failure. To examine the extrinsic NVCZ model, two fine aggregate matrix (FAM) bituminous mixtures with different fillers were evaluated experimentally and compared with the model’s numerical results. Laboratory tests were performed to obtain model inputs and outputs, and a parametric analysis of the NVCZ model was conducted to investigate the influence of each model parameter in the FAM fracture process. Linear viscoelastic properties were obtained using dynamic frequency sweep tests, and NVCZ model parameters were identified using an integrated experimental-numerical calibration procedure that employed semicircular bending (SCB) tests and finite element simulations. To validate the model, the experimental and numerical simulation results of an indirect tensile (IDT) test were compared. The numerical modeling results agreed well with the laboratory testing results. The outcomes of this study suggest that the extrinsic NVCZ model can be an efficient tool to predict the highly nonlinear and viscoelastic fracture processes of binding constituents in bituminous materials.

Smectite-bearing, expansive clayey soils are common in many areas of Texas, causing damage to pavements and building foundations by cyclic shrinking and swelling. The mechanism of shrinking...

A model is developed herein for predicting moisture-induced crack growth during a short-term rain event, considered herein to be of duration not greater than 2 hr, in a pre-cracked asphalt concrete...

This paper proposes a straightforward procedure to characterize the nonlinear viscoelastic response of asphalt concrete materials. Furthermore, a model is proposed to estimate the nonlinear viscoelastic parameters as a function of the triaxiality ratio, which accounts for both confinement and deviatoric stress levels. The simplified procedure allows for easy characterization of linear viscoelastic (LVE) and nonlinear viscoelastic (NVE) responses. First, Schapery’s nonlinear viscoelastic model is used to represent the viscoelastic behavior. Dynamic modulus tests are performed to calibrate LVE properties. Repeated creep-recovery tests at variable deviatoric stress levels (RCRT-VS) were designed and conducted to calibrate the nonlinear viscoelastic properties of four types of mixtures used in the Federal Aviation Administration’s National Airport Pavement and Materials Research Center test sections. The RCRT-VS were conducted at 55°C, 140 kPa initial confinement pressure, and wide range of deviatoric stress levels; mimicking the stress levels induced in a pavement structure under traffic. Once calibrated, the model was validated by comparing the model predictions and experimental measurements at different deviatoric stress levels. The predictions indicate that the proposed method is capable of characterizing NVE response of asphalt concrete materials.

Reliability has been incorporated in many pavement design procedures to account for the effects of inputs variabilities and uncertainties on predicted performance. The American Association of State Highway and Transportation Officials (AASHTO) mechanistic empirical pavement design guide (MEPDG) computes the reliability of pavement sections with the assumption that the variability of predicted distresses follows normal distribution. This approach does not account for the systematic contribution of each design input variability on the overall output variance. This paper evaluates a two-component reliability analysis methodology for pavement application. The two-component reliability analysis methodology uses a response surface method (RSM) for a surrogate model generation and the first order reliability method (FORM) for reliability computation. Three different response surface methods (central composite, Box–Behnken and Doehlert designs) were implemented and statistically verified for their suitability for surrogate model generation. The two-component reliability analysis methodology was further utilized for the generation of partial safety factors for the development of a load and resistance factor design (LRFD) procedure for pavement applications. Field pavement sections with a wide range in design inputs and target reliabilities were used to evaluate the proposed reliability analysis methodology. The results have shown that the three RSM can be used effectively for pavement reliability problems.

Directional dependency of the materials properties in granular soils is an integral component of the analysis and design of pavement foundations. Laboratory determination of such anisotropic properties is often overlooked by design engineers due to the lack of available protocols, equipment, time constraints, and budgetary issues. This research strives to bridge this gap by investigating an alternative approach to provide a practical and reliable framework to estimate the level of anisotropy of unbound granular materials. To achieve this objective, an experiment design was developed to establish a comprehensive aggregate feature database. Nonlinear and cross anisotropic material properties were determined using Variable Dynamic Confining Pressure (VDCP) stress path tests in the laboratory. Particle geometry was characterized using the Aggregate Imaging System (AIMS). Scale parameters and shape parameters of the form, angularity and textural properties of the particles were incorporated in the aggregate database to account for the shape-induced anisotropy of particulate soils. Moisture state and density parameters were also incorporated in the database for further post processing. Several neural network models with different architectures were developed, and the performances of the models were assessed based on an unseen set of data. The impact of the neural network topologies on the performance of the models were also investigated in this research effort. The results indicate that increasing the number of hidden layers has negligible impact on the performance of the models. Additionally, a series of sensitivity analyses were performed to investigate the level of contribution of aggregate features on the anisotropic behavior of unbound granular materials. The results of the sensitivity analysis underscores the influence of aggregate angularity, fines content, surface macro-texture, as well as the parameters of the stress path tests, on the orthogonal load distribution capacity of aggregate layers.

The effect of different configurations of normal contact stresses on the rutting performance of asphalt concrete overlays on a soft and stiff Crushed Aggregate Base (CAB) layer is investigated. A three-dimensional (3-D) finite element model of a pavement structure is generated. The effect of different types of simplified normal contact stresses and a realistic 3-D normal stress on the rutting performance is investigated. Since the failure mechanism of asphaltic materials at high temperature is mainly related to the flow of the material, the viscoelastic and viscoplastic constitutive relationships coupled with the hardening-relaxation mechanisms are utilized to represent the behavior of asphalt concrete layer. This constitutive relationship is part of the PANDA (Pavement Analysis using Nonlinear Damage Approach) model developed by the authors and their collaborators. As the result of simulation, the magnitude of the rut depth on the asphalt concrete layer is generally determined to be inversely proportional to the stiffness of the CAB layer, and the rut depth on the asphalt concrete layer under the realistic 3-D normal stress is about 1.5 times greater than the rut depth under uniformly distributed normal stress.

This paper provides a review of the research on use of polymers for soil stabilization in pavement and geotechnical engineering. First, the properties impacting the effectiveness of widely used polymer classes, including geopolymers, biopolymers, and synthetic organic polymers are discussed. These include types and ratios of the precursor and activator of geopolymers, molecular weight, particle size, charge, conformation, solubility, viscosity, pH, and moisture behavior of organic polymers. Next, the paper reviews the mechanisms governing stabilization of soils with the various polymer classes. The key mechanisms for organic polymer–clay interactions are electrostatic forces and entropy increase, which contribute differently depending on whether the polymer is cationic, neutral, or anionic. On the other hand, the interactions between polymers and coarse-grained soils composed predominantly of sands are mainly attributed to three types of structural changes: a thin film covering sand particles, the formation of polymer ties connecting noncontacted neighboring particles, and the development of adhesion between particles. The mechanism of geopolymer stabilization is through the formation of a sodium and/or calcium aluminosilicate gel, which bind the surrounding soil particles and harden into a denser, stronger matrix. The engineering properties of the soil types after stabilization using polymers, including strength improvement, permeability reduction, swell and shrinkage inhibition, and durability and stability enhancement are discussed. Finally, the paper highlights the challenges for wider use of polymer stabilization of soils including limited evaluation standards, life-cycle cost considerations, and moisture susceptibility. To this end, some future research direction to promote the widespread use of polymers in soil stabilization are recommended including the need for establishment of standard testing protocols, evaluation of in-situ properties of polymer stabilized soils, resolution of durability issues and further in-depth examination of stabilizing mechanisms.

Ionic stabilization is one of the non-traditional methods of soil stabilization. It is an advantageous stabilization method of being economic and utilizing liquid agents that can easily diffuse through soil and stabilize it. While several studies have been undertaken on ionic stabilization, the experience is still not sufficient enough and thus more research work is needed to understand the mechanism of ionic stabilization. This paper presents experimental results of soils treated in the field and the laboratory by an ionic acidic stabilizer. The experimental tests involve one-dimensional swelling, three-dimensional shrinkage, and suction measurements on treated and native natural soils from Texas and Oklahoma. The results show that the stabilizer minimized the percent swell at least to the half but had no considerable effect on the shrinkage. The results of wetting–drying cycles showed a significant reduction of the volume change rate of treated soils. Treated soil in the field revealed a noticeable reduction in suction. However, suction at high values obtained by a chilled-mirror psychrometer of treated soils manifested no considerable change from natural soils. Overall, the variation in suction measurements came consistent with the volume change results. The latter finding provides an encouragement in utilizing suction as a tool to examine the effectiveness of ionic stabilization.

Asphalt concrete is a highly heterogeneous mixture with complicated microstructures. This heterogeneity strongly affects the overall three-dimensional (3D) mechanical behavior and damage-associated performance of asphaltic mixtures, which makes accurate modeling a challenge. This paper presents a computational microstructure model using multiple two-dimensional (2D) finite element microstructures as an alternative and efficient approach to predict the actual 3D fracture-associated response of asphaltic mixtures. To simulate crack initiation and propagation, an autonomous algorithm was developed to efficiently generate multiple 2D microstructures using image processing of scanned microstructures, a phase-based segmentation module to separate particles and the surrounding matrix phase, and a finite element meshing module that allows cohesive zone elements to be embedded within the mixture microstructure. Aggregates were considered elastic, but viscoelastic and fracture properties were used to model the binding matrix phase. The validity of the multiple 2D microstructures approach was statistically investigated by comparing the model simulation results with the corresponding experimental results from two cases: (1) a three-point bending beam testing of a gap-graded mixture; and (2) a semicircular bending beam testing of a conventional dense-graded mixture. The 2D simulation results of multiple microstructures could generally capture 3D viscoelastic fracture behavior, but the prediction power of the modeling was reduced when volume fraction, distribution of coarse aggregates became high and complex. With some limitations to be further resolved, this study implies that multiple 2D microstructures can appropriately represent the complex viscoelastic-fracture behavior of 3D mixtures, which can significantly reduce the experimental and computational costs for laboratory mixture tests and 3D microstructure simulations with fracture, respectively.

Rapid traffic loading induces pore water pressure inside partially or fully saturated interconnected cracks and voids of asphalt concrete. The induced pore pressure contributes extra stresses within the pavement and accelerates crack evolution and propagation. Crack propagation facilitates diffusion of moisture through the solid phase and accelerates the degradation of the time-dependent stiffness and strength of asphalt concrete. Therefore, it is imperative to consider the coupled effects of pore water pressure, moisture diffusion, and mechanical loading on asphalt concrete pavement. The effect of pore water pressure was considered by using the effective stress concept inside deformable media. Biot’s approach was used and coupled to the nonlinear viscoelastic and viscodamage (moisture and mechanical) constitutive relationships for asphalt concrete. The models were implemented in PANDA, a finite element code developed at Texas A&M University. Capabilities of the proposed framework and constitutive relationships were demonstrated through the simulation of several realistic microstructural representations of asphalt concrete. The results of numerical simulations demonstrated how the effect of pore water pressure can intensify damage within asphalt concrete and reduce its strength. Therefore, this outcome emphasizes the importance of incorporating the effect of pore water pressure in investigating the response of asphalt concrete.

The fracture resistance of a chemically stabilized base or subbase layer is important to the durability and sustainability of a pavement structure. Thus, an appropriate test protocol to characterize the fracture resistance of stabilized bases, subbases, and subgrade soils is essential to the design of pavement materials and structures. This paper proposes a protocol developed on the basis of the semicircular bending test to measure fracture resistance (i.e., fracture energy and fracture toughness) of chemically stabilized material. The effects of three test variables, including specimen thickness, notch length, and loading rate, on fracture properties were investigated, and appropriate values for these test variables were selected for the semicircular bending test protocol. The proposed semicircular bending test method was successful in characterizing the fracture resistance of three chemically stabilized materials. To address fracture properties of the chemically stabilized material more definitively, three-dimensional zone modeling was used and the simulations agreed very well with the experimental results. Both the fracture properties obtained from the experiment and the cohesive zone modeling indicated that polymer-stabilized limestone exhibited a much higher fracture resistance than cement-stabilized limestone and cement-stabilized sand. However, the polymer used demonstrated susceptibility to degradation in the presence of water. Correction of this limitation is the focus of ongoing research on this type of polymer.

Oxidative aging is one of the most important processes affecting the time-dependent response of asphalt concrete materials, which subsequently results in brittleness of the material and fatigue damage. This paper proposes a mechanistic-based constitutive relationship of oxidative aging based on the evolution of a physically-based aging state variable. The aging constitutive relationship is coupled to the viscoelastic response of asphalt concrete by making both the creep compliance and relaxation time terms a function of the aging variable. The coupled oxidative aging-viscoelastic constitutive relationship is calibrated by analyzing the results of dynamic modulus testing conducted at different temperatures and frequencies on aged and unaged laboratory specimens with different air void contents ranging from 4% to 10%. The coupled constitutive relationships is validated against multiple repeated creep-recovery tests conducted on aged and unaged specimens at different stress levels, temperatures, and air void contents. The results illustrate the capabilities of the coupled oxidative aging-viscoelastic constitutive relationship to predict the viscoelastic response of aged asphalt concrete materials. Finally, the effect of oxidative aging on viscoelastic performance of aged pavement structures is investigated by: (a) applying a state-of-the-art experimental-computational method to determine oxygen diffusivity of asphalt concrete mixtures, and (b) conducting 2D finite element (FE) simulation of aged and unaged pavements.

Warm-mix asphalt (WMA) technologies have been used extensively in the last decade. The benefits of WMA have motivated stakeholders to expedite the implementation of this technology. However, some research studies have raised concerns regarding WMA laboratory performance in terms of resistance to moisture damage, while WMA has demonstrated good performance in the field. These experiences led to further research to understand the fundamental characteristics of WMA. This study conducted a comprehensive evaluation of WMA prepared using different aggregate sources, asphalt binders, and WMA additives. A dynamic mechanical analyser was used to test the mastic phase of conventional hot-mix asphalt and WMA. The test specimens were evaluated at different conditions – dry and wet – and at different ageing stages – unaged and three-month aged – in a controlled environmental room (i.e. 60°C). A fracture mechanics approach was used to analyse the test results. This approach incorporated fundamental material properties,...

Rutting performance of airfield pavements is predicted using mechanistic-based constitutive relationships for both asphalt and granular layers. Pavement analysis using nonlinear damage appr...

The mechanical behavior of asphalt binder is highly sensitive to temperature. The manner in which mechanical characteristics change with temperature can also vary significantly from one asp...

Ettringite formation due to sulfate attack in Portland cement concrete (PCC) and chemically stabilized soils can cause volumetric instability and strength loss resulting in reduced performance life. Evaluating and possibly predicting ettringite formation is critical if structural integrity is to be preserved. Suspensions with five different stoichiometric ratios Ca(OH)2 to Al2(SO4)3·18H2O (1:1, 3:1, 4:1, 5:1, and 6:1) are used in this study to evaluate ettringite formation both qualitatively and quantitatively. For all samples, Ca2+ ions are supplied by Ca(OH)2 reagent; Al3+ and SO 4 2 - ions are supplied by aqueous Al2(SO4)3·18H2O. Thermodynamic modeling using a Gibb’s energy minimization-based model (GEM-Selektor) is used for the quantitative evaluation of precipitated phases formed in the Ca-Al-SO4 suspension. In addition, a phase stability diagram is constructed with a law of mass action (LMA) based model (Geochemist’s Workbench (GWB)). Mineralogical characterization of precipitated solid phases is performed using quantitative X-ray diffraction (QXRD), fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Characterization of the suspension is carried out using pH and electrical conductivity. Qualitatively, GEMS and GWB predicted ettringite as a stable phase for 3 out of 5 samples which is experimentally verified by QXRD and TGA. Quantitatively, the mean error in prediction using GEMS is approximately 4%. The results demonstrate the potential to predict ettringite formation using thermodynamic modeling.

The quality of the interfacial bonding between asphalt binder and aggregates plays a significant role in determining the durability of asphalt mixtures. Warm mix asphalt (WMA) modifiers have been used extensively in the last decade primarily to reduce production and compaction temperatures as well as to improve workability of asphalt mixtures. This study aimed to provide better understanding of the effects of these WMA modifiers on the interfacial bonding between asphalt binders and aggregates. The evaluation focused on measuring surface energy of binders in unaged and aged states and aggregates and then calculating energy parameters that describe the potential of a given asphalt-aggregate combination to resist fatigue cracking and moisture damage. Results show that the combination of asphalt-WMA additive, as well as the content applied of WMA additive has a significant impact on the fatigue cracking and moisture damage resistance. The results suggest that it is poor practice to use a given type a...

This study evaluates the potential of selected ionic polymers to act as pavement subgrade binders. Investigations were based on their relative performance with a Qatari soil which was selected as typical of a pavement subgrade to be found in the Middle East and North African region. The polymeric binders chosen were three synthetic ionic variations of polyacrylamide: cationic poly(acrylamidopropyl trimethyl ammonium chloride) (designated PAMTAC), anionic hydrolysed poly(acrylamide) (HPAM) and the ampholitic terpolymer poly(acrylamide-co-sodiumacrylate-co-(3-acrylamidopropyl) trimethylammonium chloride) (TPAM). The polymers were characterised by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic spectroscopy (1H-NMR and 13C-NMR). The comparative performance of the polymer-treated soil was judged on the basis of results obtained from selected standard mechanical test data: specifically, the unconfined compressed strength, the stiffness modulus and the toughness. It is concluded tha...

It is well known that the accurate prediction of long term performance of asphalt concrete pavement requires modeling to account for viscoelasticity within the mastic. However, accounting for viscoelasticity can be costly when the material properties are measured at the scale of asphalt concrete. This is due to the fact that the material testing protocols must be performed recursively for each mixture considered for use in the final design. In this paper, a four level multiscale computational micromechanics methodology is utilized to determine the accuracy of micromechanics versus directly measured viscoelastic properties of asphalt concrete pavement. This is accomplished by first measuring the viscoelastic dynamic modulus of asphalt binder, as well as the elastic properties of the constituents, and this comprised the first scale analysis. In the second scale analysis, the finite element method is utilized to predict the effect of mineral fillers on the dynamic modulus. In the third scale analysis, the finite element method is again utilized to predict the effect of fine aggregates on the dynamic modulus. In the fourth and final scale analysis, the finite element method is utilized to predict the effect of large aggregates on the dynamic modulus of asphalt concrete. This final predicted result is then compared to the experimentally measured dynamic modulus of two different asphalt concretes for various volume fractions of the constituents. Results reveal that the errors in predictions are on the order of 60 %, while the ranking of the mixtures was consistent with experimental results. It should be noted that differences between the “final predicted results” and the experimental results can provide fruitful ground for understanding the effect of interactions not considered in the multiscale approach, most importantly, chemical interactions.

Realistic tire–pavement interface contact areas and stresses were incorporated into the Pavement Analysis using Nonlinear Damage Approach (PANDA) user interface (PUI). PANDA is a software library developed to simulate the complex thermo-viscoelastic–viscoplastic–viscodamage responses of the pavement to mechanical and environmental loads. The PUI is an interface generating a finite element representation of the pavement within PANDA. The application of realistic tire loading is necessary to calculate accurate pavement responses. The PUI incorporates a database of tire contact areas and stresses obtained from tire finite element simulations. The database includes tire interface characteristics with pavements for various applied loads, tire inflation pressures, vehicle speeds and scenarios of different rolling simulations. A parametric study was conducted to investigate the effect of simulations of tire contact stresses that match field measurements on viscoelastic and viscoplastic pavement responses...

This is a study of the temperature dependence of the mechanical behaviour of asphalt binders. Creep-recovery and steady-shear experiments were conducted on selected modified and unmodified binders at 60, 70 and 80 C, and the results were used to characterise the binders using a nonlinear viscoelastic model. Experimental and model parameters obtained in this manner were all found to follow Arrhenius relationship with temperature. Rutting parameters such as zero shear viscosity, non-recoverable creep compliance, Superpave criterion and apparent viscosity were predicted using the model, and were also found to follow an Arrhenius relationship with temperature. However, it was found that the temperature sensitivity of the binders can vary considerably. Issues with ‘failure temperature’-based grading systems, such as the Superpave high temperature specification, were analysed in the light of the Arrhenius-like temperature dependence and varying temperature sensitivities. Possible ways to consider varying temper...

This paper presents findings from a study conducted to evaluate changes in the microstructure of asphalt binder resulting from aging as well as the effect of these changes on the evolution of damage resulting from tensile deformations. Two types of asphalt binders were aged with the rolling thin film oven and pressure aging vessel aging techniques. The microstructure and the microrheology of the six binders were obtained with atomic force microscopy (AFM) imaging and creep indentation experiments. This information was then used to perform numerical simulations to examine the effect of tensile strains on the internal stress distribution in the binder. Experimentally, a microloading apparatus was used to induce tensile strains in the samples of the asphalt binder while the binder was observed for damage with the use of AFM. The damage and changes in the binder microstructure resulting from the tensile load observed experimentally were compared with the results from the numerical simulations. Results suggest that localized regions of high stress intensity between different domains act as damage nucleation sites. Results also suggest that the differences in the rheological properties of the microdomains reduce with aging. As a result, the internal distribution of stresses becomes less heterogeneous, the magnitude of stress localization decreases, and there are fewer sites where damage nucleates.

Mechanical behavior and fatigue damage characteristics of chemically stabilized soils under cyclic loading conditions are complex and require better understanding due to its large demand in many critical infrastructures including roadways. Fatigue tests are usually not easy to conduct and time-consuming, and the challenges increase when materials become more complex due to chemical stabilization. This study proposed a simple monotonic fracture test that is integrated with computational fracture modeling to identify fracture characteristics for predicting fatigue damage behavior of complex materials such as chemically stabilized soils. Toward that end, an extrinsic inelastic cohesive zone model (CZM) was used. The fracture parameters of the CZM were first obtained from a monotonic fracture test that is integrated with its model simulation. With the fracture parameters, the same CZM was used to predict fatigue behavior and ultimate failure. The simulation results indicate that the predicted fatigue behavior and performance are comparable to the fatigue test results. With limitations remained for further improvements, the proposed experimental-computational approach incorporated with the inelastic fracture model such as the CZM in this study presented its benefits for predicting time-consuming and labor-intensive fatigue behavior of complex materials.

An extended Drucker-Prager-Cap-Creep (D-P-Cap-Creep) constitutive relationship is coupled with the PANDA (Pavement Analysis using Nonlinear Damage Approach) model to predict rutting in granular and asphalt layers of flexible airfield pavements, respectively. The presented model treats the pavement structure as a system and predicts rutting performance as the summation of permanent deformation in the subgrade, subbase, base, and asphalt layers. In addition to capturing the effects of densification and shear on permanent deformation with the D-P-Cap model, a creep law is defined to capture time- and rate-dependent behavior of granular layers and the subgrade. Simulation results of D-P-Cap-Creep constitutive relationship in conjunction with PANDA are validated against test sections of Construction Cycle 3 (CC-3) at the National Airport Pavement Test Facility (NAPTF). Presented results demonstrate that incorporation of time hardening Creep law to D-P-Cap model resulted in reduction in deviation between field measurements and model predictions. It is argued that the D-P-Cap-Creep constitutive relationship may have a more pronounce effect on rutting evolution of flexible pavements with moist subgrades with high clay contents.

Shrink-swell soils are predominant in various parts of the parts of the world. Lime has been extensively used to reduce the shrink-swell mechanism as it chemically reacts with soil minerals forming pozzolanic products such as calcite and calcium-silicate-hydrate (C-S-H). Conventionally, whether chemical treatment of soils results in effective pozzolanic stabilization reactions is determined anecdotally through engineering tests including unconfined compressive strength, plasticity index (PI), and pH tests. This study builds on existing literature regarding how more direct quantification of pozzolanic products can be obtained through tests that directly identify and quantify pozzolanic products, specifically in lime-treated clay soils. Specifically, x-ray diffraction (XRD) and differential thermogravimetric analysis (DTA) are used for this testing. Expansive soils with plasticity indices above 25% were selected for this study. Engineering tests on these lime-treated soils indicated significant improvement in strength and reduction in PI. In XRD analysis, pozzolanic products are assessed by the location and intensity of x-ray peak(s). The XRD data show a decrease in the intensity of alumio-silicate minerals such as kaolinite and smectite; silica and alumina are dissolved at a high pH and converted to pozzolanic products such as calcium-silicate-hydrate (C-S-H). DTA indicates the presence of C-S-H with the characteristic weight loss from 140°C to 250°C.The methodology describes the following: ● Sample preparation steps for XRD and DTA analysis. ● Analysis of XRD results and DTA analysis., Graphical abstract Image, graphical abstract

Rheological properties of asphalt binders significantly affect distress development and performance of asphalt concrete materials. This article presents the effect of Evotherm-M1 modifications on rheological properties of asphalt binders used in the construction of test sections at the Federal Aviation Administration’s National Airport Pavement & Materials Research Center. Four different binders (i.e., polymer styrene butadiene styrene [SBS]-modified PG 76-22, PG 64-22, SBS-modified PG 76-22 plus Evotherm-M1, and PG 64-22 plus Evotherm-M1) are studied. Multiple stress creep recovery (MSCR) and strain-controlled frequency sweep (FS) test results are analyzed to construct the master curves for the binders. Results indicate high sensitivity of SBS-modified PG 76-22 to Evotherm-M1 modifications as compared with PG 64-22. Subsequently, the results of dynamic modulus tests conducted on asphalt mixture specimens (prepared using job mix formula and different binders) are analyzed to investigate the effect of binder type and modification on rheological properties and rutting performance of asphalt mixtures. It is shown that the rutting resistance and rheological properties of asphalt mixtures can be ranked based on the results of MSCR and FS tests conducted on asphalt binders. It is shown that the rutting resistivity of traffic test sections and lab-tested asphalt mixtures can be ranked as follows: SBS-modified PG 76-22, SBS-modified PG 76-22 plus Evotherm-M1, PG 64-22, and PG 64-22 plus Evotherm-M1. This is consistent with the results obtained for tested asphalt binders.