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This paper compared several mathematical models predicting chloride penetration in concrete by employing a time-dependent diffusion coefficient for a number of analytical solutions of Fick's second law. We propose calibrated models that consider a time-dependent build-up of the surface chloride concentration Cs. Predicted values and measured values of chloride profiles from experimental results were compared, which showed that the calibrated models considering a time-dependent surface chloride concentration could significantly improve the correlation compared with the conventional models employing a constant surface chloride concentration. Moreover, we investigated several factors (i.e., skin effect, aging factor m , exposure conditions, curing conditions, water/binder ratio, and fly ash content) that may affect chloride penetration in concrete by adopting the calibrated models. The results showed conclusively that these factors also significantly affected the accuracy of the chloride penetration obtained by these calibrated models. Finally, the results predicted by the calibrated Tang–Gulikers model were proved to be reasonably accurate in concrete with a small water/binder ratio compared with the experimental data. It is concluded that the calibrated Tang–Gulikers model can be applied for predicting chloride penetration and solving relevant service-life problems resulting from chloride ingress in concrete. [ABSTRACT FROM AUTHOR]

An asphalt mixture is a composite material consisting of three components: asphalt binder, aggregate, and air. The mechanical properties of asphalt mixtures are mostly evaluated from empirical approaches that are usually limited to measurement conditions. This paper takes a mechanistic approach by using micromechanics theory for composite materials to develop self-consistent micromechanics models for an asphalt mixture. The mixture analysis method described in this paper is applied to measured properties of an asphalt concrete mixture that is commonly used in Texas. These models are programmed in MATLAB using the system identification method and are applied to the analysis of the frequency-dependent magnitudes of the viscoelastic properties of an asphalt mixture at different aging periods. The inverse micromechanics model takes as input the volumetric composition of the mixture and the measured frequency-dependent bulk and shear properties of the asphalt mixture and the binder and extracts from them the bulk and shear properties of the aggregate. The forward micromechanics model takes as input the frequency-dependent bulk and shear properties of the aggregate and binder and produces the frequency-dependent properties of the asphalt mixture. It has been demonstrated that the inverse and forward micromechanics models are in fact the inverse of each other and that the inferred aggregate properties are realistic. These models provide a technique to catalog the properties of aggregates and use them in a computerized determination of the combinations of binders, aggregates, and air to produce the desired properties of asphalt mixtures. [ABSTRACT FROM AUTHOR]

Erratum for "Chloride Diffusion Prediction in Concrete through Mathematical Models Based on Time-Dependent Diffusion Coefficient and Surface Chloride Concentration" The corrected affiliation information is provided herein. The following correction should be made to "Chloride Diffusion Prediction in Concrete through Mathematical Models Based on Time-Dependent Diffusion Coefficient and Surface Chloride Concentration" by Qing Xiang Xiong, Qing Feng Liu, Xi Jin Zhang, and Chuan Chen, https://doi.org/10.1061/(ASCE)MT.1943-5533.0004429: In the original paper, the first author's affiliation information was incomplete and contained an incorrect current professional designation. [Extracted from the article]

A numerical model developed in previous work by the authors is extended in this paper and used to evaluate the influence of several factors on the degradation of cementitious materials under the combined effects of external sulfate attack and calcium leaching. The previous model included (1) diffusion of ions in and out of the structure under concentration gradients and chemical activity gradients, (2) chemical reactions under local equilibrium condition assumption, and (3) damage accumulation using continuum damage mechanics. This paper extends the model by incorporating a continuum micromechanics based approach for assessing changes in elastic properties and strength of the structure attributed to chemical reactions. Two homogenization schemes combined with Eshelby's equivalent inclusion method are used to estimate the mechanical properties of the structure that change with time because of dissolution and precipitation of solids. Sensitivity analysis is performed by using the improved numerical model to evaluate the effects of several external and internal factors (e.g., pH and composition of the external solution, and porosity and tortuosity of the material) on the degradation of the structure. It is found that the damage progression rate is mostly dependent on relative rates of sulfate ingress and calcium leaching. The relations between the factors and the damage progression rate are observed to be significantly nonlinear. [ABSTRACT FROM AUTHOR]

Resilient moduli of pavement layers are the basic input parameters for the design of pavements with multiple layers in the current mechanistic empirical pavement design guides. Field measurements are generally believed to provide accurate values to back-calculate pavement layer moduli, but the tests to measure the relevant parameters are expensive, difficult to perform, and cause disturbances to the public. Therefore, the back-calculation of pavement layer moduli from laboratory scale model testing has been a focus of recent pavement research. This paper presents a back-calculation analysis to evaluate pavement layer moduli by using a three-dimensional numerical model developed using the FLAC3D finite difference software. The pertinent measurements that are required for the back-calculation analysis were collected from a cyclic load testing facility under traffic type cyclic loading conditions, with a typical pavement structure consisting of a granular road base lightly stabilized with cement-fly ash over an expansive soft clay subgrade. This study indicates that the stabilized base material had cross-anisotropic resilient properties, with an average vertical resilient modulus of 2,875 MPa and an average horizontal resilient modulus of 1,598 MPa. From this investigation, the resilient moduli of the stabilized granular base layer and subgrade clay were reliably back-calculated from the analysis by using the FLAC3D numerical model. [ABSTRACT FROM AUTHOR]

The mechanical deterioration of concrete exposed to freeze-thaw cycles is one of the most important durability problems under subzero temperature conditions. At present, studies on concrete behavior under freeze-thaw cycles primarily focus on the degradation of concrete properties, there are few reports on testing and modeling the stress-strain relationships of concrete undergoing repeated cycles of freeze-thaw. This paper investigated the stress-strain relationship of fly ash concrete under 0, 5, 15, 30, 50, 75, 100, and 125 freeze-thaw cycles by testing 24 prism specimens. The relative dynamic modulus, compressive strength, elastic modulus, and stress-strain relationship of specimens under freeze-thaw cycles were measured. In addition, a multiple sharp degradation point model for the degradation of mechanical properties of concrete was proposed. Finally, a damage constitutive model on the base of the damage mechanics and the multiple sharp degradation point model was presented. By comparing the results calculated by the damage constitutive model with the experimental data, the proposed model was proved to be effective for evaluating the stress-strain relationship of fly ash concrete under freeze-thaw cycles. [ABSTRACT FROM AUTHOR]

Capacities of wood connections with laterally loaded dowel fasteners by plastic analysis can be predicted using the European yield models (EYM) equation. The underlying concept is that failure occurs due to crushing of wood beneath fasteners and / or formation of plastic hinges in fasteners with a rigid-plastic representation of the materials involved. EYM prediction is now “the” way within design codes to calculate the maximum attainable capacity per fastener. Subsequent adjustments discount those predictions through factors which account for unequal sharing of force between fasteners and premature connection failure by fracturing. In North America the EYM is the basis for lateral load capacities of connections made with bolts, drift-pins, screws, nails, and timber rivets. This paper addresses the capability of the EYM for predicting load carrying capacities of solid wood (sawn softwood lumber) and laminated strand lumber (LSL) connections employing tight-fitting steel tube fasteners with external diameters up to 12.7 mm. EYM prediction is compared with experimental test results for arrangements with one or four fasteners loaded in double shear. Accuracy of predictions depends on factors such as connection geometry and the type of wood member involved. Prediction is always accurate if a connection has only one fastener, or if joined members are made from LSL. If members are made from sawn softwood lumber premature brittle splitting type failure modes occur for multiple fastener situations, with impairment of capacity inversely proportional to the fastener outside diameter. Suggestions are made here regarding the nature of codified design rules for steel tube fastener connections, with the intent that such provisions be enacted within North America. [ABSTRACT FROM AUTHOR]

This paper is devoted to the experimental study of chemical degradation effects on the mechanical behavior of sandstone. The sandstone samples were immersed in acid solutions with different pH values to undergo chemical degradation. Conventional triaxial compression tests with different confining pressures were performed on chemically degraded samples. It is found that the chemical degradation induced the diminution of elastic modulus and compression failure strength. Triaxial compression creep tests were then carried out with different stress levels. The experimental data showed that the creep deformation rate is enhanced by the chemical degradation. [ABSTRACT FROM AUTHOR]

This paper presents a study on the shear load-displacement behavior of horizontal joints in unreinforced brick masonry subjected to constant compression. In general, under static shear loading masonry joints show a peak shear stress followed by a residual shear strength. To investigate these aspects in greater detail, triplet tests were conducted on masonry specimens using different types of mortar. The results found in this study and previous tests show that normal compressive stresses acting on the interface and the interface mortar strength affect the peak shear stress and the residual strength in a rather similar way. The cohesion and the internal friction angle, i.e., the two parameters required by the Mohr-Coulomb criterion, are then derived from a linear regression of the test results. The pre-peak and post-peak response of a masonry bed joint can best be represented by simple equations, and their shear stiffness depends on material properties and the magnitude of the normal compression. Computational modeling strategies are then presented considering the shear slip at the brick-mortar interface. The comparison of the model prediction with the results found in this study and previous tests shows the reliability of the proposed model for bed joint behavior. [ABSTRACT FROM AUTHOR]

One of the main obstacles to a wider use of self-compacting concrete (SCC) is its sensitivity to small variations of the constituent materials, mix proportions, and other external factors. The main objective of this paper is to illustrate how to evaluate and compare the robustness of SCC mixtures optimized according to various economic criteria while maintaining the water/cement ratio and fresh state target properties. The optimization is derived from numerical models, and a central composite design is developed to mathematically model the influence of mixture parameters and their coupled effects on deformability, passing and filling abilities, and compressive strength. The strategies to increase the robustness of SCC mixtures and the existing methodologies to assess it are presented and discussed. By applying these methodologies, it is shown that robustness can be enhanced by changing only the proportions of materials in mixtures. Minimizing the superplasticizer dosage and, consequently, increasing the paste volume (by means of a higher limestone filler content) to keep adequate fresh properties is found to be the most effective optimization criteria to enhance the robustness of SCC mixtures. [ABSTRACT FROM AUTHOR]

This paper presents results of experimental and numerical modeling of ductile fracture and failure of elements made of S235JR steel subjected to static tension. The prediction of failure was generally based on the stress modified critical strain (SMCS) model. The numerical simulations were performed using the Gurson-Tvergaard-Needleman (GTN) model, which takes into consideration the material structure. The approach applied in this study was based on the computational cells with microstructurally based length scales. The cell size and initial porosity were determined through microstructural examinations of S235JR steel. The parameters of the GTN model for S235JR steel were established on the basis of the microstructural analysis and the numerical modeling of tensile strength tests. As a result, it was possible to determine the SMCS failure criterion to predict ductile fracture for S235JR steel. [ABSTRACT FROM AUTHOR]

Because of the large grainsizes typical of railroad ballast, large triaxial samples are required to assess the reactions of these materials. The parallel gradation modeling technique was originally developed by John Lowe in 1964 to allow assessment of large grain-size geomaterial properties in smaller, more typical testing facilities. Emphasis has focused on monotonic loading, in which the material is progressively loaded to failure. Cyclic testing of this model has been absent. This paper presents an investigation of the possibility of using the parallel gradation modeling technique in a cyclic triaxial testing framework. Three separate gradations of ballast material were used in this research. The largest gradation contains a top particle size of 63.5 mm (2.5 in.) and is marketed as #3 modified railroad ballast. The second two gradations contained a top size of 38 mm (1.5 in.) and 19 mm (.), respectively. Up to 10,000 load cycles were applied for each test. Resilient modulus, permanent axial, volumetric strain, and particle shape were determined from the test results. It is concluded that applying parallel gradation technique to cyclic behavior characterization should be cautious. If particle shape is not consistent throughout the particle sizes used in the parallel gradation model, the model is invalid in the cyclic triaxial framework. [ABSTRACT FROM AUTHOR]

In this paper, state-dependent elastic characteristics of granular subgrade materials were investigated, assuming various field conditions. For this purpose, a series of resonant column tests were conducted. The test materials were cohesionless soils consisting of clean and silty sands with different fines contents. The effects of moisture content, overconsolidation ratio, relative density, and confining stress on the elastic modulus were analyzed. From the test results, it was observed that the initial shear modulus, G0, decreases with increasing moisture content because of reduced particle contact friction. Higher fines content produced a more pronounced modulus reduction at the same moisture content. It was also found that the effect of fines content on G0 becomes smaller as the relative density and confining stress increase. These results indicate that the moisture effect on G0 is important at shallow depths such as subgrade layers. A modulus reduction factor was proposed, which can reflect the effect of the soil parameters on elastic modulus. A resilient modulus (MR) model modified on the basis of the test results was proposed and finite-element analyses were conducted. Two case examples were selected from the literature to verify the proposed MR model. Predicted MR values obtained using the proposed model showed reasonable agreement with measured values from the selected case examples. [ABSTRACT FROM AUTHOR]

Chloride-induced corrosion is the most important durability issue in a reinforced-concrete structure. In this paper, the multispecies model was used to describe the chloride transport in saturated concrete. The model was solved by using the finite-difference method by inputting parameters such as porosity, density, chemical composition of pore solution, diffusion coefficient, and chloride-binding isotherm. A depth-dependent diffusion coefficient, instead of a fixed diffusion coefficient, was used in this model. The chloride-binding isotherm was directly obtained from the diffusion test. Finally, the numerical simulation results were validated with experimental results. It was found that the numerical simulation results were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

An empirical |E*| predictive equation, known as Witczak's |E*| predictive model, has been adopted in the Mechanistic-Empirical Pavement Design Guide. However, empirical approaches have significant drawbacks, particularly with application of the model for materials that vary from those used in the calibration of the model and their reliance on large calibration data sets. In order to overcome the limitations of an empirical approach, a fundamental micromechanics modeling framework based on the differential scheme effective medium theory has been developed and introduced in this paper. The proposed modeling framework herein takes a sequential approach, using a series of two-phase differential particulate composite models to predict the effective tensile complex modulus (|E*|) of a three-phase HMA mixture, which consists of the asphalt binder, aggregate particles, and air voids. The model prediction results were compared with experimentally measured |E*| of five dense graded HMA mixtures across a range of low temperatures. In general, the model was found to predict |E*| with a very reasonable level of accuracy. Additional work to extend the applicability of the modeling framework to higher temperature regimes and the need to develop a more general and systematic approach for practical implementation are discussed. [ABSTRACT FROM AUTHOR]

Bonding characteristics between pavement layers have an important influence on responses of pavement structures. This paper deals with this subject by analyzing the interlayer behavior of double-layered asphalt (DLA) specimens taken from an in-service motorway using a coaxial shear test (CAST) and a layer-parallel direct shear (LPDS) test. To analyze and model the influence of the interlayer condition, finite-element simulations of CAST DLA specimens were conducted. In the models, both idealized fully bonded and no-bonding assumptions were used to characterize the interlayer behavior of DLA specimens. Experimental results presented for CAST and LPDS tests demonstrate that there is a strong influence of temperature in the interlayer bonding mechanism. At lower temperatures, there is an increase on the bonding strength produced by the binder stiffening and aggregate interlocking. Further, it was observed that comparisons of CAST experimental and numerical results indicate that the interlayer can be close to the fully bonded condition at low temperatures below 20°C while the interlayer, at higher temperatures, behaves between fully bonded and no-bonding idealized conditions. [ABSTRACT FROM AUTHOR]

The combined effect of moisture and mechanical loading on asphalt mixtures has been recognized as one of the main causes of premature deterioration of flexible pavements. This paper presents a micromechanical model of moisture-induced damage in asphalt mixtures. The model couples the effect of moisture diffusion and mechanical loading to quantify the level of damage within the mixtures. The mechanical properties of the materials are defined as a function of the amount of moisture content. The cohesive zone modeling technique is used to simulate adhesive damage at the aggregate-mastic interfaces. Damage is evaluated based on the location and time for crack initiation and propagation at the aggregate-mastic interfaces and on the level of strains and stresses within the bulk of the mastic. Results show that micromechanical models provide a better understanding of moisture damage mechanisms in asphalt mixtures and can guide the development of continuum damage models. [ABSTRACT FROM AUTHOR]

A general relationship between cumulative pore volume and pore sizes as measured through mercury intrusion porosimetry (MIP) and BSE image analysis technique is presented in this paper. From the results of the MIP study conducted on hardened cement paste, cement silica fume paste, cement silica fume sand mortar, brick, soil cement, and concrete, it is observed that a general relationship exists between applied pressure and intruded volume of mercury. This relationship closely follows the MMF (Morgan, Mercer and Flodin) model. The general relationship between pore sizes and intrusion volume in MIP is then derived from this relationship using Washburn’s equation. A similar model is also observed to describe the relationship between cumulative volume and pore sizes obtained through BSE image analysis. The variations of the parameters namely median pore radius and dispersion coefficient (a measure of the spread of pore sizes), with silica fume content, ratio of water-to cementitious material and age are then discussed to demonstrate the utility of the model. [ABSTRACT FROM AUTHOR]

Current pavement design procedures recommend the resilient modulus of subgrade materials for pavement design and analysis. The objective of this paper is to develop two statistical models to predict the resilient modulus of subgrade cohesive soils from the dynamic cone penetration (DCP) test parameters and soil properties. The first model correlates resilient modulus to the dynamic cone penetration test parameters, while the second model correlates resilient modulus to both the dynamic cone penetration test parameters and soil properties. Field and laboratory experiments were conducted at 31 sites in Louisiana that contain four common soil types (A-4, A-6, A-7-5, and A-7-6). Field tests included DCP tests and soil sampling, while laboratory tests included determining basic soil properties and resilient modulus. Statistical analyses were conducted on the collected data, and two statistical models were developed for the prediction of resilient modulus of cohesive subgrade soils from the DCP test parameters and soil properties. The models predicted a separate data set that was not used in their development, indicating the success of the application of the dynamic cone penetration test in evaluating the resilient modulus of pavement subgrade soils. The predicted values obtained from the proposed models corresponded well with the measured resilient modulus values from the repeated load triaxial test. [ABSTRACT FROM AUTHOR]

A one-dimensional mathematical model was developed, based on the fundamental energy balance, to calculate the pavement near-surface temperatures using hourly measured solar radiation, air temperature, dew-point temperature, and wind velocity data. An analysis was conducted to predict the diurnal temperature effects of pavement thermophysical properties with the aim of seeking an optimum composition of paving materials for future infrastructure projects. Appropriate paving materials not only ensure stability and safety for road users, but also the ability to mitigate heat absorption and high surface temperatures contributing to the Urban Heat Island Effect and human comfort. This paper evaluated the effects and sensitivities of the thermophysical properties on the pavement surface temperatures. The results indicated that both albedo and emissivity have the highest positive effects on pavement maximum and minimum temperatures, respectively, while increasing the thermal conductivity, diffusivity, and volumetric heat capacity help in mitigating the maximum but not the minimum pavement near-surface temperature. [ABSTRACT FROM AUTHOR]

Various prediction models have been developed to predict the creep and shrinkage in concrete. Experimental studies to measure the creep and shrinkage in concrete have also been carried out by researchers and reported in the literature. RILEM has compiled all these experimental studies which are stored in a computerized data bank. This paper briefly describes some of the recent models which are based on the extensive research and experimental studies. Creep and shrinkage have been predicted up to 5,000 days of observation by the ACI-209R-82 model, the B3 model, the CEB-FIP model code 1990, and the GL2000 model for various grades of concrete. Predicted values of creep and shrinkage were compared with the experimental results of Russell and Larson, in 1989, as well as the RILEM data bank. Prediction of creep and shrinkage by GL2000 model is found to be the closest to the experimental results. [ABSTRACT FROM AUTHOR]

Permeability is an important property that influences the performance of hot-mix asphalt (HMA). It is a function of compaction effort, and several properties of HMA such as asphalt content, and the shape and size distribution of aggregates. Due to the different laboratory and field methods for measuring permeability, and the interaction among the factors that influence its value, it would be difficult to develop an analytical equation that accurately relates permeability to all factors contributing to HMA permeability. This paper presents a simple equation for approximating the permeability of asphalt mixes. It utilizes the percent air voids and surface area of aggregates. The equation is empirical but it is derived based on the well-known Kozeny–Carman equation for calculating the permeability of granular materials. The developed equation was used successfully to fit permeability data collected from several studies that carried field and laboratory measurements of HMA permeability. A finite element model was developed to investigate the influence of the gradient of percent air voids in HMA on water flow patterns. The x-ray computed tomography was used to measure the percent air void gradients among sublayers of the asphalt mix. The permeability of these sublayers was calculated using the developed equation, and used as an input to the finite element model. The simulation results show that air void gradients in HMA encourage lateral flow in the horizontal direction and reduce the flow in the vertical direction. [ABSTRACT FROM AUTHOR]

This technical note develops a mathematical model to calculate the electrical resistivity of soil–rock mixtures based on macroscope structure of the soil and broken rocks, and further considers that the filling of pores between coarse grains by fine grains may result in a decrease in porosity and an increase in saturation degree. Thus, based on a standard model for the electrical resistivity of unsaturated soil, this study proposes a modified model for the electrical resistivity of unsaturated soil–rock mixtures and validated the accuracy of the model using experimental results. Then a simple and easy method for calculating the electrical resistivity of soil–rock mixtures is provided. [ABSTRACT FROM AUTHOR]

A generalized theory for the viscoelastic behavior of idealized bituminous mixtures (asphalts) is presented. The mathematical model incorporates strain rate and temperature dependency as well as nonmonotonic loading and unloading with shape recovery. The stiffening effect of the aggregate is included. The model is of phenomenological nature. It can be calibrated using a relatively limited set of experimental parameters, obtainable by uniaxial tests. It is shown that the mathematical model can be represented as a special nonlinear form of the Burgers model. This facilitates the derivation of numerical algorithms for solving the constitutive equations. A numerical scheme is implemented in a user material subroutine (UMAT) in the finite-element analysis (FEA) code ABAQUS. Simulation results are compared with uniaxial and indentation tests on an idealized asphalt mix. [ABSTRACT FROM AUTHOR]

Previous research of structural composite lumber connections loaded perpendicular to grain has shown brittle failure by splitting. In previous testing, two different laminated veneer lumber (LVL) materials with single and two bolts in a row loaded perpendicular to grain were compared with fracture mechanics models proposed by Van der Put and Jensen and splitting capacity equations from Eurocode No. 5. Connection strength values of two-bolt connections were larger than single-bolt connections owing to the increased distance to the farthest fastener. The first LVL material (LVL-1) had significantly larger predicted capacity strength values than the other LVL material (LVL-2) for the same configuration owing to larger mode I fracture energy and tension perpendicular-to-grain strength values. A rederivation of the brittle failure constant CI specifically for LVL materials would improve performance of Eurocode No. 5 predictions. The different fracture models had improved connection prediction values when the tension perpendicular-to-grain strength of the main member was included in the models. This property appears to be more important than shear properties for splitting behavior. [ABSTRACT FROM AUTHOR]

The article discusses a study conducted which proposes a method to estimate pore size distribution (PSD) of hardened cement paste (HCP) from water vapor sorption isotherms (WVSIs). Topics discussed include contribution of adsorbed liquidlike layer (ALLL) to the cumulative and differential PSD curves, the importance of using appropriate method to interpret the WVSI data and requirement of more rigorous studies in the relative issues.

In this paper, we evaluate the logistic differential equation as a mathematical method for representing changes in asphalt properties during pavement aging in the field. We chose the logistic function because it appears to be theoretically consistent with the micromolecular model of asphalt aging. This choice was validated, because we did find that the logistic function gave a close fit with experimental data from a variety of pavement-aging studies. The logistic function allows us to quantify two essential characteristics of asphalt aging: the rate of aging and the ultimate degree of change in asphalt properties due to aging. Therefore, we believe that the logistic equation is a potentially powerful tool for studying asphalt aging, because it provides a method for consolidating aging data in an accurate and useful format. The importance of such a tool lies in its use for studying the relative effects on the aging process of factors such as asphalt type, void level, and climate. An understanding of the role of asphalt type on the aging process is crucial if we are to develop more durable asphalt pavements. [ABSTRACT FROM AUTHOR]

Suggests the application of the general equations provided by the principle of natural proportionality to the stress-strain curves of concrete. Details on the equations; Rejoinder from the authors of the study.

Modeling the spatial variability that exists in pavement systems can be conveniently represented by means of random fields; in this study, a probabilistic analysis that considers the spatial variability, including the anisotropic nature of the pavement layer properties, is presented. The integration of the spatially varying log-normal random fields into a linear-elastic finite difference analysis has been achieved through the expansion optimal linear estimation method. For the estimation of the critical pavement responses, metamodels based on polynomial chaos expansion (PCE) are developed to replace the computationally expensive finite-difference model. The sparse polynomial chaos expansion based on an adaptive regression-based algorithm, and enhanced by the combined use of the global sensitivity analysis (GSA) is used, with significant savings in computational effort. The effect of anisotropy in each layer on the pavement responses was studied separately, and an effort is made to identify the pavement layer wherein the introduction of anisotropic characteristics results in the most significant impact on the critical strains. It is observed that the anisotropy in the base layer has a significant but diverse effect on both critical strains. While the compressive strain tends to be considerably higher than that observed for the isotropic section, the tensile strains show a decrease in the mean value with the introduction of base-layer anisotropy. Furthermore, asphalt-layer anisotropy also tends to decrease the critical tensile strain while having little effect on the critical compressive strain. [ABSTRACT FROM AUTHOR]

Asphalt mixture is a heterogeneous, composite material consisting of aggregate, mastic, and air voids. Analysis of laboratory tests such as the dynamic complex modulus assumes that this material can be dealt with as a homogeneous material while overlooking the particulate nature of this composite. Because of the limitations of the elastic continuum theory, pavement engineers have recently paid considerable attention to the use of advanced modeling techniques for simulating the realistic behavior of asphalt mixtures. The objective of this study is to develop a three-dimensional (3D), heterogeneous model to describe the response of asphalt mixtures in the dynamic complex modulus test using an X-ray computed tomography image-based finite-element (FE)-modeling approach. Experimental testing results for two superpave mixtures, including one conventional hot-mix asphalt and one warm-mix asphalt, were used to validate and calibrate the developed FE models. Acceptable agreement between laboratory-measured and model-predicted dynamic modulus test results was achieved. Results of the developed FE models at different temperatures indicated that most of the deformations during the dynamic modulus test are derived from the mastic. In addition, the asphalt mastic had more influence than the aggregates on the results of the dynamic complex modulus test. [ABSTRACT FROM AUTHOR]

A multiphysics formulation for chloride diffusion in an RC beam with stress-induced damage quantifying the enhancement in chloride diffusivity due to damage is presented. An experimental investigation involving measurement of chloride profile was conducted on RC beams damaged under applied flexural stress. Numerical simulation of the RC beam is carried out using a two-dimensional finite-element approach incorporating the damage due to the applied stress, chloride binding, and the chloride diffusion in the model. Concrete is assumed to be a perfectly elastoplastic (Drucker-Prager) material and the steel as an elastoplastic (von Mises) material with hardening. Drucker-Prager parameters, cohesion c, and friction angle φ are obtained by calibrating numerical load-deflection (P-Δ) curve to an experimentally determined (P-Δ) plot for beams loaded in flexure. Defining a scalar damage index as the degradation in elastic modulus expressed in terms of total strains, the chloride transport problem is addressed, using an effective diffusion coefficient, Deffd, expressed as a function of the damage index and chloride binding and obtained by calibrating to data for chloride profiles as determined in flexurally damaged beams. Using the expressions for the effective diffusion coefficient, Deffd, the chloride profiles are shown to match the experimentally determined chloride profiles in beams damaged at various stress levels. [ABSTRACT FROM AUTHOR]

A numerical method, with which experimental results were processed, was adopted to measure the total emissivity of mild steel specimens at high temperatures. This method is derived from considering the transient thermal energy equilibrium between a steel specimen and its surrounding heating environment. As a first step to validate this method, the results obtained at a low temperature were compared with those using infrared thermographic techniques, and a good correlation of 87% was achieved. The numerical model was then extended to high temperatures to investigate the variation of emissivity of steel with temperatures. The convective heat transfer coefficient used in the numerical model was examined in great detail using results obtained from transient high temperature tests. The emissivity of steel obtained from this study shows that steel emissivity varies over a range of temperatures and the variation becomes more abrupt between 400 and 500°C. Formulation for the emissivity of steel at rising temperatures is recommended for steel design in fire. [ABSTRACT FROM AUTHOR]

A novel manufacturing process for wood-polypropylene composite (WPC) panels reinforced with fiber-reinforced polymer (FRP) sheets was implemented using a double belt pressing technology. FRP sheets were placed on both sides of the WPC agglomerates during fabrication, which resulted in increased productivity and reduced thermal stresses compared with secondary bonding processes. Significant improvements in the mechanical properties of the FRP reinforced sheet panels were found during flexural and tensile tests on the coupon level. Even with addition of only one layer of FRP reinforcement on both sides of a WPC panel, the flexural modulus and strength increased by a factor of 2.6 and 3.8, respectively. Furthermore, the flexural and tensile properties of the WPC material considered in this study were found to be superior compared with the properties of an extruded WPC material. The changes in the flexural modulus of the FRP reinforced WPC panels with respect to the number of FRP layers were predicted using a model based on moment-curvature analysis. [ABSTRACT FROM AUTHOR]

Recyclable fractions such as calcium and sodium aluminosilicates including zeolite sodalite (SOD) were obtained from hydrothermal treatment of autoclaved aerated concrete (AAC) waste material under addition of sodium aluminate. Three experimental series were performed using hydrothermal conditions at temperatures of 80°C and 180°C (autogeneous pressure) and AAC aluminate mass ratios of 0.8 and 2.0. Different solvents were applied in each series; whereas the reactions were carried out in water or 1-molar NaOH, a special two-step process was developed, starting with acid leaching of AAC (1-molar citric acid), followed by alkaline treatment of the whole slurry in 1-molar NaOH. Final products were analyzed by X-ray powder diffraction. Selected samples were further investigated by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The results exhibit model character for new ways of resource recycling of AAC. [ABSTRACT FROM AUTHOR]

Maxwell models have been parameterized on the basis of rheological data from the literature for bitumens used in pavements to relate differences in rheology to underlying differences in mechanical relaxation times. The data employed were previously measured for bitumens without aging, with rolling thin-film oven (RTFO) aging, and with subsequent pressure aging vessel (PAV) aging. Bitumens in different data sets included different types of bitumen modification. Full time-temperature superposition was applied, with horizontal shift factors aT based on achieving superposition of phase angle tangent (tanδ) and vertical shift factors bT determined based on overlap of storage and loss moduli. The results determined for the horizontal shift factor followed the Williams-Landel-Ferry equation with parameters that differed for each bitumen. Dynamic modulus data were represented by using a series of discrete Maxwell models. Fand suggested a continuous yet asymmetric distribution of relaxation times on a logarithmic time axis. PAV-aged bitumens showed increased modulus contributions at longer relaxation times than RTFO-aged bitumens. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the sensitivity of aggregate size within sand mastic by modeling the microstructure of an asphalt mixture. The sensitivity of the maximum aggregate size on the sand mastic phase is investigated through discrete-element simulations. A three-dimensional (3D) discrete-element model of asphalt mixture was prepared from X-ray computed tomography (X-ray CT) images. In the discrete-element model, an asphalt mixture is divided into aggregate, sand mastic, and air void phases. In this study, the sand mastic is defined as fines and fine aggregates mixed with asphalt binder. Three different nominal maximum aggregate sizes (NMASs) of sand mastic, namely, 1.18 mm, 0.6 mm, and 0.3 mm, were used in the 3D model to investigate the best gradation of sand mastic. The dynamic moduli of three different NMASs of sand mastic were measured for use in the 3D discrete-element modeling simulation. Laboratory-measured dynamic moduli of asphalt mixtures were compared with prediction results. The sand mastics with NMASs of 1.18 mm and 0.6 mm could be used to predict the asphalt mixture modulus across a range of temperatures and loading frequencies with good accuracy. The sand mastic with a NMAS of 0.3 mm overpredicted at high and low temperatures. The overprediction resulted from the difficulty of proper visualization of the smaller aggregate size in the model. [ABSTRACT FROM AUTHOR]

Although several techniques have been introduced to reduce reflective cracking, one of the primary forms of distress in hot-mix asphalt (HMA) overlays of flexible and rigid pavements, the underlying mechanism and causes of reflective cracking are not yet well understood. Fracture mechanics is used to understand the stable and progressive crack growth that often occurs in engineering components under varying applied stress. The stress intensity factor (SIF) is its basis and describes the stress state at the crack tip. This can be used with the appropriate material properties to calculate the rate at which the crack will propagate in a linear elastic manner. Unfortunately, the SIF is difficult to compute or measure, particularly if the crack is situated in a complex three-dimensional (3D) geometry or subjected to a non-simple stress state. In this study, the neural networks (NN) methodology is successfully used to model the SIF as cracks grow upward through a HMA overlay as a result of both load and thermal effects with and without reinforcing interlayers. Nearly 100,000 runs of a finite-element program were conducted to calculate the SIFs at the tip of the reflection crack for a wide variety of crack lengths and pavement structures. The coefficient of determination (R2) of all the developed NN models except one was above 0.99. Owing to the rapid prediction of SIFs using developed NN models, the overall computer run time for a 20-year reflection cracking prediction of a typical overlay was significantly reduced. [ABSTRACT FROM AUTHOR]

Cracking is a main source of structural distress in asphalt materials and asphaltic pavements. To predict crack-associated fracture damage in asphalt mixtures, this study presents a model using the finite-element method and a cohesive zone fracture model. The approach allows advanced characterization of the microstructural damage evolution in a more realistic length scale, the mixture heterogeneity, the inelastic material behavior, and the interactions among mixture constituents. The model presented herein accounts for (1) actual mixture heterogeneity by using digital image techniques; (2) inelastic material behavior based on elastic-viscoelastic constitutive relations; and (3) microscale fracture damage represented by the cohesive zone fracture model. A computational modeling framework is presented, and the applicability of the model is demonstrated through simulations. Model simulations are further analyzed by comparing numerical predictions to laboratory test results and by conducting parametric analyses of fracture properties. It is expected that the successfully developed computational model can provide better insights into the effect of mixture constituents on overall mixture performance, while minimizing modeling efforts and producing more accurate simulations than traditional approaches, with significant savings in experimental costs and time. [ABSTRACT FROM AUTHOR]

The writers recently developed a nonlinear viscoelastic-viscoplastic constitutive model, in order to represent the response of asphalt mixtures under different temperatures and rates of loading. This model has been implemented in the finite-element (FE) code Abaqus via the user material subroutine UMAT, and it was verified through comparisons with experimental data of asphalt mixtures at various stress levels and temperatures. This research develops a three-dimensional FE model using Abaqus to represent a three-layer pavement structure and to simulate the viscoelastic and viscoplastic responses under repeated loading at different temperatures. The results demonstrate the capability of the model in simulating the influence of temperature on permanent deformation and in predicting viscoelastic and viscoplastic strain distributions in the asphalt layer. The simulations show that tensile viscoplastic strain accumulates at the pavement surface, a phenomenon that could be associated with cracking of asphalt pavements. In addition, the results show that at high pavement temperature (40°C), tensile viscoplastic strain develops at the sides of the applied load due to asphalt mixture heave associated with permanent deformation and dilation. [ABSTRACT FROM AUTHOR]

Artificial neural network (ANN) and regression models are developed for the estimation of concrete slump using concrete constituent data. The concrete mix constituent and slump data from laboratory tests have been employed to develop all models. The results obtained in this study demonstrate the superiority of the ANN models. It was found that combining one or more concrete mix constituents and treating them as an independent input variable is not advantageous when using regression but can be very useful when using ANNs for modeling concrete slump. Sensitivity analyses based on the ANN models were carried out to evaluate the impact of different concrete mix constituents on the slump values. It was found that the slump attains a minimum value at the critical levels of mortar and coarse aggregates, and tends to increase with paste content and decrease with sand content in the concrete mix. [ABSTRACT FROM AUTHOR]

The Mechanistic-Empirical Pavement Design Guide (MEPDG) made available by the National Cooperative Highway Research Program in 2004 uses a power model that incorporates dynamic modulus (DM) as a factor in predicting rutting performance of asphalt concrete. The rutting model is empirical and the rutting profiles obtained from the model are based largely on the adjustment of calibration constants, not the DM. Various DM values would be capable of producing similar rutting profiles based on the current model. This study evaluates using accumulated strain data obtained from the Repeated Load Test (RLT) as an alternative to using DM. In addition, a model to represent the accumulated strain data obtained from the RLT is developed. The accuracy and behavior of the current model and the model developed in this study in representing a mix from Louisiana are compared. Alternatives for incorporating the RLT data into the MEPDG are also presented. [ABSTRACT FROM AUTHOR]

The viscoelastic behavior of asphalt mixtures can be conveniently presented in the form of a stiffness master curve in various engineering applications. However, the methods to obtain the in-service mixture stiffness are limited to the falling weight deflectometer (FWD) testing and back-calculation procedure because the pavement layer thicknesses in many cases are too thin to allow laboratory testing. The test protocol to measure the axial dynamic modulus requires cylindrical specimens with a height-to-diameter ratio higher than 2, while the cores need to be at least 38 mm thick for measuring shear stiffness. This technical note describes and compares the methods for constructing asphalt mixture master curves utilizing stiffness predictive equations for asphalt binders and mixtures, in addition to using laboratory measurements, as an alternative to FWD backcalculation analysis. This technical note also recommends constraining the low and high mixture stiffness values measured from simple shear testing to obtain stiffness comparable to the uniaxial dynamic modulus testing. [ABSTRACT FROM AUTHOR]

Increased ductility of columns made with high-strength concrete (HSC) can be accomplished through proper confinement of the concrete core. To determine the effectiveness of welded wire fabric as transverse reinforcement in HSC columns, an experimental investigation involving testing of ten full-scale columns in axial compression was conducted. The performance of columns laterally reinforced with welded wire fabric (WWF) was compared with that of unconfined concrete. Axial stress-strain diagrams of the concrete core from the experimental tests showed that substantial gains in strength and ductility of columns laterally reinforced with WWF can be achieved if the volumetric ratio of transverse steel was larger than 3.5%. Critical points on the stress-strain curve of confined concrete were determined and a mathematical model that considers the effect of the volumetric ratio of transverse steel on the stress-strain relationship is proposed. Comparison between the proposed model and the experimental results showed good agreement between the two. [ABSTRACT FROM AUTHOR]

Presents a mathematical model established for chloride penetration in saturated concrete. Development of two materials for binding capacity and chloride diffusivity; Parameters influencing chloride binding capacity and diffusivity; Numerical solution and comparison with test results.

Recently, dynamic modulus () test has gained substantial acceptance for Superpave mix performance evaluation and in designing asphalt pavements for rutting and fatigue cracking. Mechanistic empirical pavement design guide (MEPDG currently branded as AASHTOW are ME pavement design) is currently the state-of-the-art method of designing asphalt pavements and it utilizes data. Unfortunately, neither Superpave mix design method nor ME pavement design has used to evaluate asphalt concrete (AC) moisture damage. Though based rut and fatigue models are available in ME pavement design, there has not been any model for moisture damage of AC. To this end, this study attempts to correlate with moisture damage as a first step to moving toward mechanistic understanding. Moisture-induced sensitivity tester (MIST) is used for moisture conditioning of asphalt samples. Moisture damage resulting from MIST conditioning is evaluated using the dynamic modulus ratio (DMR) of wet to dry samples. MIST conditioning is found to decrease the value of asphalt concrete (AC) indicating the presence of moisture damage. Moreover, moisture damage shows an increasing trend with increasing MIST-conditioning number of cycles, temperatures, and pressures. To capture the correlation between DMR with MIST-conditioning cycles and pressures, two different models are developed. The coefficient of determination and are obtained for the MIST-cycle and MIST-pressure models. It is hoped that these models are incorporated in the ME pavement design in future. [ABSTRACT FROM AUTHOR]