Normalizing Behavior of Unsaturated Granular Pavement Materials

One of the important components of a flexible pavement structure is granular material layers. Unsaturated granular pavement materials (UGPMs) in these layers influence stresses and strains throughout the pavement structure, and have a large effect on asphalt concrete fatigue and pavement rutting (two of the primary failure mechanisms for flexible pavements). The behavior of UGPMs is dependent on water content, but this effect has been traditionally difficult to quantify using either empirical or mechanistic methods. This paper presents a practical mechanistic framework for determining the behavior of UGPMs within the range of water contents, densities, and stress states likely to be encountered under field conditions. Both soil suction and generated pore pressures are determined and compared to confinement under typical field loading conditions. The framework utilizes a simple soil suction model that has three density-independent parameters, and can be determined using conventional triaxial equipment that is available in many pavement engineering laboratories.     

Investigation of a Pavement Premature Failure on a Weak and Moisture Susceptible Base

An investigation was conducted to determine the root cause of the premature pavement failure. The premature pavement failure occurred in the form of rutting and alligator cracking. Although the affected portion was repaired by removing and replacing the top 75-mm asphalt concrete (AC), the repaired AC experienced recurring rutting and alligator cracking in a few weeks. Through extensive field and lab testing, it was found that the weak base is the root cause of the premature failure and the brittleness of the AC is secondary. However, both the base and AC were built according to plan and met the current material and field density requirements. It was concluded that density alone for construction quality control is not sufficient, as it was not able to protect against premature failures from occurring. Although there are many different ways to minimize premature failures, an immediate action is to include proof rolling in construction quality control. Proof rolling has been used with success to ensure proper compaction and to locate unstable areas, as the stability is greatly influenced by the degree of densification achieved during compaction.     

Modeling of Moisture Behavior of Wood Planks in Nonvented Flat Roofs

A computer model was extended and adapted to simulate the hygrothermal behavior of building envelope-wood components. The model was used to predict moisture movement in wood planks forming the decks of nonvented flat roofs insulated with cellulose. The gradient of water potential was considered as the driving force for moisture movement in wood. The model required the determination of convective heat- and mass-transfer coefficients, the sorption curves, the effective water conductivity for different wood species, and the hygrothermal conditions within the assembly to characterize the mass-conservation equation. Once these parameters were integrated in the computer model, this approach was then validated by carrying a simulation of the drying process of wood planks using experimental data from a large-scale test.     

Application of Hygrothermal Modeling Tool to Assess Moisture Response of Exterior Walls

The moisture design of exterior walls in a building envelope is an important task that needs to be carried out systematically to generate a sustainable and healthy built environment. Many conventional methods or practice guidelines are available for this purpose, based primarily on local traditions and with limited performance assessment records. In recent years, with the rapid development of global free trade and economy, new wall systems and unconventional materials have been introduced in every part of the world for reasons such as aesthetic appeal, cost effectiveness and so on. However, neither the long-term moisture management performance of these new wall systems nor the uses of unconventional materials have been assessed in a systematic way. The primary reason for this lack of assessment is the absence of a design-oriented methodology to perform the task. This paper presents selected results from a recently completed research project that demonstrate that it is indeed possible to assess the moisture management performance of exterior walls in a systematic way, using a hygrothermal modeling tool together with key inputs from a limited number of laboratory and field investigations. In this project the hygrothermal responses of exterior walls and their components were assessed with a novel moisture response indicator, called the RHT index, which is derived from relative humidity and temperature data over a time period. The results and discussion presented in this paper clearly show the need and usefulness of the application of hygrothermal simulation tool for the optimum moisture design of exterior wall systems in various geographic locations, when sufficient information is available from laboratory and field experiments.     

Moisture Diffusion in Shallow Clay Masses

Seasonal cycles of moisture and suction variation in shallow clay masses create repeating episodes of soil shrinkage and swelling that can adversely affect a wide variety of structures including pavements, shallow foundations, piers, and slopes. Design of such structures requires a means of adequately characterizing the depth of this moisture active zone and the magnitude of suction variations within the zone. This paper describes an analytical framework for characterizing suction variations in the moisture active zone and for estimating the soil mass moisture diffusion coefficient, one of the critical parameters governing the rate of moisture penetration in the soil. The paper presents extensions to an existing analysis for sinusoidal variations in surface suction to general nonsinusoidal conditions. It also presents a review of moisture diffusion coefficient data obtained from field measurements and shows that these data exceed laboratory measurements on intact soil specimens by up to two orders of magnitude. A conceptual model of moisture diffusion in a fractured soil mass provides an explanation of the differences between the field and laboratory values of the moisture diffusion coefficient.     

Analysis of Deep Moisture Barriers in Expansive Soils. II: Water Flow Formulation and Implementation

Several alternatives have been proposed to prevent damage to civil infrastructure founded on expansive soils. For example, deep moisture barriers have been used in highways and buildings. However, in some cases, the protected lanes or structures degrade to similar levels as the unprotected ones, although at a smaller rate. In spite of these poor results, relatively few efforts have been devoted to the development of analytical methods for rational designs on expansive soils. This paper couples the constitutive model for expansive soils developed in the companion paper with flow equations in a deforming medium and a finite element code is developed. The resulting numerical tool has the capacity of computing soil suction and volumetric strain changes of expansive soils under a defined wetting–drying regime. To verify the capabilities of this computer code, a laboratory barrier model was built. The model was instrumented to measure soil suction changes and the corresponding surface displacements. The experimental and theoretical results were compared. Finally, the numerical model was applied to a design example of a deep moisture barrier.     

Three-Dimensional Linear Behavior of Bituminous Materials: Experiments and Modeling

The linear viscoelastic properties of bituminous mixtures are used to design pavement structure. Usually, only complex moduli E* (complex Young modulus) or G* (complex shear modulus) characterizing the stiffness of the materials in one direction (1D) are measured by classical tests. In this paper, the three-dimensional (3D) behavior is investigated. The complex Poisson's ratio (ν*) is introduced. Its evolution with temperature and frequency is studied for a bitumen, a mastic, and a mix. Experimental results show that the time–temperature superposition principle is applicable in the 3D case. The same shift factor applies for E* and ν*. The Di Benedetto–Neifar model developed at Ecole Nationale des Travaux Publics de l’Etat to simulate so far the 1D thermo-elastoviscoplastic behavior of bituminous materials has been extended to simulate their 3D isotropic behavior. Calibration of the model and comparison between simulations in the linear viscoelastic domain and experimental data are proposed.     

Test Method to Measure the Relative Capacity of Wall Panels to Evacuate Moisture from Their Stud Cavity

Rainwater penetration is the source of moisture that causes the greatest damage to building envelope assemblies. The building envelope should be designed to reduce the amount of rainwater penetration by deflection and drainage. Since it is not realistic to assume a perfect wall without any leakage, the envelope should have the drying capacity to tolerate defects that may arise from the design, construction, and aging of the exterior wall system. Systems with a greater capacity to evacuate moisture from the stud cavity are less likely to undergo moisture damage. A new testing method is developed and deployed to evaluate the relative drying capacity of six wood-framed wall panels of different configurations built into a test hut and tested within a large scale environmental chamber. The wall panels used plywood, oriented strand board (OSB), or fiberboard as sheathing, but did not include cladding. A uniform moisture source was introduced in a water tray set on a load cell at the bottom of each stud cavity. The protocol is based on the hypothesis that the potential for moving a water molecule from the bottom plate to the exterior of the stud cavity is independent of the previous journey of that molecule, i.e., whether it has traveled from the interior of the bottom plate to the surface of the plate or whether it comes from free water in a tray at the level of the bottom plate. For a given set of boundary conditions, this potential is a function of the characteristics of the wall panel, and is identified as the drying capacity of the panel or its drying by evaporation index (DEI). The value of DEI corresponds to the evaporation rate. The moisture response of wall materials enclosing the stud cavity and the evaporation rate of the moisture source were monitored. The results show that this index can be used as an indicator of the relative drying capacity of different wall systems.     

Experimental Investigation of the Influence of Moisture on the Bond Behavior of FRP to Concrete Interfaces

The effects of moisture on the initial and long-term bonding behavior of fiber reinforced polymer (FRP) sheets to concrete interfaces have been investigated by means of a two-year experimental exposure program. The research is focused on the effects of (1) moisture at the time of FRP installation, in this paper termed “construction moisture,” consisting of concrete substratum surface moisture and external air moisture; and (2) moisture, in this paper termed “service moisture,” which normally varies throughout the service life of concrete. Concrete beams with FRP bonded to their soffits were prepared. Before bonding, concrete substrates were preconditioned with different moisture contents and treated with different primers. The FRP bonded concrete beams were then cured under different humidity conditions before being subjected to combined wet/dry (WD) and thermal cycling regimes to accelerate the exposure effects. Adhesives with different elastic moduli were used to investigate the long-term durability of each adhesive when subjected to accelerated WD cycling. Pull-off tests and bending tests were conducted at the beginning of the cycling and then again after 8 months, 14 months, and 2 years of exposure so as to evaluate the tensile and shear performance of the FRP-to-concrete interfaces. It was found that the effect of the concrete substrate moisture content on short-term interfacial bond performance could be eliminated if an appropriate primer was used. All FRP-to-concrete bonded joints failed at the interface between the primer and concrete after exposure while those not exposed usually failed within the concrete substrate. After exposure to an environment of accelerated WD cycles, it was also found that the interfacial tensile bond strength degraded asymptotically with the exposure time while the flexural capacity of the FRP sheet bonded plain concrete beams even increased. The mechanism behind the above, which is an apparently contradictory phenomenon, is discussed.     

Modeling of Moisture Diffusion in FRP Strengthened Concrete Specimens

Modeling the movement and distribution of moisture in the fiber-reinforced polymer (FRP) composites strengthened concrete structure is important because the interfacial adhesion between FRP and concrete is susceptible to moisture attack. Using relative humidity as the global variable, the moisture diffusion governing equation was derived for the multilayered system in this study. The moisture diffusivity (diffusion coefficient) and the isotherm curve, which correlates the moisture content to environmental relative humidity, of each constitutive material (concrete, epoxy, and FRP) were experimentally determined. A multilinear diffusivity model was developed for concrete based on desorption test, and a linear diffusivity model was proposed for epoxy adhesive based on absorption test. A simple method was developed to directly measure the FRP/concrete interface region relative humidity (IRRH). Finite-element analysis was performed to study the moisture diffusion in the FRP-adhesive-concrete system. The IRRH values were obtained for different environmental relative humidity in the numerical study. The error between the experimental and numerical results of IRRH at test locations was less than 5% RH. The good agreement between experimental and numerical results indicates that the approach developed in this study worked well.     

Experimental Study on Moisture Migration in Unsaturated Loess under Effect of Temperature

In this paper, moisture migration in loess considering temperature effect is studied by tests on unsaturated loess samples with different densities and initial moisture contents. Test results reveal that obvious changes in moisture content distribution in a loess sample can be observed after temperature difference is exerted on the two ends of the sample. Moisture content at the cold end increases and that at the hot end decreases. Under the effect of temperature difference, moisture content difference at the two ends of a soil sample is related to the initial moisture content, soil density, and magnitude of the temperature difference. Generally speaking, larger temperature differences and smaller soil densities result in more obvious moisture migration and larger moisture content differences at the two ends of the soil sample. When the initial moisture content is large, the moisture content difference caused by a temperature difference is small; when the initial moisture content is small, the moisture content difference caused by a temperature difference is also small; when the initial moisture content is moderate, the moisture content difference caused by a temperature difference is large. After the analysis of test results, taking the soil density and moisture content into account, a formula is obtained to determine the moisture content gradient resulting from the temperature gradient. Reliability of the formula is verified by comparing the measured and calculated data. Because of the reverse migration of liquid water and water vapor at the end of the experiment, it is difficult to determine the thermal potential and matrix potential. Based on the experimental data, this paper probes into the water potential equation that can be used for stability analysis. The equation considers the comprehensive impact of soil density, temperature gradient, moisture content, and moisture content gradient on water potential. It only applies to analyze stable distributions of temperature and does not apply to unstable temperature distributions.     

Modeling Pd-Catalyzed Destruction of Chlorinated Ethenes in Groundwater

Groundwater contamination by chlorinated ethenes is a widespread environmental problem. Shortcomings in conventional remediation methods have motivated research into novel treatment technologies. A palladium/alumina catalyst in the presence of molecular hydrogen gas (referred to hereafter as the Pd/H2 system) has been demonstrated to destroy chlorinated ethenes in contaminated groundwater. This study presents a model for aqueous-phase destruction of chlorinated ethenes in contaminated groundwater using the Pd/H2 system that includes catalyst deactivation and regeneration. The model is validated using published data from laboratory column experiments from Stanford University. The model is then coupled with an analytical groundwater flow model to simulate application of in-well Pd/H2 reactors for in situ treatment of chlorinated ethene contaminated groundwater in a recirculating horizontal flow treatment Well (HFTW) system. Applying the model under realistic conditions results in approximately 130 days of HFTW system operation without significant catalyst deactivation. This suggests catalyst deactivation will not significantly affect system performance in a real remediation scenario. The model presented in this study, which simulates deactivation kinetics and regeneration of an in-well catalyst that is a component of a recirculating well system designed for in situ treatment of contaminated groundwater, represents an important step in transitioning the Pd/H2 technology to the field.     

Failure in Composite Materials due to Volumetric Expansion of Freezing Moisture

A model is developed for predicting volumetric expansion induced cracking in orthotropic composite materials due to freezing of trapped moisture in a slender rectangular flaw region. Conformal transformation and the complex function method are used to obtain the stress distribution in the matrix at the interior boundary. The stress field in the rectangular inclusion is derived by solving for two important variables characterizing the expanded equilibrium boundary determined by the principle of minimum strain energy. The compressive stress acting on the long side of the rectangular inclusion acts as a crack driving force., The model is used to predict the occurrence of cracking due to volumetric expansion of ice in a specific composite, EXTREN, that has been observed in experiments. The model can be adapted to predict fatigue life of composites under freeze-thaw conditions.     

Relationship between the Undrained Shear Strength, Water Content, and Mineralogical Properties of Fine-Grained Soils

The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soils; these relationships, however, have not yet been investigated. The findings described in this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals, their quantity in soil composition, and the interlayer water quantity in the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.     

Equivalent Effective Stress and Compressibility of Unsaturated Kaolinite Clay Subjected to Drying

Three-dimensional compressibility tests performed on unsaturated kaolinite clay subjected to drying showed that the volume change is a function of the equivalent effective stress (EES). The EES in the clay at different water contents was measured by performing direct tensile tests. When the clay has high water content (saturated funicular state), its volume decreases notably as the water content is reduced, i.e., the equivalent effective stress is increased. If the clay has a water content in an intermediate interval (complete pendular state), the volume is almost constant because the equivalent effective stress is almost constant. For the interval of low water contents (partial pendular state), the volume of the clay increases as the water content is reduced. This occurs because the equivalent effective stress is reduced when the moisture content in the clay is reduced, and contrasts with the saturated funicular state. The minimum volume in the clay was reached when the maximum equivalent effective stress was developed. A conceptual framework explains the influence of the different states of water distribution to the EES.     

Modeling Cross Anisotropy in Granular Materials

A constitutive model has been developed to capture the behavior of cross-anisotropic frictional materials. The elastoplastic, single hardening model for isotropic materials serves as the basic framework. Based on the experimental results of cross-anisotropic sands in isotropic compression tests, the principal stress coordinate system is rotated such that the model operates isotropically within the rotated framework. Experimental plastic work contours on the octahedral plane are plotted for a series of true triaxial tests on dense Santa Monica Beach sand to study the effects of cross anisotropy on the evolution of yield surfaces. The amount of rotation of the yield and plastic potential surfaces decreases to zero (isotropic state) with loading. The model is constructed for cases where the principal stress and material symmetry axes are collinear and no significant rotation of principal stresses occur. The model incorporates fourteen parameters that can be determined from simple experiments, such as isotropic compression, drained triaxial compression, and triaxial extension tests. A series of true triaxial and isotropic compression tests on dense Santa Monica Beach sand are used as a basis for verification of the capabilities of the proposed model.     

Hysteresis of Capillary Stress in Unsaturated Granular Soil

Constitutive relationships among water content, matric suction, and capillary stress in unsaturated granular soils are modeled using a theoretical approach based on the changing geometry of interparticle pore water menisci. A series of equations is developed to describe the net force among particles attributable to the combined effects of negative pore water pressure and surface tension for spherical grains arranged in simple-cubic or tetrahedral packing order. The contact angle at the liquid–solid interface is considered as a variable to evaluate hysteretic behavior in the soil–water characteristic curve, the effective stress parameter χ, and capillary stress. Varying the contact angle from 0 to 40° to simulate drying and wetting processes, respectively, is shown to have an appreciable impact on hysteresis in the constitutive behavior of the modeled soils. A boundary between regimes of positive and negative pore water pressure is identified as a function of water content and contact angle. Results from the analysis are of practical importance in understanding the behavior of unsaturated soils undergoing natural wetting and drying processes, such as infiltration, drainage, and evaporation.     

Line‐of‐Balance Scheduling in Pavement Construction

Linear Scheduling Methods are best suited to projects that display repetitive characteristics, but their use in the construction industry is limited. Line‐of‐Balance (LOB) is a Linear Scheduling Method that also makes use of network technology. Its benefits and shortcomings are investigated in a high‐way surface treatment project where LOB has been used experimentally. It was determined that LOB is extremely sensitive to errors in man hour, crew size, and activity duration estimates. There are also problems of a visual nature with the presentation of the diagram. On the other hand, LOB allows a better grasp of the project than any other scheduling technique because it is possible to adjust activities' rates of production. It provides a smooth and efficient flow of resources and requires less time and effort to produce than network schedules. Research to make Linear Scheduling Methods more attractive is recommended.     

Sudden Failure of a Heavily Loaded Container Pavement

The case history of a sudden and unexpected failure in a pavement designed for 82?Mg axle loads at Port Botany in Sydney, Australia has been prepared using data derived from investigation of the failure. Failure of the pavement, comprised of an asphaltic concrete surface, unbound granular fine crushed rock base, crushed sandstone subbase, and sandy subgrade, and designed using the rational method—CIRCLY, occurred within days of being put into service. The failure resulted from a 20–30% increase in base course saturation levels following compaction that led to partial liquefaction under repeated heavy loading. There was a general failure throughout the storage area where trafficking was most intense and the pavement remained intact in lightly trafficked areas. The intact areas recovered over time without intervention through a moisture equilibration process as evidenced by an increase in measured pavement stiffness and loss of moisture within the pavement profile.     

Impact of Salinity on MS-2 Sorption in Saturated Sand Columns—Fate and Transport Modeling

This research investigated the sorption and transport of MS-2 in saturated sand under a wide range of salinities using one-dimensional column experiments. The salinity varied from 0 ppt (fresh water) to 30 ppt. The MS-2 in the fresh water showed very weak adsorption due to having the same negative charge as the sand. Increasing the salinity concentrations dramatically enhanced MS-2 adsorption. The MS-2 breakthrough revealed the existence of reversible and irreversible sorption sites in the sand. Salinity increased MS-2 attachment by compressing the double layers of MS-2 and reversible sorption sites. The salinity also changed some reversible sorption sites into irreversible sorption sites by reversing to positive surface charges of silica powder. An advection-dispersion-sorption model with a two-site reversible-irreversible kinetic sorption was developed to describe MS-2 breakthrough under different salinity conditions. The sorption parameters were estimated and their independence was evaluated by minimizing the total squared error of the MS-2 data. The proposed model showed good agreement with the experimental data for a wide range of salinity levels from fresh water to near seawater. The strong sorption shown in the MS-2 breakthrough at high salinity levels above 8 ppt was able to distinguish the proposed model from other sorption models. This study promotes the understanding of the viral sorption with salinity and provides a useful model for coastal management of viral migration in saline coastal groundwater.