Journal of Materials in Civil Engineering

This paper presents a computational micromechanics modeling approach to predict damage-induced mechanical response of asphalt mixtures. Heterogeneous geometric characteristics and inelastic mechanical behavior were taken into account by introducing finite element modeling techniques and a viscoelastic material model. The modeling also includes interface fracture to represent crack growth and damage evolution. The interface fracture is modeled by using a micromechanical nonlinear viscoelastic cohesive-zone constitutive relation. Fundamental material properties and fracture characteristics were measured from simple laboratory tests and then incorporated into the model to predict rate-dependent viscoelastic damage behavior of the asphalt mixture. Simulation results demonstrate that each model parameter significantly influences the mechanical behavior of the overall asphalt mixture. Within a theoretical framework of micromechanics, this study is expected to be suitable for evaluating damage-induced performance of asphalt mixtures by measuring only material properties and fracture properties of each mix component and not by recursively performing expensive laboratory tests that are typically required for continuum damage mechanics modeling.

This paper focuses on the effect of filler on the low-temperature creep of asphalt mastic. Based on experimental results obtained from bending-beam rheometer (BBR) experiments for both pure bitumen and mastic characterized by different filler types and content, a recently proposed multiscale model is employed for the prediction of low-temperature creep properties of the bitumen-filler composite. Accounting for the distinct matrix-inclusion morphology present at the so-called mastic-scale, the Mori–Tanaka scheme is employed for homogenization. This homogenization scheme is applied to the bitumen-filler composite, giving insight into the effect of filler on the low-temperature behavior of mastic. Hereby, the filler particles are considered as rigid inclusions with spherical shape, resulting in excellent agreement between the creep parameters of the homogenized material and the respective experimental BBR results. This agreement indicates that only the volume fraction of the filler, entering the Mori–Tanaka scheme, and neither the filler geometry nor the chemical composition of the filler influence low-temperature creep of asphalt mastic.

In this paper, an analytical method utilizing the transfer function method has been proposed to evaluate the thermal and moisture transfer behavior in porous building material. Both heat and moisture transfer are simultaneously considered and their interactions are modeled. The coupled partial differential equations and boundary conditions are first subjected to Laplace transformation, and then the equations are solved by introducing the transfer function method. The transient temperature and moisture content distribution across the building material can thus be easily obtained from the solutions. The results are compared with the experimental data and the other numerical solution available in the literature. A good agreement is obtained.

Aggregates are an important constituent of asphalt concrete, hydraulic cement concrete, and granular base. The shape, angularity, and surface texture of aggregates are basically variations of asperities at different dimensional scales and affect mixture properties in different ways. This paper presents a unified Fourier morphological analysis method to quantify the shape, angularity, and surface texture of aggregates. Evaluation of these characteristics of 10 aggregates of known quality indicates that Fourier morphological analysis quantitatively ranks these aggregates in consistence with qualitative evaluations.

A new methodology is presented in this paper for determining cross-anisotropic aggregate base properties, i.e., directional dependency of moduli and Poisson’s ratios, as inputs into mechanistic pavement analysis considering effects of actual traffic or moving wheel loading. The proposed materials characterization requires conducting constant stress path triaxial tests and incrementally varying loading stress path slopes at similar stress states that are representative of various moving wheel loading conditions in the laboratory. In accordance, cross-anisotropic aggregate properties are determined by varying slightly the stress path slopes during testing and then by employing an error minimization approach to interpret the test results. Crushed aggregate specimens were prepared and tested to obtain cross-anisotropic properties at five different stress path slopes representative of various moving wheel load induced compression and extension type pavement stress states. Vertical resilient moduli were commonly found to be larger than horizontal ones and critically low resilient moduli were also obtained for some extension states. The findings point to advances needed in granular materials characterization such as incorporating anisotropic and stress dependent behavior into mechanistic pavement analysis and properly considering the effects of moving wheel loading on pavement response.

Ladle furnace reducing slag is a common byproduct in steelmaking of carbon and low alloy steels. After air cooling and weathering over several days, this material is completely ground into fine white particles. Physical, chemical, and crystalline characterizations were performed in order to verify possibilities for its direct application as a construction material. Two ways are proposed for the immediate use of ladle furnace slag: masonry mortars and paving mixes for rural roads with low levels of traffic.

Based on the idea of taking simultaneous advantage of the effects of different types of fibers, new materials called hybrid fiber reinforced concretes have been developed by combining fibers of different geometry and material. In the present paper, the benefits in terms of concrete toughness from a combination of micro- and macrosteel fibers are evaluated under both bending and uniaxial tensile tests on specimens of different sizes. Experimental results are very sensitive to the strain gradient in the cracked section, to the fiber geometry and to the area of the cracked surface. In fact, a larger scatter in the experimental results was observed in specimens with smaller cracked surfaces where a greater variation of the macrofiber density occurred. For this reason, beside the size effects, the fiber size and the dimension of the cracked section markedly influence the characteristic value of the fracture parameters. A numerical simulation based on nonlinear fracture mechanics of the experimental test was carried out in order to better identify the fiber contribution in the fracture propagation.

A viscoelastic (VE)–viscoplastic (VP) model for characterizing asphalt concrete behavior is described. The parameters of the model are determined in the prepeak region of the loading, under small load. It includes two separate damage functions, one for each component of the deformation, to describe the material behavior under heavy load and in the postpeak region of the fracture. In order to extend the material characterization to the postpeak region, the size of the fracture process zone (FPZ) is evaluated from mapping the strain in a fracture test. The deformation in the FPZ, in the continuum framework is computed from total and local measurements. Uniaxial tests, including frequency sweep for the undamaged, linear VE component, repeated triaxial load for the undamaged VP component are conducted and used to derive the material properties in the prepeak region. A tension up to failure test is used to determine the damage functions.

Asphalt concrete has been recognized as an anisotropic material, but the degree of anisotropy and its implications for pavement design and analysis have not been well understood. This paper illustrates the difference between the stress fields of an isotropic and an anisotropic pavement under wheel load through analytical solution and finite-element simulation for several cases. A servocontrolled true triaxial (cubical) testing device was used to test $4\text{-}\mathrm{in.}$ cubical asphalt concrete specimens under general stress states to characterize the anisotropic properties of asphalt concrete. It was discovered that (1) the stiffness of a cored field specimen has significant differences in the vertical and horizontal direction; and (2) the significant difference may result in larger shear stress and tensile stress in a pavement. These findings indicate that characterization and modeling of the anisotropic properties of asphalt concrete are an important area that deserves further investigation.

This paper reports the findings of experimental studies with regard to some common engineering properties (e.g., grain size, specific gravity, compaction characteristics, and unconfined compression strength) of both low and high calcium fly ashes, to evaluate their suitability as embankment materials and reclamation fills. In addition, morphology, chemistry, and mineralogy of fly ashes are studied using scanning electron microscope, electron dispersive x-ray analyzer, x-ray diffractometer, and infrared absorption spectroscopy. In high calcium fly ash, mineralogical and chemical differences are observed for particles, $>75\mu \mathrm{m}$ and the particles of $<45\mu \mathrm{m}$ size. The mode and duration of curing significantly affect the strength and stress–strain behavior of fly ashes. The geotechnical properties of fly ash are governed by factors like lime content (CaO), iron content $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$ and loss on ignition. The distinct difference between self-hardening and pozzolanic reactivity has been emphasized.

It is estimated that about $40\text{billion}\text{tons}$ of oil shale is available in the southern part of Jordan. Several studies are being carried out to utilize this source of energy efficiently. Upon direct combustion of this oil shale, more than 50% of its quantity will be left as fly ash. Resulting fly ash is considered undesirable and environmentally hazardous. This investigation was conducted to make use of the fly ash in the modification of local asphalt mixes. The modification efficiency was evaluated by the improvement in the performance of prepared asphalt concrete mixes. To carry out this study, enough quantity of oil shale was collected from Al-Lajjoun quarries (about $100\mathrm{km}$ south of Amman, Jordan). This material was then crushed, sieved, and burned to obtain the fly ash. Chemical and physical analyses of the fly ash were then performed. Asphalt concrete mixes having different percentages of fly ash (0, 10, 50, and 100%) as a replacement of the mineral filler, material passing the $0.075\mathrm{mm}$ sieve, were prepared. These samples were characterized using the Marshall Stability, indirect tensile strength, stripping resistance, resilient modulus, dynamic creep, fatigue, and rutting tests. Test results were statistically analyzed and indicated that, in general, the addition of fly ash improved both strength, and water sensitivity of the asphalt concrete mixes. Replacing 10% of the mineral filler by fly ash proved to be the most effective percentage in improving the mechanical properties of all the prepared samples.

The objective of this paper is to assess the potential use of the geogauge and the light falling weight deflectometer (LFWD) as quality control/quality assurance $(Q_C∕Q_A)$ devices for testing subgrades, base courses, and compacted soil layers. A comprehensive laboratory experimental program was conducted on compacted layers of silty clay, clayey silt, cement-treated clay, sand, gravel, recycled asphalt pavement, and limestone aggregates. The geogauge, LFWD, static plate load test (PLT), and the dynamic cone penetration (DCP) measurements were acquired for the constructed layers. The geogauge elastic modulus and the LFWD dynamic modulus were correlated with the PLT initial and reloading elastic moduli and with the DCP penetration rates. The results of this study show that the geogauge and the LFWD can be used to calculate the elastic modulus/stiffness characteristics of compacted layers. Whereas the geogauge and the LFWD determined the initial modulus of the cement-treated clay, they did not yield accurate measurements of strength gain with time. Good statistical correlations were found between elastic moduli measured by the devices used in this investigation.

The aim of this paper is to develop a model for simulating carbonation of fly ash concrete. The model describes the diffusion of gases ( $\mathrm{C}{\mathrm{O}}_2$ and water vapor) in concrete by the mass balance equations and the Fick’s law of diffusion. The time dependent hydration, and pozzolanic and carbonation reactions were considered for evaluating the amount of calcium hydroxide in concrete. The rate of carbonation reaction was formulated based on the Arrhenius’s formulation. The model was verified by using the results of relative water content, amount of calcium hydroxide, and carbonation depth tested in accelerated and real environments. The influence of changes in parameters on mix proportion and environmental condition were investigated. The verification results were found to be satisfactory in the prediction of carbonation of fly ash concrete.

The effect of wood decay on the fully reversed cyclic performance of nailed oriented strand board (OSB) sheathing to Douglas-fir framing member connections was investigated. The connection geometry evaluated in this study was representative of lateral force resisting systems of light-framed wood structures, including shear walls and horizontal diaphragms. Maximum loads, slip at maximum loads, yield loads, initial stiffnesses, and cumulative energy dissipation of nailed connections exposed to increasing intervals to the brown rot fungus, Postia placenta, were characterized using fully reversed cyclic loading. After the destructive connection tests, portions of the sheathing and framing member from the samples were further evaluated for specific gravity. The OSB sheathing specific gravity was the best descriptive variable for the mechanical properties measured in this study. Cumulative energy dissipation was the connection property most affected by decay damage.

This paper discusses the interpretation of electrical conductivity measurements in concrete to assess water penetration. Specifically, a series of finite element simulations were performed to develop an analytical function that relates the measured electrical conductivity to the position of the moisture front inside a concrete specimen. The effects of specimen size and electrode location were considered in the simulations. An approach is demonstrated whereby the measured conductivity was used to determine the position of the moisture front after rewetting thereby enabling the sorption properties of the cover concrete to be evaluated. The method described in this paper improves on previous approaches in that it enables resolving the position of moisture front based on only one electrical measurement and properties of the saturated and unsaturated concrete. This allows the use of one electrode pair to detect the position of moisture front at any time a measurement is performed.

To realize the potential of micro- and macrofiber blends in a concrete matrix, a concrete containing polyvinyl alcohol (PVA) or steel microfibers and steel macrofibers was designed using a mixture proportioning method that provides good workability in concretes containing microfibers. This procedure is based on an optimum paste volume fraction determined from the relationship between flow and paste content. The mechanical performance, water permeability of the cracked material, and shrinkage crack resistance of cast concrete were evaluated. In the hybrid concrete, the microfibers delayed the development of macrocracks and so the composite demonstrated greater strength and crack resistance than a similar matrix reinforced with macrofibers only. This influence was less pronounced than was observed with a mortar matrix in a previous study. This is explained by differences in the failure mechanism of the fibers: A stronger fiber-matrix bond resulting from a lower water-to-binder ratio caused the microfibers to break instead of pull out. The macrofibers were also more likely to break in the hybrid fiber-reinforced concrete than in the same matrix containing macrofibers alone—since the microfibers reinforced the matrix, increasing the macrofiber pullout resistance.