Showing papers in "Journal of Materials in Civil Engineering in 2005"
TL;DR: In this article, the characteristics of engineered cementitious composites (ECCs) subjected to dynamic tensile loading and high-velocity projectile impact have been investigated and are reported in this paper.
Abstract: The characteristics of engineered cementitious composites (ECCs) subjected to dynamic tensile loading and high-velocity projectile impact have been investigated and are reported in this paper. Hybrid-fiber ECC containing a combination of high-modulus steel fibers and relatively low modulus polyethylene fibers was adopted to achieve a desired balance between the ultimate strength and the strain capacity of the material required for impact- and blast-resistant structures. Dynamic uniaxial tensile tests at varying strain rates of 2× 10−6 to 0.2 s−1 were carried out, and ECC was found to be able to provide much higher enhancement in tensile strength than plain concrete and still be able to maintain pronounced tensile strain-hardening behavior. At higher rates of strain, ECC showed multiple-cracking behavior, similar to that observed from quasi-static tests, with tight crack width of about 0.1 mm . The results from high-velocity (300–750 m∕s) impact tests demonstrated the potential of ECC in providing improved...
236 citations
TL;DR: In this paper, the influence of bond strength on masonry compressive strength has been examined through an experimental program using local bricks and mortars, and the results clearly indicate that an increase in bond strength, while keeping the mortar strength constant, leads to a significant increase in the compressive strengths of masonry.
Abstract: This paper focuses on some issues pertaining to brick-mortar bond and masonry compressive strength Failure theories for masonry under compression make the assumption that the bond between brick and mortar remains intact at the time of failure of the brick or mortar The influence of bond strength on masonry compressive strength is not fully accounted for in these failure theories In this investigation, the influence of bond strength on masonry compressive strength has been examined through an experimental program using local bricks and mortars Masonry prism compressive strength has been determined when the brick-mortar bond strength is varied over a wide range without altering the strength and deformation characteristics of the brick and mortar Brick-mortar bond strength has been determined through flexure bond strength and shear bond strength tests A relationship between the masonry prism compressive strength and bond strength has been obtained The results clearly indicate that an increase in bond strength, while keeping the mortar strength constant, leads to an increase in the compressive strength of masonry
207 citations
TL;DR: In this paper, hydrated lime is evaluated as a filler in bitumen and is compared to similarly sized filler comprised of calcium carbonate, limestone, and limestone-concrete.
Abstract: Hydrated lime is evaluated as a filler in bitumen and is compared to similarly sized filler comprised of calcium carbonate, limestone. Extensive laboratory testing is considered, including rheological testing of mastics (with a dynamic shear rheometer, a dynamic mechanical analyzer, and a bending beam rheometer); low temperature elongation and fracture tests on mastics; torsional fatigue testing of mastics; fatigue testing of mixtures; and permanent deformation testing of mixtures. These tests confirm that hydrated lime as a filler significantly impacts the rate and level of microcrack-induced damage, microdamage healing, and plastic and viscoelastic flow in both mastics and mixtures across a wide range of temperatures (from low to high temperatures, representative of the pavement environment). Hypotheses are presented based on rheological models of filled liquids and bitumen microstructure to explain the test results and the fact that the response of hydrated lime as a filler in bitumen requires an understanding of the physical and chemical interactions on both the micro- and nanoscale. Furthermore, the impact of hydrated lime as a filler is dependent on its interaction with a specific bitumen.
194 citations
TL;DR: In this paper, the degree of dispersion of short microfibers in cement, as assessed by electrical resistivity measurement for the case of electrically conductive fibers at a volume fraction below the percolation threshold, is improved by the use of admixtures (namely, silica fume, acrylic particle dispersion, methylcellulose solution, and silane) and fiber surface treatment (such as ozone treatment).
Abstract: The degree of dispersion of short microfibers in cement, as assessed by electrical resistivity measurement for the case of electrically conductive fibers at a volume fraction below the percolation threshold, is improved by the use of admixtures (namely, silica fume, acrylic particle dispersion, methylcellulose solution, and silane) and fiber surface treatment (such as ozone treatment). Acrylic particle dispersion is more effective than latex particle dispersion.
181 citations
TL;DR: In this article, a transient, two-dimensional finite-difference model is developed to assess temperature fluctuations in asphalt pavements due to thermal environmental conditions, and sensitivity analyses are performed to study the impact of a number of thermal environmental and pavement geometric parameters on predicted temperature responses.
Abstract: A transient, two-dimensional finite-difference model is developed to assess temperature fluctuations in asphalt pavements due to thermal environmental conditions. Fluctuations in temperatures significantly affect pavement stability and the selection of asphalt grading used in pavements. The ability to accurately predict asphalt pavement temperature at different depths and horizontal locations based on thermal environmental conditions will greatly help pavement engineers in performing back-calculations of pavement modulus values and in selecting the asphalt grade to be used in various pavement lifts through detailed examination of predicted pavement temperature distributions on various pavement mixes. A more sophisticated selection of asphalt through specification of less expensive asphalt binders in lower lifts is thus possible for the provision of more economical solutions to rising pavement construction costs. As part of the model validation, sensitivity analyses are performed to study the impact of a number of thermal environmental and pavement geometric parameters on predicted temperature responses.
167 citations
TL;DR: In this article, the use of Class F fly ash amended soil-cement or soil-lime as base layers in highways was investigated, and a battery of tests were performed on soil-fly ash mixtures prepared with cement and lime as activators.
Abstract: Class F fly ash cannot be used alone in soil stabilization applications as it is not self-cementing. An activator such as Portland cement or lime must be added to produce cementitious products often called pozzolan stabilized mixtures. The developed mixture must possess adequate strength and durability, should be easily compacted, and should be environmentally friendly. Roadways have a high potential for large volume use of the fly ash stabilized soils. The main objective of this study is to investigate the use of Class F fly ash amended soil–cement or soil–lime as base layers in highways. A battery of tests were performed on soil–fly ash mixtures prepared with cement and lime as activators. Unconfined compression, California bearing ratio, and resilient modulus tests were conducted. Finally, required base thicknesses were calculated using the laboratory-based strength parameters. Results of the study show that the strength of a mixture is highly dependent on the curing period, compactive energy, cement c...
151 citations
TL;DR: In this article, a mixture proportioning method was used to realize the potential of micro-and macro-fiber blends in a concrete matrix, a concrete containing polyvinyl alcohol (PVA) or steel microfibers and steel macrofiberers was designed using a mixture proportionaling method that provides good workability in concretes containing microfiber.
Abstract: 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 t...
148 citations
TL;DR: In this paper, a new laboratory procedure for the determination of thermal properties of asphalt concrete specimens was discussed, and the effect of compaction on thermal properties was tested by compacting the briquettes to 67, 99, 133, and 212 gyrations using the superpave gyratory compactor.
Abstract: Reliable implementation of transient temperature prediction models for asphalt pavements has been impeded by lack of reliable thermo–physical properties data. The existing methodology based on ASTM C177-85 is not conducive to asphalt concrete specimens due to the difficulty to meet the slab requirements of the standard. This paper discusses a new laboratory procedure for the determination of thermal properties of asphalt concrete specimens. The new device can accommodate small specimens derived from either laboratory compacted 150 mm diameter briquettes or cores from in-service pavements. The effect of compaction on thermal properties was tested by compacting the briquettes to 67, 99, 133, and 212 gyrations using the superpave gyratory compactor. Thermal conductivity (λ) was determined after the experiment reached steady state, whereas thermal diffusivity (α) was determined during the transient state. Analytical curve fitting technique was applied to the test data to compute the thermal diffusivity. Therm...
131 citations
TL;DR: In this article, a unified Fourier morphological analysis method is presented to quantify the shape, angularity and surface texture of aggregates, which can be used to rank aggregates.
Abstract: 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.
128 citations
TL;DR: In this article, 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, respectively.
Abstract: 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.
117 citations
TL;DR: In this article, the authors investigated the impact of hydrated lime on the moisture resistance of paving mixtures of asphalt and limestone and granite aggregates by freeze-thaw cycling of the mixtures.
Abstract: Experiments were performed to investigate the impact on the moisture resistance of paving mixtures of the addition of hydrated lime directly to the asphalt prior to mixture preparation. Moisture resistance was evaluated on mixtures prepared using a strategic highway research program asphalt and limestone and granite aggregates by freeze–thaw cycling of the mixtures in water. Other parameters investigated in addition to hydrated lime that might affect moisture damage were oxidative aging and the addition of a model ketone to the asphalt. After the freeze–thaw cycling experiments, the specimens were subjected to selective solvent extractions to isolate the polar organic materials strongly adsorbed on the aggregate surfaces. Results of the extraction experiments indicate that the composition in the asphalt–aggregate interfacial region may change during repeated freeze–thaw cycling. Oxidative aging improved the resistance of the mixtures to moisture damage. Hydrated lime, when added to the asphalt prior to pr...
TL;DR: In this paper, 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.
Abstract: 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 ( QC ∕ QA ) 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 accura...
TL;DR: In this article, the properties of fly ashes have been studied using scanning electron microscopy, electron dispersive x-ray analyzer, xray diffractometer, and infrared absorption spectroscopy.
Abstract: 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 μm and the particles of <45 μm 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 ( Fe2 O3 ) and loss on ignition. The distinct difference between self-hardening and pozzolanic reactivity has been emphasized.
TL;DR: In this paper, it was demonstrated that short fiber reinforced geopolymer composites (SFRGCs) could be extruded without additional rheological modifier. But, the extruded products were thin plates with 6 mm thickness, and the experimental results showed that the addition of PVA fiber could largely increase the ductility of SFRGC, resulting in fiber failure modes changing from brittle to ductile.
Abstract: Geopolymer composites reinforced with short polyvinyl alcohol (PVA) fibers have been manufactured using the extrusion technique. The extruded products were thin plates with 6 mm thickness. It was demonstrated that short fiber reinforced geopolymer composites (SFRGCs) could be extruded without additional rheological modifier. Bending tests have been conducted with the extruded samples to investigate their mechanical properties. The fiber failure patterns in SFRGCs with various formulations were examined by scanning electron microscope and energy dispersive x-ray analysis techniques. The experimental results showed that the addition of PVA fiber could largely increase the ductility of SFRGCs, resulting in fiber failure modes changing from brittle to ductile. The effects of varying the amount of fly ash on the flexural behavior of various SFRGCs were also investigated. The SFRGCs incorporating small percentage of fly ash showed higher flexural strengths but smaller defections, while the SFRGCs incorporating a large percentage of fly ash had lower flexural strengths, but larger deflections. This could be attributed to the change of the bonding between fiber and matrix that led the change of failure mode from fiber fracture to fiber pullout.
TL;DR: In this article, a four-layer feed-forward neural network is constructed and applied to determine a mapping associating mix design and testing factors of asphalt concrete samples with their performance in conductance to flow or permeability.
Abstract: In this study, a four-layer feed-forward neural network is constructed and applied to determine a mapping associating mix design and testing factors of asphalt concrete samples with their performance in conductance to flow or permeability. To generate data for the neural network model, a total of 100 field cores from 50 different mixes (two replicate cores per mix) are tested in the laboratory for permeability and mix volumetric properties. The significant factors that affect asphalt permeability are identified using simple and multiple regression analysis. The analyses results show that permeability of an asphalt concrete is affected mainly by five factors: (1) air void ( Va ) ; (2) the grain size through which 10% materials pass ( d10 ) ; (3) the grain size through which 30% materials pass ( d30 ) ; (4) saturation, or the CoreLok Infiltration Coefficient (CIC); and (5) effective asphalt to dust ratio ( Pbe ∕ P0.075 ) . The significant factors are then used to define the domain of a neural network. Regar...
TL;DR: In this paper, the results of a study investigating four different OGFC mixes containing no additives, cellulose fibers, styrene butadiene rubber (SBR) polymer, and a combination of both fibers and SBR polymer were presented.
Abstract: Open-graded friction course (OGFC) or porous mixtures consist of an open gradation, mostly of coarse size aggregate with little fines. The benefits of an OGFC mixture are typically increased surface permeability, noise reduction, and enhanced surface friction, especially in wet weather. This paper presents the results of a study investigating four different OGFC mixes containing no additives, cellulose fibers, styrene butadiene rubber (SBR) polymer, and a combination of both fibers and SBR polymer. Mix designs were performed according to the design procedure proposed by the National Center of Asphalt Technology for a range of 4.5–6.5% asphalt content. The mixture containing fibers and SBR polymer was selected as an acceptable mix design with an optimum asphalt content of 6.5%. The moisture susceptibility of the selected mix at optimum asphalt content was evaluated. Results were compared with that for a dense mix.
TL;DR: In this article, a computational micromechanics modeling approach is presented to predict damage-induced mechanical response of asphalt mixtures using finite element modeling techniques and a viscoelastic material model.
Abstract: 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 rep resent 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.
TL;DR: In this article, the authors evaluated the benefits in terms of concrete toughness from a combination of micro-and macro-steel fibers under both bending and uniaxial tensile tests on specimens of different sizes.
Abstract: 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. This paper evaluated the benefits in terms of concrete toughness from a combination of micro- and macrosteel fibers 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 cracked surface. 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.
TL;DR: In this paper, the authors present results of an investigation carried out to study the fatigue life distribution of plain and steel fiber reinforced concrete with different fiber volume fractions and aspect ratios for various levels of the applied fatigue stress.
Abstract: The paper presents results of an investigation carried out to study the fatigue life distribution of plain and steel fiber reinforced concrete with different fiber volume fractions and aspect ratios for various levels of the applied fatigue stress. An extensive experimental investigation was planned in which 210 flexural fatigue tests and 84 complementary static flexural tests were conducted on prismatic plain concrete and fibrous concrete specimens of 100×100×500 mm size under three point loading in an MTS closed loop testing machine. Two types of crimped-type flat steel fibers with 25×2.0×0.6 mm and 50×2.0×0.6 mm , corresponding to fiber aspect ratios of 20 and 40, respectively, were used at each of the fiber volume fractions of 0, 1.0, 1.5, and 2.0%. It has been observed that the probabilistic distribution of fatigue life can be approximately modeled using the two-parameter Weibull distribution with statistical correlation coefficient exceeding 0.90. The shape parameter of the Weibull distribution for ...
TL;DR: In this article, the authors evaluated reclaimed building materials (RBM), including waste concrete, brick, and tile, used as aggregate for hot mix asphalt (HMA), and the analysis method of gray relational analysis (GRA) was presented to determine the best performance of the varying proportions of RBM with igneous crush stone (ICS) on HMA mixtures.
Abstract: This study evaluates reclaimed building materials (RBM), including waste concrete, brick, and tile, used as aggregate for hot mix asphalt (HMA). The analysis method of gray relational analysis (GRA) is presented to determine the best performance of the varying proportions of RBM with igneous crush stone (ICS) on HMA mixtures. Four types of aggregates are used for the mixtures: (a) 100% ICS; (b) 100% RBM; (c) 50% coarse and fine RBM plus 50% coarse and fine ICS (50% RBM plus 50% ICS); and (d) coarse RBM plus fine ICS (C-RBM plus F-ICS). Two types of asphalt cement, AC-10 and AC-20, are used as a binder for the mixtures. Laboratory tests of permanent deformation, resilient modulus, and stripping were evaluated by analysis of variance (ANOVA) and GRA. On the basis of this study, the ANOVA of the permanent deformation test shows that the type of aggregate has a significant effect, no matter what test temperatures and binders are used. The ANOVA of the resilient modulus test shows that the types of binder and aggregate do not significantly affect at test temperatures of 25°C, but significantly affect the types of binder at 40°C. The GRA result indicates that the best performance is the C-RBM plus F-ICS mixtures. For the stripping test, all 4 mixture types satisfied the Agency's requirements.
TL;DR: In this article, the physical and mechanical properties of new and recycled crushed clay brick aggregates for use in portland cement concrete (PCC) were determined and compared with the limits set out in the British Standards for aggregate from natural sources used in concrete.
Abstract: The testing described in this paper was performed to establish the physical and mechanical properties of new and recycled crushed clay brick aggregates for use in portland cement concrete (PCC). Various physical and mechanical properties of eight different types of aggregates were determined and compared with the limits set out in the British Standards for aggregate from natural sources used in concrete. The results were also compared with granite aggregate that has been proved to be a good natural aggregate for producing PCC. The results showed that most of the crushed clay-brick aggregates tested can be used in producing PCC for low-level civil engineering applications and that some kinds of brick aggregate possess good physical and mechanical properties that qualify them for producing high-quality concrete.
TL;DR: In this paper, a two-phase approach is proposed to predict the modulus of asphalt concrete from existing micromechanical models, which consists of a large spherical aggregate particle surrounded by a spherical shell of fine aggregate-filler-binder mixture as the matrix.
Abstract: A two-step approach is proposed to predict the modulus of asphalt concrete from existing micromechanical models. The asphalt concrete microstructure is represented by a two-phase model, which consists of a large spherical aggregate particle surrounded by a spherical shell of fine aggregate-filler-binder mixture as the matrix. The fine aggregate-filler-binder mixture is further represented by a two-phase model, which treats fine aggregate as a spherical inclusion and the mixture of filler and binder as the matrix. The modulus of asphalt concrete is predicted from the volumetric fractions, Poisson’s ratios, and moduli of the aggregate and filler-binder mixture by applying the appropriate two-phase models in two steps. An asphalt concrete and two mixtures that replicate the fine aggregate-filler-binder submixture and the filler-binder submixture in the asphalt concrete have been tested for modulus. The tests results show that the predicted results from the appropriate models reasonably approximate the measur...
TL;DR: In this paper, the effect of filler on the low-temperature creep of asphalt mastic is investigated based on experimental results obtained from bending-beam rheometer (BBR) experiments for both pure bitumen and mastic characterized by different filler types and content.
Abstract: 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 ...
TL;DR: Based on shear failure of concrete, a simple strain-based model is proposed in this article, which is developed using prevailing test results for high strength concrete with active confinement, and it is used to establish axial stress, axial strain and lateral strain relationships.
Abstract: High strength concrete (HSC) with highly desirable structural properties can lead to significant cost savings in heavily loaded lower story columns of concrete structures. Its use has however, been limited by a concern regarding an increased brittleness compared to normal strength concrete. It is well established that the ductility of HSC columns can be increased by confinement of the core of concrete columns by lateral steel reinforcement. Confining pressure applied by the reinforcement is a function of the lateral strain of concrete. Therefore establishing axial stress, axial strain, and lateral strain relationships is a timely concern. Based on shear failure of concrete, a simple strain-based model is proposed in this paper. It is developed using prevailing test results for HSC with active confinement.
TL;DR: In this paper, the influence of ultrafine fly ash on the early age property development, shrinkage, and shrinkage cracking potential of concrete is investigated, and the performance of ultra fine fly ash as cement replacement is compared with that of silica fume.
Abstract: In this paper, the influence of ultrafine fly ash on the early age property development, shrinkage, and shrinkage cracking potential of concrete is investigated. In addition, the performance of ultrafine fly ash as cement replacement is compared with that of silica fume. The mechanisms responsible for an increase of the early age stress due to restrained shrinkage were assessed; free shrinkage and elastic modulus were measured from an early age. In addition, the materials resistance to tensile fracture and increase in strength were also determined as a function of age. Results of the experimental study indicate that the increase in elastic modulus and fracture resistance with age are comparable for the control, ultrafine fly ash, and silica fume concretes. Autogenous shrinkage is shown to play a significant role in determining the age of cracking in restrained shrinkage tests. A significant reduction in the autogenous shrinkage and an increase in the age of restrained shrinkage cracking were observed in the ultrafine fly ash concrete when compared with the control and the silica fume concrete. Increasing the volume of ultrafine fly ash and decreasing the ratio of water-to-cementitous materials resulted in further increase in the age of restrained shrinkage cracking and a significant increase in the compressive strength.
TL;DR: In this paper, the authors used fly ash in the modification of local asphalt mixes and evaluated the modification efficiency by the improvement in the performance of prepared asphalt concrete mixes, which indicated that the addition of fly ash improved both strength, and water sensitivity of the asphalt concrete mix.
Abstract: It is estimated that about 40 billion 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 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 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.
TL;DR: In this paper, a servocontrolled true triaxial (cubical) testing device was used to test 4-in. cubical asphalt concrete specimens under general stress states to characterize the anisotropic properties of asphalt concrete.
Abstract: 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-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.
TL;DR: This study presents the probabilistic technique for predicting the compressive strength of concrete on the basis of concrete mix proportions and it has been found that the present methods are very efficient and reasonable in predicting theCompressive Strength of concrete probabilistically.
Abstract: The compressive strength of concrete is a commonly used criterion in producing concrete. However, the tests on the compressive strength are complicated and time consuming. More importantly, it is too late to make improvements even if the test result does not satisfy the required strength, since the test is usually performed on the 28th day after the placement of concrete at the construction site. Therefore, accurate and realistic strength estimation before the placement of concrete is very important. This study presents the probabilistic technique for predicting the compressive strength of concrete on the basis of concrete mix proportions. The estimation of the strength is performed using the probabilistic neural network which is an effective tool for the pattern classification problem and provides a probabilistic viewpoint as well as a deterministic classification result. Application of probabilistic neural networks in the compressive strength estimation of concrete is performed using the mix proportion data and test results of two concrete companies. It has been found that the present methods are very efficient and reasonable in predicting the compressive strength of concrete probabilistically.
TL;DR: In this article, a failure surface for plain concrete cubes and steel fiber-reinforced (SFRC) beams was proposed for biaxial, triaxial, or axisymmetric loads.
Abstract: A new unified five-parameter failure surface has been proposed for use with normal strength (NC), high strength (HSC), and steel fiber-reinforced (SFRC) concrete under biaxial, triaxial, or axisymmetric loads. The study covers concrete with strengths ranging from 20 to 130 MPa. The failure surface developed for plain concrete has been modified to account for the presence of steel fibers. The proposed failure surface was verified against experimental data of unconfined NC, HSC, and SFRC under multiaxial loads, as well as concrete confined by steel tubes. To facilitate the implementation of the failure surface into a finite-element package, a closed-form solution for predicting the state of stress in concrete has been developed. This failure criterion was successfully incorporated into constitutive models for plain concrete and SFRC. Experiments of plain concrete cubes and SFRC plates under multiaxial loads, as well as SFRC beams under two-point load, were modeled to illustrate the application of the failure surface to a wide range of concrete under varying load conditions. Good agreement between analytical and experimental results is observed.
TL;DR: In this article, a simple test device is proposed to directly measure the critical temperatures for thermal cracking of asphalt binders, which can be used to evaluate the effect of thermal contraction of asphalt binder and aggregate.
Abstract: A new simple test device is proposed to directly measure the critical temperatures for thermal cracking of asphalt binders. Using the dissimilar coefficients of thermal expansion for asphalt binders and common metals, the asphalt binder cracking device (ABCD) was developed to simulate thermal cracking of asphalt pavement in the laboratory. The ABCD consists of a metal ring, a strain gauge glued to the inner side of the ring, an environmental chamber, and a data acquisition system. Development of thermal stress within the asphalt binder during cooling is monitored by the strain gauge and the cracking temperature can be directly determined from the strain reading. A simplified theoretical analysis of the ABCD shows that the effects of thermal contraction of the asphalt binder and aggregate and the elastic properties of aggregates on thermal cracking could be reproduced in an ABCD test by adjusting the specimen and device geometries. Preliminary test data support the concept of the ABCD.