Showing papers in "Journal of Materials in Civil Engineering in 2007"
TL;DR: The uniaxial monotonic compressive stress-strain behavior and other characteristics of unreinforced masonry and its constituents, i.e., solid clay bricks and mortar, have been studied by several laboratory tests.
Abstract: The uniaxial monotonic compressive stress-strain behavior and other characteristics of unreinforced masonry and its constituents, i.e., solid clay bricks and mortar, have been studied by several laboratory tests. Based on the results and observations of the comprehensive experimental study, nonlinear stress-strain curves have been obtained for bricks, mortar, and masonry and six “control points” have been identified on the stress-strain curves of masonry, which can also be used to define the performance limit states of the masonry material or member. Using linear regression analysis, a simple analytical model has been proposed for obtaining the stress-strain curves for masonry that can be used in the analysis and design procedures. The model requires only the compressive strengths of bricks and mortar as input data, which can be easily obtained experimentally and also are generally available in codes. Simple relationships have been identified for obtaining the modulus of elasticity of bricks, mortar, and ...
550 citations
TL;DR: In this paper, the authors presented the results from an experimental program and an analytical assessment of the influence of addition of fibers on mechanical properties of concrete, which is at variance with both existing models and formulations based on the law of mixtures.
Abstract: This paper presents the results from an experimental program and an analytical assessment of the influence of addition of fibers on mechanical properties of concrete. Models derived based on the regression analysis of 60 test data for various mechanical properties of steel fiber-reinforced concrete have been presented. The various strength properties studied are cube and cylinder compres- sive strength, split tensile strength, modulus of rupture and postcracking performance, modulus of elasticity, Poisson's ratio, and strain corresponding to peak compressive stress. The variables considered are grade of concrete, namely, normal strength 35 MPa, moderately high strength 65 MPa, and high-strength concrete 85 MPa, and the volume fraction of the fiber Vf=0.0, 0.5, 1.0, and 1.5%. The strength of steel fiber-reinforced concrete predicted using the proposed models have been compared with the test data from the present study and with various other test data reported in the literature. The proposed model predicted the test data quite accurately. The study indicates that the fiber matrix interaction contributes significantly to enhancement of mechanical properties caused by the introduction of fibers, which is at variance with both existing models and formulations based on the law of mixtures. 85 MPa with various fiber dosages Vf=0, 0.5, 1.0, and 1.5%. An empirical relationship for various mechanical properties of SFRC has been proposed. The proposed model attempts to bring out the significance of fiber matrix interaction in all the strength properties. This study reports the experimental results of the strength properties of SFRC, namely, cube and cylinder compressive strength, split tensile strength, modulus of rupture, modulus of elasticity, Poisson's ratio, and strain corresponding to peak com- pressive stress. Empirical relationships were developed for vari- ous strength properties based on the regression analysis of the 60 test data. It is expected that these proposed models would be helpful in assessing the strength properties of fiber-reinforced concrete based on the matrix strength and fiber-RI.
410 citations
TL;DR: The use of high percentages of recycled aggregates in concrete would usually worsen the concrete properties as discussed by the authors, and the use of fly ash as a substitute for natural aggregate is not beneficial.
Abstract: The use of high percentages of recycled aggregates in concrete would usually worsen the concrete properties. This paper tries to address the deficiency of the use of recycled aggregates by systematically presenting results on the influence of incorporating Class F fly ash on concrete properties. In this study, two series of concrete mixtures were prepared with water-to-binder (W/B) ratios of 0.45 and 0.55. The recycled aggregate was used as 0, 20, 50, and 100% by weight replacements of natural aggregate. In addition, fly ash was used as 0, 25, and 35% by weight replacements of cement. The results showed that the compressive strengths, tensile strengths, and static modulus of elasticity values of the concrete at all ages decreased as the recycled aggregate and the fly ash contents increased. Further, an increase in the recycled aggregate content decreased the resistance to chloride ion penetration and increased the drying shrinkage and creep of concrete. Nevertheless, the use of fly ash as a substitute for...
380 citations
TL;DR: In this paper, the effects of polyester fiber inclusions and lime stabilization on the geotechnical characteristics of fly ash-soil mixtures were investigated, and it was concluded that the expansive soil can be successfully stabilized by the combined action of fibers, lime, and fly ash.
Abstract: An experimental program was undertaken to study the effects of polyester fiber inclusions and lime stabilization on the geotechnical characteristics of fly ash-soil mixtures. An Indian fly ash was mixed with expansive soil in different proportions. The geotechnical characteristics of fly ash-soil specimens, lime-soil specimens and lime-fly ash-soil specimens mixed with different proportions of randomly oriented fibers were investigated. Lime and fly ash were added to an expansive soil at ranges of 1–10% and 1–20%, respectively. Test specimens were subjected to compaction tests, unconfined compression tests and split tensile strength tests. Specimens were cured for 7, 14, and 28 days after which they were tested for unconfined compression tests and split tensile tests. Based on optimum values obtained for lime and fly ash, tests were conducted on test specimens prepared from fly ash-expansive soil- lime-fiber mixture after 28 days of curing. Samples were tested with 0, 0.5, 1.0, 1.5, and 2% plain and crimped polyester fibers by dry weight. Based on the favorable results obtained, it can be concluded that the expansive soil can be successfully stabilized by the combined action of fibers, lime, and fly ash.
290 citations
TL;DR: In this article, the authors investigated the rutting resistance characteristics of the rubberized asphalt mixtures through a laboratory testing program, which included use of two rubber types ambient and cryogenically produced, four rubber contents, and three crumb rubber sizes.
Abstract: Improved understanding of rutting resistance of a rubberized asphalt concrete pavement that contains reclaimed asphalt pavement RAP is important to stimulating the use of rubberized asphalt mixtures. Use of RAP in the past has proved to be economical, environmentally sound, and effective in increasing the rutting resistance of asphalt mixtures. Rubberized asphalt has been used success- fully in improving the mechanical characteristics, such as rutting resistance, of typical hot mix asphalt HMA mixture around the country and the world. The objective of this research was to investigate the rutting resistance characteristics of the rubberized asphalt mixtures through a laboratory testing program. The experimental design included use of two rubber types ambient and cryogenically produced, four rubber contents, and three crumb rubber sizes. The results of the experiments indicated that the use of RAP and crumb rubber in the HMA can effectively improve the rut resistance of these mixes.
258 citations
TL;DR: In this paper, a rejuvenator is used in recycling of reclaimed asphalt pavement (RAP) for rutting using the asphalt pavement analyzer (APA) and the results indicated that properties of the recycled mixtures using the rejuvenator such as ITS and APA were better than those containing the softer binder.
Abstract: Rejuvenator is not a commonly used softening agent to be used in recycling of reclaimed asphalt pavement (RAP). In this study, Superpave mixtures containing RAP were designed using rejuvenating agents, including a rejuvenator and a softer binder, and subsequently evaluated in terms of the volumetric results, obtained the indirect tensile strength (ITS) of samples as well as evaluating the mixtures for rutting using the asphalt pavement analyzer (APA). The content of the rejuvenator used for those mixtures containing the rejuvenator was determined from the blending charts of RAP binders containing the rejuvenator. A total of 12 Superpave mixtures including 10 containing RAP and two virgin were designed. The results indicated, for the mixtures tested for this project, that: (1) properties of the recycled mixtures using the rejuvenator, such as ITS and APA, were better than those containing the softer binder; (2) 10% more RAP could be incorporated in the Superpave mixtures by using the rejuvenator than using the softer binder; and (3) the blending charts established under the Superpave binder specifications can be used to determine the content of the rejuvenator for the recycling.
244 citations
TL;DR: In this paper, 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.
Abstract: 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.
238 citations
TL;DR: In this paper, a commercially available ultra-high performance concrete (UHPC) was independently evaluated through six standardized durability tests and the results are reported in the article "Concrete Durability Evaluation: Cement-Based, Fiber-Reinforced Composite Materials".
Abstract: Significant recent advancements in cement-based, fiber-reinforced composite materials have stretched the bounds of concrete into the realm of ultrahigh-performance concrete (UHPC). The durability of a commercially available UHPC was independently evaluated through six standardized durability tests and the results are reported herein. Regardless of the curing treatment applied, this concrete exhibits significantly enhanced durability properties as compared to normal and high performance concretes. The concrete exhibited minimal damage after being subjected to two times the normal number of ASTM C 666 freeze–thaw cycles. It was innocuous to ASTM C 1260 ASR deterioration, to ASTM C 672 scaling deterioration, and to AASHTO T259 chloride penetration. The ASTM C 1202 Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration test result was negligible if any steam-based curing treatment was applied, and was very low otherwise. Steam-based curing treatments significantly enhanced the ASTM C 9...
206 citations
TL;DR: In this paper, slag was utilized as an additive for fly ash-based geopolymers in order to increase the compressive strength of the geopolymer, and the results showed that the addition of slag could generate amorphous products and accelerate the reaction rate of raw materials.
Abstract: Slag was utilized as an additive for fly ash-based geopolymers in this study. It was found that the incorporation of slag could significantly increase the compressive strength of the geopolymer. The compressive strength of geopolymer with 4.0% slag reached 50 and 70 MPa when cured for 14 days at 30 and 70°C , respectively. The mechanism of slag as additive on the enhancement of compressive strength of geopolymer was investigated using X-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and mercury intrusion porosimetry (MIP). The XRD and FTIR results showed that the addition of slag could generate more amorphous products and accelerate the reaction rate of raw materials. From XPS results, the decrease of binding energy and a broadening of peaks were observed for Si 2p , Al 2p , and O 1s elements due to the Ca2+ provided by slag. The decrease in binding energy was more favorable to zeolite formation. The results of MIP suggested that the 4% sl...
201 citations
TL;DR: In this article, the surface energy components of bitumen and aggregate are used to calculate their interfacial bond strength and effectively quantify moisture susceptibility of asphalt concrete mixes, which has several advantages over conventional mechanical tests currently being used to identify moisture susceptible mixes.
Abstract: Moisture damage in asphalt concrete pavements is a major cause for high maintenance costs of state and federal highways. Moisture damage in asphalt concrete is largely due to loss of adhesion between bitumen and aggregate, and loss of cohesive strength in the mastic (bitumen and mineral filler). Surface energy components of bitumen and aggregate are used to calculate their interfacial bond strength and effectively quantify moisture susceptibility of asphalt concrete mixes. This technology has several advantages over conventional mechanical tests currently being used to identify moisture susceptible mixes. However, accurate surface energy characterization of bitumen and aggregate is the key element to calculate interfacial bond strengths. This paper presents development of a sorption based method to measure specific surface area and surface energy components of aggregate. Measured surface energy components and precision statements are presented for five aggregates. The paper also illustrates application of bond strengths calculated from surface energy components of aggregate and bitumen in the selection process of compatible pairs of aggregate and bitumen to produce a durable mix.
179 citations
TL;DR: In this paper, the long-term stability characteristics of FoCa bentonite soil (FoCa represents the first two letters of the two towns between which this type of soil is excavated: Fourgues and Cahaignes) using 4% lime treatment were examined taking into account the influence of wetting-drying and freezing-thawing cycles on key engineering properties.
Abstract: There are several questions that are not well understood with respect to the long-term stability characteristics of lime-treated expansive soils in spite of being used as a conventional technique to improve the properties of expansive soils. This paper examines the long-term stability characteristics of FoCa bentonite soil (FoCa represents the first two letters of the two towns between which this type of soil is excavated: Fourgues and Cahaignes) using 4% lime treatment. The long-term stability characteristics referred to as durability in the paper were interpreted taking into account the influence of wetting–drying and freezing-thawing cycles on key engineering properties which include swelling and strength behavior of both untreated and lime-treated FoCa. In addition, leaching tests were carried out to study the Ca2+ ions and pH concentration changes of the percolating water from both treated and untreated compacted expansive soil specimens analyze the permanence of the clay treatment. Finally, to highl...
TL;DR: In this article, the analysis of the bond between fiber-reinforced polymer (FRP) rebars and concrete was performed referring to different kinds of FRP rebars.
Abstract: The structural performance of reinforced concrete elements is related to the interface behavior of rebars to concrete. In the last decade several research works were carried out to investigate the bond between fiber-reinforced polymer (FRP) rebars and concrete, however some aspects need further studies in order to obtain reliable design indications. In this paper the analysis of bond was performed referring to different kinds of FRP rebars and some varying influential parameters (surface treatment, kinds of fibers, and kinds of test). Results obtained show the role of the investigated parameters on bond stress law; in particular the surface treatments involve different transfer mechanisms passing from simple chemical adhesion and friction, for sanded rebars, to a relevant contribution of mechanical interlocking for deformed rebars. The kind of test utilized influences the most significant parameters of the bond stress–slip law and in different ways depending on the kind of rebars. Finally the kind of fibe...
TL;DR: In this article, the viability of using reclaimed polyethylene (PE) derived from low-density PE carry bags collected from domestic waste as an additive in asphalt concrete mixtures was investigated.
Abstract: This paper deals with the viability of using reclaimed polyethylene (PE) derived from low-density PE carry bags collected from domestic waste as an additive in asphalt concrete mixtures. Different ratios of PE (2.5, 5.0, 7.5, and 10% by weight of asphalt) were blended with (80/100)-paving grade asphalt. The dynamic creep test (unconfined), indirect tensile test, resilient modulus test, and Hamburg wheel track tests were carried out on asphalt concrete mixtures blended with PE. The analyses of test results show that the performance of PE-modified asphalt mixtures are better when compared to conventional mixtures. The rutting potential and temperature susceptibility can be reduced by the inclusion of PE in the asphalt mixture. A PE content of 5% by weight of asphalt is recommended for the improvement of the performance of asphalt concrete mixtures similar to that investigated in this study.
TL;DR: In this paper, the effects of aggregate gradation, amount, and size on pervious portland cement concrete (PCC) static modulus of elasticity were compared using four different mixtures.
Abstract: The effects of aggregate gradation, amount, and size on pervious portland cement concrete (PCC) static modulus of elasticity were compared using four different mixtures. A standard mix and three variable mixes using a uniform gradation, increased aggregate amount, and increased aggregate size were used. The effective air void content was determined for each mixture. The compressive strengths and static elastic moduli were determined and compared at equal void contents. For a uniform gradation, the compressive strengths and static elastic moduli appeared to be higher within an optimal range of voids; however, there was no statistically significant difference between the results from the different gradations. An increased aggregate amount resulted in a statistically significant decrease in both compressive strength and static elastic moduli due to the subsequent decrease in paste amount. While the compressive strengths were higher for mixtures containing smaller aggregate sizes, there was no significant difference between the static elastic moduli when different aggregate sizes were used. Further research is needed to understand the effects of aggregate size on the static modulus of elasticity of pervious PCC.
TL;DR: In this paper, the durability of concrete and mortar, including aggregate of discarded car tires under environmental conditions, was evaluated using physical, mechanical, and durability experiments on mortar and concrete specimens and it was determined that in the regions where the environmental conditions are not harsh, use of concrete produced with 10% rubber aggregate is appropriate as it is e...
Abstract: This study aims at determining the durability of mortar and concrete, including aggregate of discarded car tires under environmental conditions. These conditions are freeze-thaw, seawater, and high temperature. Concrete specimens produced with a cement dosage of 300, a 0.5 water-cement ratio, and 0, 10, 20, and 30% rubber aggregate in volume, where the grain size is 1–4 mm instead of fine aggregate, and portland compose cement (CEM II/B 32.5) are used for freeze-thaw. The effect of seawater on specimens produced with 10, 20, 30, and 40% rubber aggregate in volume instead of sand was investigated. For specimens produced with 10, 20, and 30% rubber aggregate in volume, the effect of high temperature was investigated. During this research physical, mechanical, and durability experiments were performed on mortar and concrete specimens. As a result it was determined that in the regions where the environmental conditions are not harsh, use of concrete produced with 10% rubber aggregate is appropriate as it is e...
TL;DR: In this article, a mixture of rigid sand particles and soft fine-grained rubber particles is tested to investigate their small and large-strain responses to small, middle, and large deformation moduli.
Abstract: Mixtures of rigid sand particles and soft fine-grained rubber particles are tested to investigate their small and large-strain responses. Mixtures are prepared with different volumetric sand fraction sf to identify the transition from a rigid to a soft granular skeleton using wave propagation, k0 loading, and triaxial testing. Deformation moduli at small, middle, and large strains do not change linearly with the volume fraction of rigid particles; instead, deformation moduli increase dramatically when the sand fraction exceeds a threshold value between sf=0.6-0.8 that marks the formation of a percolating network of stiff particles. The friction angle increases with the volume fraction of rigid particles. Conversely, the axial strain at peak strength increases with the content of soft particles, and no apparent peak strength is observed in specimens with low sand fraction sf0.6. The presence of soft particles alters the formation of force chains. Although soft particles are not part of high-load carrying chains, they play the important role of preventing the buckling of stiff particle chains.
TL;DR: In this paper, three relatively new applications for controlling wind and water erosion using polyacrylamide copolymers are described that take advantage of their ability to stabilize and add structure to soil.
Abstract: Three relatively new applications for controlling wind and water erosion using polyacrylamide copolymers are described that take advantage of their ability to stabilize and add structure to soil. In the first application, low concentrations of anionic, high purity polyacrylamide (PAM) eliminates sediment in runoff water by more than 90% when added to irrigation water at 10 ppm , or at a rate of 1 to 2 kg ha−1 per irrigation. Lab-furrow tests were utilized to characterize the role of molecular weight, charge, and ion concentrations in applying PAM during irrigation. In the second application, PAM is applied at construction sites and road cuts at rates of 22.5 kg ha−2 (tenfold higher rates than in irrigation control) resulting in reduction in sediment runoff by 60–85% during (simulated) heavy rains. Finally, a formulation of PAM mixed with aluminum chlorohydrate and cross-linked poly(acrylic acid) superabsorbent at a ratio of (6:1:1) has been applied to create helicopter landing pads that minimize dust clou...
TL;DR: In this article, the effect of colloidal silica treatment on the liquefaction and deformation resistance of loose, liquefiable sands during centrifuge in-flight shaking was investigated.
Abstract: Passive site stabilization is a new technology proposed for nondisruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. It is based on the concept of slowly injecting colloidal silica at the edge of a site with subsequent delivery to the target location using natural or augmented groundwater flow. Colloidal silica is an aqueous dispersion of silica nanoparticles that can be made to gel by adjusting the pH or salt concentration of the dispersion. It stabilizes liquefiable soils by cementing individual grains together in addition to reducing the hydraulic conductivity of the formation. Centrifuge modeling was used to investigate the effect of colloidal silica treatment on the liquefaction and deformation resistance of loose, liquefiable sands during centrifuge in-flight shaking. Loose sand was successfully saturated with colloidal silica grout and subsequently subjected to two shaking events to evaluate the response of the treated sand layer. The treated soil did not liquefy during either shaking event. In addition, a box model was used to investigate the ability to uniformly deliver colloidal silica to loose sands using low-head injection wells. Five injection and two extraction wells were used to deliver stabilizer in a fairly uniform pattern to the loose sand formation. The results of the box model testing will be used to design future centrifuge model tests modeling other delivery methods of the grout.
TL;DR: In this article, the results of an extensive laboratory testing program using a large direct shear device, in which four different soils including one sand and three clays of different plasticities were reinforced by three different geogrids and one woven geotextile.
Abstract: Geosynthetics have increasingly been used to reinforce many earth structures and are now a well-accepted means to improve engineering properties of various types of soil. However, most previous studies and applications of geosynthetic stabilization are confined to noncohesive soils. Few research efforts have been dedicated to the feasibility and benefits of geosynthetic reinforcement on cohesive soils. This paper presents the results of an extensive laboratory testing program using a large direct shear device, in which four different soils including one sand and three clays of different plasticities were reinforced by three different geogrids and one woven geotextile. Reinforcement mechanisms were analyzed and the soil-geosynthetic interface parameters were obtained from the testing results. The increase in molding moisture content and/or decrease in dry density caused an appreciable reduction in interface shear resistance, which suggests that it should be more rational to use interface parameters of soils at their 95% maximum dry density and moisture content 2% above their optimum values. This study also provides a basis for future research and modeling the behavior between cohesive soils and geosynthetics.
TL;DR: In this article, the effect of fly ash on the volume change of two different types of clay, one a highly plastic expansive clay and the other a nonexpansive clay, also of high plasticity, was studied.
Abstract: This paper presents, by way of comparison, the effect of fly ash on the volume change of two different types of clay, one a highly plastic expansive clay and the other a nonexpansive clay, also of high plasticity. Expansive clays swell on absorbing water and shrink on drying. Nonexpansive clays undergo large compression at high water contents. The effect of fly ash content on free swell index, swell potential, and swelling pressure of expansive clays was studied. Compression index and secondary consolidation characteristics of both expansive and nonexpansive clays were also determined. Swell potential and swelling pressure, when determined at constant dry unit weight of the sample (mixture), decreased by nearly 50% and, when determined at constant weight of clay, increased by nearly 60% at 20% fly ash content. Compression index and coefficient of secondary consolidation of both the clays decreased by 40% at 20% fly ash content.
TL;DR: In this article, a laboratory test results showed that HVFA concrete mixtures containing 50 − 60% fly ash can be designed to fulfill the requirement of strength and workability suitable for cement concrete pavement construction.
Abstract: The work reported in this paper is based on a laboratory study of superplasticized high-volume fly-ash (HVFA) concrete suitable for pavement construction. Three control concrete mixtures having 400 kg/m³ of ordinary portland cement (OPC) and water – cementitious material (w – cm) ratios of 0.30, 0.34, and 0.40 were prepared. Other concrete mixtures were then prepared by substituting 20, 30, 40, 50, and 60% fly ash in all control mixtures. Compressive and flexural strengths at ages of 7, 28, 90, 180, 256, and 365 days, drying shrinkage, and abrasion resistance of concrete were measured for all the mixtures. The laboratory test results showed that HVFA concrete mixtures containing 50 – 60% fly ash can be designed to fulfill the requirement of strength and workability suitable for cement concrete pavement construction. At all w – cm ratios, the concrete mixture containing 60% OPC and 40% fly ash developed maximum strength at the age of 90 days and beyond. However, a maximum increase in the strength of concrete at 365 days over the 28 days strength was observed in the mixtures containing equal amount of OPC and fly ash. Drying shrinkage of concrete decreased with decreasing w – cm ratio and increasing fly-ash content. Among all the concrete mixtures, the mixture with w – cm ratio of 0.30 and containing 60% fly ash showed least shrinkage. Abrasion resistance of concrete, measured by the sand-blasting method, decreased with increasing fly-ash content and decreasing compressive strength. However, abrasion resistance of HVFA concrete mixture with 60% fly ash at 0.30 w – cm ratio was adequate from concrete-pavement considerations.
TL;DR: In this article, the superelastic behavior of shape memory alloy, Nitinol (NiTi), when used as reinforcement in concrete beams was investigated and it was found that a hybrid system that incorporated NiTi combined with high strength steel or carbon fiber reinforced plastic bars was a better choice for design.
Abstract: This paper discusses the superelastic behavior of shape memory alloy, Nitinol (NiTi) , when used as reinforcement in concrete beams. The ability of NiTi to recover and reduce permanent deformations of concrete beams was investigated. Small-scale concrete beams, with NiTi reinforcement were tested under half-cycle loads. The reinforcement ratio varied from 0.1 to about 0.9%. The experimental results showed that the average residual displacement in the NiTi reinforced beams was less than one-fifth of that of the steel reinforced test beams. The stiffness of NiTi reinforced test beams however was lower than those of the steel reinforced test beams. An analytical study of load–deflection relationship for a series of hybrid beams was undertaken. It was found that a hybrid system that incorporated NiTi combined with high strength steel or carbon fiber reinforced plastic bars was a better choice for design because of their relatively high stiffness.
TL;DR: In this article, the authors present the results of an experimental study to evaluate the damage and failure mode of hybrid-fiber engineered cementitious composite (ECC) panels caused by large projectiles or fragments.
Abstract: This paper presents the results of an experimental study to evaluate the damage and failure mode of hybrid-fiber engineered cementitious composite (ECC) panels caused by large projectiles or fragments. The aim is to quantify the extent to which hybrid-fiber ECC improves the resistance of blast panels against impact loading. Drop weight tests were conducted on full-scale hybrid-fiber ECC blast/shelter panels (2 m×1 m×0.05–0.1 m) to study their response and performance under impact loading. Conventional steel reinforced concrete (RC) and steel fiber-reinforced concrete (FRC) blast panels were also tested to identify the advantages of using ECC in this application. Both the drop weight projectile with a hemispherical head and the panel specimen were instrumented to facilitate evaluation of the global and local response. The impact resistance of blast panels of different materials is evaluated in terms of the extent of damage, energy absorption capacity and residual resistance against multiple impacts. The dr...
TL;DR: In this article, the hydration process of fresh concretes with different proportions was studied using electrical resistivity measurement and the minimum point (Pm) and the transition point ( Pt ) were identified on the electrical resistivities development curves.
Abstract: The hydration process of fresh concretes with different proportions was studied using electrical resistivity measurement. The minimum point ( Pm ) and the transition point ( Pt ) were identified on the electrical resistivity development curves. The time tm at which Pm occurred, represented the time when the curve dropped to a minimum and before increasing as a result of the onset of hydration. The time tt at which Pt occurred, marked the time when the kinetics of hydration transition changed from the setting to the hardening stage. To evaluate the significance of tm and tt in terms of the setting process, they were compared to the initial setting time ( ti ) and final setting time ( tf ) measured with the traditional penetration resistance method. The quantitative relationships between the setting time of concrete and the electrical resistivity critical points were developed. The equations can be used to estimate the setting times of concrete as an alternative method.
TL;DR: In this article, the relationship between the air void distribution in asphalt mixes and their moisture susceptibility was evaluated using an x-ray computed tomography system to capture the internal structure of the specimens.
Abstract: This paper evaluates the relationship between the air void distribution in asphalt mixes and their moisture susceptibility. Asphalt mix specimens were prepared to have different air void distributions through using two different gradations, using two different compaction angles in the Superpave gyratory compactor, and trimming the specimens at different locations. An x-ray computed tomography system was used to capture the internal structure of the specimens, and image analysis techniques were used to quantify the air void distribution and connectivity. Specimens in unconditioned (dry) and moisture-conditioned (wet) states were subjected to dynamic loading, and damage was evaluated using a crack growth index based on fracture theory. The parameters required for the crack growth index were obtained from mechanical and surface energy tests. The analysis results clearly demonstrate the influence of air void distribution on moisture susceptibility. Consequently, the analysis method presented in this paper can be used to evaluate alternative mix designs and internal structures, even when the same materials are used, in order to optimize the resistance to moisture damage.
TL;DR: In this article, the influence of soil grading on the characteristics of soil-cement blocks and shear-bond strength of masonry triplets was examined. And the major conclusions of the study were: (1) optimum clay content leading to maximum strength is in the range of 14-16%; (2) saturated water content of the blocks increases with increase in clay content of a block; (3) initial rate of absorption decreases with an increase in the block's clay content; (4) weight loss after ASTM wire scratch test is minimum when the clay content
Abstract: Large numbers of soil-cement block masonry buildings exist in India and many other countries. The paper deals with an experimental study on the influence of soil grading on the characteristics of soil-cement blocks and shear-bond strength of soil-cement block masonry triplets. Influence of clay content of the soil-cement block on strength, absorption and durability characteristics, and interfacial mortar-block bond strength has been examined. Some of the major conclusions of the study are: (1) optimum clay content leading to maximum strength is in the range of 14–16%; (2) saturated water content of the blocks increases with increase in clay content of the block; (3) initial rate of absorption decreases with increase in clay content of the block; (4) weight loss after ASTM wire scratch test is minimum when the clay content of the block is about 16%; and (5) optimum clay content for the highest modulus for the blocks and for highest shear-bond strength is about 16%.
TL;DR: In this article, several prediction models have been developed to predict the creep and shrinkage in concrete, including the ACI-209R-82 model, B3 model, the CEB-FIP model code 1990, and the GL2000 model for various grades of concrete.
Abstract: 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.
TL;DR: In this article, two metakaolins, with similar mineralogical composition but differing in their surface area (11.1 versus 25.4 m2 ∕g ), were evaluated for use as supplementary cementitious materials through measurements of workability, setting time, strength, elastic modulus, heat evolution, calcium hydroxide (CH) content, and surface area.
Abstract: Two metakaolins, with similar mineralogical composition but which vary in their surface area (11.1 versus 25.4 m2 ∕g ), were evaluated for use as supplementary cementitious materials through measurements of workability, setting time, strength, elastic modulus, heat evolution, calcium hydroxide (CH) content, and surface area. Compressive and flexural strength of concrete were greater and increased at a faster rate when the finer metakaolin was used, as expected. The addition of metakaolin increased early age (i.e., 1–3 days ) flexural strength by as much as 60%. The effect of metakaolin surface area on compressive strength was particularly evident at the lower water-to-cementitious materials ratios (w/cms) examined and generally at later ages (i.e., 7 days or later). However, although greater in the metakaolin–cement concretes than the ordinary concretes (particularly at the lowest w/cm examined, 0.40) elastic modulus measured at 28 days , was not affected by the metakaolin surface area. The greater surfac...
TL;DR: In this article, the Naamam 1991 pullout model was modified in this paper and used to investigate the bond mechanism expressed as shear strength diagram, which is agreed well with the nominal shears strength obtained directly from the experiments.
Abstract: Fabric reinforced cement based composites are a new class of composites with superior tensile strength and ductility which have the potential for becoming load bearing structural members. This enhanced behavior is primarily governed by interfacial bond characteristics between fabrics and matrix. Pullout tests were conducted using several different matrices and fabric types: two different mix designs (control and with fly ash); and four fabric types: alkali-resistant glass, polypropylene, polyethylene, and polyvinyl alcohol. The effects of processing methods: cast, pultrusion, and vacuum as well as fabric embedded lengths (7.6 and 12.7 mm) were also evaluated. The Naamam 1991 pullout model was modified in this paper and used to investigate the bond mechanism expressed as shear strength diagram. The shear strength parameters obtained by fitting the pullout simulation curves to the experimental responses are agreed well with the nominal shear strength obtained directly from the experiments. It was found that the pullout responses are highly dependent on the fabric type, mixture design, and processing method.
TL;DR: In this article, the authors investigated the mechanical properties of self-consolidating concretes subjected to elevated temperatures up to 700°C and found that compressive strength, splitting tensile strength, and ultrasonic pulse velocity were significantly reduced.
Abstract: Mechanical characteristics of self-consolidating concretes subjected to elevated temperatures up to 700°C were experimentally investigated in this paper. Eight different concretes [four self-consolidating concretes (SCC) and four conventional concretes (CC)] of different strength categories were produced. At the age of 120 days, specimens were placed in an electrical furnace and the heating was applied at a rate of 5°C∕min until the desired temperature was reached. A maximum temperature of 100, 300, 500, and 700°C was maintained for 1 h . Specimens were then allowed to cool in the furnace and tested for compressive strength, splitting tensile strength, and ultrasonic pulse velocity. Similar tests were also performed at room temperature (20°C) for the reference specimens. Residual strength of both SCC and CC was reduced almost similar up to the maximum temperature tested. Explosive spalling occurred in both SCC and CC of the highest strength category at temperatures greater than 380°C . The residual compre...