Showing papers in "Aci Materials Journal in 1993"
TL;DR: In this paper, a fire test was conducted on 2 specimens, one of high strength concrete and the other of normal strength concrete, and it was found that the length of the path for moisture to escape also has a significant influence on the spalling of high-strength concrete.
Abstract: A fire test was conducted on 2 specimens, one of high strength concrete and the other of normal strength concrete. At the time of test, sepcimen strengths were 27 and 105 MPa respectively. Details of the beam slabs and the specimens are described. The specimens were tested after 3.5 months of drying in an indoor environment. Explosive spalling was observed in high strength concrete while no spalling occurred in the normal strength concrete. However, spalling in the high strength concrete was confined to a region with 75 mm cover to steel. It was also found that the length of the path for moisture to escape also has a significant influence on the spalling of high-strength concrete.
179 citations
TL;DR: In this article, an experimental research investigation of the fresh and hardened material properties of the fibrillated polypropylene fiber reinforced concrete is reported, where fiber lengths were 1/2 and 1/4 inch and volume fractions were 0.1, 0.3, and 0.5%.
Abstract: An experimental research investigation of the fresh and hardened material properties of the fibrillated polypropylene fiber reinforced concrete is reported. Fiber lengths were 1/2 and 1/4 inch, and volume fractions were 0.1, 0.3, and 0.5%. Fiber effects on concrete properties were assessed. Properties studied were slump, inverted slump cone time, air content, compressive and flexural behaviors, impact resistance and rapid chloride permeability, and volume percent of permeable voids. An innovative method of characterizing the flexural behavior of fibrillated polypropylene fiber concrete was proposed. The new method was dependent on the post-peak flexural resistance of concrete. For impact resistance and flexural behavior, it was concluded that 1/4-inch-long fibers were more effective than 1/2-inch-long fibers for volumes of 0.3% or less, while 1/2-inch-long fibers were more effective for 0.5% volume.
179 citations
TL;DR: In this article, service-life methdology is used to develop a technical basis for predicting the service lives of construction materials, including estimates based on experience, deductions from performance of similar materials, accelerated testing, mathematical modeling based on the chemistry and physics of degradation processes, and applications of reliability and stochastic concepts.
Abstract: An objective of service-life methdology is to develop a technical basis for predicting the service lives of construction materials. They include (a) estimates based on experience, (b) deductions from performance of similar materials, (c) accelerated testing, (d) mathematical modeling based on the chemistry and physics of degradation processes, and (e) applications of reliability and stochastic concepts. These methods are discussed in this paper, along with some examples of their applications.
132 citations
TL;DR: The results of an experimental study of fatigue fracture of geometrically similar high-strength concrete specimens of very different sizes are reported and analyzed in this article, where an adjustment for the size effect needs to be introduced, of a similar type as previously introduced for normal concrete.
Abstract: The results of an experimental study of fatigue fracture of geometrically similar high-strength concrete specimens of very different sizes are reported and analyzed. Three-point bend notched beams were subjected to cyclic loading. The number of cycles to failure ranged from 200 to 41,000. It was found that Paris law for the crack length increment per cycle as a function of the stress intensity factor, which was previously verified for normal concrete, is also applicable to high-strength concrete. However, for specimens of different sizes, an adjustment for the size effect needs to be introduced, of a similar type as previously introduced for normal concrete. A linear regression plot estimating the size-adjustment parameters is derived. An LEFM (linear elastic fracture mechanics)-type calculation of the deflections under cyclic loading on the basis of the size-adjusted Paris law yields correct values for the terminal phase but grossly underpredicts the initial deflections. Overall, the results underscore the importance of considering fatigue fracture growth in the case of high-strength concrete structures subjected to large, repeated loads, and taking into account the very high brittleness under fatigue loading.
130 citations
TL;DR: In this paper, a high-speed framing camera was used to record the gross deformation and cracking during the fracture process in split tensile concrete specimens at strain rates of 10 to the power -7/sec to 10 to power 2/sec in a low speed material test machine and in a 50.8mm diameter Split Hopkinson Pressure Bar (SHPB).
Abstract: Splitting tensile concrete specimens were tested at strain rates of 10 to the power -7/sec to 10 to the power 2/sec in a low speed material test machine and in a 50.8-mm diameter Split Hopkinson Pressure Bar (SHPB). A comprehensive finite element method (FEM) analysis was conducted on the same test speciments. A high-speed framing camera was used to record the gross deformation and cracking during the fracture process in the SHPB tests. In addition, an ultra high speed image converter camera with equivalent framing rates of 10,000 to 1,000,000 frames per sec was used to record some of the early crack formations during the fracture process in the SHPB tests. Results of tensile strength versus strain rate are presented and compared with compressive strength at similar strain rates. These same tensile data are compared with strength data obtained using a fracture mechanics model. Computer generated crack patterns are presented and compared to experimentally observed crack patterns in the fracture of concrete at high strain rates.
113 citations
TL;DR: In this article, the modulus of elasticity, shrinkage, and creep coefficient in terms of developed concrete strength was calculated based upon a survey of published experimental data, and the proposed equations, together with those recommended by ACI 209-82 and the CEB 1990 Model Code, are compared with the published data.
Abstract: Modern construction techniques and the changes they have engendered in the construction process, toghether with the increasing use of finite element programs, warrant a review of the validity of current creep and shrinkage provisions. Based upon a survey of published experimental data, equations were developed to calculate the modulus of elasticity, shrinkage, and creep coefficient in terms of developed concrete strength. The time function used was the product of a Ross-type relationship for size effects and logarithmic time. The proposed equations, together with those recommended by ACI 209-82 and the CEB 1990 Model Code, are compared with the published data.
107 citations
TL;DR: In this article, a theory for crack formation in reinforced concrete elements based on an analysis of slip, bond stresses, and steel stresses is presented, and the problem is treated as an initial value problem both for initial crack formation when the cracks are independent, and for stabilized cracks when the zones of bond stresses reach each other.
Abstract: A theory for crack formation in reinforced concrete elements based on an analysis of slip, bond stresses, and steel stresses is presented. The problem is treated as an initial value problem both for initial crack formation when the cracks are independent, and for stabilized crack formation when the zones of bond stresses reach each other. Simple rules for analysis are presented for initial crack formation derived from the analytical solution of the mathematical model using homogeneous initial values. As an application, the spalling crack width control of a prestresesd pretensioned bridge girder is estimated. Numerical analysis is presented for stabilized crack formation. Tension stiffening is analyzed as a result of the interface behavior.
104 citations
TL;DR: In this paper, the authors present the results of studies to determine the properties of fresh and hardened high volume fly ash concretes using 8 fly ashes and 2 portland cements from the U.S. The details of the studies are described.
Abstract: This paper presents the results of studies to determine the properties of fresh and hardened high volume fly ash concretes using 8 fly ashes and 2 portland cements from the U.S. The details of the studies are described. The anslysis of the test results lead to the conclusion that high performance air entrained high volume fly ash concrete can be produced with the fly ashes and cements used in this investigation. The concretes so produced have low bleeding, satisfactory slump and setting characteristics and low autogenous temperature rise. These concretes also have excellent mechanical properties at both early and late ages with compressive strengths reaching as high as 50 MPa at 91 days. The creep and drying shrinkage of the concretes investigated are relatively low.
93 citations
TL;DR: In this article, the efficiency of cellulose fiber reinforcement in arresting cracks in cementitious composites was studied and a ring-type specimen was developed for the restrained shrinkage craking test.
Abstract: The efficiency of cellulose fiber in arresting cracks in cementitious composites was studied. A ring-type specimen was developed for the restrained shrinkage craking test. Concretes reinforced with 6 different types of cellulose fibers with a fiber content of 0.5% by volume were tested. Cellulose fiber reinforcement showed an ability to reduce the crack width significantly. For comparison concrete reinforced with 0.5% cellulose fibers showed equally excellent performance as 0.5% polypropylene fibers. The long-term mechnical performance of cellulose and polypropylene fiber reinforced concrete was also evaluated. The details of the study and the findings are presented. The influence of cellulose fiber reinforcement on other properties of concrete was also studied.
83 citations
TL;DR: In this article, the properties of silica fume concrete were investigated, including slump, air-content, compressive strength, flexural strength, permeability, and permeable void volume.
Abstract: The properties of silica fume concrete was studied. Various properties of silica fume cocnrete, including slump, air-content, compressive strength, flexural strength, permeability, and permeable void volume were investigated, and the effect of the silica fume replacement ratio of cement is described. The effects of aggregate content and graduation, water-binder (cement plus silica fume), and superplasticizer dosage rate also are discussed. In this investigation, silica fume-binder ratios ranged from 0.00 to 0.40, water binder ratios from 0.41 to 0.47, aggregate binder ratios from 1.0 to 4.0, and superplasticizer binder ratios from 0.01 to 0.05.
76 citations
TL;DR: In this paper, the bond strength between a high-performance concrete (HPC having a 28-day strength of 95 MPa) and reinforcing bars was measured in a series of beam tests in which the concrete type and ordinary concrete, reinforcement diameter, and surface condition (smooth and deformed bars) were varied.
Abstract: The paper discusses the bond strength between a high-performance concrete (HPC having a 28-day strength of 95 MPa) and reinforcing bars. This was measured in a series of beam tests in which the concrete type (HPC and ordinary concrete), reinforcement diameter (between 10 and 25 mm), and reinforcement surface condition (smooth and deformed bars) were varied. In general, concrete-reinforcement bond strength increases with the tensile strength of the concrete, and at a hgher rate with smaller reinforcement (a more marked scale effect).
TL;DR: In this article, the authors report the results of an experimental investigation whose object was measuring the energy-dissipation capacity of concrete with and without fiber reinforcement under uniaxial stress cycles.
Abstract: The paper reports the results of an experimental investigation whose objecteve was measuring the energy-dissipation capacity of concrete with and without fiber reinforcement under uniaxial stress cycles. This test program is the first phase of a major investigation underway at Columbia University to establsish a data base that can be used to develop damage prediction tools and facilitate low cycle fatigue analysis of concrete and concrete members subjected to arbitrary load histories. A new energy based damage index is proposed, which is well suited for quantifying concrete residual strength and predicting its remaining life.
TL;DR: In this article, a preliminary experimental study on the behavior of concrete members reinforced with FRP (fiberglass reinforced plastic) reinforcing bars, in which both the bending capacity and bond strength of FRP-reinforced concrete specimens were tested.
Abstract: The paper presents a preliminary experimental study on the behavior of concrete members reinforced with FRP (fiberglass reinforced plastic) reinforcing bars, in which both the bending capacity and bond strength of FRP-reinforced concrete specimens were tested. Flexural behavior was studied by testing 6 simply supported FRP-reinforced beams to failure under third-point loading, while bond strength was investigatged by conducting 24 pullout tests. Experimental results showed that the FRP-reinforced beams behaved in the same manner as would be expected in beams reinforced with steel bars. Also, strength design methods for steel-reinforced beams adequately predict ultimate moment capacity of FRP-reinforced beams. These and other findings are presented and discussed.
TL;DR: In this paper, an empirical model based on experimental results was developed to account for the reflection produced from reinforcing bars embedded within the concrete. And the model was applied to synthesize waveforms for representative reinforced concrete bridge deck geometries.
Abstract: Deterioration of reinforced concrete infrastructure is a major problem in the United States. Electromagnetic (EM) waves have shown increasing potential for the rapid evaluation of concrete conditions in situ. The objective of this research is to develop models for synthesis and inversion of radar waveforms from reinforced concrete structures. These models can be used to analyze radar data and predict the condition of the structure. A previous paper presented several models to predict the velocity and attenuation of EM waves in concrete. This paper develops an empirical model based on experimental results to account for the reflection produced from reinforcing bars embedded within the concrete. Concrete and reinforcing bar models were used to synthesize waveforms for representative reinforced concrete bridge deck geometries. Numerical studies were carried out to observe the influence of various conditions on the computed waveforms. A least squares inversion procedure was applied to the synthetic waveforms. Results indicate that spatial variations in volumetric water content, salt content, and reinforcing bar cover can be determined by analyzing radar waveforms.
TL;DR: In this paper, the velocity and attenuation of electromagnetic waves in concrete are predicted by aggregating the individual properties of its constituents: water, salt, air, cement paste, and aggregate solids.
Abstract: Models are presented to predict the velocity and attenuation of electromagnetic waves in concrete as a function of frequency, temperature, moisture content, chloride content, and concrete mix constituents. The electromagnetic properties of concrete are predicted by aggregating the individual properties of its constituents: water, salt, air, cement paste, and aggregate solids. The mixture models have been used as a basis for parametric studies which show the sensitivity of the electromagnetic properties to these constituents. An experimental study has been carried out to confirm the predictions of the theoretical models. Results predicted by these models have been found to compare favorably with those obtained from laboratory experiments.
TL;DR: In this article, it was shown that condensation of the water-soluble chloride ion in concrete and on embedded steel bars is surprisingly significant in concrete structures submerged in seawater, and the chloride ion concentration of the pore solution in these concrete structures can be a great deal higher than the surrounding seawater.
Abstract: It is shown that condensation of the water-soluble chloride ion in concrete and on embedded steel bars is surprisingly significant in concrete structures submerged in seawater. That is, the chloride ion concentration of the pore solution in these concrete structures can be a great deal higher than the surrounding seawater. Also, the chloride ion concentrations of the solution on steel bars can exhibit much higher, and these concentrations are closely related to the electrochemical property of steel bars. Also, the formation of Friedel's salt is confirmed to be closely related to the binding of intruded chloride ion in materials with cement matrix.
TL;DR: In this paper, the authors performed experimental and modeling studies on two types of fibers, polypropylene and steel fibers, in conjunction with or without conventional stirrups, in high-strength concrete, increasing both ultimate load and overall ductility.
Abstract: Experimental and modeling studies were performed on two types of fibers, polypropylene and steel fibers, in conjunction with or without conventional stirrups. In general, fibers proved to be more effective in high-strength concrete than in normal strength concrete, increasing both ultimate load and overall ductility. For specimens with steel fibers, significant increases in ultimate load and ductility were observed. With polypropylene fibers, a lower increase in ultimate load was obtained when compared to the increase due to steel fibers. Ductility of the polypropylene fiber specimens was greater than that of the steel fiber reinforced specimens. In tests with combinations of fibers with stirrups, slight increases in ultimate load with major improvements in ductility were noted in comparison to the values for plain concrete specimens with conventional stirrups.
TL;DR: In this paper, a new approach for studying bond characteristics of pretensioned strand along the transfer length and the flexural bond length is presented, which is the determination of average bond stresses in a more direct manner, from measured forces in the strand rather than from strains measured on the strand or on the concrete in beam specimens.
Abstract: The paper presents a new approach for studying bond characteristics of pretensioned strand along the transfer length and the flexural bond length. The key feature of this method is the determination of average bond stresses in a more direct manner, from measured forces in the strand rather than from strains measured on the strand or on the concrete in beam specimens. The loading technique enables the complete bond stress-versus-slip response to be determined including the post-peak response.
TL;DR: In this paper, the experimental results involving the application of the size effect law to early-age concrete for determining the material fracture parameters K sub If and c sub f were reported, showing that this test method is applicable both in the laboratory and at the construction work site.
Abstract: This paper reports the experimental results involving the application of the size effect law to early-age concrete for determining the material fracture parameters K sub If and c sub f. these parameters were determined for concrete with several different coarse aggregates at 1-day age, showing that this test method is applicable both in the laboratory and at the construction work site. Tests for concrete at different ages from 1 half day to 28 days showed that early-age concrete is more brittle than mature concrete. Increases in K sub If and c sub f with concrete age are observed. The K sub If and c sub f values at early ages may be used as a criterion to evaluate concrete quality.
TL;DR: In this article, an analytical approach, based on the energy changes associated with cracking, was used in expanding the occurrence of multiple micro-cracking, and the analysis predicts that the major energy term determining cracking behavior is the fiber debonding energy.
Abstract: From experiments using fiber reinforced densified small particles containing high volume fraction of fine and short steel fibers, it was found that the formation of multiple cracking which occurs between the point of first cracking and the peak load, was the main cause for the improvement in total strain capacity. This region, which is the inelastic strain region due to microcracking, is a unique property of high-performance fiber reinforced concrete (FRC). Multiple microcracking is a property of the bulk material, since no strain localization occurs. The details of the study are described, in which an analytical approach, based on the energy changes associated with cracking, was used in expanding the occurrence of multiple microcracking. The analysis predicts that the major energy term determining cracking behavior is the fiber debonding energy. The study also derived predictions of the number of microcracks and the minimum fiber volume fraction needed for the occurrence of multiple microcracking.
TL;DR: In this paper, a new approach to describe aggregate shapes and the change in shape associated with different aggregate types quantitatively using fractals (a family of mathematical functions that are used to characterize natural phenomena and shape).
Abstract: This paper suggests a new approach to describe aggregate shapes and the change in shape associated with different aggregate types quantitatively using fractals (a family of mathematical functions that are used to characterize natural phenomena and shape). The technique is based on the development of a mathematical relationship for boundary of an aggregate referred to as a slope density function. This includes a method of computing the fractal dimension using grids of different scales and sizes. Thus the fractal dimension may be applied successfully to characterize the shape of aggregates both quantitatively and objectively.
TL;DR: In this article, the authors present a new model for the analysis of strength development of a Class F fly ash concrete, which shows that the contribution of that fly ash to strength development is dependent on two parameters of the mix: nucleation and pozzolanic factors.
Abstract: The paper presents a new model for the analysis of strength development of a Class F fly ash concrete. The analysis shows that the contribution of that fly ash to strength development is dependent on 2 parameters of the mix: nucleation and pozzolanic factors. These parameters fully conform to the effects of proportioning the fly ash mixes. The parameters were adequate to account for the strength development of fly ash concrete. The results show that the methods for the design of fly ash concrete based on a single parameter like the 'cementing efficiency' may not be capable of modeling the strength developments accurately. The results show that the strength contribution up to 28 days can be broadly attributed to nucleation factor after 28 days to pozzolanic factor. The onset of the pozzolanic reaction depends on the fly ash/cementitious ratio of the mix.
TL;DR: In this paper, it was shown that eccentricity of less then 4 mm between the testing machine and specimen axis does not affect the compressive strength values, but the results are similar to those obtained when the ends are faced by grinding.
Abstract: Comparative testing reveals that high strength concrete (HSC) compressive strength values are greater by 5% when measured on 100 x 200 mm specimens. Moreover, the coefficient of variation on one set of three 100 x 200 mm specimens is as small as, or smaller than that for 150 x 300 mm specimens. Furthermore, a high performance capping compound testing 60 to 70 MPa using 50-mm cubes has proved to be effective when used for testing HSC up to 120 MPa due to the confinement of the capping compound between the platen and the specimen, but the capping layer has to be less than 3 mm thick. Under these conditions, the results are similar to those obtained when the ends are faced by grinding. Nevertheless, it is safer to grind the specimen ends when the strength of the concrete exceeds 100 MPa. It is shown that eccentricity of less then 4 mm between the testing machine and specimen axis does not affect the compressive strength values.
TL;DR: In this article, the feasibility of using gamma ray computerized tomography (CT) to inspect reinforced concrete specimens was evaluated using an objective to verify the CT resolution in determining the size and location of voids and reinforcing bars.
Abstract: This paper presents the feasibility of using gamma ray computerized tomography (CT) to inspect reinforced concrete specimens. An objective was to verify the CT resolution in determining the size and location of voids and reinforcing bars. It is described how the efficiency of CT in determining large voids was assessed, and how the efficiency of CT in establishing the location of reinforcing bars was evaluated. Study results show that CT was able to resolve the many different phases in reinforced concrete with great accuracy.
TL;DR: In this paper, a brief review of the technique of mercury porosimetry, and assumptions and corrections relevant to the application of the method to cement-based materials are presented.
Abstract: The paper gives a brief review of the technique of mercury porosimetry, and presents assumptions and corrections relevant to the application of mercury porosimetry to cement-based materials. The paper examines the impact of these corrections and assumptions on calculations based upon porositmetry data. The paper shows that assumptions and corrections employed in processing porosimetry data have a significant effect on porosimetry results, affecting total porosity values, threshold pore size values, and curve shape. Different assumptions and corrections can, therefore, lead to significantly different predictions of strength, permeability, and durability.
TL;DR: In this article, the authors explain the interaction of transient stress waves with steel bars in concrete and show the effects that bars have on impact-echo signals, which can be used to identify the effects caused by bars on impact echo signals obtained from reinforced concrete structures.
Abstract: The paper explains the interaction of transient stress waves with steel bars in concrete and shows the effects that bars have on impact-echo signals. Numerical (finite element) and experimental results are shown to demonstrate the effects that different variables have on impact-echo results. Equations for the relationships between bar diameter, bar depth and the measured impact echo response are presented. It is shown that these relationships can be used to identify the effects caused by bars on impact-echo signals obtained from reinforced concrete structures. Finally, the changes in the impact echo response caused by the presence of a void around the top or bottom of a bar are also explained.
TL;DR: In this paper, geometric probability concepts and stereological principles are used to derive an equation for the mean spacing of air voids in hardened concrete, and the input paramerers for the equation are the same as those obtained from the standard air void system analysis of hardened concrete.
Abstract: In this study geometric probability concepts and stereological principles are used to derive an equation for the mean spacing of air voids in hardened concrete The equation is presented and it is shown that the input paramerers for the equation are the same as those obtained from the standard air-void system analysis of hardened concrete The equation is valid for all values of paste-to-air ratio The mean spacing yields a better estimate of the actual spacing of the air voids in hardened concrete than the standard spacing factor
TL;DR: In this paper, the authors evaluated the relationship between the early age properties, such as compressive strength, pulse velocity, porosity, and permeability, and the long-term corrosion resistance of plain, fly ash, pozzolanic, and blast furnace slag cement concretes.
Abstract: This investigation evaluated the relationship between the early age properties, such as compressive strength, pulse velocity, porosity, and permeability, and the long-term corrosion resistance of plain, fly ash, pozzolanic, and blast furnace slag cement concretes. The details of the study are described. The data that was developed were statistically analyzed to establish relationships bestween the long-term corrosion rate and the early age properties of plain and blended cement concretes. The results of regression analyses indicate excellent correlation between permeability and corrosion rate, and porosity and corrosion rate for both plain and blended cement concretes.
TL;DR: In this paper, seven shrinkage models were compared with data measured on 46 Australian concretes containing over 1500 data points, using the method of residual plotting, and the simple Australian Code AS1481 performed better than the other models for the prediction of shrinkage.
Abstract: Seven shrinkage models were compared with data measured on 46 Australian concretes containing over 1500 data points, using the method of residual plotting. This method is superior to the current methods of presenting shrinkage data, as the method of plotting shrinkage residuals enables inaccuracies in the shape of shrinkage-time curves to be identified readily. The more complex shrinkage models were not necessarily more accurate than simple models. The introduction of such parameters as water-cement ratio, aggregate grading, and air content may not necessarily lead to improved accuracy of the models, and some of the recently presented models performced poorly for the Australian concretes used in this study. The simple Australian Code AS1481 performed better than the other models for the prediction of shrinkage.