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The corrosion on concrete from seawater has an ion coupling effect. This paper analyzed the results of two species ionic coupling attack, three species ionic coupling attack, and seawater attack, which obtained the following results: (1)... more
The corrosion on concrete from seawater has an ion coupling effect. This paper analyzed the results of two species ionic coupling attack, three species ionic coupling attack, and seawater attack, which obtained the following results: (1) The internal pores will be blocked by the attack products of $\mathrm{SO}_{4}^{2-}$ and Mg2+ in the early stage, which inhibits the transportation of $\mathrm{C}1^{-}$; the degradation of concrete will increase the transport speed of $\mathrm{C}1^{-}$. (2) Sulfate attack is influenced by cation type. Taking expansion rate as deterioration index, Na2So4 and K2SO4 have the highest attack speed and degree, while CaSO4 has the lowest attack degree. Taking compressive strength as the deterioration index, the attack degree of MgSO4 is the highest, and that of Na2SO4 and K2SO4 is the lowest. (3) Temperature will affect the deterioration degree of concrete, and the deterioration degree of concrete is more severe at low temperatures. $\mathrm{CO}_{3}^{2-}$ and $\mathrm{C}1^{-}$ will aggravate the MgSO4 attack at low temperature $(5^{\circ}\mathrm{C})$ but not affect the MgSO4 attack at room temperature. (4) Due to the different transport rates of ions in concrete, the surface layer of concrete is divided into Mgrich zone, S-rich zone, and Cl-rich zone according to the rich elements.
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AbstractThis work studied the influence of pores of different scales on the strength of cementitious materials. A method to make pores in cementitious materials with particles of soft materials was...
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AbstractCores with diameters of 74 mm and length-to-diameter (l/d) ratios of 0.5, 1.0, 1.5, 2.0, 3.0, and 4.0, were removed from concrete beams. Compressive strength tests were conducted on 300 core specimens. The compressive strengths of... more
AbstractCores with diameters of 74 mm and length-to-diameter (l/d) ratios of 0.5, 1.0, 1.5, 2.0, 3.0, and 4.0, were removed from concrete beams. Compressive strength tests were conducted on 300 core specimens. The compressive strengths of concrete cores were fitted to the modified Weibull distribution. This information is useful in the theoretical description of concrete failure. Furthermore, on the basis of the Kolmogorov-Smirnov goodness-of-fit tests, the test data have been verified to follow this modified Weibull distribution. In addition, the modified Weibull model can predict the length effect more accurately than the conventional model.
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The water conveyance tunnel is an important structural form in the allocation of water resources. The corrosion of the steel bars in the concrete lining makes it difficult to reach the required useful life. In order to solve the adverse... more
The water conveyance tunnel is an important structural form in the allocation of water resources. The corrosion of the steel bars in the concrete lining makes it difficult to reach the required useful life. In order to solve the adverse effect of reinforcement corrosion on the durability of the concrete lining structure of water conveyance tunnel, BFRP reinforcement is proposed in shotcrete lining instead of steel reinforcement. In this paper, the ultimate bearing capacity of BFRP reinforced fiber shotcrete flexural members are studied through experiments. The results show that the flexural failure modes of BFRP reinforced fiber shotcrete flexural members can be divided into three types: under-reinforced, ideally reinforced and over-reinforced. Basalt fiber can ensure the integrity of beams in failure. The ultimate flexural bearing capacity of beams increases with the increment of BFRP reinforcement ratio. Under the same reinforcement ratio, the flexural ultimate bearing capacity of high content basalt fiber specimens is higher than that of low content basalt fiber specimens while the difference is small. In this paper, a calculation method of normal section bearing capacity of fiber shotcrete flexural members with BFRP reinforcement is proposed.
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ABSTRACT The flexural behavior of concrete is often different from its behavior under direct tension. This paper presents an experimental program aimed at the testing method and strain rate effects on the tensile behavior of concrete.... more
ABSTRACT The flexural behavior of concrete is often different from its behavior under direct tension. This paper presents an experimental program aimed at the testing method and strain rate effects on the tensile behavior of concrete. Concrete specimens were tested with different testing methods (direct tension and four-point loading) and four strain rates (10-6, 10-5, 10-4, and 10-3s-1). The results show that the peak stresses increase with an increase in the strain rate; the strain rate dependence of the peak stress is stronger for direct tensile specimens than for four-point loading specimens. The dynamic increase factor is expressed as a function of the strain rate and highly stressed volume method. The continuous damage model is also used to predict the strain rate effects on the ascending stress-strain behavior of concrete. Using the model parameters for the stress-strain curve of concrete at a static strain rate, the stress-strain curves of concrete for dynamic strain rates in four-point loading and direct tension are satisfactorily predicted.
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AbstractEarly-age cracking of base restrained concrete walls is a common problem. To provide the owner with an early warning of in-place quality problems resulting primarily as a result of thermal and shrinkage effects, it is helpful to... more
AbstractEarly-age cracking of base restrained concrete walls is a common problem. To provide the owner with an early warning of in-place quality problems resulting primarily as a result of thermal and shrinkage effects, it is helpful to apply monitoring and analytical techniques to examine the early-age behavior of basement concrete walls. In this paper, the temperature and strain monitoring on a basement concrete wall is conducted. Major factors that contribute to the early-age behavior of concrete walls constructed in cold weather are evaluated using analytical models along with measured field data and finite-element modeling. The results show that the monitoring process eliminated much of the guesswork frequently associated with basement concrete walls constructed in cold weather. Temperature varies laterally within the wall. The strain remains unchanged after six days with formwork removal. And the numerical predictions for strains and temperature are in agreement with the measured results, during bot...
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Abstract In the marine environment, concrete in both submerged zone and non-submerged zone could be attacked by seawater. To study the deterioration of sea-sand concrete partially submerged in seawater, an accelerated test with simulated... more
Abstract In the marine environment, concrete in both submerged zone and non-submerged zone could be attacked by seawater. To study the deterioration of sea-sand concrete partially submerged in seawater, an accelerated test with simulated marine environment was designed for seawater and siliceous sea-sand concrete (SSC), coral aggregate seawater concrete (CASC) and tap water and desalted siliceous sea-sand concrete (DTC). The mass, water absorption, mechanical properties (compressive strength and dynamic modulus) were tested. Thermodynamic simulation, EDS and MIP test were used to analyze the strength deterioration of different sea-sand concrete. With the dry-wet cycle, the dynamic modulus and mass of sea-sand concrete increased first and then decreased. After 365 days of dry-wet cycles, the water absorption of sea-sand concrete with high initial strength would increase more significantly. Different sea-sand concrete in the submerged zone and the non-submerged zone was mainly subjected to chemical seawater attack, and ettringite and gypsum were the main expansion phases. The most important influence of internal sea salt attack from mixing materials on the deterioration of concrete partially submerged in seawater was the change of pore distribution. Due to the combined effect of capillary transport and crystallization pressure, SSC and CASC with higher initial compressive strength had greater compressive strength loss in the submerged zone. In the non-submerged zone, under the combined action of capillary transport, crystallization pressure and “wick action”, the compressive strength of SSC, CASC and DTC varied with height in an “S”, parabolic and linear shape, respectively.
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ABSTRACT A value of tensile strength of cement-based materials is required for the design of pavements, for the analysis of concrete dams to prevent thermal cracking and sometimes for the design of prestressed beams. Cementitious... more
ABSTRACT A value of tensile strength of cement-based materials is required for the design of pavements, for the analysis of concrete dams to prevent thermal cracking and sometimes for the design of prestressed beams. Cementitious materials exhibit a significant variability in their tensile strength, depending on the test method used. The three common test methods are direct tension, three-point bending, and four-point bending, and it is commonly found that bending tests yield higher strengths than direct tension tests. During this investigation, tests were carried out on cement mortar and concrete for each type of test. A two-parameter Weibull model was found to fit each individual set of data well. For both cement mortar and concrete, the Weibull moduli calculated for the test methods were approximately the same. The Weibull modulus is used to relate the values of strength obtained with different test methods, using the Weibull effective volume concept, the predicted results are in remarkably good agreement with the experimental results.
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ABSTRACT A comprehensive test program was conducted on the compressive strength of concrete cores. The tests involved eight mixes of concrete. Because over 200 tests were conducted, it was possible to undertake an analysis of the concrete... more
ABSTRACT A comprehensive test program was conducted on the compressive strength of concrete cores. The tests involved eight mixes of concrete. Because over 200 tests were conducted, it was possible to undertake an analysis of the concrete cores using the probabilistic treatment of strength. The present work reports a comparative study of alternative probabilistic models to describe the compressive strength of concrete cores. A large class of probability models including two-parameter Weibull, three-parameter Weibull, normal, lognormal, and gamma distributions were validated using test data. This information is useful in the theoretical description of concrete failure. Furthermore, the results were compared in terms of modified Kolmogorov-Smirnov, log-likelihood, and minimum chi-square criterion. The results suggested that none of the described probability methods are adequate for determining the variability of the compressive strength of concrete cores. (C) 2014 American Society of Civil Engineers.
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ABSTRACT A pulse-shaped split Hopkinson pressure (SHPB) was employed to determine the dynamic compressive mechanical responses of concrete cores. The loading pulses in SHPB experiments were precisely controlled to ensure that the core... more
ABSTRACT A pulse-shaped split Hopkinson pressure (SHPB) was employed to determine the dynamic compressive mechanical responses of concrete cores. The loading pulses in SHPB experiments were precisely controlled to ensure that the core specimen deforms at a nearly constant strain rate under dynamically equilibrated stress during compression. A modified two-parameter Weibull distribution was used to analyze the test data. The Kolmogorov-Smirnov goodness-of-fit test was used to decide whether test data come from a population with this distribution. On the basis of the test data, Kolmogorov-Smirnov goodness-of-fit test, and probability plot, it is found that the modified Weibull model can be applied to compressive strength for concrete cores. In addition, the strain rate effect on the compressive strength of cores can be accurately predicted from the modified Weibull model. (C) 2014 American Society of Civil Engineers.
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AbstractThe dynamic characterization of cement-based materials under high strain rates is fundamental to understand the material behavior in case of heavy earthquakes and dynamic events. Abram’s law, which was originally formulated for... more
AbstractThe dynamic characterization of cement-based materials under high strain rates is fundamental to understand the material behavior in case of heavy earthquakes and dynamic events. Abram’s law, which was originally formulated for cement-based materials under static loading, is not directly applicable to the dynamic loading condition. In this paper, a modified relationship has been proposed to evaluate the tensile strength of cement mortar. An extensive experiment was carried out to determine the effect of strain rate and water-to-cement (w/c) ratio on tensile strength of cement mortar. The dynamic characterization of tensile strength has been carried out by the split Hopkinson pressure bar at high strain rates. The results of the tests show a significant strain rate–sensitive behavior, exhibiting dynamic tensile strength of cement mortar increases with an increase in strain rate. The influence of w/c ratio on dynamic increase factor is minor.
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The internal relative humidity (RH) and humidity gradients in concrete at early ages have a significant influence upon the properties of concrete, where exists a great discrepancy among the test results under different methods. By... more
The internal relative humidity (RH) and humidity gradients in concrete at early ages have a significant influence upon the properties of concrete, where exists a great discrepancy among the test results under different methods. By comparing and analyzing the traditional measuring methods of the RH in concrete, a new measuring method will be developed in this study, which could measure the internal RH in cement-based materials accurately, conveniently and digitally. The changing laws of the internal RH in concrete at early ages were discussed. The results indicate that the measuring results under the new developed system was more accurate than that by the predrilled hole method, while the external environment does not have any effect on the measured results obtained by using the new measurement system. What’s more, the results achieved by the new developed system approached the real RH in concrete very quickly; the RH near the surface of the specimen decreased quickly, while the RH in the center of the specimen decreased slowly, the moisture contents unevenly distributed through the various height of the specimen. Hence, there exists an obvious humidity gradient in concrete.
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Abstract The paper aims to propose a pressure-filtration method for cement-based materials and investigate its effect on water-cement ratio, porosity, pore size distribution, and compressive strength. A pressure-filtration device is... more
Abstract The paper aims to propose a pressure-filtration method for cement-based materials and investigate its effect on water-cement ratio, porosity, pore size distribution, and compressive strength. A pressure-filtration device is designed to filter out water and compact hardened cement paste with a regular water-cement ratio. Different compact pressure was applied on cement paste, ranging from 0.2 MPa to 2.0 MPa, and the pressure remained constant from the initial setting to the final setting time. The specimens were cured in water at 20 ℃ for 9 days and 28 days before their compressive strength and microstructure were measured. The density of specimens was increased, and the compressive strength was increased by 86% at maximum, with the increment of compact pressure, while the total porosity and the water-cement ratio were decreased. The pressure-filtration method improves compressive strength evidently by reducing the pores larger than 10 nm in diameter, which is found to have a significant impact on strength.
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AbstractExperimental studies have showed that the static preload increases the dynamic tensile strength of concrete under certain conditions. But its mechanism still remains open. In this study the...
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AbstractThe objective of this study was to determine the tensile behavior for dam concrete under simulated earthquake loading conditions (loading frequency 5 Hz). Four-point loading tests were conducted on large beam specimens... more
AbstractThe objective of this study was to determine the tensile behavior for dam concrete under simulated earthquake loading conditions (loading frequency 5 Hz). Four-point loading tests were conducted on large beam specimens (1,700×450×450 mm). This paper describes the behavior of dam concrete subjected to dynamic elevated-amplitude cyclic loading with different initial static load levels. Stress-strain measurements were made on the concrete specimens. The test results show that dynamic increase factor of dam concrete increases with increasing initial static stress levels. The results of this study should be useful in determining the earthquake resistance of dam structures.