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Menashi D. Cohen - One of the best experts on this subject based on the ideXlab platform.
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Hydration of type K Expansive Cement paste and the effect of silica fume: II. Pore solution analysis and proposed hydration mechanism
Cement and Concrete Research, 1993Co-Authors: Colin Lobo, Menashi D. CohenAbstract:This is the second part of a two-part paper on the hydration characteristics of Type K Expansive Cement pastes and the effect of silica fume addition. Data concerning expansion of pastes and quantitative analysis of the solid phases related to expansion were presented in Part I. Part II presents the portion of the study related to the pore solution analysis. The results presented in Parts I and II used to propose a hydration mechanism of Expansive Cement pastes and the effect of silica fume. In the Expansive Cement paste without silica fume, ettringite formation and the consequent expansion terminated due to the depletion SO42− in the pore solution after 11 days of hydration. In the presence of silica fume, the initial formation of ettringite was accelerated leading to an increased rate and magnitude of expansion. After two days of hydration, a reduction in the concentration of alkali cations in the pore solution was observed. This resulted in a decrease in the OH-concentration in the pore solution and subsequent decrease in the rate of ettringite formation. The expansion stopped at about five days of hydration even though approximately 55% of the original C4A3S remained unhydrated and SO42− still remained in pore solution. It is speculated that the reduction of the pH of the pore solution after two days of hydration may provide an explanation for the termination of ettringite formation in the Expansive Cement paste containing silica fume.
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Hydration of type K Expansive Cement paste and the effect of silica fume: I. Expansion and solid phase analysis
Cement and Concrete Research, 1992Co-Authors: Colin Lobo, Menashi D. CohenAbstract:The hydration reactions of Type K Expansive Cement pastes and the effect of silica fume were studied. Part I reports on the expansion characteristics of pastes and the corresponding changes occuring in the quantities of solid phases associated with expansion. Results of the rate of heat evolution curves of the pastes during the first 48 hours are also reported. Part II∗∗ present results of the pore solution analysis and a proposed hydration mechanism. In pastes, with and without silica fume, expansion was associated with the formation of ettringite. Expansion continued as long as ettringite was forming. The expansion rate and magnitude at early age (the first two days of hydration) was larger when silica fume was added to the Expansive Cement paste. Solid phase analysis and the rate of heat evolution curves of the pastes also indicated that the addition of silica fume accelerated the hydration of the paste. These suggest that the silica fume resulted in a more efficient use of ettringite that formed during the early age. Silica fume also reduced the duration of expansion. This reduction was deemed advantageous because delayed expansion and, therfore, microcracking and degradation of the hardened Expansive Cement paste could be prevented with the use of silica fume.
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Pore structure development in type K Expansive Cement pastes
Cement and Concrete Research, 1991Co-Authors: Colin Lobo, Menashi D. CohenAbstract:Abstract This paper presents the results of an experimental investigation of pore structure development of Expansive Cement paste as a function of expansion strain and curing time. The expansion strain, bulk density, dynamic modulus, and evaporable water content of paste specimens were monitored periodically during and after termination of expansion and correlated with the pore size distribution data obtained by mercury intrusion porosimetry. It is shown that expansion results in the formation of large pores (and/or microcracks) in the paste. It appears that MIP has a limitation in that it cannot register the pores that form during the later stage of expansion. The mass of evaporable water appears to be a better way of characterizing changes in porosity during expansion, however, it does not reveal any information as to the pore size distribution The effect of restraint by steel reinforCement on pore structure developmebt of Expansive Cement paste was also studied. It was found that restraining Expansive Cement paste results in reduction of the size of large pores. However, even with a large degree of restraint, Expansive Cement paste is still more porous and contains larger pores than portland Cement paste of the same age.
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Procedure for Mix Proportioning of Type K Expansive Cement Blends For Use in Shrinkage-Compensating Mortars
ACI Materials Journal, 1991Co-Authors: Jan Olek, Menashi D. CohenAbstract:This paper presents a procedure for mix proportioning of Type-K Expansive Cement blends for use in shrinkage-compensating mortars. The proposed procedure is based on a simple linear regression model correlating maximum expansion in Type K-Expansive Cement mortars with expansion time of mortar and composition of Expansive Cement ingredients. The model provides a practical means of correlating such parameters as the composition and relative proportions of Expansive Cement mortar ingredients with the duration of curing so that the resulting mortar can satisfy expansion criteria specified in ASTM C 806.
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Effects of sulfate and Expansive clinker contents on expansion time of Expansive-Cement paste
Cement and Concrete Research, 1991Co-Authors: Menashi D. Cohen, Barzin MobasherAbstract:The objective of this paper is to discuss the relationships between sulfate content and expansion time and between Expansive-clinker content and expansion time in Expansive-Cement pastes. Generally, as the amount of sulfate increases, expansion time increases as well. In addition, sulfate content versus expansion time relationship depends on the size distribution of Expansive-clinker particles. The increase is linear for monosize Expansive-clinker particles and curvilinear for polysize particles. Increase in amount of Expansive clinker up to a critical mass results in increase of expansion time. Addition of Expansive clinker beyond the critical mass content results in reduction of expansion time. The above relationships serve as a basis for a model which can be used for optimizing mixture proportions. Such mixture proportioning will require only a small number of trial mixtures in order to achieve the optimum expansion strain, mechanical properties, and cost. (Author/TRRL) (Author/TRRL)
Chris P. Pantelides - One of the best experts on this subject based on the ideXlab platform.
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Concrete column shape modification with FRP shells and Expansive Cement concrete
Construction and Building Materials, 2011Co-Authors: Z. Yan, Chris P. PantelidesAbstract:Fibre Reinforced Polymer (FRP) composites are an effective material for confining circular concrete columns. FRP confinement for square and rectangular columns is less effective due to stress concentrations at the sharp corners and loss of the membrane effect. Shape modification using post-tensioning of FRP shells through Expansive Cement concrete is described. In the field, shape modification can be achieved by utilizing pre-fabricated FRP shells as the permanent forms. An analytical model is briefly introduced to predict results of the experiments regarding the enhanced stress-strain behaviour of FRP-confined concrete. The confinement model and shape modification technique with FRP shells and Expansive Cement concrete are used in simulations of seismic rehabilitation of square columns for existing reinforced concrete bridges and are compared to in-situ tests of square columns with bonded FRP jackets.
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Posttensioned FRP Composite Shells for Concrete Confinement
Journal of Composites for Construction, 2007Co-Authors: Zihan Yan, Chris P. Pantelides, Lawrence D. ReaveleyAbstract:Experiments have shown that externally bonded fiber-reinforced polymer (FRP) jackets for square and rectangular columns are not as effective as they are for circular columns. The results of experiments on shape-modified concrete columns using posttensioned FRP shells are presented. Posttensioning was achieved by radially straining the precured FRP shell outwards to a substantial strain level, using Expansive Cement concrete, over a period of 60 days . The prefabricated FRP shell was also used as a stay-in-place formwork. The effectiveness of shape modification using posttensioned FRP shells is compared to FRP-confined original square and rectangular columns, as well as shape-modified columns with nonshrink grout and externally bonded FRP jackets. It is shown that shape modification with posttensioning of FRP shells, using Expansive Cement concrete, can change the confinement from passive to active and improve significantly the axial strength and ultimate compressive axial strain capacity of square and rec...
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Fiber Reinforced Polymer Jacketed and Shape-Modified Compression Members: I –Experimental Behavior
Aci Structural Journal, 2006Co-Authors: Chris P. Pantelides, Lawrence D. ReaveleyAbstract:Fiber-reinforced polymer (FRP) composites are effective for strengthening circular concrete columns. In the case of square and rectangular columns, FRP confinement for axial strength is less effective due to the shape of the section; however, axial strain capacity can still be increased. Shape modification can eliminate column comers and flat sides, thereby improving the axial strength capacity of FRP-confined square and rectangular concrete columns. In this paper, shape modification of square and rectangular concrete compression members confined using post-tensioned FRP composite shells with Expansive Cement concrete is investigated; confinement effectiveness is compared with square and rectangular compression members confined with bonded FRP jackets. The experimental results demonstrate the effectiveness of shape modification with Expansive Cement concrete using chemical post-tensioning of the FRP shell. Compared with specimens confined with bonded FRP jackets without shape modification, shape-modified square compression members with post-tensioned FRP shells achieved a significant increase in axial strength, axial compressive strain, and energy absorption; shape-modified rectangular compression members with aspect ratios of 2:1 and 3:1 achieved moderate increases in axial strength. In addition, confinement concepts for different FRP confinement types, including bonded FRP composite jackets and post-tensioned FRP composite shells are introduced for developing an analytical stress-strain confinement model.
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FRP-JACKETED AND SHAPE MODIFIED COLUMNS USING CHEMICAL POST- TENSIONING
2006Co-Authors: Chris P. Pantelides, Z. Yan, Lawrence D. ReaveleyAbstract:The axial compressive strength and ultimate compressive strain of columns inadequately designed for seismic forces can be improved by confinement with fiber reinforced (FRP) composites. To improve the confinement effectiveness of FRP composite jackets for square and rectangular columns, shape modification is performed by using prefabricated FRP shells combined with Expansive Cement concrete. Chemical post-tensioning using Expansive Cement concrete is used to change the FRP confinement from “passive” to “active”. Experimental results of large-scale columns in compression with externally bonded FRP jackets, or posttensioned FRP shells were performed on plain concrete columns. Square sections modified with FRP shells and Expansive Cement concrete to circular columns demonstrated a compressive strength increase by a factor of three and a ductility increase by a factor of two. Rectangular sections had a smaller but significant increase in both strength and ductility.
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Shape Modification of Rectangular Columns Confined with FRP Composites
2004Co-Authors: Chris P. Pantelides, Zihan Yan, Lawrence D. ReaveleyAbstract:The study investigates Fiber Reinforced Polymer (FRP) strengthening for axial capacity improvement of concrete columns in confinement. Thirty full-scale concrete columns were tested in uniaxial compression until failure. A wet-layup procedure for columns in the as-is condition is adequate for strengthening square or rectangular columns to improve axial capacity. For strengthening existing square or rectangular columns to resist seismic forces, it is preferable to transform the square and rectangular cross-sections to circular, and elliptical or oval, respectively. This study has found that the use of FRP composite straps or hoops is beneficial for columns with a circular cross-section but not for columns with a square or rectangular cross-section. In the case of using FRP composite prefabricated shells, it is advantageous to use Expansive Cement concrete rather than non-shrink grout to achieve the shape modification. Square columns, which were modified to circular using FRP composite prefabricated shells and Expansive Cement concrete, showed a higher increase in axial strength capacity and ductility, compared to square columns, which were modified to circular using FRP composite prefabricated shells and non-shrink grout. Design guidelines for the FRP composite retrofit of circular columns, square columns, rectangular columns, and elliptical columns are provided in this report. Guidelines for the retrofit of columns with FRP composite prefabricated shells and either non-shrink grout or Expansive Cement concrete are also provided.
Lawrence D. Reaveley - One of the best experts on this subject based on the ideXlab platform.
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SEISMIC RETROFIT OF BRIDGE COLUMNS USING FIBER REINFORCED POLYMER COMPOSITE SHELLS AND SHAPE MODIFICATION
2008Co-Authors: Z. Yan, Lawrence D. ReaveleyAbstract:Fiber Reinforced Polymer (FRP) composites can provide effective confinement to circular concrete columns for the purpose of seismic retrofit of bridges. However, the retrofit effectiveness of FRP confinement for square and rectangular columns is greatly reduced due to the flat sides and sharp corners. Shape modification is a possible approach for eliminating the effects of column corners and flat sides, thereby restoring the membrane effect and improving the compressive behavior of FRP-confined square and rectangular concrete columns. An effective method for performing shape modification with FRP composites is to use prefabricated (non-bonded) FRP composite shells with Expansive Cement concrete. A prefabricated elliptical/oval/circular FRP shell may be used as stay-in-place formwork for casting additional Expansive Cement concrete around the column with a square or rectangular cross-section to achieve shape modification. The restraint of the expansion caused by hydration of the component of Expansive Cement induces the active confinement pressure. Large-scale experimental results have shown that shape-modification using Expansive Cement concrete can achieve a higher axial compressive strength and ductility for modified square and rectangular columns compared to the original columns with the same number of FRP composite layers. An analytical model was developed to determine the stress-strain behavior of shape-modified columns with Expansive Cement concrete. In addition, a parametric study for the practical use of shape modification is carried out.
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Posttensioned FRP Composite Shells for Concrete Confinement
Journal of Composites for Construction, 2007Co-Authors: Zihan Yan, Chris P. Pantelides, Lawrence D. ReaveleyAbstract:Experiments have shown that externally bonded fiber-reinforced polymer (FRP) jackets for square and rectangular columns are not as effective as they are for circular columns. The results of experiments on shape-modified concrete columns using posttensioned FRP shells are presented. Posttensioning was achieved by radially straining the precured FRP shell outwards to a substantial strain level, using Expansive Cement concrete, over a period of 60 days . The prefabricated FRP shell was also used as a stay-in-place formwork. The effectiveness of shape modification using posttensioned FRP shells is compared to FRP-confined original square and rectangular columns, as well as shape-modified columns with nonshrink grout and externally bonded FRP jackets. It is shown that shape modification with posttensioning of FRP shells, using Expansive Cement concrete, can change the confinement from passive to active and improve significantly the axial strength and ultimate compressive axial strain capacity of square and rec...
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Fiber Reinforced Polymer Jacketed and Shape-Modified Compression Members: I –Experimental Behavior
Aci Structural Journal, 2006Co-Authors: Chris P. Pantelides, Lawrence D. ReaveleyAbstract:Fiber-reinforced polymer (FRP) composites are effective for strengthening circular concrete columns. In the case of square and rectangular columns, FRP confinement for axial strength is less effective due to the shape of the section; however, axial strain capacity can still be increased. Shape modification can eliminate column comers and flat sides, thereby improving the axial strength capacity of FRP-confined square and rectangular concrete columns. In this paper, shape modification of square and rectangular concrete compression members confined using post-tensioned FRP composite shells with Expansive Cement concrete is investigated; confinement effectiveness is compared with square and rectangular compression members confined with bonded FRP jackets. The experimental results demonstrate the effectiveness of shape modification with Expansive Cement concrete using chemical post-tensioning of the FRP shell. Compared with specimens confined with bonded FRP jackets without shape modification, shape-modified square compression members with post-tensioned FRP shells achieved a significant increase in axial strength, axial compressive strain, and energy absorption; shape-modified rectangular compression members with aspect ratios of 2:1 and 3:1 achieved moderate increases in axial strength. In addition, confinement concepts for different FRP confinement types, including bonded FRP composite jackets and post-tensioned FRP composite shells are introduced for developing an analytical stress-strain confinement model.
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FRP-JACKETED AND SHAPE MODIFIED COLUMNS USING CHEMICAL POST- TENSIONING
2006Co-Authors: Chris P. Pantelides, Z. Yan, Lawrence D. ReaveleyAbstract:The axial compressive strength and ultimate compressive strain of columns inadequately designed for seismic forces can be improved by confinement with fiber reinforced (FRP) composites. To improve the confinement effectiveness of FRP composite jackets for square and rectangular columns, shape modification is performed by using prefabricated FRP shells combined with Expansive Cement concrete. Chemical post-tensioning using Expansive Cement concrete is used to change the FRP confinement from “passive” to “active”. Experimental results of large-scale columns in compression with externally bonded FRP jackets, or posttensioned FRP shells were performed on plain concrete columns. Square sections modified with FRP shells and Expansive Cement concrete to circular columns demonstrated a compressive strength increase by a factor of three and a ductility increase by a factor of two. Rectangular sections had a smaller but significant increase in both strength and ductility.
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Shape Modification of Rectangular Columns Confined with FRP Composites
2004Co-Authors: Chris P. Pantelides, Zihan Yan, Lawrence D. ReaveleyAbstract:The study investigates Fiber Reinforced Polymer (FRP) strengthening for axial capacity improvement of concrete columns in confinement. Thirty full-scale concrete columns were tested in uniaxial compression until failure. A wet-layup procedure for columns in the as-is condition is adequate for strengthening square or rectangular columns to improve axial capacity. For strengthening existing square or rectangular columns to resist seismic forces, it is preferable to transform the square and rectangular cross-sections to circular, and elliptical or oval, respectively. This study has found that the use of FRP composite straps or hoops is beneficial for columns with a circular cross-section but not for columns with a square or rectangular cross-section. In the case of using FRP composite prefabricated shells, it is advantageous to use Expansive Cement concrete rather than non-shrink grout to achieve the shape modification. Square columns, which were modified to circular using FRP composite prefabricated shells and Expansive Cement concrete, showed a higher increase in axial strength capacity and ductility, compared to square columns, which were modified to circular using FRP composite prefabricated shells and non-shrink grout. Design guidelines for the FRP composite retrofit of circular columns, square columns, rectangular columns, and elliptical columns are provided in this report. Guidelines for the retrofit of columns with FRP composite prefabricated shells and either non-shrink grout or Expansive Cement concrete are also provided.
Paulo J.m. Monteiro - One of the best experts on this subject based on the ideXlab platform.
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The influence of Expansive Cement on the mechanical, physical, and microstructural properties of hybrid-fiber-reinforced concrete
Cement and Concrete Composites, 2019Co-Authors: Vahid Afroughsabet, Guoqing Geng, Alex Lin, Luigi Biolzi, Claudia P. Ostertag, Paulo J.m. MonteiroAbstract:Abstract This work reports the properties of hybrid-fiber-reinforced concrete (HyFRC) made with Expansive (Type K) Cement. Combinations of metallic and non-metallic fibers at total fiber volume fraction of 1% were studied. The effectiveness of double hooked-end (DHE) steel fibers in concrete containing Expansive Cement is investigated for the first time in this study. The mechanical, physical, and microstructural properties of concretes have been assessed. Additionally, the fiber pull-out test was also performed to investigate the effectiveness of Type K Cement in improving the fiber-matrix interfacial bond. The results indicate that Type K Cement has small influence on the mechanical properties of concrete fabricated at the same water-Cement ratio of 0.35 with a similar consistency. However, as expected, it enhances the volume stability of concrete subjected to drying condition. The pull-out resistance of steel fibers increased by 26% as a result of full replaCement of ordinary Portland Cement (OPC) with Type K Cement. A deflection-hardening performance is achieved by introducing of DHE steel fibers in HyFRC. The partially replaCement of DHE steel fibers with other type of fibers results in a reduction in the strengths of HyFRC. The results obtained in this study proves that the bond between fiber and Cement matrix is enhanced by fully replaCement of OPC with Expansive Cement, which subsequently improves the mechanical properties of HyFRC.
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A hydration study of various calcium sulfoaluminate Cements
Cement and Concrete Composites, 2014Co-Authors: Antonio Telesca, Milena Marroccoli, M. L. Pace, Michele Tomasulo, Gian Lorenzo Valenti, Paulo J.m. MonteiroAbstract:Abstract The present work studies the hydration process and microstructural features of five calcium sulfoaluminate (CSA) Cements and a ternary mixture including also ordinary Portland Cement (OPC). The pastes were studied with simultaneous differential thermal-thermogravimetric (DTA-TG) analysis, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and expansion/shrinkage tests. The DTA-TG analysis confirmed the role of the hydration reactions involving the main CSA clinker constituent, tetracalcium trialuminate sulfate, which produced (i) ettringite when combined with lime and calcium sulfate, (ii) ettringite and aluminum hydroxide in the presence of calcium sulfate alone, and (iii) monosulfate and aluminum hydroxide in the absence of both lime and calcium sulfate. The MIP and SEM were able to discriminate between Expansive (ternary mixture and CSA Cement containing 50% gypsum) and non-Expansive Cements. Expansive Cement pastes had (i) a nearly unimodal pore size distribution shifted toward higher radii and (ii) ettringite crystals smaller in size during the first day of curing. In a SEM image of a hardened paste of the CSA Cement containing 50% gypsum, a stellate ettringite cluster was observed.
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concrete microstructure properties and materials
2005Co-Authors: P.k. Mehta, Paulo J.m. MonteiroAbstract:Comprehensive, up-to-date coverage of the properties, behavior, and technology of concrete Fully revised to include the latest advances in concrete technology, Concrete: Microstructure, Properties, and Materials provides complete details on the microstructure-property relationship approach to provide scientific explanation for the strength and durability of concrete. This in-depth resource discusses the microstructure and properties of hardened concrete; concrete-making materials and concrete processing; and current developments in concrete technology, mechanics, and nondestructive testing methods. New to this Edition Inclusion of recently built/ongoing construction projects worldwide Information on shrinkage-reducing admixtures Coverage of the latest advances in concrete technology-self-consolidating concrete; nanotechnology of concrete; shotcrete; Expansive Cement; and concrete for nuclear radiation Details on modeling of ice formation and alkali-aggregate reaction in concrete 1,000 PowerPoint slides and videos that illustrate topics presented in the book
Z. Yan - One of the best experts on this subject based on the ideXlab platform.
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Concrete column shape modification with FRP shells and Expansive Cement concrete
Construction and Building Materials, 2011Co-Authors: Z. Yan, Chris P. PantelidesAbstract:Fibre Reinforced Polymer (FRP) composites are an effective material for confining circular concrete columns. FRP confinement for square and rectangular columns is less effective due to stress concentrations at the sharp corners and loss of the membrane effect. Shape modification using post-tensioning of FRP shells through Expansive Cement concrete is described. In the field, shape modification can be achieved by utilizing pre-fabricated FRP shells as the permanent forms. An analytical model is briefly introduced to predict results of the experiments regarding the enhanced stress-strain behaviour of FRP-confined concrete. The confinement model and shape modification technique with FRP shells and Expansive Cement concrete are used in simulations of seismic rehabilitation of square columns for existing reinforced concrete bridges and are compared to in-situ tests of square columns with bonded FRP jackets.
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SEISMIC RETROFIT OF BRIDGE COLUMNS USING FIBER REINFORCED POLYMER COMPOSITE SHELLS AND SHAPE MODIFICATION
2008Co-Authors: Z. Yan, Lawrence D. ReaveleyAbstract:Fiber Reinforced Polymer (FRP) composites can provide effective confinement to circular concrete columns for the purpose of seismic retrofit of bridges. However, the retrofit effectiveness of FRP confinement for square and rectangular columns is greatly reduced due to the flat sides and sharp corners. Shape modification is a possible approach for eliminating the effects of column corners and flat sides, thereby restoring the membrane effect and improving the compressive behavior of FRP-confined square and rectangular concrete columns. An effective method for performing shape modification with FRP composites is to use prefabricated (non-bonded) FRP composite shells with Expansive Cement concrete. A prefabricated elliptical/oval/circular FRP shell may be used as stay-in-place formwork for casting additional Expansive Cement concrete around the column with a square or rectangular cross-section to achieve shape modification. The restraint of the expansion caused by hydration of the component of Expansive Cement induces the active confinement pressure. Large-scale experimental results have shown that shape-modification using Expansive Cement concrete can achieve a higher axial compressive strength and ductility for modified square and rectangular columns compared to the original columns with the same number of FRP composite layers. An analytical model was developed to determine the stress-strain behavior of shape-modified columns with Expansive Cement concrete. In addition, a parametric study for the practical use of shape modification is carried out.
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FRP-JACKETED AND SHAPE MODIFIED COLUMNS USING CHEMICAL POST- TENSIONING
2006Co-Authors: Chris P. Pantelides, Z. Yan, Lawrence D. ReaveleyAbstract:The axial compressive strength and ultimate compressive strain of columns inadequately designed for seismic forces can be improved by confinement with fiber reinforced (FRP) composites. To improve the confinement effectiveness of FRP composite jackets for square and rectangular columns, shape modification is performed by using prefabricated FRP shells combined with Expansive Cement concrete. Chemical post-tensioning using Expansive Cement concrete is used to change the FRP confinement from “passive” to “active”. Experimental results of large-scale columns in compression with externally bonded FRP jackets, or posttensioned FRP shells were performed on plain concrete columns. Square sections modified with FRP shells and Expansive Cement concrete to circular columns demonstrated a compressive strength increase by a factor of three and a ductility increase by a factor of two. Rectangular sections had a smaller but significant increase in both strength and ductility.
