I Recommendations for Upgrading of Concrete Structures with Use of Continuous Fiber Sheets

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1 CHAPTER 3 MATERIALS 3.1 General The continuous iber sheets or continuous iber strands used or upgrading shall be those whose quality has been conirmed. Quality shall be conirmed or the primer, the impregnation resin, and the smoothing material and surace preparation material or concrete suraces. The upgrading method by bonding continuous iber sheets to concrete structures or jacketing with the sheets (continuous iber sheet method) or with continuous iber strands (continuous iber strand method) are those in which upgrading is carried out ater impregnation resin applied to the continuous ibers hardens and bonds to concrete surace.. In addition to continuous iber sheets, continuous iber strands, and impregnation resin, the materials used include smoothing agents (used to smooth the surace irregularities and level dierences in the concrete), surace preparation material, grout or illing cracks on the surace, and primer to improve bonding. The eect o upgrading using continuous ibers varies depending on the quality o the materials and their combination. Thereore, the quality o each material should be conirmed in advance. 3.2 Quality o Materials Continuous iber sheets and continuous iber strands The quality o continuous iber sheets and continuous iber strands shall be speciied in terms o the characteristic values o tensile strength, Young's modulus, and ultimate strain with the combination o impregnated resin. The continuous ibers covered by these recommendations are carbon ibers or aramid ibers. Both o these ibers have excellent properties (lightweight, high strength, high - 9 -

2 lexibility and high resistance to corrosion), making it possible to select the iber with the quality required or the application. However, dierent rom the ordinary steel reinorcement, these materials are quite elastic up to racture without yield phenomena. The tensile strength and Young's modulus depend on the type and use conditions o the impregnation resin. Thereore, the characteristic values o continuous ibers and those combined with the impregnation resin should be conirmed in accordance with the JSCE-E 541 "Test method or tensile properties o continuous iber sheets." Impregnation resin Impregnation resin shall satisy the ollowing requirements. (1) As a binding material o ibers, it shall have a suitable viscosity and work lie or the operation. It shall also impregnate the continuous iber sheets and continuous iber strands and harden thoroughly. (2) Ater the impregnated continuous ibers have hardened, the quality o the composite shall be ensured. (3) The quality required or the bonding o the continuous iber sheets to concrete surace through the primer or smoothing agent shall be ensured. (4) The quality required or the overlap splice or continuous iber sheets shall be ensured. (1) Hardening o the impregnation resin produces the binding o continuous ibers to one another, and creates a composite material with the appropriate strength, Young's modulus, and other properties. Accordingly, the impregnation resin should thoroughly impregnate the continuous iber sheets or continuous iber strands. Also, during the construction process, it should have suitable viscosity to hold the sheet in place during attachment work. As the viscosity varies depending on the temperature, a resin with good viscosity at the anticipated temperature during construction should be selected. It is also important or the resin to have a certain work lie or the completion o operation without dripping during upward application

3 (2) The quality o continuous iber sheets or that o continuous iber strands is evaluated ater the impregnation resin has hardened, and a composite material has ormed. Without the impregnation resin, the ibers break one ater another under tension orce, as in a rope, and it is impossible to eectively use the strength o individual ibers. Moreover, even i the ibers are thoroughly impregnated with the impregnation resin, dierences in the type o impregnation resin and the orming method result in dierent tensile strength and Young's modulus. Thereore, a suitable impregnation resin should be selected and the composite should be tested in accordance with the JSCE-E 541 "Test method or tensile properties o continuous iber sheets" to ensure the quality required or continuous iber sheets. (4) When it is necessary to place an overlap splice between the continuous iber sheets,, the bond strength o the overlap splice should be conirmed in accordance with the JSCE-E 542 "Test method or overlap splice strength o continuous iber sheets" to prevent the overlap splice rom becoming a weak point Primer The primer shall have the required bond strength or bonding continuous iber sheets to concrete suraces. The primer is applied to the concrete surace in advance to ensure a thorough bond between concrete surace and the continuous iber sheets. The primer also prevents air bubbles rom developing between the continuous iber sheets and the surace o concrete during construction or curing as a result o exposure to direct sunlight. In other words, the primer penetrates the surace o concrete and strengthens the surace layer, creating the required bond strength between the continuous iber sheets and the surace o concrete. As noted previously, the bond strength o the primer should be conirmed by examining the combination o the primer with the impregnation resin

4 3.2.4 Smoothing agent (1) The smoothing agent shall be able to smooth level dierences and comparatively small irregularities in the concrete surace. It shall also have suicient viscosity and stickiness to enable the application work to be perormed smoothly. (2) The smoothing agent shall be able to bond suiciently with the primer and impregnation resin. (1) I there is any unevenness caused by the joints o ormwork or traces o bubbles in the surace o concrete, construction deects such as wrinkles, new bubbles, and resin accumulations tend to occur. Also, the continuous iber sheets that contact the overhangs tend to break. Large overhangs should be removed with a disc sander or the like, but minor irregularities can be smoothed by coating with a smoothing agent. To ensure that the smoothing work is accomplished without any problem, it is important to select a proper smoothing agent which has viscosity, stickiness and work lie that matches the temperature, climate and other construction conditions. In general, epoxy resin putties or the like can be used. (2) In the veriication o upgrading perormance, the smoothing agent should have the required bond strength with the primer when the continuous iber sheets are expected to be bonded to the existing concrete Other materials (1) Surace preparation materials shall have suicient bond strength at the damaged sections o the existing concrete, and their strength shall be at least equal to that o the existing concrete. (2) Crack grout shall penetrate to the deepest portion o the cracks, shall have the bond strength needed to bond with the concrete, and shall be able to prevent iniltration o water through the cracks. (3) Surace protection materials shall maintain the required quality o continuous iber sheets or continuous iber strands during the prescribed period o time

5 (1) I the cover o the existing concrete is missing in places, these sections are restored to the original condition by coating with surace preparation materials. I the surace preparation material tends to come loose rom the existing concrete or has low strength, the transmission o orce is hindered between the continuous ibers and the existing concrete. Normally, resin mortar and polymer cement mortar with high adhesion properties and high strength are used as surace preparation materials. (2) Both epoxy resin type and cement type crack grout are available and a suitable material should be selected to match the situation o cracking and water leakage. (3) through both the continuous iber sheet method and the continuous iber strand method, the composite material made o continuous ibers with impregnation resin is placed on the outer surace o the structure. In order to prevent deterioration o the continuous iber composite material during the service lie, a protective layer should be created by coating the surace with paint, concrete, or mortar when necessary. However, surace protection is not necessary i it can be conirmed that the quality o the continuous iber composite material will not change over time by the results o suitable numerical simulations and accelerated exposure tests (JSCE-E 547 "Test method or accelerated artiicial exposure o continuous iber sheets") or actual exposure tests, or, that the required quality can be maintained. I a noncombustible cover or lame-resistant cover is needed or protection against ire, or i protection against impacts caused by driting wood or automobiles or other type o protection is needed, a surace protection material should be selected to match the environment where the structure is located. 3.3 Characteristic Values and Design Values o Materials General The ollowing method shall be used to determine characteristic values and design values or continuous iber sheets and continuous iber strands

6 (1) The characteristic values or material strength and ultimate strain o continuous iber sheets and continuous iber strands shall be deined as the values which ensure that most o the test results do not all below the values, assuming variations in the test results. (2) The design material strength and design ultimate strain or continuous iber sheets and continuous iber strands shall be obtained by dividing the characteristic value by the material actor. The continuous iber sheet method and continuous iber strand method involve primer and impregnation resin as supplementary materials. For this reason, the tensile strength, Young's modulus and other values o continuous iber sheets or continuous iber strands used or upgrading design should generally be determined or the composite material ormed ater impregnating with resin and allowing it to harden. Accordingly, the method used to determine the characteristic values and design values or continuous iber sheets and continuous iber strands is described here Continuous iber sheets (1) As a rule, the characteristic value or the tensile strength o continuous iber sheets shall be determined based on the test results. The tension test shall be done in accordance with the JSCE-E 541 "Test method or tensile properties o continuous iber sheets." (2) As a rule, the characteristic values or the bond strength o continuous iber sheets to concrete, the characteristic values or the interacial racture energy and the relationship between bond stress and relative displacement shall be determined by the bond test. The bond test shall be done in accordance with the JSCE-E 543 "Test method or bond properties o continuous iber sheets to concrete." (3) The compressive strength and shear strength o continuous iber sheets shall not be considered in the design. (4) As a rule, the Young's modulus or continuous iber sheets shall be determined by the tension test. The tension test shall be done in accordance with the JSCE-E 541 "Test method or tensile properties o continuous iber sheets (drat)."

7 (5) The tensile stress-strain relationship or continuous iber sheets, used to veriy saety and serviceability, may be a straight line passing through the origin with the Young's modulus. (6) The coeicient o thermal expansion or continuous iber sheets shall be calculated rom the coeicient o thermal expansion, Young's modulus and the volume ratio o the constituent materials, such as the continuous ibers and impregnation resin. (7) As a rule, the characteristic values or the tensile atigue strength shall be determined by the tensile atigue test. The tensile atigue test shall be done in accordance with the JSCE-E 546 "Test method or tensile atigue strength o continuous iber sheets." (8) The material actors or continuous iber sheets shall be determined using Section 2.6 (2) in the Standard Speciications or Design and Construction o Concrete Structures (Design). (1) Continuous iber sheets unction as a composite material with continuous ibers bonded using impregnation resin. Even i the same strengthening ibers are used, the strength o continuous iber sheets may vary depending on the shape o the sheets and the bond with the impregnation resin. Thereore, this value is measured using the condition o the composite material ater the sheet is impregnated with the resin and it has hardened. It is known that variations in the tensile strength o continuous iber sheets are generally greater than those o steel, but the distribution can be thought o as conorming almost completely to a normal distribution. In general, the characteristic value or tensile strength is derived by subtracting three times the standard deviation (σ n ) rom the mean strength (X):(X-3σ n ). This is equivalent to a 99.9% conidence limit or the tensile strength. However, i the material manuacturer has established guaranteed strengths based on suicient test results, these values may be used as the characteristic values or the tensile strength o continuous iber sheets. (2) The bond strength between continuous iber sheets to concrete, the relationship between interacial racture energy, bonding stress and relative displacement vary depending on the type o continuous iber sheet and number o plies, the type o primer and impregnation resin, the strength and surace processing

8 condition o the concrete and other actors. Thereore, as a rule, these values should be determined through testing. (3) Since continuous iber sheets are extremely thin compared to the size o the members to be upgraded, they have little inluence on the compressive rigidity/load-carrying capacity and shear rigidity/ o the members. For this reason, the compression rigidity/strength and shear rigidity/strength o continuous iber sheets are not considered in the design. (4) In general, the mean value obtained through testing may be used as the Young's modulus or continuous iber sheets. I the material manuacturer has established a value or Young's modulus based on suicient test results, the value may be used as a characteristic value. (6) At present, there is almost no sample measurement or the coeicient o thermal expansion o continuous iber sheets. However, it is known that the coeicient o thermal expansion or unidirectional strengthened iber-reinorced composite materials can be estimated rom the thermal expansion coeicients and Young's modulus values o each constituent material, such as the continuous ibers and impregnation resin, and the speciic volume o continuous ibers, using Equation C α L = E α V E V + E + E m m α (1 V m (1 V ) )...(C3.3.1) where: α L : Coeicient o thermal expansion o the continuous iber sheet in the direction o the ibers α : Coeicient o thermal expansion o continuous ibers α m : Coeicient o thermal expansion o impregnation resin E : Young's modulus o continuous ibers E m : Young's modulus o impregnation resin V : Speciic volume o continuous ibers in continuous iber sheet

9 (7) When the characteristic values or atigue strength is determined through testing, considerations should be given to the type o continuous iber sheet, the size and requency o applied stress, and the environmental conditions. (8) In general, when appropriate construction and protection are conducted, the values used in Table C3.3.1 may be used as the material actors or the continuous iber sheets. Table C3.3.1 Standard values or material actor o continuous iber sheets Type o veriication Material actor Saety and restorability Serviceability Continuous iber strands (1) As a rule, the characteristic values or the tensile strength o continuous iber strands shall be determined through the tension test. (2) The compressive strength and shear strength o continuous iber strands shall not be considered in design. (3) As a rule, the bond strength between continuous iber strands and concrete shall not be considered in design. (4) As a rule, the Young's modulus or continuous iber strands shall be determined through the tension test. (5) The tensile stress-strain relationship or continuous iber strands, used to veriy saety and serviceability, may be a straight line passing through the origin with the Young's modulus derived rom the tension test. (6) The coeicient o thermal expansion or continuous iber strands shall be calculated rom the thermal expansion coeicient, Young's modulus and the volume ratio o the constituent materials, such as the continuous ibers and impregnation resin. (7) As a rule, the characteristic value or the atigue strength o continuous iber strands shall be determined through the atigue test. (8) The material actor or continuous iber strands shall be determined using Section 2.6 (2) in the Standard Speciications or Design and Construction o Concrete Structures (Design)

10 (1) JIS R 7601 "Testing methods or carbon ibers" should be used as the standard or tensile properties tests or continuous iber strands. However, when the material manuacturer has established guaranteed strength values based on adequate test results, those values may be used as the characteristic values or the tensile strength o continuous iber strands. (2) Since continuous iber strands have extremely tiny cross-sectional area in comparison with the members to be upgraded, they have little inluence on the compressive rigidity/load-carrying capacity and shear rigidity/ o the members. For this reason, the compressive rigidity and strength and shear rigidity and strength o the continuous iber strands are not considered in the design. (3) With the method o winding continuous iber strands, the continuous iber strands and concrete in contact with the bond area o each strand is very small. There is little data on the bond strength o the continuous iber strands to concrete. Thereore, as a rule, the bond strength o the continuous iber strands to concrete is not considered in design. (4) JIS R 7601 "Testing methods or carbon ibers" should be used as the standard or tensile properties tests. In general, the cross-sectional area used to calculate Young's modulus o the continuous iber strands is that o the continuous ibers only, as calculated rom the iber weight. I the material manuacturer has established values or Young's modulus based on adequate test results, these values may be used as Young's modulus o the continuous iber strands. (6) The coeicient o thermal expansion in the axial direction o the continuous iber strands should be calculated using equation (C3.3.1) or unidirectional iber-reinorced composite materials, in the same manner as or continuous iber sheets. (7) When characteristic values or atigue strength is determined through testing, considerations should be given to the type o continuous iber strand, the size and requency o applied stress, and the environmental conditions

11 (8) When appropriate construction and protection are conducted, the values used in Table C3.3.2 may be used as the material actors or continuous iber strands. Table C3.3.2 Standard values or material actor o continuous iber strands Type o veriication Material actor Saety and restorability Serviceability