Field evaluation of composite materials for bridge strengthening

FIELD EVALUATION OF COMPOSITE MATERIALS FOR BRIDGE STRENGTHENING by ALEXIS ANDRES LOPEZ-INOJOSA A DISSERTATION Presented to the Faculty of the Graduate School of the UNIVERSITY OF MISSOURI-ROLLA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY in CIVIL ENGINEERING 2006 Antonio Nanni, Advisor Genda Qhen John Myers Cesar Mendoza K Chandrashekhara Reproduced with permission of the copyright owner Further reproduction prohibited without permission UMI N um ber: 3229186 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted Also, if unauthorized copyright material had to be removed, a note will indicate the deletion ® UMI UMI Microform 3229186 Copyright 2007 by ProQuest Information and Learning Company All rights reserved This microform edition is protected against unauthorized copying under Title 17, United States Code ProQuest Information and Learning Company 300 North Zeeb Road P.O Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner Further reproduction prohibited without permission Copyright 2006 Alexis Lopez-Inojosa All Rights Reserved Reproduced with permission of the copyright owner Further reproduction prohibited without permission PUBLICATION DISSERTATION OPTION The present dissertation has been prepared in the form of five technical papers for publication The first paper “Field Validation of FRP Strengthening Technologies on Five Reinforced Concrete Bridges,” pages 79 through 99, has been accepted for publication in the ACI Journal Concrete International: Design and Construction The second paper “Validation of FRP Composite Technology Through Field Testing,” pages 100 through 115, has been published in the World Conference on Nondestructive Testing, Montreal, Canada August 30- September 3, 2004 The third paper “Strengthening of a Reinforced Concrete Bridge with Externally Bonded Steel Reinforced Polymer (SRP),” pages 116 through 136, has been submitted to the Journal Composites Part B: Engineering (Elsevier) The fourth paper “Bonded and Mechanically Fastened FRP Strengthening Systems: A Case of Study,” pages 137 through 162, has been accepted for special publication of ACI committee 440: 7th International Symposium on Fiber Reinforced Polymer Reinforcement for Reinforced Concrete Structures (FRPRCS-7), to be held in New Orleans, Louisiana, November 9, 2005 The fifth paper “Moment Redistribution in Continuous Reinforced Concrete Slabs Strengthened with Carbon NSM Bar,” pages 163 through 187, has been submitted to the Journal Composites Part B: Engineering (Elsevier) Reproduced with permission of the copyright owner Further reproduction prohibited without permission iv ABSTRACT This dissertation document consists on five technical papers, compiling the results of the research done on two projects related to the uses of FRP materials on the strengthening RC bridges structures Four papers are related to the first project “Validation of FRP Composite Technology Through Field Testing,” and one paper to the second project “Moment Redistribution on Composite-Strengthened RC Slabs.” The work of the first project focuses on field validation of five variances of FRP techniques for strengthening of concrete bridges Fundamental issues related to bridge strengthening with composites are identified and studied, in particular those associated to construction, analysis and design, load testing, load rating and monitoring One of the intellectual merit of the present dissertation consist of development of materials and construction specifications, a comprehensive document developed to make the technology of composite available to bridges owners and intended to be used in future FRP-related projects These specifications cover material and construction requirements for strengthening RC bridges with composites materials and cover the phases of concrete repairs, surface preparation, material specification, storage, handling, installation process, for five technologies used in the project The work of the second project is focuses on analytical and numerical work to discuss if moment redistribution can be neglected in Reinforced Concreted (RC) flexural slabs strengthened with externally-bonded carbon FRP system Two 22-ft continues slabs were tested to validate the model Reproduced with permission of the copyright owner Further reproduction prohibited without permission v ACKNOWLEDGMENTS The author wishes to express his sincere appreciation and gratitude to his advisor Dr Antonio Nanni for the opportunity to work under a high performance and professional team Also, to Dr Shamsher Prakash for his appropriate and disinterested advise Special thanks are given to his partner Estela Melian and to his colleagues and friends: Dr Nestore Galati, Eli Hernandez, William Otero, Abigayle Sherman, Gayle Spitzmiller, Jason Cox, Travis Hernandez, Silvia Rocca, Marta Matana, Jess Moss and Wesley Merkle for their cooperation, friendship and help The author is grateful to the University of Missouri-Rolla (UMR) for the opportunity to pursue PhD studies Also, to Missouri Department of Transportation (MoDOT), to the Center for Infrastructure Engineering Studies (CIES) at UMR and to the University Transportation center (UTC) at UMR for their financial support Reproduced with permission of the copyright owner Further reproduction prohibited without permission TABLE OF CONTENTS Page PUBLICATION DISSERTATION O PT IO N iii ABSTRACT iv ACKNOWLEDGMENTS v LIST OF ILLUSTRATIONS xv LIST OF T A B LE S xix SECTION INTRODUCTION DESCRIPTION OF THE FIELD VALIDATION PR O JE C T 2.1 BACKGROUD AND DESCRIPTION 2.2 LOAD TESTING AND MONITORING .5 2.2.1 Load Testing 2.2.2 Fiber Optic .6 2.2.3 Crack S ensor 2.2.4 Installation Criteria for FRP to be Used for Strengthening 2.2.5 Delamination and Substrate C ondition 2.2.6 Microwave Near-Field N D T MATERIALS AND CONSTRUCTION SPECIFICATIONS 10 3.1 CONCRETE R E PA IR 10 3.1.1 Site D em olition 10 3.1.1.1 General requirem ents 10 Reproduced with permission of the copyright owner Further reproduction prohibited without permission vii 3.1.1.2 Submittals 10 3.1.1.3 Dust and debris control 11 3.1.1.4 Protection 11 3.1.1.5 Execution 11 3.1.2 Deck Repairs 12 3.1.2.1 Description of work 12 3.1.2.2 Locations 12 3.1.2.3 M aterials 13 3.1.2.3.1 Cementitious patch material 13 3.1.2.3.2 A ggregate 14 3.1.2.3.3 Reinforcing b a rs 14 3.1.2.4 Equipm ent .14 3.1.2.5 Construction m ethod 15 3.1.2.6 Surface preparation .16 3.2 MANUAL LAY-UP CARBON/EPOXY FRP L A M IN A TE 17 3.2.1 G eneral 18 3.2.2 Delivery, Handling and Storage 20 3.2.3 Products 21 3.2.3.1 Carbon fabric 21 3.2.3.2 Epoxy prim er/sealer 22 3.2.3.3 Epoxy putty surface/void filler 22 3.2.3.4 Epoxy saturant 23 Reproduced with permission of the copyright owner Further reproduction prohibited without permission viii 3.2.4 Execution .23 3.2.4.1 Concrete repair .23 3.2.4.2 Surface preparation 23 3.2.4.3 Carbon manual lay-up laminate installation .25 3.2.4.3.1 Application of filler/surface .27 3.2.4.3.2 Application of carbon fiber sheet 27 3.2.5 Rework and Repairs 29 3.2.6 Acceptance Testing 30 3.3 NEAR SURFACE MOUNTED COMPOSITE BAR SYSTEM 31 3.3.1 G eneral 31 3.3.2 Delivery and Storage 33 3.3.3 Products 34 3.3.3.1 Carbon/epoxy FRP bars .34 3.3.3.2 Epoxy adhesive system 35 3.3.3.2.1 Epoxy adhesive .35 3.3.3.2.2 UV protection .36 3.3.4 Execution .36 3.3.4.1 Concrete repair .37 3.3.4.2 Surface preparation 37 3.3.4.3 Carbon bar installation 38 3.3.5 Rework and Repairs 40 3.4 BONDED CARBON/EPOXY PRE-CURED LAMINATE .41 Reproduced with permission of the copyright owner Further reproduction prohibited without permission ix 3.4.1 G eneral 41 3.4.2 Delivery, Handling and Storage 43 3.4.3 Products .44 3.4.3.1 Carbon/epoxy FRP pre-cured lam inate 44 3.4.3.2 Epoxy prim er/sealer 45 3.4.3.3 Adhesive 45 3.4.4 Execution .46 3.4.4.1 Concrete repair .46 3.4.4.2 Surface preparation 46 3.4.4.3 Pre-cured CFRP laminate installation .47 3.4.5 Rework and Repairs 50 3.4.6 Acceptance Testing 51 3.5 STEEL REINFORCED POLYMER LAMINATES 52 3.5.1 G eneral 52 3.5.2 Delivery and Storage 54 3.5.3 Products 55 3.5.3.1 Steel cord lam inates 55 3.5.3.2 Epoxy resin 55 3.5.4 Execution .56 3.5.4.1 Concrete repairs 56 3.5.4.2 Surface preparation 56 3.5.4.3 Steel reinforced polymer laminate installation 57 Reproduced with permission of the copyright owner Further reproduction prohibited without permission 194 Table - Summary of Bill olf All Material as Built Bar 392 ft 119 m NSM Bars Adhesive 392 ft 119 m 2,994 l r 278 mSheet Primer 1643 lr 153 nr Manual Lay-up 1643 fr 153 m7 Putty Laminates Saturant 4377 fr 407 nr 1643 fr 153 m“ Coating 203 fr Hardwire 3X2 19 m“ SRP Hardwire 3SX 47 m2 503 fr Saturant 1395 fr 130 m" Coating 632 ft* 59 nr The detailed compilation for the bill of materials reported in the Tables above is given at the end of this report as Appendix Reproduced with permission of the copyright owner Further reproduction prohibited without permission 195 STRENGTHENING 3.1 Substrate Repair The performance of a composite system depends not only on the quality and strength of the concrete substrate but also on the bond between the composite and substrate A clean and sound substrate is essential for composite repair systems Unsound concrete, concrete which emits a relatively dead or hollow sound when its surface is tapped with a metal tool, was removed and patched Holes through the deck were filled; all concrete surfaces to be strengthened were thoroughly prepared according to the minimum requirement defined in the Master Materials and Construction Specification The concrete repair work consisted of the following parts: • Partial-depth repairs of deteriorated concrete on deck and bents • Removal of sound concrete along the deck, bents and girders to establish a suitable surface profile In order to place CFRP and SRP on the underside of the bent system, repair work was done by removing 20 cubic feet (0.57 m3 ) of concrete from the deteriorate areas, cleaning the area, installing repair materials, finishing and texturing (Figure 4) Figure Repair of deteriorated areas on one bent Bent after repair 3.2 Surface Preparation To promote continuous intimate contact between concrete and FRP, several important issues had to addressed in the surface preparation: concrete surface irregularities, fins, and/or sharp angles that may result in separation and delamination of carbon laminate from the concrete and/or in localized stress concentration Concrete surface irregularities were removed and smoothed to less than mm Rounding of comers using grinders reduces stress concentration and results in improved bond between the FRP and concrete surface The concrete angles were rounded to no less than 1/2-inch (12.7 mm) (see Figure 5) Reproduced with permission of the copyright owner Further reproduction prohibited without permission 196 Figure Rounding of comers on girder Abrasive sandblasting was used to clean the concrete surfaces of dust, dirt, laitance, oil and any curing substance Concrete surface roughness was equivalent to CSP (Concrete Surface Profile number 3) as defined by the International Concrete Repair Institute The sandblasting must be applied prior to CFRP and SRP installation All loose particles, oil, dust, cement, paint and other contaminants were contained in accordance with State regulation (Figure 6) Figure Preparation of appropriate roughness by sandblasting 3.3 E xtern ally B onded C om posite R einforcem ent Spans and 2, numbered from South to North, were strengthened with manual lay-up laminates and NSM bars Span was reinforced with SRP laminates The installation process for each technology will be described in the following sections 3.3.1 Manual Lay-up CFRP Laminates The carbon fabric for the manual lay-up system consists of uni-axial carbon fiber sheets for strengthening the positive moment and shear region of reinforced concrete In this instance, a high strength carbon fiber was used (Table 2) Reproduced with permission of the copyright owner Further reproduction prohibited without permission 197 3.3.1.1 Primer application to All voids Two-component epoxy primer (Table 2) was used to fill voids in the concrete surface All surfaces to receive the carbon fiber fabric were primed with the penetrating primer (Figure 7) Primer was mixed in accordance with the manufacturer’s recommendations (See Manufacturer’s Literature) using brushes and rollers The volume of primer to be prepared at one time was such that could be applied within its pot life Primer was thoroughly mixed with a hardener at the manufacturer’s specified ratio Application was uniform in a sufficient quantity to fully penetrate the concrete and produce a non-porous film in the surface after full penetration A four-way method, application in all four direction, was used When necessary, a second coat was applied after the first coat penetrated into the concrete Figure Filling of voids and defects by primer and putty collocation 3.3.1.2 Epoxy filler/surfacer Remaining minor surface irregularities and defects were corrected using epoxy filler/surfacer or putty It is not desirable that the epoxy putty filler cover the entire concrete surface A trowel was used to apply the putty in order to fill any surface defect (Figure 7) The material properties of the primer and putty that were used are listed in Table 3.3.1.3 Application of carbon fiber sheets The carbon fiber sheets were cut beforehand into prescribed sizes using scissors and a simple made-in-place device (Figure 8) Reproduced with permission of the copyright owner Further reproduction prohibited without permission 198 A saturant coating (Table 2) was applied with a medium nap roller after application of the primer and putty (Figure 9) Afterward, the pre-cut fiber sheets were attached according to Contract drawings Figure Cutting process of CFRP sheet The carbon fiber sheets were installed by manual lay-up method (Figure 10) The sheets were properly aligned and set into the surface saturant The fiber plies were aligned on the structural member according to the Contract Documents Any deviation in the alignment more than 5° (approximately 87 mm/m or in/ft) was not acceptable The sheets were saturated by rolling out the external surface This operation also removed excess of saturant and bubbles (Figure 11) After appropriate time (10 minutes), a second saturant application over the carbon fiber sheets were applied to a complete impregnation (Figure ll).T h e saturant was applied in strict accordance with the manufacturer’s recommendations (Manufacturers Literature) Figure Saturant application Reproduced with permission of the copyright owner Further reproduction prohibited without permission 199 Figure 10 Manual lay-up CFRP sheet installation Figure 11 Squeezing of air bubbles and saturation over laminates The process must allow sufficient working time for the rolling of the carbon fiber sheet and saturant to produce a uniform system that is completely free of voids and trapped air It must be completed within the limits of saturant pot-life Because saturant is susceptible to temperature, special care shall be taken to minimize the elapsed time between mixing and application of the saturant This must be applied to the sheet at least 15 minutes prior to any thickening In order to avoid vibrations during the installation, traffic control was used (see Figure 12) Speed of the car was limited to 15 mph (24.14 km/hr) Finally, a topcoat was applied to the sheet to provide a cosmetic finish and environmental protection (see Figure 12) Reproduced with permission of the copyright owner Further reproduction prohibited without permission 200 Figure 12 Traffic control and topcoat protection 3.3.2 N ear Surface M ounted (N SM ) B ars The carbon/epoxy CFRP Bars are pultruded carbon fiber reinforced epoxy These bars are reinforcing elements for positive moments The material properties of the bars and epoxy paste used are listed in Table Installation of the bars was achieved first by grooving the concrete surface The grooves have square cross section, 5/8 inch (15.9 mm) per side, to allow embedment This value is equivalent to the diameter of the bar plus one eighth of an inch per side) Concrete was grooved making parallel saw cuts of 5/8 in depth and spaced at 5/8 in The groove is created by chipping out the concrete between the two cuts (see Figure 13) The system included a primer/sealer for the concrete surface (see Figure 14) Figure 13 Grooving of girder surface for the NSM bars Reproduced with permission of the copyright owner Further reproduction prohibited without permission 201 Figure 14 Epoxy resin and epoxy adhesive in slot cut in the concrete surface A high modulus, high strength and high viscosity epoxy adhesive was used (Table 3) This epoxy paste is chemically compatible with the individual properties of the primer and bars, so a solid bonding can be developed (see Figure 14) Figure 15 Bar installation Figure 16 Installed NSM bars Reproduced with permission of the copyright owner Further reproduction prohibited without permission 202 The NSM bars were then placed into the grooves and lightly pressed to force the paste to flow around the bar The bars are sometime placed with the help of wedges Excess material was removed manually and the surface was leveled (Figure 15 and Figure 16) The NSM FRP technique does not require any surface preparation work and requires minimal installation time compared to FRP laminates Nevertheless, the grooving work can take more time and cost more than the normal surface preparation of in-place-cured or pre-cured laminates 3.3.3 Steel Reinforced Polymers (SRP) The Steel Reinforced Polymers (SRP) tape consists of steel cord tape and epoxy resin (see Table 4) Two types of high strength SRP tape were used: a type-1 SRP cord tape of 0.0173 in2/in (0.44 mm2/mm) of net area per width, used for flexural reinforcement; and a 9 type-2 SRP cord tape of 0.0104 in /in (0.26 mm /mm) of net area per width, U-wrapped on the longitudinal girders Installation of SRP systems is generally similar to single ply wet lay-up but the material is more rigid Repair of concrete substrate and surface preparation to provide an open roughened texture are procedure similar as described in sections 3.1 and 3.2 of this report Nevertheless, because the steel cord is typically bent with mechanical equipment that makes 90° sharp bents, it is not recommended to round the comers in the concrete section as is typically done for FRP installation SRP system strips were cleaned and cut in length specified in the contractor drawings (see Figure 17) using commercial quality handheld electric shears or other appropriate shearing cutters The number of sheets cut was limited to the number to be installed that day Figure 17 Cutting of SRP laminates and epoxy adhesive application to the surface A coating resin was roller-applied to the concrete to prime and seal the surface (Figure 17) The steel sheet was then installed and properly aligned by the manual lay-up method The laminates were mechanically pressed onto the concrete with enough force to impregnate them and to squeeze out the extra resin (Figure 18) Reproduced with permission of the copyright owner Further reproduction prohibited without permission w JS w Figure 18 SRP installation and full impregnation by rolling The process was carefully planned to allow sufficient working time for the rolling of the carbon fiber sheet and resin to produce a uniform system that is completely free of voids and trapped air and to be completed within the time limits of the resin pot life Sheets were then completely impregnated with an application of a second roller-applied epoxy resin to the external surface (Figure 19) Figure 19 Full impregnation by a second epoxy application Flexural and shear reinforcement was originally designed to be installed in alternating ways Nevertheless, for construction reasons, all the flexural reinforcement was collocated first (see Figure 20) Additionally, all U-Wraps collocated after that were divided in two L-shape parts (see Figure 20), fully overlapped in the bottom of the girders (see Figure 21) Finally, a topcoat was applied to the sheet to provide a cosmetic finish and environmental protection Reproduced with permission of the copyright owner Further reproduction prohibited without permission Figure 20 Installation of flexural reinforcement U-Wrap formed by two L-Shapes Figure 21 Overlapping to form a U-Wrap Reproduced with permission of the copyright owner Further reproduction prohibited without permission 205 ACCEPTANCE TESTING A direct pull-off test based on ASTM D 4541-93 was used by the contractor in this project This test allows to check the quality of the installation of the FRP It consists in gluing an aluminum square plate on the strengthened part to be checked; afterwards, a core is drilled close to the aluminum plate through the laminate strip into the concrete substrate, providing an isolated test location for attachment of the pull-off tester (Figure 27) The tester records the force causing the failure, which, if divided by the core cross sectional area, will result in tensile strength (psi) Upon failure of the core specimen, a visual examination of the failure plane location reveals whether the failure occurred at the bond line or within the substrate Failure of the concrete and not at the bond line was the only acceptable failure The tensile bond strength must be more than 200 psi (1.4 MPa) 9 One pull-off test was performed every 200 ft (20 m ) of area strengthened with carbon fiber strip system or once every deck span Figure 22 Pull-off test The results of single tests made on spans and are summarized in table They show values of tensile bond strength bigger than the minimum required Based on these results and that all failures occurs in the concrete and not at the bond line, installation of FRP was considered successful Table Results of direct T est# Test Results psi [MPa] 400 [2.8] 300 [2.1] 650 [4.55] 700 [4.9] pull-off test for Dallas County bridge P-0962 Description Work Area Carbon Fiber-U Wrap sheet Bent A carbon Fiber Deck Span Carbon Fiber-U Wrap sheet Internal girder-Span Carbon Fiber-U Wrap sheet Bent B Reproduced with permission of the copyright owner Further reproduction prohibited without permission APPENDIX B DVD: INSTALLATION PROCESS FOR FIVE VARIATIONS OF COMPOSITE MATERIALS Reproduced with permission of the copyright owner Further reproduction prohibited without permission 207 INTRODUCTION Included with this dissertation is a DVD, which contains didactical audiovisual documents that processed the activity developed during construction phases It represents material support in the form of videos and presentations (PowerPoint) for courses and presentations It covers aspects regarding to construction and installation using composite materials, like their storage, handling, installation, and required quality procedures for the strengthening of RC bridges with FRP CONTENTS Adhered Techniques: Surface Preparation Manual Lay-up Laminate Pre-cured laminates Steel Reinforced Polymer Other Techniques: Near Surface Mounted Bars Mechanically Fastened FRP Reproduced with permission of the copyright owner Further reproduction prohibited without permission 208 VITA Alexis Andres Lopez-Inojosa was bom on August 24, 1970, in Caracas, Venezuela He received his B.Sc degree in Civil Engineering (1993) and his M.Sc in Structural Engineering (1996) in the University of Los Andes, Venezuela, where he became Lecturer in the Structural Department of Civil Engineering Faculty, in 1997 From January 2002 to December 2005, he worked as a Research Assistant in Department of Civil Engineering at the University of Missouri-Rolla In May 2006, he received his Ph.D degree in Civil Engineering from the University of Missouri-Rolla Reproduced with permission of the copyright owner Further reproduction prohibited without permission ... Technology Through Field Testing” focus on field validation of five variances of FRP techniques for strengthening of concrete bridges Fundamental issues related to bridge strengthening with composites... Sides of the Bridge 155 Geometry of the Bridge 156 FRP Materials Used in Strengthening System 157 MF-FRP System for the Strengthening of the Major Deteriorated Areas 157 Strengthening. .. results of the research performed on two research projects related to the uses of FRP materials on the strengthening RC bridges structures The work of the first project “Validation of FRP Composite