Digest1003

Research Digest FORWARD ALL REQUESTS TO: The University of Texas at Austin Center for Transportation Research LIBRARY 3208 Red River • Suite 115 • Austin • Texas • 78705-2650 Phones: (512) 232-3126 and (512) 232-3138 • Fax: (512) 232-3088 Email: ctrlib@austin.utexas.edu

In this Issue: TxDOT Reports

Table of Contents Item 1. Aggregate Distribution Investigation in Box Beams Fabricated with Self Consolidating Concrete (CTR 5197-01-1) ........................................................................................................................................... 1 Item 2. Evaluation of MEPDG with TxDOT Rigid Pavement Database (CTR 5445-3) .............................. 2 Item 3. Arterial Intelligent Transportation Systems -- Infrastructure Elements and Traveler Information Requirements (CTR 5865-1) ......................................................................................................................... 3 Item 4. Feasibility of Speed Harmonization and Peak Period Shoulder Use to Manage Urban Freeway Congestion (CTR 5913-1) ............................................................................................................................. 3 Item 5. Effects of Wet Mat Curing Time and Earlier Loading on Long-Term Durability of Bridge Decks: Compressive Strength, Maturity and Strength Durability Index (SDI) (TechMRT 2116-4A) ...................... 4 Item 6. Study of Elastometric Bearings for Superelevated U-Beam Bridges (TechMRT 5834-1) ............... 4 Item 7. Culvert Rating Guide (TechMRT 5849-P1) ..................................................................................... 5 Item 8. Rubblization and Base Overlay of FM 912 and FM 1155 (TTI 4687-01-1 ) .................................. 5 Item 9. Roadway Safety Design: An Engineer's Guide to Evaluating the Safety of Design Alternatives (TTI 4703-01-P3) .......................................................................................................................................... 5 Item 10. Laboratory and Field Evaluation of Concrete Paving Curing Effectiveness (TTI 5106-3)............ 6 Item 11. NCHRP Report 350 Crash Testing and Evaluation of the S-Square Mailbox System (TTI 5210-7) .................................................................................................................................................. 6 Item 12. Guidance on Mitigating the Impacts of Large Distribution Centers on Texas Highways (TTI 5335-1) .................................................................................................................................................. 7 Item 13. Workshops on Using the GPS Method to Determine Curve Advisory Speeds (TTI 5439-01-1) . 7 Item 14. Revised Text for TxDOT Manual Procedures for Establishing Speed Zones, Chapter 5, Section 2 (TTI 5439-01-P2) ....................................................................................................................................... 8 Item 15. Design, Construction, and Performance Monitoring of the Very Thin Overlay Placed on Bus 59 in the Lufkin District (TTI 5598-01-2).......................................................................................................... 8 Item 16. Development of Guidelines for Cable Median Barrier Systems in Texas (TTI 5609-2) ............... 9 Item 17. Video over IP Design Guidebook (TTI 5942-P1) .......................................................................... 9 Item 18. Long-Term Performance of GFRP Reinforcement: Technical Report (TTI 6069-1) ................. 10 Research and Technology Implementation Office March 2010

Research Digest Item 1 Aggregate Distribution Investigation in Box Beams Fabricated with Self Consolidating Concrete UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR) CTR 5197-01-1 • 2009 In 2004, the Texas Department of Transportation initiated Project 0-5197 to investigate the feasibility of increasing the allowable compressive stress limit at prestress transfer. Initially, the live load performance of 36 specimens was evaluated by Birrcher and Bayrak (TxDOT Report 5197-1, 2007). Report 5197-4 presents the subsequent research conducted based on recommendations of Birrcher and Bayrak (2007). In this portion of TxDOT Project 0-5197, 45 Type-C beams and 10 4B28 box beams were tested to experimentally determine their cracking load. The Type-C beams were produced in four different fabrication plants using conventionally consolidated concrete. The 10 4B28 box beams were produced in two fabrication plants using concrete mixture designs of both self consolidating concrete as well as conventional concrete (Schnittker and Bayrak, CTR, 2008). After testing the 10 box beams procured in TxDOT Project 0-5197, Schnittker and Bayrak (2008) reported increased amounts of top flange cracking at release, substantially lower modulus of elasticity (along with increased deflections under live loading), slightly higher cambers near 28-days, and lower than expected flexural cracking loads under live loads. The present investigation is carried out in an effort to explain the poor performance of the beams fabricated with SCC as reported in research report 0-5197-4.

Full-text PDF of this report is available for free download from http://www.utexas.edu/research/ctr/pdf_reports/0_5197_01_1.pdf

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Research Digest Item 2 Evaluation of MEPDG with TxDOT Rigid Pavement Database UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR) CTR 5445-3 • 2009 TxDOT initiated the rigid pavement database project to collect information on the general performance of portland cement concrete (PCC) pavement as well as to collect project-level information on PCC pavement responses and performance. A total 27 sections were selected statewide and detailed information was collected such as load transfer efficiency at small, medium, and large crack spacing and for two different seasons: summer and winter. Also collected were crack spacing information and slab deflections. Efforts were made to calibrate the punchout model in MEPDG. Review of the punchout model in MEPDG revealed that it is quite sophsticated, with a number of variables involved. It assumes that longitudinal cracking is induced by top-down cracking. The model is more applicable to CRCP with an asphalt shoulder. On the other hand, the model might not be appropriate for the punchout analysis of CRCP with tiedconcrete shoulder. Sensitivity analyses were conducted to investigate the effects of selected input variables on punchouts. Zero-stress temperature (ZST) had quite a large effect, because crack width and LTE depend to a large extent on ZST. The MEPDG equation for crack width tends to over-predict crack width and appropriate calibration constant needs to be determined. The comparison of actual punchout with a predicted value from MEPDG using national calibration constants shows a marked difference. MEPDG over-predicted punchout more than 30 times. When the calibration constant for crack width was reduced from 1 to 0.5, the predicted punchout became more reasonable.

It appears that many distresses identified and recorded as punchouts in Texas are not actually punchouts caused by structural deficiency. Rather, most of them are due to imperfections in design details and/or construction/materials quality issues. Horizontal cracking appears to be the major cause of distresses in CRCP in Texas. The interactions between longitudinal steel and concrete in response to dynamic wheel loading applications appear to be the cause of horizontal cracking. Efforts should be made to accurately identify punchout during field evaluations. At this point, the punchout information in TxDOT’s PMIS doesn’t appear to be accurate.

Manual for administrator of the database developed in this study is contained in this report.

Full-text PDF of this report is available for free download from http://www.utexas.edu/research/ctr/pdf_reports/0_5445_3.pdf

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Research Digest Item 3 Arterial Intelligent Transportation Systems -- Infrastructure Elements and Traveler Information Requirements UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR) CTR 5865-1 • 2009 Applying Intelligent Transportation Systems (ITS) to arterial systems allows TxDOT to significantly enhance transportation system operation efficiency and improve traffic mobility. However, no guidelines are available to assist TxDOT staff in selecting the most beneficial arterial ITS elements and desirable ITS technologies. To address these gaps, this study was initiated by TxDOT to investigate the arterial ITS elements, technologies, arterial performance measures, information dissemination technologies, and financial considerations for arterial ITS deployments and to enhance the arterial traffic operation efficiency.

A variety of techniques are available to monitor and manage the traffic on arterial roadways, and ITS applications can support many of these strategies. Evaluation of these ITS strategies and available technologies to meet TxDOT needs is the essence of this research project. The research addresses two TxDOT goals: making the current transportation system more efficient through innovative arterial ITS deployments, and maximizing the benefits of existing ITS infrastructure and new arterial ITS deployments. The research team first synthesized the state-of-the-art in arterial ITS technologies and management strategies. Then critical performance measures were investigated and identified through a survey study. Next, the most beneficial ITS elements were examined and desirable ITS technologies and solutions were identified for arterial management enhancement. Various traveler information dissemination modes were studied and evaluated, and the guideline was developed to prioritize arterials suitable for ITS implementations. Finally, a case study was conducted to demonstrate representative arterial ITS applications. It was found deploying ITS technologies can significantly improve arterial system operation efficiency. The study findings provide new knowledge and practical guidance to help TxDOT better utilize existing ITS infrastructure elements and to make wise investments in future arterial ITS applications.

Full-text PDF of this report is available for free download from http://www.utexas.edu/research/ctr/pdf_reports/0_5865_1.pdf

Item 4 Feasibility of Speed Harmonization and Peak Period Shoulder Use to Manage Urban Freeway Congestion UNIVERSITY OF TEXAS AT AUSTIN. CENTER FOR TRANSPORTATION RESEARCH (CTR) CTR 5913-1 • 2009 Traffic congestion is an increasing problem in the nation’s urban areas, leading to personal inconvenience, increased pollution, hampered economic productivity, and reduced quality of life. While traffic congestion tends to continuously increase, growth in transportation infrastructure is limited by financial and land availability constraints. This has placed an increasing emphasis on using dynamic traffic management strategies, such as speed harmonization and peak-period shoulder use, to efficiently manage congestion using existing freeway capacity. This project implemented various strategies of variable speed limits and shoulder use and assessed their impact on traffic operations and safety of freeway. These strategies were found to homogenize traffic and create safer driving conditions, but did not increase the throughput of the system. The ITS devices required to implement these strategies, enforcement issues, potential impediments in their implementations, and a framework for cost-benefit analysis to determine the economic viability are also discussed.

Full-text PDF of this report is available for free download from http://www.utexas.edu/research/ctr/pdf_reports/0_5913_1.pdf _____________________________________________________________________________________________

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Research Digest Item 5 Effects of Wet Mat Curing Time and Earlier Loading on Long-Term Durability of Bridge Decks: Compressive Strength, Maturity and Strength Durability Index (SDI) TEXAS TECH UNIVERSITY (TECHMRT) TechMRT 2116-4A • 2009 There is increasing pressure from owners, contractors, and the public to open bridge decks sooner to full traffic loads. As a result, a set of criteria or guidelines is needed to determine when concrete bridge decks can safely be opened. Today, current practice allows many bridge decks and concrete pavements to be opened to traffic once a desired compressive strength is achieved from a representative field-cast test cylinder. Though generally untrue, many believe that this strength value serves as a measure of the durability of the placed concrete. In a collaborative research effort between Texas Department of Transportation and researchers at Texas Tech University, studies were undertaken to collect research data that could potentially lead to the development of new guidelines as to when bridge decks can be open to (a) construction traffic and (b) full traffic without sacrificing concrete durability. This report presents detailed findings of two research thrusts: compressive strength and maturity curves commonly used on bridge deck concrete mixes and comparative assessment of the effectiveness of three curing methods that led to the development of a framework for a Strength-Durability Index (SDI).

Full-text PDF of this report is available for free download from http://www.depts.ttu.edu/techmrtweb/Reports/Complete%20Reports/0-2116-4A.pdf

Item 6 Study of Elastometric Bearings for Superelevated U-Beam Bridges TEXAS TECH UNIVERSITY (TECHMRT) TechMRT 5834-1 • 2009 The primary objective of this research was to determine the best way to consider the effects of transverse superelevation on uniform-height steel-reinforced elastomeric bearing pads for U-Beam bridges. Existing TxDOT design provisions did not specifically account for the effects of the transverse superelevation. A nationwide survey of Departments of Transportation (DOTs) revealed that the country was nearly evenly split on whether or not superstructure elements such as U-Beams should be placed on a transverse superelevation.

Specific modifications to the AASHTO Method “A” design of elastomeric bearing equations were developed to account for the transverse superelevation. The proposed modifications were evaluated over typical U-Beam span/spacing combinations for both the U-40 and U-54 sections. The ability of the proposed modifications to predict actual behavior was evaluated by inspecting existing bridges and performing full-scale laboratory testing. Both the field inspections and the laboratory testing validated the need for the proposed revisions. These proposed revisions have been submitted as suggested revisions to the TxDOT LRFD Bridge Design Manual.

The feasibility of electronic monitoring in-situ bearings that have experienced significant transverse deflections was investigated. The bulging on the sides of the bearings made monitoring unreliable. Instead, a method to manually record pertinent information during the routine bridge inspection is recommended.

Full-text PDF of this report is available for free download from http://www.depts.ttu.edu/techmrtweb/Reports/Complete%20Reports/0-5834-1_final.pdf

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Research Digest Item 7 Culvert Rating Guide TEXAS TECH UNIVERSITY (TECHMRT) TechMRT 5849-P1 • 2009 The purpose of this Culvert Rating Guide is to present a clear, repeatable and valid procedure for Texas Department of Transportation (TxDOT) engineers and their consultants to use for load rating culverts in the TxDOT roadway system.

Full-text PDF of this report is available for free download from http://www.depts.ttu.edu/techmrtweb/Reports/Complete%20Reports/Culvert%20Rating%20Guide%20%20complete.pdf

Item 8 Rubblization and Base Overlay of FM 912 and FM 1155 TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 4687-01-1 • 2010 In many instances rubblization may be a good option to convert a deteriorated concrete pavement into a flexible pavement structure. In this project, the Texas Department of Transportation conducted rubblization on portions of a concrete pavement originally constructed in the 1920s to validate project analysis and construction specifications. This project truly pushed the limit with respect to how poor the concrete pavement support can be before rubblization is not a viable option. Fortunately, project personnel knew from the start that this project was a marginal candidate for rubblization, so contingency plans were already in place. Rubblization on this project showed that the project analysis procedures and construction specification worked well. These procedures and specification are included in this report as Appendices A and B, respectively, and should be used for planning and controlling construction of future rubblization projects. Post-construction monitoring revealed no differences in ride existed among the sections of differing treatments. The main structural differences observed were between sections rubblized with different equipment. The sections rubblized with Type II equipment had rubblized and base layer modulus values greater than those observed in the section where Type I equipment was used.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/5-4687-01-1.pdf

Item 9 Roadway Safety Design: An Engineer's Guide to Evaluating the Safety of Design Alternatives TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 4703-01-P3 • 2010 Course notes and software from the Multilane highways and freeways workshop, July 2009.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/5-4703-01-P3.pdf

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Research Digest Item 10 Laboratory and Field Evaluation of Concrete Paving Curing Effectiveness TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 5106-3 • 2009 Ensuring that sufficient water is available in hydrating concrete is of great importance to produce durable concrete and achieve both short- and long-term performance of concrete pavement. Excessive early-age evaporation from the surface of concrete pavement often results in high porosity delaminated and low strength concrete. Application of curing compounds in concrete paving is widely used to minimize evaporation.

However, the Texas Department of Transportation (TxDOT) standard specifications for pavement construction (Item 526) only defines the use of the membrane curing in terms of key characteristics such as percent solids, density, viscosity, color, and the application rate, but does not specify curing performance or limits on the rate of evaporation.

This research utilized several techniques to evaluate curing effectiveness from both a moisture retention and physical properties standpoint, to develop a laboratory-based curing evaluation protocol that has application to the field.

A series of tests were carried out to identify factors controlling curing quality under field conditions.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/0-5106-3.pdf

Item 11 NCHRP Report 350 Crash Testing and Evaluation of the S-Square Mailbox System TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 5210-7 • 2010 The Texas Department of Transportation desired to evaluate an alternate mailbox support system for use in Texas. S-Square® Tube Products manufactures a system that is adaptable for use with single, dual, and multiple mailboxes and is considered to provide the desired ease of installation and maintenance. Two full-scale crash tests were conducted to evaluate the safety performance of the S-Square® Tube Products dual and multiple-mailbox mounts in accordance with NCHRP Report 350.

The S-Square® Tube Products mailbox system successfully passed all requirements of NCHRP Report 350 and is considered ready for field implementation in single, dual, and multiple mailbox configurations.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/0-5210-7.pdf

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Research Digest Item 12 Guidance on Mitigating the Impacts of Large Distribution Centers on Texas Highways TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 5335-1 • 2010 Numerous distribution centers (DCs) have been built in Texas over the past 20 years. They serve retail, grocery, oil, motor vehicle, manufacturer, and other types of business. These DCs vary in size and truck traffic.

Depending on the type of DC and roads providing access, a DC will have some level of traffic operations, safety, and pavement wear impact on those roads. DC site selection often involves the DC site selector/owner/operator/developer negotiating with local agencies, including economic development agencies, to identify potential sites and obtain the best incentives. TxDOT is typically brought into the process very late and is then asked to accommodate local agency and DC owner requests without having prior input. This project assessed the DC site selection and development process as it affects TxDOT. The project also developed tools, guidelines, and strategies for gaining early collaboration with DC owners and local agencies in planning and engineering the DCs and their access and funding improvements to state highways. This project analyzed obstacles resulting in TxDOT not being involved earlier in the DC site selection process. Research products included in this report summarize the research performed and present a handbook containing tools and recommendations for working with proposed DC site selectors, developers, and others.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/0-5335-1.pdf

Item 13 Workshops on Using the GPS Method to Determine Curve Advisory Speeds TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 5439-01-1 • 2009 Curve warning signs are intended to improve curve safety by alerting the driver to a change in geometry that may not be apparent or expected. However, several research projects conducted in the last 20 years have consistently shown that drivers are not responding to curve warning signs or complying with advisory speed plaques.

A new engineering study method was developed to improve consistency in curve signing and driver compliance with advisory speeds. This report documents two activities that were conducted to promote implementation of the new method. One activity is the development of a software program to measure curve geometry while driving through the curve. The geometric data are then used to determine an appropriate curve advisory speed and to select effective, curve-related traffic control de vices.

The second activity for this project was a series of workshops that described use of the new method. The workshop provided a mixture of classroom discussion and hands-on training activities for the participants. The workshop participants generally indicated that they believed the new method would benefit their districts and looked forward to implementing it. Recommended for future research in this area were identified.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/5-5439-01-1.pdf

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Research Digest Item 14 Revised Text for TxDOT Manual Procedures for Establishing Speed Zones, Chapter 5, Section 2 TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 5439-01-P2 • 2010 Revised Text for TxDOT Manual Procedures for Establishing Speed Zones, Chapter 5, Section 2 Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/5-5439-01-P2.pdf

Item 15 Design, Construction, and Performance Monitoring of the Very Thin Overlay Placed on Bus 59 in the Lufkin District TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 5598-01-2 • 2010 A thin overlay 1-inch thick was placed as a surface layer on the jointed concrete pavement on Business 59 in the Lufkin District. This mix was designed in the laboratory to have a balance of good rut resistance as measured by TxDOT’s Hamburg Wheel Tracking test (HWTT) and good reflection cracking resistance as measured by the Overlay Tester (OT). These Crack Attenuating Mixes (CAM) were designed and constructed based on TxDOT’s special specification SS 3109. A top quality granite aggregate was used with 1 percent lime and an asphalt content of 8.3 percent with a PG76-22 binder.

This project was tested with both Ground Penetrating Radar (GPR) and the Rolling Dynamic Deflectometer (RDD). One area of poor load transfer efficiency (LTE) was noted. The overlay was placed in the summer of 2008. Performance to date has been good. After 1 year some low severity reflection cracks were found in the location where the RDD found poor LTE, and some additional low severity longitudinal cracks were found in one location where the longitudinal joint was directly in the wheel path. The one area of concern with this mix was the relatively low skid values, which averaged around a skid number of 20.

A subsequent laboratory evaluation was made of the mix design developed under SS 3109. Using the balanced mix design approach it was found that the HWTT and OT performance criteria were met at binder contents ranging from 7.0 to 8.5 percent. Future applications of this mix should consider reducing the binder content from 8.3 percent to 7.5 percent.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/5-5598-01-2.pdf

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Research Digest Item 16 Development of Guidelines for Cable Median Barrier Systems in Texas TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 5609-2 • 2009 Since 2003, the Texas Department of Transportation (TxDOT) has embarked on an aggressive campaign to install median barriers to prevent cross-median crashes on freeway facilities statewide. In the few years prior to 2003, virtually all fatalities on interstate facilities (96 percent) were the result of cross-median crashes. TxDOT used special safety funding to accelerate projects and decided to primarily implement high-tension cable/wire rope median barrier systems in lieu of concrete so that more roadway miles could be protected.

This report documents the development of guidelines for use of cable barrier systems in Texas. The research team performed a comprehensive review of currently available guidance on cable barrier systems. The guidelines review included four broad categories: guidance on barrier selection, guidance on barrier design, guidance on barrier placements, and guidance on general system considerations.

The development of guidelines for cable median barrier systems in Texas concentrated on existing information in state departments of transportation (DOT) design manuals and memorandums, manufacturer product manuals, and completed studies -- including the results of the in-service performance evaluation in Texas.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/0-5609-2.pdf

Item 17 Video over IP Design Guidebook TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 5942-P1 • 2008 TxDOT engineers are responsible for the design, evaluation, and implementation of video solutions across the entire state. These installations occur with vast differences in requirements, expectations, and constraints.

Because the systems require extensive interoperability to other systems, agencies, and deployments, a systems engineering process (SEP) is employed to develop a consistent and structured approach to the development of concepts, needs, requirements, design, testing, and ongoing operations. The guidebook contains an accompanying CD which illustrates many aspects of video which are more easily understood from a visual perspective.

The goal of this guidebook is two-fold: (1) to establish a fundamental level of knowledge in video concepts, and (2) to frame the discussion within the concept of systems engineering to provide a logical, consistent, and structured approach to video system development and deployment.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/0-5942-P1.pdf

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Research Digest Item 18 Long-Term Performance of GFRP Reinforcement: Technical Report TEXAS A&M UNIVERSITY. TEXAS TRANSPORTATION INSTITUTE (TTI) TTI 6069-1 • 2009 Significant research has been performed on glass fiber-reinforced polymer (GFRP) concrete reinforcement. This research has shown that GFRP reinforcement exhibits high strengths, is lightweight, can decrease time of construction, and is corrosion resistant. Regarding the corrosion resistance, research has shown that the chemical reactions that occur in GFRP bars do not result in expansive products—products that can damage the concrete surrounding the reinforcement. Although not classical steel corrosion, much research that has been performed shows that GFRP reinforcing bars do corrode, reducing the tensile capacity of the GFRP reinforcing bars as a function of time. The American Concrete Institute (ACI) recognized this and places a reduction factor on the allowable design strength of GFRP reinforcing bars. A drawback of the majority of the research is that GFRP reinforcing bars have typically been directly exposed to aggressive solutions, exposure conditions possibly not similar to the exposure they would encounter while embedded in concrete. Limited research has been performed evaluating the tensile capacity reduction of bars embedded in concrete; however, these bars were only exposed for relatively short durations. This research investigated the characteristics of GFRP reinforcing bars embedded in concrete for 7 years and exposed to a mean annual temperature of 69 oF (23 oC) and an average precipitation of 39.7 inches (1008 mm), fairly evenly distributed throughout the year. Three manufacturers provided #5 and #6 bars for this research. Results indicate that GFRP reinforcing bars do exhibit reduced capacities when embedded in concrete. A model was developed to assess the tensile capacity of bars embedded in concrete. The model was based on a general diffusion model, where diffusion of water or ions penetrate the bar matrix and degrade the glass fibers. The model is dependent on time, diffusion characteristics of the matrix material, and the radius of the GFRP reinforcing bar. The model indicates that GFRP reinforcement bars with larger diameters exhibit lower rates of capacity loss. However, the times required for the tensile capacity of the GFRP bars to drop below the ACI design requirements for #3, #5, and #6 bars were less than 6 years. Further research is needed to determine how this will affect the design of GFRP-reinforced concrete structures; however, consideration of changing the ACI design requirement may be warranted.

Full-text PDF of this report is available for free download from http://tti.tamu.edu/documents/0-6069-1.pdf

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