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Prestressed concrete has been used as a bridge construction method in the United States since 1949. Presently, there are thousands of pretensioned prestressed concrete bridges in service in North America. Each year, approximately 200 girders are damaged as a result of impact damage (primarily overheight vehicles striking a bridge from below). This report describes the results of a four girder test series used to evaluate impact damage and effectiveness of repairs. The girders used for the study were fabricated in 1967 and placed into service. The girders were removed from service in 1984 as a result of a road realignment project. The objectives of the research project were to: 1) determine the effective prestress in the strands after 20 years; 2) determine the influence of impact damage on girder performance; 3) evaluate the performance of two impact damage repair schemes under static, fatigue and ultimate loadings; and 4) develop a model to estimate the strand stress ranges in damaged girders.

This study was conducted with the aim of improving the state of knowledge on the behavior of joints in concrete pavements, and to explore the feasibility of developing a non-destructive testing technique based on frequency response of dynamically loaded joints. One of the objectives of this study was to numerically investigate the existence of a relationship between load transfer capacity of a joint in rigid pavements and its dynamic response. The approach adapted for the present study is based on a numerical model which accurately represents the mechanism of shear transfer in reinforced concrete members implemented it in a commercially available finite element code. That tool is then used for the analysis of two models which consisted of various joint conditions. One model represented an ideal condition of full load transfer across a joint, while the other model was used to simulate variable load transfer conditions. The results obtained are analyzed in the time and frequency domains. These results provided a comprehensive description of the joint response characteristics, and enabled the derivation of a clear relationship between the response frequencies and the joint's shear transfer capabilities. The results may be used as the starting point for the development of a precise/non-destructive testing method for a wide range of cases in which shear transfer across discontinuities in concrete systems is a principal load resisting mechanism. Specific conclusions and recommendations on future developments have been provided.

The Minnesota Department of Transportation is continually investigating ways to improve the cold temperature performance of its asphalt concrete pavements. One reported method is to modify the asphalt binder with ground reclaimed automobile and truck tire rubber. In 1984, a project on TH 7 (State Project 4703-17) was selected for the field trial of an asphalt-rubber cement dense graded concrete utilizing a product produced by Arizona Refining of Phoenix Arizona. Construction of the asphalt-rubber cement dense graded asphalt concrete required some special effort and specialized equipment to maintain adequate mixing and placing temperatures. Evaluations included crack counting, resilient modulus, inplace air voids rutting, roughness, recovered penetration and cost considerations. Interesting results regarding the resilient modulus of the asphalt rubber samples were found. However, the formulation used provided little or no perceived benefits to the roadway at much higher costs. The high costs were due in part to the nature of the project. However, this appears to be a cumbersome and expensive procedure with the primary benefit being waste tire utilization.

Many chemical additives designed to inhibit the corrosive effect of salt on rebars are being marketed. Their effort on Portland Cement Concrete is neither known or understood. This study is an attempt to determine if there is an effect and to understand the nature and results of the effects

To address climate change mitigation goals, alternative concrete paving mixtures are being investigated that are claimed to have a lower global warming potential (GWP) at time of construction with equal or better long-term performance compared to conventional concrete paving mixtures currently in use by the Minnesota Department of Transportation (MnDOT). The objectives of this study are to develop a final matrix of test sections and a construction quality assurance (QA) plan for the construction of a Minnesota Road Research Facility (MnROAD) experimental section, consisting of 16 test cells, to assess the environmental impact and constructability of various concrete paving mixtures designed to reduce environmental impact, with the opportunity to assess in-service performance over a three-year period following test cell construction. This report documents the concrete mixtures being evaluated, the list of tests to be performed on the plant-produced concrete, construction observations, and a preliminary assessment of environmental impact. Follow-up studies are ongoing, which will document the lab testing results and provide yearly performance updates on the test cells. These reports will be made available by MnDOT.

This Phase 1 study was undertaken to evaluate cracking related to dowel bars and tie bars in concrete pavement. The results of the literature review and field studies suggest that under some conditions, restraint caused by dowel bars and tie bars in the concrete result in high early age stresses that contribute to cracking. Field evaluation of six sites conducted as part of this research suggests that this type of cracking is not an isolated phenomenon. While a notional description of the potential mechanism is described in this report, details regarding the extent to which various factors impact this type of cracking and appropriate reasonable steps to take to mitigate this type of cracking is not fully understood. To gain a more detailed understanding, a combination of finite element (FE) analysis with laboratory experiment is proposed for Phase 2. The analysis proposed includes an evaluation of key parameters and their influence on dowel bar cracking followed by validation through laboratory experimentation and model refinement.

This report presents the results of a research project to evaluate the performance of six full-depth silica fume bridge decks, constructed between 1997 and 1999. The Minnesota Department of Transportation (Mn/DOT) constructed these decks to compare their performance and constructability in Minnesota, which involves the use of a seven-inch structural slab followed by a two-inch low slump overlay. Researchers conducted air content and slump field testing, visual inspections, and laboratory testing on chloride permeability, compressive strength, and hardened air system properties. In addition, they compared initial costs between the current deck system and the full-depth silica fume decks. The overall performance of the silica fume bridge decks has been good; however, two of the bridge decks did have problems related to the development of silica fume balls. Laboratory testing has shown that silica fume concrete performs better in terms of chloride permeability and compressive strength. Field tests have shown that placement of the silica fume concrete is comparable to a conventional concrete mix. Finally, cost comparisons have shown the placement of a full-depth silica fume deck to be slightly lower than the current deck system.

Sealing the edge joints on concrete pavements with bituminous shoulders reduces the volume of water entering the pavement system by as much as 85 percent. Longitudinal edge joint sealing should be considered as a pavement preventive maintenance treatment.

This report summarizes an experimental program that investigated the development length and variability in bond of glass-fiber-reinforced-polymer (GFRP) reinforcement in concrete.

An area of concern common to portland cement concrete (PCC) pavements is load transfer across joints and cracks. The current design standard for load transfer in new jointed PCC pavements and the rehabilitation of old PCC pavement is to place steel dowel bars at mid-depth of the pavement across the joint or crack (1). The main issues with the use of retrofit and/or new dowels are the high expense associated with the retrofitting operation and the corrosion that has been associated with the use of steel dowels. Three new and experimental dowel bar retrofit designs, that address the issues of high retrofit cost and corrosion susceptibility, were tested in an accelerated manner in order to determine the potential viability of their use for the restoration of load transfer in PCC pavements. Innovations in the three designs included the use of fiber reinforced polymer dowels, grouted stainless steel pipe dowels, and a change in the geometric configuration of the design. An evaluation of test results and recommendations, regarding the use of the designs for the restoration of load transfer in PCC pavements, are presented.

The Minnesota Department of Transportation's (Mn/DOT's) recent implementation of a 0.40 maximum water-to-cementitious ratio specification for concrete pavements has raised some concerns regarding the availability of bleed water at the pavement surface and the moisture retained in the concrete for strength development with current curing practices. A study was initiated in the spring of 1998 to evaluate Mn/DOT's concrete pavement curing requirements. First, an assessment of the effectiveness of various compounds frequently used on state funded projects was performed and the test methods used to evaluate these compounds were examined. Changes were made to Mn/DOT's curing specifications based on the finding of the first portion of this study and implemented during the 1999 construction season. Methods used by contractors to apply curing compounds were also reviewed to insure that a uniform coat of acceptable thickness is applied and recommendations were made for improving these methods. This paper summarizes the findings of this study and the resulting changes that were made to Mn/DOT concrete pavement curing specifications. Recommendations for further improvements are also provided.

A section of Trunk Highway 23 near Mora, Minnesota, underwent concrete rehabilitation in 1998, which included the installation of retrofit dowel bars over a portion of the project. The Minnesota Department of Transportation (Mn/DOT) established several different test sections to evaluate the performance of different dowel bar configurations, group materials, and dowel bar lengths. During dowel bar installation, researchers monitored and evaluated construction procedures. They also conducted pavement testing before and after installation of the retrofit dowel bars to determine any immediate improvements to the joint performance. As expected, early age testing has shown improvements in joint load transfer efficiency after installation of the retrofit dowels. Testing also revealed that the rapid-setting mortar performed better than Mn/DOT's standard 3U18 patching mix. After only two years, there has been no noticeable differences in ride quality or faulting at the joints between retrofit and nonretrofit joints. Testing of pavements and joint performance will continue on a yearly basis to determine the long-term performance of the retrofit dowels.

This is the fourth and final report of a study to determine the effect of concrete shoulders, lane widening and frozen subgrade on concrete pavement performance. In this portion of the study, Falling Weight Deflectometer tests were conducted seasonally over a two-year period to determine the seasonal variation in pavement deflection. Tests were also conducted to determine the change in pavement deflection throughout the day. An analysis was run to verify earlier results determined by the Construction Technologies Laboratory of the Portland Cement Association.

This report documents the current practices of Minnesota in rehabilitating Hot Mix Asphalt pavement with thin and ultra-thin Portland cement concrete overlays, i.e. thin and ultra-thin whitetopping. The current practices of thin whitetopping (TWT) in Minnesota and its adjacent states have shown that TWT has been used successfully and is an important alternative for rehabilitating HMA pavements of medium-volume roads. If designed and constructed properly, TWT is also an important alternative for rehabilitating HMA pavements of highway volume roads with more requirements in HMA quality, bonding and fiber reinforcement. The performance of ultra-thin whitetopping (UTW) projects in Minnesota ranges from very good to failing. The sections that perform poorly are short sections under stopping trucks or buses and over thin or poor condition HMA pavement. UTW has been used successfully in Minnesota when inlaid into thick and sound HMA pavements even in high-volume traffic. The quality of the HMA substrate, bonding, fiber reinforcement, and joint spacing all significantly affect the success of UTW. Great caution should be used when rehabilitating HMA pavements at bus stops, weigh stations, and intersections. The Minnesota Department of Transportation (Mn/DOT) does not recommend UTW for major highways and heavy traffic areas.

This manual has been designed to be used as specifications for concrete repair of local city streets and county concrete pavements. It is intended to be used as supplemental specifications for constructing this work throughout the state of Minnesota. All standard plates have been designated as SA, which is an abbreviation for State Aid. This is intended to allow the State Aid office to track bid prices with a consistent title throughout the state. This manual was developed from existing concrete repair standards that have been developed and used by the Minnesota Department of Transportation since 1981. This manual also incorporates successful modifications to the Mn/DOT standards by the City of Owatonna and the City of Austin, Mn. This manual keeps the Mn/DOT system of labeling repairs in the A,B,C nomenclature developed in 1981 as follows; SA-A repairs are joint or crack repairs. SA-B repairs are partial depth repairs. SA-C repairs are full depth concrete repairs. For the first time this manual incorporates standards for sidewalk and curb and gutter repairs into a specification format. These sidewalk and curb and gutter standards have been successfully performed by the cities of Austin and Owatonna, Minnesota.

Effective load transfer across Portland cement concrete pavement joints significantly decreases pavement deterioration. Dowel bars placed transversely across a joint or crack provide a mechanism for effective load transfer to take place. Dowel bars are used in new construction as well as retrofitted into existing pavements for restoration of load transfer. Areas of concern with using dowel bars include high costs, due to the labor-intensive procedure of retrofitting, and corrosion associated with standard mild steel epoxy-coated dowels. This research addresses these problems by evaluating four dowel bar details tested in an accelerated manner. Retrofit testing was performed using mild-steel epoxy coated dowels and fiber reinforced polymer (FRP) dowels. The details tested provide comparisons among dowel bar materials, depth of placement, number of dowels used, and dowel diameter. Verification testing of previously tested details is also presented.

Three instrumented ultra-thin whitetopping (UTW) pavement test sections were constructed in 1997 at the Minnesota Road Research facility (MnROAD). The sections were installed on the interstate highway portion of MnROAD to accelerate the traffic loadings compared to typical applications of UTW. By spring 2004, significant deterioration of the sections had occurred. Prior to replacement of the three test sections in fall 2004, a forensic investigation of the distresses was carried out. The focus of this report was to describe the forensic investigation procedures carried out, and to summarize findings from the investigation. The investigation revealed that the performance of ultra-thin whitetopping test cells at the MnROAD project was related to traffic volume, wheel placement, and layer bonding. Distresses were more frequent and severe in the higher-volume driving lane. Panel sizes that place wheelpaths near the edges of UTW slabs resulted in accelerated distress and poor performance. Bonding of UTW to the underlying asphalt layer was essential for long-term performance. Reflective cracking occurs in bonded concrete overlays for thicknesses less than 5 inches (over 6 inch minimum asphalt layer). Large polyolefin fibers did provide some benefit to crack containment in UTW, but added significant cost to the concrete mix.

The Minnesota Department of Transportation (Mn/DOT) has selected a 316L stainless steel schedule 40 pipe as a new dowel bar to be used as a bid alternative for its high performance Portland Cement Concrete (PCC) pavements. Although this dowel bar should provide sufficient shear transfer capacity and low concrete bearing stresses, there was a concern that lack of a solid core may not provide sufficient resistance of the cross-section to distortion under a heavy axle loading. In this study, long-term performance of the 316L stainless steel schedule 40 pipe was investigated by subjecting a doweled joint to accelerated repeated loads through the use of the Minnesota Accelerated Loading Facility (Minne-ALF-2). Assessment of the new dowel bar performance was performed based on comparison with the standard 1.5 inch diameter epoxy -coated round steel dowel. The following tasks were accomplished: redesign, assembly and calibration of new version of Minne-ALF, development of experimental design matrix, conduct of accelerated full-scale testing, and post-testing evaluation. The results from the MinneALF-2 tests illustrated that while the LTE for the stainless steel dowel tubes was lower than the LTE for the epoxy-coated dowels, the stainless steel tubes are capable of providing over 70% LTE in the long-term when installed in concrete pavement joints. The ability to withstand deformation and corrosion while providing sufficient long-term performance suggests that the stainless steel tube dowel is an attractive alternative to the solid epoxy-coated dowel for use in long-life pavements.

The behavior of concrete integral abutment bridges was investigated through a field experiment and a numerical parametric study. The field investigation focused on Bridge #55555 in Rochester, Minnesota, which was monitored from November 1996 to February 2004. Over 150 instruments were installed during construction of the bridge to measure abutment horizontal movement, abutment rotation, abutment pile strains, earth pressure, pier pile strains, prestressed girder strains, concrete deck strains, thermal gradients, and weather. The collected data were used to understand the behavior of Bridge #55555 due to the effects of temperature, creep and shrinkage. Two live load tests were conducted in 1997 and 1999, to examine the behavior of the bridge under live load. The overall performance of the integral abutment bridge was good. Bridge shortening was observed from the readings of different sensors. A steadily increasing tendency of average pile curvatures was observed from the measured data. Possible reasons were investigated through a time-dependent numerical analysis. A 3D finite element model of the test bridge was developed which took into account soil-structure interaction. The model was calibrated using data collected from the truck tests and the data from the seasonal and daily temperature variations. A parametric study was conducted to extend the results of the test bridge to other integral abutment bridges with different design variables including pile foundation type, bridge span and length, and orientation and length of wingwalls. Several design recommendations are made regarding the temperature range, use of predrilled holes around the piles, pile analysis method, and the applications of simplified design approaches for concrete integral abutment bridges.

Study goals included: 1) identify mechanisms causing premature failure in Minnesota concrete pavements; 2) evaluate the accuracy of existing tests of aggregate freeze-thaw durability using Minnesota aggregate sources and pavement performance records; 3) develop a new methodology for quickly and reliably assessing aggregate freeze-thaw durability; and 4) evaluate techniques for mitigating D-cracking. Research results indicate that the poor durability performance of some Minnesota PCC pavement sections can often be attributed to aggregate freeze-thaw damage. However, secondary mineralization, embedded shale deposits, poor mix design and alkali-aggregate reactions were also identified as problems. Petrographic examination can help to differentiate between these failure mechanisms. A reliable and universal method for quickly identifying D-cracking aggregate particles was not identified. A test protocol was developed for improved aggregate durability evaluation. It includes several tests which are selected for use based on aggregate geological origin and composition and the results of previous tests. Further validation of the proposed test protocol is recommended. Several techniques appear to be effective in improving the freeze-thaw durability of concrete prepared using marginally durable aggregate: mix design modifications, reductions in aggregate top size, and the blending of durable and nondurable aggregates. Some chemical treatments showed promise, but may not be economical.

This manual, a reformatted version of LRRB manual 2005-33, has been designed to be used as specifications for concrete repair of local city streets and county concrete pavements. It is intended to be used as supplemental specifications for constructing this work throughout the state of Minnesota. This manual was developed from existing concrete repair standards that have been developed and used by the Minnesota Department of Transportation (Mn/DOT) since 1981.

This report investigates the effect of the type of coarse aggregate used in concrete on chloride ions penetrability as indicated by the rapid chloride penetration test (RCPT). Twelve coarse aggregate types, commonly used in Minnesota Department of Transportation highway construction projects, were identified and used for this study. The coarse aggregate types were subjected to laboratory testing to determine their physical properties and ambient chloride content. The aggregate types were used to prepare fresh concrete according to Mn/DOT specifications in which silica fume and fly ash were used. In order to characterize the concrete in terms of resistance to chloride ions penetration, concrete specimens made of these aggregate types were subjected to the rapid chloride permeability test at different ages. All mix parameters including gradation and quantities of different aggregates were held constant in different mixes. The only variable was the aggregate type. For concrete specimens tested at 28 days of age, the average total charge passed varied between 1,452 and 2,606 Coulombs, which can be described as "low" to "moderate" chloride ions penetrability, according to AASHTO designation. The average total charge passed decreased with time (age) for all of the concrete specimens tested. Considering specimens at 91 days of age, the average total charge passed ranged from 601 to 1,236 Coulombs, which can be characterized as "very low" to "low" chloride ions penetrability. The aggregate type has a noticeable influence on the RCPT results for the concrete mix design that was utilized.

The Minnesota Department of Transportation (Mn/DOT) documented the appearance of excessive cracks in the reinforced concrete pier cap overhangs of State Highway Bridges 19855 and 19856. As a part of this study, the ultimate capacity of the pier cap overhangs was estimated by comparing predicted capacities calculated using standard design specifications to experimental results published in the worldwide literature. It was determined that the ultimate capacity of the pier cap overhangs was more than sufficient to assure that a cracked, but undeteriorated, pier cap is not prone to structural failure. An estimate of the initial cracking load of the pier cap overhangs was also created to determine what changes to pier cap design would be required to prevent future overhangs from cracking. It was determined that the depth of the overhangs would have to be increased by approximately 20% to prevent them from cracking. The changes to pier cap overhang design required to prevent cracking or meet recommendations to reduce crack widths may not be economically feasible. Therefore, other methods for controlling crack widths must were examined. An experimental study was conducted to investigate the use of externally bonded (EB) FRP sheets and near surface mounted (NSM) FRP tape for shear strengthening of reinforced concrete beams. This report describes the experimental program, presents the results of the study, and discusses the outcome of that investigation.

A total of 12 sealant products were applied on the Smith Avenue High Bridge in St. Paul and evaluated over a three-year period. Details, such as surface preparation and application methods, were documented for each product and are conditions specific to each product. Sealant performance was evaluated through field permeability testing, visual observations, and petrographic examination. Visual observations provided evidence that approximately 67 percent of test sections were performing effectively after one winter but only 4 percent after two winters. After three winters, 58 percent of the test locations were visually characterized as ineffective and 42 percent as partially effective. Product performance significantly reduced over the third winter, primarily due to major loss of sealant and surface sand materials. Coring was performed after the second winter, and the cores were photographed and subjected to a petrographic evaluation. The observed depth of sealant penetration was highly variable and likely is dependent on the presence of debris within the crack, original crack width, and the deck temperatures during application. The predominant failure mode observed under magnification was detachment from the crack face and not within the sealant materials. Based on numerous factors, four epoxy and three methacrylate products were recommended for consideration on MnDOT's Approved Products List. Each product recommendation contains the surface preparation and application method conditions under which they were applied. It is also recommended that MnDOT look into increasing the frequency of its routine crack sealing maintenance program from the current five-year cycle.

The Minnesota Department of Transportation has typically used epoxy-coated, straight-legged stirrups anchored in the tension zone as transverse reinforcement in prestressed concrete bridge girders. This configuration is readily placed after stressing the prestressing strands. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) specifications require stirrups with bent legs that encompass the longitudinal reinforcement to properly anchor the stirrups. Such a configuration is specified to provide mechanical anchorage to the stirrup, ensuring that it will be able to develop its yield strength with a short anchorage length to resist shear within the web of the girder. AASHTO specifications for anchoring transverse reinforcement are the same for reinforced and prestressed concrete; however, in the case of prestressed concrete bridge girders, there are a number of differences that serve to enhance the anchorage of the transverse reinforcement, thereby enabling the straight bar detail. These include the precompression in the bottom flange of the girder in regions of web-shear cracking. In addition, the stirrup legs are usually embedded within a bottom flange that contains longitudinal strands outside the stirrups. The increased concrete cover over the stirrups provided by the bottom flange and the resistance to vertical splitting cracks along the legs of the stirrups provided by the longitudinal prestressing reinforcement outside the stirrups help to enhance the straight-legged anchorage in both regions of web-shear cracking and flexure-shear cracking. A two-phase experimental program was conducted to investigate the anchorage of straight-legged, epoxy-coated stirrups, which included bar pullout tests performed on 13 subassemblage specimens that represented the bottom flanges of prestressed concrete girders, to determine the effectiveness of straight-legged stirrup anchorage in developing yield strains. Additionally, four girder ends were cast with straight-legged stirrup anchorage details and tested in flexure-shear and web-shear. The straight leg stirrup anchorage detail was determined to be acceptable for Minnesota Department of Transportation (MnDOT) M and MN shaped girders as nominal shear capacities were exceeded and yield strains were measured in the stirrups prior to failure during each of the tests.