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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.