Search Content

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.