Search Content

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.

This report presents the results of a research project to investigate the design and performance of thin and ultra-thin whitetopping. To learn more about whitetopping, the Minnesota Department of Transportation (Mn/DOT) constructed a whitetopping project consisting of six test sections on I-94 at a research facility and three test sections at intersections on US-169 at Elk River. This report includes a brief description of Mn/DOT history with whitetopping and a detailed description of the construction of the heavily instrumented whitetopping test sections on I-94 and US-169. All concrete mixes contained either polypropylene or polyolefin fibers. The compressive strength, flexural strength, Poisson's ratio, and elastic modulus were measured for these mixes, and the results are provided.

The Minnesota Department of Transportation (Mn/DOT) constructed an ultra-thin whitetopping (UTW) project at three intersections on US-169 at Elk River to gain more experience in both the design and performance of ultra-thin whitetopping. A brief description of the Mn/DOT's history in the area of whitetopping is presented followed by a detailed description of the construction of the instrumented whitetopping test sections on US-169. All concrete mixes contained either polypropylene or polyolefin fibers. The compressive strength, flexural strength, Poisson's ratio and elastic modulus were measured for these mixes and the results are provided. Distinct cracking patterns developed within each test section. The UTW test sections with a 1.2-m x 1.2-m (4-ft x 4-ft) joint pattern included corner breaks and transverse cracks. Corner breaks were the primary distress in the test section with a 1.8-m x 1.8-m (6-ft x 6-ft) joint pattern, although very little cracking was exhibited. The strain measurements emphasize the importance of the support provided by the HMA layer. A reduction in this support occurs when the temperature of the HMA is increased or when the HMA begins to ravel. Cores should be pulled from the pavement when evaluating whether UTW is a viable rehabilitation alternative to determine if the asphalt is stripping and if the asphalt layer has adequate thickness. UTW can be successfully placed on as little as 76 mm (3 in.) of asphalt, if the quality of the asphalt is good. The cores should also reveal the asphalt layer is of uniform thickness and stripping/raveling has not occurred. If these conditions exist, UTW is a good option for rehabilitating asphalt pavements.

This report provides an integrated selection procedure for evaluating whether an existing hot-mix asphalt (HMA) pavement is an appropriate candidate for a bonded concrete overlay of asphalt (BCOA). The selection procedure includes (1) a desk review; (2) coring; (3) visual examination (site visit); (4) additional coring and/or laboratory testing (optional); (5) preparation of preliminary estimates (optional); and (6) a final report with design recommendations. This project also included an analysis of material testing performed by the Minnesota Department of Transportation (MnDOT) on numerous HMA cores to determine if the performance of existing BCOAs could be correlated to HMA material properties. The results of the laboratory testing were inconclusive. None of the existing HMA material properties tested could be correlated to long-term BCOA performance due to the high variability among the measured parameters within a section; the small number of cores per section; and the fact that the sections investigated exhibited little or no distress that could be attributed to the asphalt layer's properties. Although no conclusions could be made from the limited laboratory testing; it is fair to say that the BCOAs from these projects were performing as designed.

The existing ultra-thin whitetopping (UTW) and thin whitetopping (TWT) design methods are reviewed so that any gaps in the design process can be identified. Four design methods are included, namely the Colorado Department of Transportation (CDOT) method, the New Jersey Department of Transportation method, the Portland Cement Association (PCA) method, and the Illinois Centre for Transportation (ICT) method. The structural response and performance models used in these methods are evaluated using field data from the whitetopping sections at MnROAD. Based on these evaluation, the PCA structural model developed for the calculation of stress in the corner and at the top of the overlay seems more suitable for the prediction of the structural response of UTW and the CDOT structural model developed for the calculation of stress at the lane/shoulder edge and at the bottom of the overlay is more suitable for TWT. It is also found that the use of a temperature-dependent asphalt modulus of elasticity results in significantly higher fatigue damage in the overlay, which is ignored by all four methods. Finally, the asphalt fatigue analysis incorporated in some of these design procedures is does not result in fatigue failure of the hot mix asphalt and therefore need not be considered when designing these overlays.

Maintenance wastes include all levels of toxicity and require many different methods of disposal. This report highlights the requirements for treatment of maintenance wastes, including solvents, waste paint, waste oil, fuel and oil filters, batteries, antifreeze, shop rags, road maintenance wastes, and pesticides. It gives criteria for what makes a waste hazardous and outlines methods of reducing waste. The report also includes information on lead paint removal and disposal; current regulations for lead content in air, soil, and water; and human exposure requirements. Case studies in the report illustrate current removal and containment techniques. PLEASE NOTE: The regulations regarding the proper treatment and disposal of maintenance wastes and lead paint especially are complex and always changing. The user is encouraged to check current rules for changes.

Thin and ultra-thin whitetopping overlays are becoming a more common method of pavement rehabilitation. It is important to gain information on the types of distresses that occur in the overlays and effective repair techniques. In 1997, the Minnesota Department of Transportation constructed several thin and ultra-thin whitetopping test cells at the Minnesota Road Research (Mn/ROAD) facility. The test cells varied in overlay thickness from 76-mm (3-in) to 152-mm (6-in). The joint spacing of these cells ranged from 1.2-m by 1.2-m (4-ft x 4-ft) to 3.1-m by 3.7-m (10-ft x 12-ft). Over 3.5 years of existence and 4.7 million ESALS, both temperature- and load-related distresses were observed on the 76-mm (3-in) and 102-mm (4-in) thick sections. There were no noticeable distresses in the 152-mm (6-in) sections. Typical distresses included corner breaks, transverse cracks, and reflective cracks. The finite element program ISLAB2000 was used to investigate stress patterns and their relation to the distresses. This paper was submitted to the Transportation Research Board for Publication and Presentation at the 2002 Transportation Research Board Annual Meeting

An unbonded portland cement concrete overlay of concrete pavements (UBOL) is a rehabilitation technique in which the new overlay is isolated from the existing distressed pavement using a separator layer. Typically; a 1-to 2-in asphalt separator layer (or interlayer) is used. Recent innovations in the unbonded overlay technology have led to the adoption of new types of interlayers; such as non-woven geotextile fabric; as well as the use of overlays with joint spacings and layouts that are much shorter than conventional joint spacings. The effect of these design alternatives on the performance of the UBOL cannot be accounted for using currently available design procedures. This report documents the development of a new mechanistic-empirical design procedure for UBOL. It presents the results of laboratory and field studies; the calibration of an advanced structural (Totski) model that better captures the effects of the interlayer and separation between the overlay and the existing pavement; and the development of cracking and faulting performance prediction models for UBOL. The performance prediction models were incorporated into a rudimentary software tool; Pitt UBOL-ME; that can be used for the design and analysis of UBOL. Unlike prior UBOL design procedures; Pitt UBOL-ME can be used to quantify the effect of the performance of the interlayer on the performance of the UBOL and can be used for both conventional and short joint spacings.

The use of admixtures for stabilizing soils involves adding granular materials or chemical compounds to improve the engineering properties of a soil. This report will be limited to the discussion of surface soil stabilization, which consists of excavating and breaking up the soil, adding the admixture, mixing the soil and the additive(s), compacting the soil and then allowing the mixture to cure.