Voller, Vaughan R.

Poor compaction can lead to early deterioration of an asphalt pavement. It often happens when paving occurs during adverse weather conditions. Yet, in Minnesota, paving must often occur under adverse conditions. A new tool now simulates the cooling of an asphalt mat behind the paver under a variety of environmental conditions. The software, PaveCool Version 2.0, offers users insights into how adverse climate conditions will affect their ability to produce a durable, quality road surface. Users input the type of existing surface, type of asphalt mix, and weather conditions. The output shows a cooling curve with recommended compaction starting and stopping times. Field tests confirm the value of this program as an aid to cold weather paving. A Windows program, PaveCool 2.0 runs on laptop computers (Windows 95, 98, or NT required). This report documents the study of thermal properties and compactibility of hot-mix asphalt, related laboratory tests on the thermal diffusivity and thermal conductivity of hot-mix asphalt at typical compaction temperatures, a literature review, and testing results. It also includes a copy of the PaveCool Version 2.0 software.

Across the state of Minnesota, asphalt roads under the jurisdiction of counties, cities and townships have been controlled by restrictions that limit the total weight of each truck that uses those roads during the spring thaw period. During this time, the pavement weakens and the bearing capacity of the roadway is reduced. These policies vary from county to county and from road to road, depending on the capacity of the roads - typically, 5, 7 and 9 tons. While spring load restrictions serve to extend the useful life of the road, they also add significant burdens to truckers who are forced to re-route their vehicles and/or increase the number of trips in order to adhere to the policies. This study assesses the economic impact of lifting all vehicle restrictions during the spring thaw period. Economic benefits of lifting the bans include reduced cost to carriers; potential cost includes reduced pavement life. Their research concludes that if the policy is changed, the costs of additional damage could be recovered from those who use the roads. Recovering those costs could take the form of annual fees, appropriate fuel taxes and/or user charges paid by vehicle operators.

This report investigates the low temperature behavior of asphalt pavements based on experimental results obtained for three mixtures used in the construction of cells 33, 34, and 35 at Mn/ROAD facility as well as field information acquired over the years at Mn/ROAD. As a result of this research a new test method was developed to determine the low temperature fracture properties of asphalt mixtures based on tests performed on semi circular specimens tested in bending. This method can be used to select materials with better fracture resistance and therefore better performance in the field. Two models were developed to predict the low temperature cracking performance of asphalt pavements. The first model predicts the crack spacing in asphalt pavements exposed to low temperatures based on continuum mechanics and the frictional restraint provided by the aggregate base. The second model predicts the accumulation of damage and the propagation of the crack through the asphalt layer as temperature drops based on cohesive zone model.

The objective of this report is to complete work undertaken at the University of Minnesota in the mid 1990's. This work was directed at developing an understanding of frost heaves in relationship to the lifting of buried objects such as shallow sewers. The critical findings in the field investigation were detailed in a 1995 final report by Ray Sterling, "Progressive Lifting of Shallow Sewers: Field Investigation." Preliminary details of the modeling work were provided in an interim project report and complete details were provided in the MS thesis of Lingjun Hou, "An Investigation of a Lumped Parameter Frost Heave Model," published by the University of Minnesota in January 1994. The objective of the current report is to outline the critical findings in the modeling work detailed in the previous interim report and Hou's thesis. This document should be seen as a complement to the original final report submitted by Sterling in 1995. The central objective of the modeling study is the investigation of the lumped parameter frost heave model developed by Blanchard and Fremond. The work in this report shows that a lumped porosity model can generate an accurate comparison with experiments and is a feasible tool for the investigation of the effect of freeze thaw on buried infrastructure.

This report outlines the development of a suite of computer codes collectively referred to as MnDrain. These codes, embedded in a standard spreadsheet program, provide a user-friendly environment in which the consequences of an edge drain design decision can be investigated. The purpose of an edge drain is to remove moisture from the granular base of the road system. The rate at which moisture is removed will depend on the geometry and materials used in the base and the soil type in the subgrade. MnDrain allows for evaluation of a given drain design against Federal Highway Administration requirements. In MnDrain, the user can chose from three basic scenarios, select material types and adjust geometries for each scenario, and calculate the moisture removal versus time curve over a two-hour drainage time. The work in this report shows that MnDrain is easy to use, flexible, and produces accurate approximate solutions of the Richard's model of variable saturated flow in a layered media. MnDrain also offers the advantage of offering free access to all source codes, which means that MnDrain can be reconfigured to deal with a large array of pavement drainage issues.

Asphalt mixture variations that result from moisture fluctuations in aggregate stockpiles pose a serious problem at dryer-drum plants. The moisture content of a stockpile is infrequently measured, if at all. If the proportion of aggregate is not adjusted to account for its moisture content, an improper mix will result. This project looked at identifying a practical and accurate field method or probe for measuring the moisture content of aggregates, testing the probe in a hot-mix plant, and developing a control strategy for asphalt oil addition to the mix. Researchers identified a suitable commercial probe by reviewing past research and conducting laboratory studies. Testing in the plant showed that this probe could rapidly measure aggregate moisture in plant conditions at the same level of accuracy as gravimetric measurements. Researchers also developed a control strategy for the asphalt oil addition. Testing showed the effectiveness of this control, in conjunction with commercial probe moisture measurements in the feed bin. A problem with probe operations robustness was identified.

This report presents the results of a cooperative study on the field use of a permeameter, built by researchers at the Minnesota Department of Transportation (Mn/DOT) and the University of Minnesota, to estimate the saturated hydraulic conductivity of pavement base materials. Field measurements using the permeameter were taken on various highway construction projects, and researchers measured the saturated hydraulic conductivity of samples in the laboratory. Researchers also reviewed theories for converting a field-measured flow rate into a saturated hydraulic conductivity estimate. By numerical simulation and analysis of the field data, researchers determined an appropriate method for converting the Mn/DOT permeameter flow measurements into estimates of hydraulic conductivity. Variations between the field estimated and laboratory measured hydraulic conductivity are within one order of magnitude. Variations between the field estimate and numerical simulation, however, are much closer. The study found the Mn/DOT permeameter can be used to obtain a reliable estimate of the base hydraulic conductivity provided that the base layer is at least 15 cm (6 in.) deep. When the base is too thin, permeameter readings are restricted to early infiltration times.