Ultra-Thin Portland Cement Concrete Overlay Extended Evaluation, January 2005

In this day of the mature highway systems, a new set of problems is facing the highway engineer. The existing infrastructure has aged to or past the design life of the original pavement design. In many cases, increased commercial traffic is creating the need for additional load carrying capacity, causing state highway engineers to consider new alternatives for rehabilitation of existing surfaces. Alternative surface materials, thicknesses, and methods of installation must be identified to meet the needs of individual pavements and budgets. With overlays being one of the most frequently used rehabilitation alternatives, it is important to learn more about the limitations and potential performance of thin bonded portland cement overlays and subsequent rehabilitation. The Iowa ultra-thin project demonstrated the application of thin portland cement concrete overlays as a rehabilitation technique. It combined the variables of base preparation, overlay thickness, slab size, and fiber enhancement into a series of test sections over a 7.2-mile length. This report identifies the performance of the overlays in terms of deflection reduction, reduced cracking, and improved bonding between the portland cement concrete (PCC) and asphalt cement concrete (ACC) base layers. The original research project was designed to evaluate the variables over a 5-year period of time. A second project provided the opportunity to test overlay rehabilitation techniques and continue measurement of the original overlay performance for 5 additional years. All performance indicators identified exceptional performance over the 10-year evaluation period for each of the variable combinations considered. The report summarizes the research methods, results, and identifies future research ideas to aid the pavement overlay designer in the successful implementation of ultra-thin portland cement concrete overlays as an lternative pavement rehabilitation technique.

Ultrathin Portland Cement Concrete Overlay Extended Evaluation, Construction Report, TR-432, 2000

In recent years, ultra-thin whitetopping (UTW) has evolved as a viable rehabilitation technique for deteriorated asphalt cement concrete (ACC) pavement. Numerous UTW projects have been constructed and tested, enabling researchers to identify key elements contributing to their successful performance. These elements include foundation support, interface bonding condition, portland cement concrete (PCC) overlay thickness, synthetic fiber reinforcement usage, joint spacing, and joint sealing. The interface bonding condition is the most important of these elements. It enables the pavement to act as a composite structure, thus reducing tensile stresses and allowing an ultra-thin PCC overlay to perform as intended. The Iowa Department of Transportation (Iowa DOT) UTW project (HR-559) initiated UTW in Iowa. The project is located on Iowa Highway 21 between Iowa Highway 212 and U.S. Highway 6 in Iowa County, near Belle Plaine, Iowa. The objective of this research was to investigate the interface bonding condition between an ultra-thin PCC overlay and an ACC base over time, considering the previously mentioned variables. This research lasted for five years, at which time it was extended an additional five years. The new phase of the project was initiated by removing cracked panels existing in the 2-inch thick PCC sections and replacing them with three inches of PCC. The project extension (TR 432) will provide an increased understanding of slab bonding conditions over a longer period, as well as knowledge regarding the behavior of the newly rehabilitated areas. In order to accomplish the goals of the project extension, Falling Weight Deflectometer (FWD) testing will continue to be conducted. Laboratory testing, field strain gage implementation, and coring will no longer be conducted. This report documents the planning and construction of the rehabilitation of HR 559 and the beginning of TR 432 during August of 1999.

Ultrathin Portland Cement Concrete Overlay Extended Evaluation, Interim Report, TR-432, 2002

The Iowa Department of Transportation (Iowa DOT) UTW Project (HR-559) initiated Ultra-Thin Whitetopping in Iowa. The project is located on Iowa Highway 21 between Iowa Highway 212 and U.S. Highway 6 in Iowa County, near Belle Plaine, Iowa. The above listed research project lasted for five years, and then was extended for another five year period. The new phase of the project (TR 432) was initiated by removing cracked panels existing in the 2-inch thick PCC sections and replacing them with three inches of PCC. The project extension provides an increased understanding of slab bonding conditions over a longer period, as well as knowledge regarding the behavior of the newly rehabilitated areas. This report documents the rehabilitation of the PCC patching of all fractured panels and several cracked panels, taking place in September of 2001.

A Progress Report on Treating Loess, Fine Sands and Soft Limestones with Liquid Binders, HR-20, 1954

Certain areas of Iowa abound in loess, others contain soft limestones that are readily and cheaply available, and a large portion of the state is underlaid with sand. None of these materials is considered suitable in present practices for use in all-weather road construction. The loess is too fine and too difficult to handle; the limestones are considered too soft, and some of the harder ones unsound for this use; the sands are not naturally of the desired gradation and do not lend themselves to blending into satisfactory gradations. The purpose of this project is, therefore, to study and develop means and to determine the feasibility of using these materials, loess, fine sand, and soft limestones, either separately or in combinations in conjunction with liquid binders to produce paving mixtures applicable for all-weather road construction. Also included in the project was the development of methods of processing any of these materials, if necessary, to make them suitable for the desired purpose