Much of the almost two million miles of asphalt roadways in the United States are severely distressed and in need of repair or replacement. Over the last few decades increasing traffic demands combined with decreasing funding for repairs, environmental concerns and an emphasis on safe, efficient, transportation systems have stimulated research and field demonstration projects to explore methods to reuse and recycle pavement materials.

In response to this need, the Department of Civil and Environmental Engineering and Geodetic Science at Ohio State University (OSU) has partnered with the two fastest growing counties in Ohio (Delaware and Warren) to construct and monitor two pavement sections in which sections of failing asphalt pavements were recycled in 2006 using Ohio coal-generated fly ash as a cementing agent.

"The value of this technology and demonstration project to the contractor is at a minimum two-fold," says Chris Anspaugh, construction manager, Base Construction. "With the price of cementitious additives continuing to rise in price due to the substantial energy costs involved in producing them it would be of value to the contractor, from a competitive standpoint, to have alternative products available that will achieve the same end results.

"Secondly, the contractor needs testing data available that can be submitted to the owner to assure them that the product will perform as we are claiming," he continues. "This research will go a long way in providing that information." and lime-activated Class F fly ash

On this Full Depth Reclamation (FDR) research preservation project, the complete depth of the flexible pavement section consisting of the asphalt layer, base, subbase and a pre-determined amount of the underlying existing subgrade soil were uniformly pulverized, blended with chemical additives (Class F fly ash in combination with lime or lime kiln dust), and compacted to construct a new stabilized base course.

An asphalt overlay was then placed over the stabilized base. Class F fly ash in itself is not self-cementing. It needs additional lime to undergo a cementitious reaction. It's important to note that fly ash, when used in combination with lime or lime kiln dust, performs two important functions in FDR work:

1. Fly ash provides the silica and alumina needed for cementitious reaction with lime to increase the strength, stiffness, and durability of the stabilized base layer
2. Fly ash acts as a mineral filler to fill the voids in the granular pulverized pavement mix, reducing the permeability of the FDR stabilized base layer. Lime or lime kiln dust by itself will not provide adequate stabilization for pavement materials deficient in silica and alumina. The addition of fly ash is necessary for cementitious reactions to occur.

Objective and goal
The overall objective of this work is to demonstrate the effective use of Class F fly ash in combination with lime or lime kiln dust in the FDR of asphalt pavements.

The goal of the proposed program is to establish field-verified relationships for the service performance, structural and environmental behavior of FDR pavements constructed using lime-activated fly ash.

The project goal is being pursued with four interrelated activities. In the first, laboratory studies specifically designed to investigate the physical, chemical, and engineering properties of fly ash FDR mixes were conducted. This allowed the research team to determine the optimal material mixes that were implemented in the two pavement preservation projects.

In the second activity, two highway pavements were constructed and instrumented in 2006, and will be monitored for two years. The purpose of this activity is to obtain robust field results on the structural, service and environmental performance of field constructed FDR bases.

In the third activity, existing flexible pavements constructed in Ohio using FDR will be investigated. This will allow for evaluation of the performance of existing projects for which no performance data has been collected to date.