With the escalating costs of materials and construction for highways and streets, many agencies chargedwith the repsonsibility of designing and constructing highwyas are utilizing by-product materials. One application of by-product materials has involved the use of stabilized aggregate bases where pozzolanic materials are used as a stabilizing agent.

The use of pozzolanic materials is not new. However, the use of pozzolanic materials is relatively new to Kentucky. This may be primarily attributed to the availability o an abundant supply of economical aggregate materials. However, as costs of production and processing of aggregate materials have increased, so has the feasibility of stabilized bases, and particularly pozzolanic base materials. Also, use of stabilized base materials tends to reduce requirements for higher quality materials in the pavement structure.

Pozzolanic base materials have been utilized on an experimental basis for a number of Lexington street projects. One project for the Kentucky Department of Highways also is currently being studed. Thus, performance experience currently is limited, but at the same time evolutionary. Therefore, modifications in designs presented in this report may be requried in the future to reflect additional experience and performance of field projects.

Specific procedures utilized in the development of thickness designs using pozzolanic bases will be presented later in this report. However, the designs were developed on the basis of layer elastic theory, using a range of moduli (strengths) for the pozzolanic base materials.

The most common measure of strength for pozzolanic base materials is unconfined compressive test. Modulus of elasticity is a required strength parameter for layer elastic analyses. Thus, it was necessary to develop a relationship between unconfined compressive strength and modulus of elasticity so that design input parameters could be estimated from more conventional measurements of material strength. Laboratory test data were used to develop the required correlation. The specifics of the correlation will be presented later in this report.

Other agencies have developed layer coefficients for pozzolanic base materials for use with the AASHTO Interim Guide for flexible pavements. There has been considerable discussion regarding the use and reliability of layer coefficients for flexible pavement design. The use of more rationally based design systems have been advocated by others, including the Kentucky Department of Highways. The current flexible pavement design procedures used by the Kentucky Department of Highways were developed using layer elastic theory, the Chevron N-layer computer program, and matched with Kentucky experience. The designs presented herein are based on the same concepts and experience used to develop thickness design curves for the Kentucky Department of Highways.

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The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented. The report does not necessarily reflect the official views or policies of the University of Kentucky nor of the Lexington Fayette Urban County Government. This report does not constitute a standard, specification or regulation.