In 1982 the Iowa DOT allowed a successful bidder the option of submitting materials and proportions using fly ash to produce a portland cement concrete (PCC) paving mixture to meet a specified compressive strength. The contractor, Irving F. Jensen, received approval for the use of a concrete mixture utilizing 500 lbs. of portland cement and 88 lbs. of fly ash as a replacement of 88 lbs. of portland cement. The PCC mixture was utilized on the Muscatine County US 61 relocation bypass paved as project F-61-4(32)--20-70. A Class "C" fly ash obtained from the Chillicothe electric generating plant approximately 100 miles away was used in the project. This use of fly ash in lieu of portland cement resulted in a cost savings of $64,500 and an energy savings of approximately 16 billion BTU. The compressive strength of this PCC mixture option was very comparable to concrete mixtures produced without the use of fly ash. The pavement has been performing very well. The substitution of fly ash for 15% of the cement has been allowed as a contractor's option since 1984. Due to the cost savings, it has been used in almost all Iowa PCC paving since that time.

Much attention has been focused in recent years on conserving natural resources and energy. Numerous waste products and/or byproducts from various industrial and commercial processes, normally deposited in landfills, have been proposed for use as alternate construction materials. One byproduct that has shown considerable promise as an alternate construction material is fly ash when used in a lime-fly ash (LFA) base course. This paper describes the use of this waste product in LFA stabilized granular materials as an alternative to cement treated materials for base construction. The primary disadvantage of a cement treated base (CTB) is the environmental (shrinkage) cracking that leads to the infiltration of rain water and incompressibles, pumping of subgrade soils, spalling of the crack faces and other problems that adversely effect pavement performance. It has been shown that the slow strength gain associated with LFA leads to a condition where the microcracks in the material are generally healed before they can develop into macrocracks. Continued chemical reactions, known as autogenous healing, within the mix are largely responsible for this behavior.

Coal fly ash is a coal combustion product that has numerous applications in highway construction. Since the first edition of "Fly Ash Facts for Highway Engineers" in 1986, the use of fly ash in highway construction has increased and new applications have been developed. This document provides basic technical information about the various uses of fly ash in highway construction that advances its use in ways that are technically sound, commercially competitive and environmentally safe.

"TRB's National Cooperative Highway Research Program (NCHRP) 749: Methods for Evaluating Fly Ash for Use in Highway Concrete presents suggested changes to coal fly ash specifications and test protocols contained in American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Transportation Materials and Methods of Sampling and Testing (AASHTO M 295). The changes suggested include modifications to the test methods currently specified for evaluating acceptability of fly ash for use in highway concrete as well as the introduction of new test methods for enhancing such evaluations. Attachment C: Details of the Research into Methods for Evaluating Fly Ash Use in Highway Concrete is only available online."--Publisher description.

This report is essentially a synthesis of pertinent information concerning the use of fly ash as an ingredient in concrete for highway construction. It has been prepared to provide a basis for an adequate response by the Department of Highways and Transportation to requirements of the Resource Conservation and Recovery Act and the Environmental Protection Agency pertaining to the use of this by-product in concrete purchased with federal funds. Special attention is given to the quality control and acceptance problems associated with highway usage of fly ash concrete, with emphasis on problems relating to air entrainment. References to the background literature that established the suitability of fly ash as a pozzolan and its use in concrete are The requirements for fly ash as set forth in ASTM Specification C618 are reviewed and the- characteristics to be expected from concrete containing fly ash are discussed. It is recommended that the Virginia Department of Highways and Transportation permit the use of fly ash in concrete at the option of the contractor with prior approval by the state. It is also recommended that suitable specifications for this use be prepared following the guidelines previously recommended by the Concrete Research Advisory Committee.

This synthesis summarizes available information concerning the use of fly ash in hydraulic-cement concrete, and attempts to establish consensus concerning a number of applications relating to highway construction. Fly ash marketing procedures are briefly reviewed, and the amount of fly ash now being used is summarized. The results are reported of a questionnaire survey of the status of the use of fly ash concrete (FAC) in each state of the U.S. and the provinces of Canada. There is an increase in FAC use since 1980. This trend is aided by the development of a flyash industry. Trends also indicate a developing technology that will be oriented around performance of the hydraulic cement concrete. Currently, most states view the proportioning of of FAC from the standpoint of the amount of portland cement to be replaced by the fly ash and have maximum replacement limits. It has been noted that the same fly ash with different cements may react differently and develop different early and ultimate strengths. The need is emphasized for preliminary tests to establish optimum proportioning of ingredients in the concrete using materials from the sources to be supplied to the job.