vater. The unconfined compressive strength of specimens molded with an RASHTO T9o Compactive effort and cured at 73° is shown in Table 3. Strength was found to increase with increasing lime content as well as with the addition of sulfate and the use of dolomitic lime instead of calcitic lime. The tests indicated that lime-pozzolan mixtures can be designed to develop strength and thus act as a stabilizing agent even when sewage sludge is included in the mixtures. To further explore this approach to disposing of the sewage sludre, a demonstration embankment was constructed in the conventional manner using a mixture of sludge, fly ash and soil stabilized with lime and sulfate. Soil was included in the design in the same quantity as fly ash as a matter of economics since it would be difficult to obtain the large volume of fly ash required for the planned I-95 construction if fly ash was to constitute the sole filler material. Preliminary tests indicated that the soil reduced the strength of the mixture at any particular age but did not materially change the rate of strength development from that found for mixtures without soil. During the construction of the demonstration embankment, the mixture was found to be very cohesive, compactible and stable. Cores taken from the embankment after it had cured for two months were evaluated for leachability and durability with respect to moisture and freezing and thawing. Leaching tests performed by the Environmental Protection Agency established the environmental acceptability of the stabilization procedure from the point of view of possible ground water contamination. When removed from the erbankment, the cores yielded an average strength of about 350 psi. This level of strength was maintained even after immersion in water for 60 days but a rapid loss of strength resulted from freezing and thawing. Table 3- Unconfined Compressive Strength of Sludge-Fly Ash-Sulfate, Lime ixtures 1/ Amounts shown are on a total mix, wet weight basis. 2/ Dolomitic Lime Our study of the particular problem posed by the construction of I-95 in the city of Philadelphia provides convincing evidence that the stabilization technique is a viable engineering solution for disposing of digested sewage sludge. A properly stabilized mixture can be used as enbankment material below the water table as well as above with the only limitation being that it not be exposed to freezing and thawing cycles: a condition that would normally be met in the '. S. when side slopes are covered with a suitable layer of earth for support of vegetation and a capping of natural soil or pavement material is provided. Closure The research and applications covered in this paper represent some of the more promising approaches to the use of waste materials in highway construction based on their technical, economic, and environmental feasibility. Many other waste products can also serve as material for highways but are handicapped, in many cases, by economic factors. For example, the problem of disposing of waste rubber tires could be greatly alleviated by using ground rubber as an admixture in bituminous concrete for pavements. This practice, however, has not been widely adopted because it increases the cost of the bituminous concrete without producing definable benefits in performance of pavements. In fact, it can be said generally that economic considerations pose a serious deterrent to the use of waste products in highway construction, including those having the greatest potential for being less costly than conventional materials. Waste products are often not produced in the best condition for convenient handling and use. For example, pover companies may dispose of fly ash and bottom ash so they become intermingled. The matter of location, of course, is an important factor since the cost of moving large volumes of material can quickly override all other costs. Contractors customarily cushion their bids when new or unfamiliar materials are involved. Waste materials may also be handicapped by the fact that a regular system of distribution or marketing does not exist. The experience with fly ash usage has demonstrated that most progress is made in the use of such materials then commercial organizations become established specifically to assume the function of quality control and supply so that they can be supplied under the same conditions as most conventional materials. In spite of these problems, we believe that there is a future in the highway field for vaste utilization and that the results of our studies on specific applications will provide the background information on which decisions can be reached concerning the economics of using such wastes in highways. References 1 Waste laterials as Potential Replacements for Highway Aggregates, Final report of Project. No. 4-10/A, National Cooperative Highway Research Program, Highway Research Board. 2 Use of Waste Sulfate on Transpo '72 Parking Lot, R. H. Brink, POWER PLANT AGGREGATES FOR HIGHWAYS OF THE FUTURE First FCP Research Progress Review, U.S. Department Compiled by Allan W. Babcock1 and John H. Faber 2 A new dimension is being added to highway construction through the growing utilization and application of power plant ashes in all phases of road building from sub-grade stabilization to wearing courses. This has been due in large measure to the development and publication of hard data by both the public and private sector on the preparation and use of these materials for highway construction and maintenance. In all fairness, we must admit much of this research has surfaced in response to major efforts at the national and local level toward the recycling of waste products in an attempt. to improve our environment. Our industry is answering this challenge to the end. We are developing practical processes and procedures that will permit substantial tonnages of power plant ashes to be consumed in the imporvement of our nation's highways. Several other important factors are influencing this growth, including increased acceptance by the engineering profession itself, the shortage of suitable natural aggregates and portland cement in many sections of the country, and the all important economic struggle with soaring costs. However, we are approaching this new role with cautious optimism for if these ashes are to be used effectively in highway work, new construction techniques must be adopted by 1. Industrial Development Representative, Monongahela Power Company. 2. Executive Vice President, National Ash Association, Inc. road contractors, utility suppliers improving present quality control procedures, and new specifications must be developed which take into consideration the unusual properties of the ash to insure adequate performance. Power plant ashes are not miracle materials, but they do have certain unique chemical, physical, and engineering properties that make them suitable substitutes for conventional aggregates or easily combined with them to achieve satisfatory performance. This is not meant to imply we have all the answers, for additional study is needed before expanded markets can be developed. Additionally, while total ash production in the United States is growing at a tremendous rate, the geographic location of the coal-burning power stations themselves can be a limiting factor as well as an advantage. Thus, this four day conference takes on added significance for perhaps the development of new compositions of domestic, industrial, and domestic wastes will remove or at least minimize present transportation restrictions. For those of you who are not intimately acquainted with power plant ashes, I should like to explain that these versitile materials come in two basic forms fly ash and bottom ash; although the availability of SO2 sludges could be an important third source in coming months and years. Not all ash is the same. Variances in equipment, burning |