Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board's recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs.
The physical and chemical properties of fly ash produced at Ottumwa Generating Station have been monitored since April, 1985. The fly ash is produced from burning a low sulfur, sub-bituminous coal obtained from the Powder River Basin near Gillette, Wyoming. One-hundred and sixty samples of fly ash were obtained during the two year period. All of the samples were subjected to physical testing as specified by ASTM C 311. About one-hundred of the samples were also subjected to a series of tests designed to monitor the self-cementing properties of the fly ash. Many of the fly ash samples were subjected to x-ray diffraction and fluorescence analysis to define the mineralogical and chemical composition of the bulk fly ash as a function of sampling date. Hydration products in selected hardened fly ash pastes, were studied by x-ray diffraction and scanning electron microscopy. The studies indicated that power plant operating conditions influenced the compressive strength of the fly ash paste specimens. Mineralogical and morphological studies of the fly ash pastes indicated that stratlingite formation occurred in the highstrength specimens, while ettringite was the major hydration product evident in the low-strength specimens.
The influence of the chemical composition of fly ash on the autoclave expansion of portland cement-fly ash pastes has been studied. The autoclave expansion tests were performed as described in ASTM C 151–81. Several of the cement-fly ash pastes tested exhibited severe expansive behavior. Free lime (CaO) was the only single variable that correlated well with the expansion observed in the autoclave tests. A multivariable model was generated in which lime, magnesium oxide, and tricalcium aluminate were the significant variables. The autoclave expansion of portland cement-fly ash pastes appears to be quite sensitive to the amount of free lime present in a given mixture.
Fly ashes from the Lansing and Ottumwa power plants in Iowa were agglomerated by means of a continuous pan agglomerator, a continuous auger and a batch turbine agglomerator. In order to compare agglomeration mechanisms the following parameters were determined: (a) particle size distributions of the untreated fly ashes; (b) particle size distributions of the agglomerated fly ashes; (c) pore size distribution of agglomerates; (d) crystalline hydration products by X-ray diffraction; and (e) morphological characterization by scanning electron microscopy.In the batch system coalescence mechanisms were favoured. The agglomerates were fairly irregular in shape and had a rough surface texture. As residence time in the system increased breakage of agglomerates occurred, reducing the average agglomerate size. In the continuous systems layering of the fine feed particles onto established agglomerates was the predominant growth mechanism. The agglomerates were smooth and spherical. The layer structure was observed by scanning electron microscopy. Agglomerates of widely varying size, strength, and pore matrix can be produced in both systems. It is envisaged that while agglomerates could be produced with characteristics essential for their proposed end use by either method, continuous pan agglomeration would be the most versatile system to utilize.
The Materials Analysis and Research Laboratory has been monitoring the soundness of several sources of fly ash since the early 1980's. The soundness tests were generally conducted in accordance with ASTM Test Method C 311 (the autoclave expansion test utilizing 20% fly ash and 80% portland cement, specimens prepared at normal consistency). To date, several thousand tests have been performed on various samples of fly ash that were submitted to the laboratory. Also, additional studies were conducted to investigate the influence of water content (W/CM ratio) and curing regime on the volume stability of portland cement pastes containing a fly ash that exhibited soundness problems.
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