Lime and Fly Ash Proportions in Soil, Lime and Fly Ash Mixtures, and Some Aspects of Soil Lime Stabilization MANUEL MATEOS and DONALD T. DAVIDSON, Respectively, Research Associate and Director, Soil Research Laboratory, Engineering Experiment Station, Iowa State University of Science and Technology The main objects of the investigations were to find a possible best ratio of lime to fly ash and the optimum amount of the lime and fly ash admixture for stabUizing various textured soUs; to determine the effects of lime content and curing period on the strength of soU and lime mixtures; and to compare the strengths of soils treated with lime, lime and fly ash, or cement. Four soUs were used: dune sand, friable loess, aUuvial clay, and gumbotU. Four limes (a calcitic hydrated and three dolomitic monohydrated) and eight fly ashes were tried. Seven-day and 28-day curing periods were used with soil, lime, and fly ash mixtures, and strength contour lines for 28-day results are presented. Ninety-day curing was also used with soU-lime mixtures. Moisture-density and moisture-strength relationships of soU-lime mixtures are compared. The best ratio of lime to fly ash and the optimum amoimt of lime and fly ash were found to depend on the kind of lime, fly ash, and soU used. Recommended amounts of lime and fly ash for stabUizing the different soUs are given. Data are presented to show the influence of type of lime and kind of fly ash on the unconfined compressive strength of sta• bilized soils. A durabUity evaluation of selected soU-lime- fly ash and soU cement mixtures by the Iowa freeze-thaw test is presented. The optimum amount of lime for strength improvement increases with length of curing mixtures of soU and lime. Dolomitic monohydrate lime proved to be better than cal• citic hydrated lime, although the calcitic lime may be more beneficial in the additions of small amounts. Additions of lime to such clayey soils as gumbotU and alluvial clay modify the lubrication effect of water when the mixtures of soil and lime are compacted, and the mixtures may not have a well-defined optimum moisture content. • SEVERAL SOIL admixtures are used to obtain a construction material with better engineering properties than those of the original soU. The most extensively used are cement and lime. Others, like lime with fly ash, appear to be satisfactory stabilizers but have not been much used because their characteristics and behavior when added to soUs are not well known. Since the early 1950's the Engineering Experiment Station SoU Research Labora• tory of Iowa State University, in cooperation with the Iowa State Highway Commission and the Iowa Highway Research Board, has been conductmg an extensive evaluation of 1*0 41 different methods of soil stabilization for road courses. Special attention has been given to the use of by-product or waste materials such as fly ash. Producers have the costly problem of disposing of over 10,000,000 tons of fly ash every year. Inasmuch as laboratory and field evaluations of soil stabilized with lime and fly ash have given promising results,- highway engineers and power industry management are interested in further improving this use of fly ash. The work done to evaluate lime plus fly ash as an admixture to soils has been re• stricted. General conclusions on the use of these materials have been based on results obtained with a limited variety of the component materials (soil, lime, and fly ash) or have been based on limited testing. An attempt has been made in this investigation to introduce a reasonable number of variables in the soil, lime, and fly ash. To have a comparative evaluation, the soils used were also stabilized with cement and with lime. MATERIALS AND METHODS Materials Used Four natural soils (a dune sand, a friable loess, an alluvial clay, and a highly plastic gumbotil) were selected as representative of important Iowa soil types (Tables 1 and 2), Eight fly ashes were selected to represent variations in the properties of this by• product material (Table 3): Fly ash 1, collected by multiple cyclone and electrical precipitators, was from coal from districts 3 and 8 in Ohio and from northern West Virginia, and was processed through pulverizing mills so that 70 percent passed a No. 200 mesh. The sample was sent from the St. Glair (Mich.) Power Plant ol the Detroit Edison Company. Fly ash 2, collected by mechanical equipment, was from coal from northern niinois. The coal was burned in a B and W boiler. This sample was sent from the Sixth Street Power Station of the Iowa Electric Light and Power Company in Cedar Rapids. Fly ash 3 was collected by electrical precipitators from a dry bottom type of boiler using unwashed coal from western Kentucky. The sample was sent from the Paddy's Run Power Station of the Louisville Gas and Electric Company in Louisville, Ky. TABLE 1 DESCRIPTION OF NATURAL SOILS Property Dune Sand Friable Loess Alluvial Clay Kansan Gumbotil Soil Res. Lab. No. (S-6-2) (20-2) (627-1) (528-8) Location Benton Co., Harrison Co., Harrison Co., Keokuk Co., Iowa Iowa Iowa Iowa Geological Wisconsin- Wisconsin-age Recent fill, allu• Kansan-age gum• description age eolian loess, friable, vial plastic, botil, highly sand fine• oxidized, cal• slightly calcar• weathered, grained, careous eous plastic, noncal- oxidized, careous leached Soil series Carrington Hamburg None Mahaska^ Horizon C C Undefined Fossil B Sampling depth (ft) 6-11 49-50 0-4 7.5-8.5 Underlies C-horizon loess of Mahaska series. 42 Fly ash 4, collected by mechanical precipitators, was from coal from northern Illinois burned in a Springfield boiler in the Sixth Street Power Station of the Iowa Electric Light and Power Company in Cedar Rapids. Fly ash 5 was collected by mechanical (centrifugal) precipitators. The coal from Illinois was pulverized in a ball mill before burning in the Riverside Station Power Plant of the Iowa-Illinois Gas and Electric Company at Davenport, Iowa. Fly ash 6 was collected by mechanical precipitators (multicone dust collector). The coal from Iowa (Monroe, Polk, Marion, and Mahaska Counties) was unwashed steam coal which was pulverized and tangential fired in the Des Moines Power Plant of the Iowa Power and Light Company. Fly ash 7 was collected by mechanical equipment (VGR multicone) in the Waterloo Power Plant of the Iowa Public Service Company. The coal from southern Illinois was washed, dried, and pulverized with Riley mills. Fly ash 8 was collected by mechanical precipitators (cyclone type). The coal from several Missouri and Kansas nunes was pulverized and burned in suspension in com• bustion engineering boilers in the Hawthorn Station Power Plant of the Kansas City Power and Light Company, Mo. TABLE 2 PROPERTIES OF SOILS Property Dune Sand Friable Loess Alluvial Clay Kansan Gumbotll Textural composi- Uon^ (5f): Gravel (> 2 mm) 0.0 0.0 0.0 0.0 Sand (2-0.074 mm) 95.5 0.7 2.4 19.4 Silt (0.074-0.005 mm) 1.5 82.3 25.6 14.6 Clay (< 0.005 mm) 3.0 17.0 72.0 66.0 CoUoids (< 0.002 mm) 2.6 14.0 61.0 63.0 Atterberg Umits^: Liquid limit (?S) - 32 72 76 Plastic limit Cf-) - 25 26 26 Plasticity mdex Nonplastic 7 46 50 Classification: Textural^ Sand Silty loam Clay Clay fjnginecring (AASHO)a A-3 (0) A-4 (8) A-7-6 (20) A-7-6 (20) Chemical: Cat. exch. cap.® ' (me/100 g) 1.0 14.5 44.4 39.2 6.6 8.4 7,7 7.4 CarbonatesS 0.4 10.4 3.6 2.0 Organic matter'* (^ 0.1 0.1 1.6 0.1 Predominant clay Montmoril- Montmoril- Montmoril- Montmoril- mineral^ lonite (trace) lonite lomte lonite *ASTM Method Dlj22-51»T. ''ASTM Method Dlt23-S1»T and Dl»2lt-51lT. "Triangular chart developed by U.S. Bureau of Public Roads. •^AASHQ Method MII4S-U9. ^Anmonium acetate (pH = 7) method on soil fraction 0.1*2 mm (No. 1*0 sieve). ^Glass electrode method using suspension of 1$ g soil in 30 cc distilled water, ^ersenate method for total calcium. '^Potassium bichromate method. hi-raf diffraction analysis. 43 Most of this investigation was made using two commercial grade limes of the U. S. Gypsum Company. One is a hydrated calcitic lime, brand name "Kemikal"; and the other is a type N monShydrate dolomitic lime, brand name "Kemidol." Two dolomitic mono- hydrate limes, from Western Lime and Cement Company and from Rockwell Lime Company, were also used m a comparative study of some commercial dolomitic mono- hydrate limes with dune sand and fly ash 3 only. The analysis of all limes is given in Table 4. The Portland cement used was commercial type I of the Penn-Dixie Cement Corpora• tion of Des Moines, Iowa. The analysis of the cement can be found in O'Flaherty et al. (13). Distilled water was used throughout to eliminate the variable that might result from impurities added with ordinary tap water. Procedures The proportions of soil plus lime or lime-fly ash or cement are based on the dry weight of the soil and lime; soil, lime, and fly ash; or soil and cement mixtures. Mixing and Molding. —Mixmg of batches for preparing test specimens was done in a kitchen mixer at low speed. The dry ingredients were machine mixed for 30 sec. The mix water was added and machine mixed for 1 min. The mixture was hand mixed for about 30 sec to clean the sides and bottom of the mixing bowl.