SOIL STABILIZATION Nechanical strength of calcium polyacrylate stabilized systems appeared to be associated with the Atterberg limits initially measured on the monomer-Fort Belvoir soil. The most important, factor affecting strength was the position of the equilibrated samples with respect to the Atterberg limits. Mechanical strength data are presented in Table 11. Samples 1, 2, and 6 were heterogeneous, causing poor strength. They were deliberately prepared above the flocculation limit, and they were useful in water equilibration determination. Samples 3, 7, 11, and 12 with final soil moisture contents above the liquid limit of the monomeric system, showed high tensile and high elongation, but poor utilization of calcium acrylate. Samples 4 and 8 gave maximum tensile and minimum elongation with good utilization of acrylate. The most noticeable evidence of the importance of Atterberg limits on properties of solidified soil appears in the comparison of points 5 and 10, which were on either side of the plastic limit line. The relationships between equilibrium water content, tensile strength, and elongation of calcium acrylate stabilized soil are further illustrated with Figure 7 . Conclusions
1. The equilibrium moisture content of calcium acrylate stabilized soil after immersion in water, depends principally on the amount of)polymerpresent.
2. The water equilibrating role of calcium polyacrylate in the soil is important in determining wet strength of treated soil. 3. Triaxial figures are useful in studies of chemical soil solidification. Acknowledgment
We are indebted to the Massachusetts Institute of Technology and to the U. S. Army Corps of Engineers for much of the background information on calcium acrylate treatment of soil. The Corps of Engineers has conducted considerable field work and has demonstrated the ability of calcium acrylate to impart mechanical strength to soil and to reduce its water permeability. Literature Cited (1) Dannenberg, E. M., and Hauser, E. A,, U. 8. Patent 2,383,647
(August 28,1945). (June 0,1940). (3) De hlello, V. F. B., Hauser, E. A,, and Lambe, T. W., U. S, Patent 2,651,619 (Sept. 8,1953). (4) Lambe, T. W., Boaton SOC.C$viZ Engrs., 38, No.200 (April 1951). (6) Lambe, T.W., and Michaels, A. B., Chem. Eng. News,32, 48892 (1954). (0) Rohm & Haas Co., unpublished data, August 1953. (2) Ibicl., 2,401,348
RECEIVED for review May 16. 1955.
ACCEPTED August 10. 1955,
Aluminum Sulfate and Iron Sulfates as Auxiliaries in Bituminous Stabilization of Soils C. KINNEY H A N C Q C K TEXAS ENC3INEERING EXPERIMENT STATION, TEXAS A. & M. COLLEGE SYSTEM, COLLEGE STATION. T E X .
Even t h o u g h there are m a n y literature references t o t h e use of metallic salts as auxiliaries in t h e b i t u m i n o u s stabilization of soils, few quantitative data resulting f r o m economically feasible methods of application are t o be found. Data presented on eight abnormally hydrophilic soils indicate t h a t increased stabilization of t h e m a j o r i t y of these soils can be attained by using cutback asphalt w i t h 0.5 t o 4% ferrous, ferric, or a l u m i n u m sulfate as auxiliary. Ferric chloride glves similar results if t h e excess salt i s washed out, b u t t h i s is n o t economically feasible on a large scale. Ferric and a l u m i n u m sulfates have about t h e same auxiliary stabilizing action while ferrous sulfate has a slightly smaller effect. For seven of t h e soils, use of 2% auxiliary salt resulted in a n approximate t w o t o tenfold increase in modified bearing value accompanied by a corresponding significant decrease in water absorption. In many cases, auxiliary salt treatment reduced t h e q u a n t i t y of asphalt needed f o r satisfactory stabilization. The auxiliary effect of these salts in bituminous soil stabilization is of interest in highway construction for it m a y lead t o t h e use of otherwise unusable right-of-way soils.
I
N THE construction of modern highways, the use of soils from the immediate right of way is an important economic consideration since it eliminates both the purchase and transportation costs of materials brought from outside. Certain such soils, if wetted to optimum moisture content, compacted to maximum density, partially dried, and covered with a wearing surface, will have good load-carrying characteristics; however, this will be true only over a rather narrow range of moisture contentLe., if the moisture decreases significantly, crumbling will occur, and, if the moisture content increases considerably, the soil will become plastic and undergo severe deformation under traffic loads. November 1955
As a result, it has become rather common practice to add a stabilizing agent a t some point in the process of wetting, compacting, and drying the soil. Among the widely used stabilizing agents are asphalt, portland cement, and lime. The use of asphalt as stabilizing agent has become quite common in Texas. Recently, many significant developments, including the use of trace chemicaIs, have occurred in the field of soil stabilization. Many of these new methods have been reported or reviewed by Lambe ( 6 4 ,Michaels (8, 11), and Murray (12). The present article is concerned with the results of a 194142 study of the auxiliary action of several metallic salts in bituminous stabilization of soils. The results of modified bearing
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
2269
ENGINEERING. DESIGN. AND EQUIPMENT
a RC-2 Figure 1.
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Comparison of effect of 0 and 2% FeS04
value and capillary water absorption tests indicated that the majority of the soil samples used in this study could not be stabilized satisfactorily by the usual treatment with cutback asphalt. The progress of this study was guided by three objectives: 1. To add the auxiliary metallic salt under conditions that would be economically feasible in actual highway construction 2. To use effective, inexpensive metallic salts 3. To test soil-asphalt specimens with and without auxiliary before use in highway construction Certainly, it would be desirable to be able to predict from soil properties if the soil could be stabilized with asphalt alone or with asphalt plus auxiliary. However, even if this prediction were possible, the practical highway engineer would still insist on laboratory tests on soil-asphalt specimens both with and without auxiliary. Previous Work
During the past two decades, both the periodical and patent literature have been relatively abundant on the subject of auxiliaries for bituminous stabilization of mineral aggregates. This review will be limited largely to some of the more significant developments in the use of metallic salts as auxiliaries in the stabilization of soils with cutback asphalt or road oil. Winterkorn (16) leached soils with salt solutions, washed out the excess salt, and then determined the physical constants of the resulting soils. The greatest improvement in physical properties was noted in the soils resulting from leaching with ferric chloride and aluminum sulfate. Saal ( 1 6 )treated siliceous mineral aggregates with a solution of ferrous sulfate or ferric ohIoride, then with asphalt, and noted increased adhesion by visual comparison. Drying the aggregate between the two treatments was preferable but not absolutely necessary. McLeod (9) found increased adhesion of bitumen to aggregate from using solutions of metallic salts along with sodium oleate. Of twenty salts studied, he found lead nitrate, cupric chloride, potassium aluminum sulfate, and ferric chloride to be most effective. Winterkorn and Eckert (88)made a similar study with ten salts and obtained best results with potassium aluminum sulfate, ferric chloride, and lead nitrate. It has been claimed ( d o ) that better adherence results by mixing a mineral aggregate, pretreated with a salt of a multivalent metal, with asphalt containing fatty or naphthenic acids which react with the multivalent metal salt. Later, it was claimed ( I I ) that improved adherence resulted from mixing a mineral aggregate pretreated with a water-soluble saIt of silver, copper,
2210
aluminum, or iron with asphalt containing a naphthenate of calcium, of lead, or of zinc. Winterkorn and Eckert ( d 7 ) made an extensive physicochemical study of nine homoionic modifications of each of six soils prepared as in the earlier study (26). The air-dried modified soils (40-mesh) were wetted to the plastic limit and mixed with 7.5y0bitumen; then, compacted laboratory tes6 specimens were prepared. After being submerged in water for 36 days, the penetration of the specimens was determined with an asphalt penetrometer. Less penetration occurred in cases of soils that had been treated with ferric chloride or with aluminum sulfate. It has been claimed (19) that better adhesion to mineral aggregate results if there is incorporated in the asphalt a small proportion of a salt of a multivalent metal containing in the molecule a t least one relatively small organic acid radical and a t least one relatively large organic acid radical. Benson and Becker (1)found that the strength of soil-cutback asphalt mixtures was affected only slightly by the addition of 0.25 t o 3y0aqueous solutions of the chlorides of calcium, copper, lead, iron, or aluminum. McLeod ( I O ) has described a process for waterproofing aggregate by heating it with bituminous material in the presence of an activating agent, e.g., lead nitrate, and of a wetting agent, e.g., sodium oleate. Roediger ( 1 6 ) has claimed that improved durability of pavements results from the use of a damp mineral aggregate pretreated with hydrated lime and then treated with liquid asphalt containing 1 to 3y0 lead naphthenate and 1 to 3% naphthenic acid. Sprague (18) studied the effect of nine commercial additives on the stripping of asphalt from mineral aggregate. Of the nine materials, two, which were complex mixtures containing aluminum sulfate, gave the best resistance to stripping. Gzemski and Hersberger ( 5 ) have claimed that the adhesion of bitumen t o mineral aggregate is increased by the addition of 0.1 t o 10% of a hydroxy aluminum sulfonate, e.g., a hydroxy aluminum salt of an oil-soluble petroleum sulfonic acid. Dupas ( 4 )has claimed improved adhesion of bitumen to mineral aggregate resulting from the incorporation of 0.1 to 10% of a complex compound of a multivalent metal chloride and an organic dye containing a basic group. I n spite of numerous articles or patents on the use of metallic salts as auxiliaries in the stabilization of soils with liquid bitumen, there are very few published data on the quantitative effect of such additives on the load-carrying values and water resistance
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 11
16
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% R C - 2 CUTBACU ASPHALT
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Comparison of effect of 0 and 2y0 F e S 0 4
of soil-bitumen mixtures. The purpose of this paper is to present data that show that certain salts of iron and of aluminum significantly increase the bearing value of many soil-bitumen mixtures. Materia Is RC-2 Cutback Asphalt. An unopened 55-gallon drum of RC-2 cutback asphalt was thoroughly mixed by rolling and then tested by the methods of the Texas Highway Department which conform to the test procedures of the American Association of State Highway Officials (1). The results of the tests were
1. 2. 3. 4. 5.
Furol viscosity 240 a t 122' F. 76% residue by weight from distillation to 680' F. Penetration of residue 134 Ductility of residue 110 Volume distilled, % F. 29
