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A desorption technique was employed to evaluate chemisorption of ammonia by clays under moist conditions. In equilibria involving ammonia, all factors favoring volatilization losses of gaseous ammonia would undoubtedly exert an influence on the ultimate equilibria which are reached. Investigation of the relationship between pH and ammonia equilibria in soils revealed that an increase in the concentration of ammonium ions, applied as ammonium sulfate, stimulated ammonia losses from fine-textured soils at pH's ranging from 4.5 to 7.1. Ammonia volatilization was directly related to the initial pH of the soil and increased with an increase in pH. It was postulated that ammonia may be volatilized, even from acid soils, due to the equilibrium NH₄⁺ + OH⁻ ⇌ NH₃ + H₂O. By using initial concentrations of ammonium ions from ammonium sulfate applied, initial pH of an aqueous suspension of the soil and a value K_b = 1.80 x 10⁻⁵, values of ammonia losses were predicted. The linear relationship found between predicted and measured amounts of ammonia losses from acid as well as neutral soils, was interpreted as evidence of the existence of the proposed volatilization mechanism in soils. In attempting to evaluate the characteristics of ammonia retention by homo-ionic bentonites and kaolinites under moist conditions, it was found that base-saturated clays did not chemisorb ammonia in a fashion which could be described by Langmuir's adsorption isotherms. The S-shaped curves did not necessarily reflect polymolecular sorption. In strong contrast, chemisorption of ammonia by Al-saturated clays, followed Langmuir's equation almost perfectly. Evaluation of the inverse values of the differential slopes of two straight line segments obtained in the desorption isotherms corresponded closely to values obtained for the permanent charge (CEC) and the total charge (total CEC) developed at a specific pH higher than 6 respectively. It was shown that if sufficient ammonia is applied, exchangeable Al⁺⁺⁺ of Al-compounds may be precipitated as Al(OH)₃. An attempt to evaluate pseudo-equilibrium constants for aluminum-clay ammonia equilibria by using Langmuir's adsorption equation, was unsatisfactory. Chemical kinetic studies indicated that ammonia volatilization reactions could be described by a fast reaction and a slow reaction. The slow reaction represented chemisorption of ammonia on the permanent charge exchange sites. Extrapolation of the slow reaction to zero time yielded values corresponding closely to the CEC permanent charge. Investigation of the effects of CO₂, the NH₄⁺ concentration is increased, resulting in more effective replacement of basic cations for "permanent charge" exchange spots. The lower pH and higher effective NH₄⁺ concentration resulted in higher retention of NH₄⁺ in Na⁺- and K⁺-clays. The most striking retention of NH₄⁺ was obtained in Mg- and particularly in Ca-bentonites. It is believed that the Ca and Mg ions, exchanged by NH₄⁺ ions, are effectively removed from the soil solution as a result of the precipitation of these compounds which are sufficiently insoluble to ensure conservation of ammonia as chemisorbed ammonium ions. / Ph. D.

The main purpose behind this thesis was to study the variations of strength in a soil after it had been stabilized with various percentages of lime, cement, and combinations of the two. In both cases where the additives were added separately to the soil, the percentages used were 5 and 10 per cent by dry weight of soil. In the additive combination study, lime-cement percentage additions were 2-3, 3-2, 4-6, and 6-4 by dry weight of soil. The first two percentages, when added together, amount to 5 per cent stabilizing agent, while the latter two total 10 per cent. Since these two totals were the same as those used in the separate lime and cement studies, an analysis of strength changes when lime, cement, and lime-cement combinations were added to the soil could be made. Strength studies which were made consisted of unconfined compression immediately after compaction and after a four-day curing period in a 100 per cent humidity curing room. Atterberg limit tests were also run at the various percentages of additive. The laboratory test results indicate: 1. For cured specimens containing a stabilizing agent, the greatest four-day strengths will occur at or above OMC, in most cases. This may not always be true in the case of cement, since moisture condition is not as significant in cement stabilization as it is in other types. 2. Control of moisture at or near OMC during field compaction appears to be much more important in lime stabilization than in cement stabilization if maximum strengths are to develop. This statement is supported by a statistical analysis which was performed on the strength data. 3. The variation of' the lime-cement percentage trom 6-4 to 4-6 has no effect on four-day cured strengths. / M.S.

Swelling attributable to intracrystalline water adsorption by montmorillonite (MT) and vermiculite (VR) saturated with cations which limit interlayer expansion were calculated as the product of one-half the change in interlayer spacing determined by x-ray diffraction and the difference between total surface area taken as 800 m²/g and external crystal surface area measured by N₂ gas adsorption. Swelling directly attributable to osmotic adsorption was calculated as the product of external surface area and theoretical double layer thickness. In homoionic, monomineralic systems of Ca- and Al-MT and Na-, Ca- and Al-VR, intracrystalline expansion accounted for 60, 70, 21, 56 and 44%, respectively, of total expansion during saturated vapor-wetting and 15, 50, 4, 12 and 13% during submersion in 0.01 N electrolyte solutions. Osmotic adsorption of these systems accounted for < 10% of the expansion on submersion in all cases. Dry, static compaction of Ca-MT resulted in an increase in expansion with increasing initial density which was not explained by changes in predicted osmotic or intracrystalline expansion. This was attributed to expansion caused by gaseous pressures developing ahead of advancing wetting fronts. An inverse relationship was found between pore size and swelling caused by entrapped air pressures. Slow wetting ameliorated this expansion by allowing dissipation of entrapped air. Relaxation of crystal strains during wetting was also implicated as contributing to expansion. Electron microscopy revealed crystal strain decreased in the order: Na-MT > Ca-HT > Al-MT > Na-VR ≃ Ca-VR ≃ Al-VR. Greater expansion by freeze-dried than oven-dried Ca-MT was explained by greater crystal strain observed in the former clay. Greater strain broadening of the (060) x-ray diffraction peak was observed for the freeze-dried clay and its mean b-dimension was slightly smaller than the oven-dried clay. Crystal strain relaxation is suggested to explain the relationship between b-dimension and swelling reported in the literature. Predicted osmotic expansion for two soils was greater than in the pure clay systems and intracrystalline expansion smaller, due to a greater ratio of external to internal surface area in the soils. Osmotic adsorption accounted for 30-70% of the soil swelling during submersion in 0.0lM electrolyte solutions, while intracrystalline expansion accounted for < 10%. The magnitude of swelling due to entrapped air pressures was evaluated from the difference between expansion of atmospheric pressure-wet and vacuum-wet clods. This component accounted for 10-60% of the expansion of undisturbed and compacted samples during the second cycle of wetting from the air-dry state, but did not appear to be directly related to pore size. Changes in structure accompanying air-drying appeared to enhance expansion, especially for the high MT Iredell soil. It was suggested that this may be the result of increases in crystal strain during drying. / Ph. D.

The main purpose of this study was two-fold: 1. To show any existing correlation between OBR and UCS tests. 2. To show variation in UCS due to various methods of curing Using a Harvard miniature apparatus, compactive curves were determined for standard AASHO compactive effort for 0, 5, and 10 percent lime. From these curves the moisture contents to be used for strength tests were determined. These were dry of optimum (optimum -6 percent), optimum, and wet of optimum (optimum -̷6 percent). CBR specimens were fabricated at the above moisture contents for 0, 5, and 10 percent line. In all, nine samples were prepared. This was repeated using the miniature apparatus for the unconfined compression test. Six samples were prepared for each test condition. Two of these were tested as molded, two after damp curing (four days 67ºF), and two after oven curing (two days 120ºF). The results of this study indicated the following: 1. Lime increases the strength of the soil. This effect was very significant on the dry side. 2. Up to five percent addition of lime produced little increase in strength. This value may be considered as a fixation value of lime for this soil. 3. Curing increased the UCS and CBR of lime-treated soil. Accelerated oven curing 120ºF for two days given significant increase in strength, especially with 10 percent lime. 4. No definite conclusions could be derived between as molded CBR and as molded UCS, between soaked CBR and damped cured UCS, and between soaked CBR and oven cured UCS. / Master of Science

M.S.