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It is often necessary to improve the strength of fly ash to enable its use for many geotechnical applications. Lime in some form or other is normally used as an admixture. Methods are established to determine the optimum lime content for fly ash, as the addition of lime beyond the optimum lime content may not be beneficial or economically viable. This paper examines the use of sodium salts to enhance the effect of lime on fly ash. Based on unconfined compression strength tests on a compacted fly-ash–lime–salt specimen, it has been shown that sodium salts improve the strength of a fly-ash–lime mixture. The improvement is salt-specific. This improvement in strength can be attributed to the formation of a greater volume of sodium calcium silicate hydrate gel as opposed to a calcium silicate hydrate. The improvement in strength is greater for sodium hydroxide than for sodium chloride. The increased pH with sodium hydroxide dissolves more silica and can produce more cementitious compounds after reaction with lime. Although sodium sulphate increases the strength initially, its long-term effect is suspect.

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Lime has been used extensively to improve the shear strength of fine-grained soils. It has been recently reported that the presence of sulphate causes abnormal volume changes in lime-stabilized soil. The paper presents the strength behaviour of lime-treated montmorillonitic natural black cotton soil in the presence of varying sulphate contents after curing for periods of up to 365 days. Alteration of soil-lime reactions in the presence of sulphate affects the strength development by cementation. Consequently, the stress-strain behaviour effective stress paths of soil cured with sulphate are similar to those of normally consolidated soil rather than cemented soils. The reduction in shear strength due to a reduction in effective cohesion intercept occurs for lime-treated soil cured with sulphate for long periods. Résumé : La chaux a été abondamment utilisée pour améliorer la résistance des sols à grains fins. On a fait rapport récemment du fait que la présence de sulfate produit des changements anormaux de volume dans le sol stabilisé à la chaux. Cet article présente le comportement en résistance d'un sol organique noir naturel montmorillonitique traité à la chaux en présence de diverses teneurs en sulfate après des périodes de mûrissement allant jusqu'à 365 jours. L'altération des réactions sol-chaux en présence de sulfate affecte le développement de la résistance par cimentation. En conséquence, le comportement contrainte-déformation, les cheminements de contrainte effective du sol mûri avec le sulfate montrent un comportement de sol normalement consolidé plutôt que de sols cimentés. La réduction de la résistance au cisaillement due à la réduction de l'interception cohésion effective se produit pour le sol traité à la chaux mûrissant avec du sulfate pour de longues périodes

: Index properties are extensively used in geotechnical engineering practice. Among them, liquid limit is an important physical property used in classification and correlations with engineering properties of soils. Liquid limit, plastic limit and shrinkage limit of Black cotton soil (BCS) and mine tailings (MT) mixtures treated with lime are investigated and are presented in this paper. In the present investigation an attempt has been made to utilize the mine tailings in geotechnical applications and to evaluate the index properties of black cotton soil and mine tailings mixture treated with lime. The test results indicate that the progressive decrease in liquid limit, decrease in plastic limit and increase in shrinkage limit with curing time. The liquid limit in particular is used in many correlations with engineering properties and it is significant to know the stress history and general properties of the soil met with constructions. Liquid limit is used for the estimation of compression index and compression index is useful for the settlement analysis of soils. The Physico-chemical mechanism which alter the index properties of black cotton soil and mine tailings mixture treated with lime and the mechanisms have been explained based on thickness of diffused double layer and alteration of the reaction products of soil-lime reaction .for various curing periods.

The role of moulding water content, from the dry side of the optimum to the wet side of optimum, in the strength development in lime-treated soils was investigated in the present study. During compaction, the structure of clay particles can change from a flocculated to a dispersed structure as the water content is increased from the dry side of optimum to the wet side of optimum. For efficient formation of pozzolanic compounds, the water content of the soil–lime mixture should be kept as high as possible. The improvement in the strength of Indian black cotton soil treated with different amounts of lime content at different water contents and cured for varying curing periods was studied. The results clearly showed that the strength of black cotton soil treated with lime content increased better when compacted on the dry side of optimum, the other parameters remaining the same. Further, the optimum lime varied with moulding water content and curing period.

Black cotton soils exhibit high shrinkage and swelling characteristics due to the variation in moisture content. To overcome this problem, many techniques are adopted, among which is the soil stabilization technique. Rapid industrialization and urbanization lead to the generation of waste products; the major by-products are rice husk ash (RHA) and carbide lime (CL). These by-products show excellent pozzolanic property. In this paper, an attempt has been made to stabilize black cotton soil with rice husk ash (RHA) along with carbide lime (CL) and other additives. Based on strength test results, the optimum dosage of RHA and CL was found to be 20% and 8%, respectively. The effect of sodium salts on index properties and unconfined compression strength (UCC) test at different moulding water contents for immediate testing and at different days of curing are studied. Results show that plasticity index of the soil treated with additives was decreased both for immediate and for 7 days of curing period due to the decrease in diffuse double-layer thickness. Soil-RHA-CL composite treated with 1% sodium chloride and 1% sodium hydroxide improves the Unconfined compression strength and shows a better strength compared to carbide lime-treated soil due to the formation of alkali silicate and alkali aluminate hydrated gel along with other cementitious products. The microstructural changes in the stabilized composite can be observed with XRD and SEM analysis. The addition of carbide lime and salts binds the particle with hydrated gel and shows denser environment compared to unstabilized soil.

Lime has been extensively used to improve the strength of fine-grained soils. It has recently been reported that the presence of sulphate in soils causes abnormal volume changes in lime stabilised soil. This paper presents the strength behaviour of lime-treated kaolinitic natural red earth in the presence of varying sulphate contents, up to 3%, after curing for periods of up to 365 days. Alteration of soil–lime reactions in the presence of sulphate leads to the formation of ettringite after curing for longer periods. The formation of these compounds affects strength development by cementation. However, after curing for short periods, the strength of lime-treated soil is improved in the presence of sulphate. It is only after curing for longer periods that the strength is decreased. Consequently the stress–strain behaviour and effective stress paths of treated soil cured for long periods show the behaviour of a normally consolidated soil rather than of cemented soils. The reduction in strength is due primarily to a reduction in the effective cohesion intercept. The effective friction angle has not been affected significantly. La chaux est largement utilisée pour améliorer la résistance des sols à grains fins. On a noté récemment que la présence de sulfate dans les sols cause des changements de volume anormaux dans les sols stabilisés à la chaux. Cet exposé montre le comportement de résistance d'une terre kaolinique naturelle traitée à la chaux en présence de diverses teneurs en sulfate, allant jusqu'à 3%, et après cuisson pendant des périodes allant jusqu'à 365 jours. Le changement de la réaction sol-chaux en présence de sulfate conduit à la formation d'ettringite après les périodes de cuisson les plus longues. La formation de ces composés affecte le développement de la résistance par cimentation. Cependant, après cuissons plus courtes, la résistance du sol traité à la chaux est améliorée par la présence de sulfate. Ce n'est qu'après la cuisson pendant des périodes plus longues que la résistance diminue. En conséquence, le comportement contrainte-déformation et les chemins de contrainte effective du sol traité et cuit pendant de longues périodes reflètent le comportement d'un sol consolidé de manière normale plutôt que celui de sols cimentés. La baisse de résistance est due principalement à une réduc-tion de l'interception de cohésion effective. L'ange de friction effectif n'est pas affecté de manière significative.