Leach Tests on Lime-Treated Clays

Abstract

This paper describes the design, use, and results of a multiple leach-cell operation to test the changes in permeability and calcium removal of a lime-treated expansive clay under continuous water leaching. Seventy laboratory-prepared lime-treated clay specimens were subjected to continuous accelerated leaching for periods of 45 and 90 days with varying lime contents and compactive moisture contents. Permeability, leachate pH, and leachate cation changes were continuously recorded during the leach process. Results indicate that lime dramatically increased the soil's permeability, with maximum permeability occurring at the lime modification optimum (LMO). Leachate pH increased as the lime content of the soil increased but decreased linearly during the leach cycle. Calcium concentration in the leachate was lowest in specimens prepared at their LMO but increased as the lime content increased. There is strong evidence to suggest that calcium removal and permeability are in direct correlation to the complex ion interaction within the soil-lime mixture, and therefore the LMO is central in determining leaching effects on lime-treated soils.

Laboratory Measurement and Analysis of the Deteriorated Layer Permeability Coefficient of Soil-Cement Deteriorated in a Saline Environment

“…The ettringite was expandable, which plays a positive role in reducing the permeability of the cement soil. And this can be proved by previous studies [20,21,22]. However, as the curing age increased, a large amount of ettringite was produced in the soil-cements, which makes them loose and causes micro-cracks, as shown in Figure 11b.…”

Impact of initial state on the fabric and permeability of a lime-treated silt under long-term leaching

“…It can reasonably be concluded in this study that the process of formation of cementitious compounds is in competition with the dissolution process induced by the fluid circulation, leading to the stability of the permeability. The significant permeability decreases recorded by McCallister and Petry (1992) for three clayey soils during leaching over long-term periods (45 and 90 days) indicates that in their case the for- mation of cementitious compounds may have dominated the dissolution process induced by the fluid circulation. It should be mentioned that their samples were treated with lime and cured for 48 h at 49 8C before leaching.…”

“…However, other authors (El-Rawi and Awad 1981;McCallister and Petry 1992) evidenced that the moisture content could also have significant effects on the permeability of lime-treated soils. In fact, they found that the permeability of specimens compacted dry of optimum or at the optimum was higher than that of the untreated soil by about one order of magnitude, whereas the permeability of specimens compacted wet of optimum was of the same order of magnitude as that of the untreated soil.…”

“…Also, the authors mentioned that strength loss, as well as calcium leaching, seems to be minimized by increasing the curing time because of a better crystallization of the cementitious compounds. McCallister (1990) and McCallister and Petry (1992) studied the effect of leaching on lime-treated plastic clays compacted under different compaction moisture contents (dry of optimum, at the optimum, and wet of optimum). They also found that leaching leads to a decrease in soil strength of 15.1% to 86% depending on the soil nature and lime content, and that this strength decrease could be slowed down by adding large amounts of lime.…”

“…In fact, they found that the permeability of specimens compacted dry of optimum or at the optimum was higher than that of the untreated soil by about one order of magnitude, whereas the permeability of specimens compacted wet of optimum was of the same order of magnitude as that of the untreated soil. Other authors (Brandl 1981;McCallister and Petry 1992) showed that the permeability of lime-treated specimens is also related to the amount of lime added -the permeability of lime-treated soils increases with lime content until a certain value corresponding to the lime-modification optimum of the soil (LMO), which is the minimal amount of lime required to promote pozzolanic reactions in the long term (Hilt and Davidson 1960;Eades and Grim 1966). According to these authors, the permeability reaches a maximum at this specific lime content and begins to slowly decrease for higher lime contents due to the precipitation of cementitious compounds blocking the flow channels and reducing the water flow.…”