| dc.description.abstract | Stabilization of expansive soils with various calcium–based stabilizers (lime and cement) directly or in combinations with other solid waste materials such as fly ash and ground granulated blast furnace slag (GGBS) etc. is common approach by many foundation engineers to improve the properties, and conquer the distress caused by undesirable swell–shrink in the soil. Several researches have also been dedicated to understanding the complex ionic reactions and their products, and the mechanisms by which they affect the behaviour of expansive soils. Also, protocol for the lime stabilization of soil is established for the determination of optimum lime content (OLC) based essentially on the compressive strength test. The mechanism of lime treatment works mainly through cementation of flocculated matrix caused by the reduction in repulsion between soil particles with pozzolanic reaction compounds. However, no detailed studies have been carried out to establish the relation between change in fabric and its influence on the properties of expansive soil. It is also not clear whether the optimum lime content will be the same to improve different properties viz., strength and volume change. Hence, the research is directed to address these issues by performing elaborate experimental investigations on geotechnical properties and understanding the mechanism in improvement through fundamental physico–chemical and micro–analytical studies.
There are several cases documented in literatures where recent heaving and premature failures of structures constructed on lime and cement–treated soils containing sulfates exhibits, leading to question the validity of calcium-based stabilization. The failures in sulfate bearing soils are attributed to the formation and growth of ettringite/thaumasite minerals in certain environmental regime. It is Stabilization of expansive soils with various calcium–based stabilizers (lime and cement) directly or in combinations with other solid waste materials such as fly ash and ground granulated blast furnace slag (GGBS) etc. is common approach by many foundation engineers to improve the properties, and conquer the distress caused by undesirable swell–shrink in the soil. Several researches have also been dedicated to understand the complex ionic reactions and their products, and the mechanisms by which they affect the behaviour of expansive soils. Also, protocol for the lime stabilization of soil is established for the determination of optimum lime content (OLC) based essentially on the compressive strength test. The mechanism of lime treatment works mainly through cementation of flocculated matrix caused by the reduction in repulsion between soil particles with pozzolanic reaction compounds. However, no detailed studies have been carried out to establish the relation between change in fabric and its influence on the properties of expansive soil. It is also not clear whether the optimum lime content will be the same to improve different properties viz., strength and volume change. Hence, the research is directed to address these issues by performing elaborate experimental investigations on geotechnical properties and understanding the mechanism in improvement through fundamental physico–chemical and micro–analytical studies.
There are several cases documented in literatures where recent heaving and premature failures of structures constructed on lime and cement–treated soils containing sulfates exhibits, leading to question the validity of calcium-based stabilization. The failures in sulfate bearing soils are attributed to the formation and growth of ettringite/thaumasite minerals in certain environmental regime. It is reported that this swell is either by crystal growth or, expansion by hydration of the new minerals formed. Research findings contradict the swell mechanism caused by ettringite and it is still a matter of active current research. Further, the mechanism related to strength behaviour of lime treated sulfate containing soil is not well understood. Among several factors influencing ettringite formation, sources and form of sulfate and availability of water play a key role to induce the expansion in lime treated soil which is often termed as “Sulfate Induced Heave” and soil as “Manmade Expansive Soil”. Gypsum is the main source of sulfate in the soil and soil containing gypsum is termed as gypseous soil. Gypsum is an unpredictable material due to its property of changing the chemical structure under certain temperature–pressure and situations where water exists, and hence gypseous soils are not preferred as construction material. Therefore, prior to investigation of sulfate induced heave in lime treated soil, the role of gypsum in the geotechnical behaviour of soil needs to be investigated to make clear the inconsistencies and contradictions in the research findings of different investigations. Hence, the study has been taken up to investigate the impact of varying gypsum content on behaviour of lime treated expansive soil after curing for different period. The mechanism of changes in strength and volume change behaviour of lime treated soil in the presence of gypsum has been elucidated through detailed micro–mechanistic analytical study.
Several remedial measures are adopted to control the sulfate induced heave in lime treated soil. Fly ash is often used to suppress this undesirable heave. Utilization of fly ash supplies additional pozzolans (silica and aluminium) with collection of adequate divalent and trivalent cations (Ca2+, Al3+, Fe3+, etc.). However, the effect of additional aluminium supplied by the fly ash on ionic reactions, particularly with ettringite formation in lime treated gypseous soil is not well understood.
It is interesting to know that gypsum is frequently used as an accelerating agent to improve properties of fly ash with lime. Hence, an attempt has been made to understand the role of fly ash on the properties of expansive soil treated with varying lime content and the same combination by using diminutive amount of gypsum with a view to find a solution to overcome the adverse effect of sulfate, particularly in the form of gypsum. Mechanism of the strength and volume change behaviour of soil treated with varying lime content in the presence of diminutive gypsum content are investigated and explained.
Though, fly ash has been recommended to control the sulfate induced heave in lime treated soil, no particular attention is given to quantify the amount of fly ash to suppress the heave. Also, the effect of intrusion of additional ions (silica and alumina), which are known to affect mineralogy and microstructure, altering the particle size by fly ash to soil is not understood. Hence, work is extended to compare and explore the effect of varying fly ash content on the behaviour of soil, lime treated soil and lime treated gypseous soil and deduce the mechanism through physico–chemical and micro–analyses studies. | en_US |
