The soil particales finer than two( 2)micron size (0.002mm) zero point zero zero two) are reffered to as clay particals. The word 'Clay's indicates a materials composed of small mineral particals, which exhibit the property of plasticity in association with certain quantities of water. These small crystalline mineral partical are essentially hydrous aluminum silicates and are commonly known as clay minerals. Clay material can also contain organic matter and water soluble salts.
There are three types of important clay minerals are:-
1) Kaloinite, for example China clay
2) Montmorillonite, for example Black cotton soil
3) Illite for example, Shale
The basic structural unit of these clay minerals consist of an Alumina sheet combined with silica sheet. The thickness of these structural units is measured in termes of Angstorm ( 1 Angstorm = 10–⅞) .
In case of kaolinite or china clay the structural unit are joined together by strong hydrogen bond together where in case of Illite or shale, by non exchange potassium ions. But in case of montmorillonite two sucessive structural units are only linked between oxygen ions of two silica sheets . This link is weak and negatively charged silica partical attract water which enter in space and results in expansion of the minerals. It is the reason that the soil containing large amount of montmorillonit or black cotton soil minerals shows high shrinkage and swelling characteristics.
There are also particales, which are finer than the clay particales. These are termed as colloids or colloidal particales. The size of such partical is less than 1 micron (0.001mm) . More the presence of colloidal matter into soil, more is the plasticity of soil. The term colloid is derived from Greek word kolla and oidos meaning glue like material.
The properties of clay soil greatly depend upon their minerological composition of clay mineral . These properties include cohesion, plasticity characteristics, compressibility, permeability, shear strength etc.
The properties of clay soil different from one another on the basis of arrangements of atoms present in crystals of these minerals. This part of study is known as clay minerals and is beyond the scope of this book. But from the above discussion, it has become clear the particales size, shape and clay minerals play an important role on controlling the engineering behavior of cohesionless and cohesive soils.
Clay minerals are composed essentially of silica, alumina or magnesia or both, and water, but iron substitutes for aluminum and magnesium in varying degrees, and appreciable quantities of potassium, sodium, and calcium are frequently present as well. Some clay minerals may be expressed using ideal chemical formulas as the following: 2SiO2·Al2O3·2H2O (kaolinite), 4SiO2·Al2O3·H2O , 4SiO2·3MgO·H2O (talc).
There are three types of important clay minerals are:-
1) Kaloinite, for example China clay
2) Montmorillonite, for example Black cotton soil
3) Illite for example, Shale
The basic structural unit of these clay minerals consist of an Alumina sheet combined with silica sheet. The thickness of these structural units is measured in termes of Angstorm ( 1 Angstorm = 10–⅞) .
In case of kaolinite or china clay the structural unit are joined together by strong hydrogen bond together where in case of Illite or shale, by non exchange potassium ions. But in case of montmorillonite two sucessive structural units are only linked between oxygen ions of two silica sheets . This link is weak and negatively charged silica partical attract water which enter in space and results in expansion of the minerals. It is the reason that the soil containing large amount of montmorillonit or black cotton soil minerals shows high shrinkage and swelling characteristics.
There are also particales, which are finer than the clay particales. These are termed as colloids or colloidal particales. The size of such partical is less than 1 micron (0.001mm) . More the presence of colloidal matter into soil, more is the plasticity of soil. The term colloid is derived from Greek word kolla and oidos meaning glue like material.
The properties of clay soil greatly depend upon their minerological composition of clay mineral . These properties include cohesion, plasticity characteristics, compressibility, permeability, shear strength etc.
The properties of clay soil different from one another on the basis of arrangements of atoms present in crystals of these minerals. This part of study is known as clay minerals and is beyond the scope of this book. But from the above discussion, it has become clear the particales size, shape and clay minerals play an important role on controlling the engineering behavior of cohesionless and cohesive soils.
Clay minerals are composed essentially of silica, alumina or magnesia or both, and water, but iron substitutes for aluminum and magnesium in varying degrees, and appreciable quantities of potassium, sodium, and calcium are frequently present as well. Some clay minerals may be expressed using ideal chemical formulas as the following: 2SiO2·Al2O3·2H2O (kaolinite), 4SiO2·Al2O3·H2O , 4SiO2·3MgO·H2O (talc).
3SiO2·Al2O3·5FeO·4H2O .
The SiO2 ratio in a formula is the key factor to determining the clay mineral types. These type of minerals can be classified on the basis of variations of atomic structure and chemical composition into nine(9) groups:
The SiO2 ratio in a formula is the key factor to determining the clay mineral types. These type of minerals can be classified on the basis of variations of atomic structure and chemical composition into nine(9) groups:
(1) kaolin-serpentine (kaolinite, halloysite, lizardite, chrysotile).
(2) pyrophyllite-talc.
(3) mica (illite, glauconite, celadonite) .
(4) vermiculite.
(5) smectite (montmorillonite, nontronite, saponite).
(6) chlorite (sudoite, clinochlore, chamosite).
(7) sepiolite-palygorskite.
(8) interstratified clay minerals.
(9) allophane-imogolite.
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