Fine-grained natural soil material with clay minerals is known as clay. Due to the molecular water film that surrounds the clay particles, clays become plastic when wet but become hard, brittle, and non-plastic when dried. The majority of clay minerals are white or light in color, however, natural clays come in a variety of hues due to impurities, like a reddish or brownish hue brought on by trace levels of iron oxide.
Since clay minerals are created as a result of the weathering of primary rock-forming minerals, they are also known as secondary silicates. The negative electrical load on the crystal edges and the positive electrical load on the crystal face distinguish clay minerals from sand, gravel, and silt. Clay minerals are found in microscopic particle sizes (0.002 mm), are very fine-grained, and are flake shaped. There are two distinct basic structures in clay minerals. First, silicon ions link with oxygen atoms on all four sides to create silica oxygen (tetrahedron). Second, an octagon emerges when oxygen and hydroxyl ions coordinate on eight of the sides with aluminum and magnesium ions.
Problem with Clay in Construction
Studies on soil behavior that don’t take into account clay soils’ physicochemical and microstructural characteristics may be losing out on crucial details about the soil’s physical and mechanical capabilities. This is because the physicochemical and microstructural characteristics of the soil can account for the majority of physical and mechanical behaviors.
Clay is often undesirable because it poses serious technical challenges. When combined with water, clay produces mud, in contrast to other minerals of the same size. Clay is malleable, can be formed into a dough, and when heated, transforms into a solid with extremely high strength levels. When clay is wet, it typically expands in volume; however, when it dries, it contracts in volume, leading to numerous fissures.
Every country has clayey soil. Due to its tendency to respond to variations in moisture content, clayey soil can damage the structures present there. The superstructure of a building can sustain damage from the foundation failure caused by the uplift pressure induced by changes in the volume of clay. On the other hand, clay also contracts when it dries out, which contributes to the foundation settlement. The foundations are repeatedly stressed by the clay’s expansion and contraction. Clay’s volume change has the potential to seriously damage the concrete floor slabs and foundation, as well as the floors above them. Therefore, before starting any building work, it is crucial to understand the characteristic of clayey soil.
On the other hand, clay is a very useful construction material.
Uses of Clay in the Construction Industry
Along with other building materials like stone and wood, clay is a naturally occurring, fine-grained rock or soil that has been used for thousands of years. It is made up of one or more clay minerals, together with traces of quartz, metal oxides, and occasionally organic material.
Some of the important applications of clay are
Brick
A brick is a sort of block used to construct masonry structures such as walls, pavements, and other features. The term “brick” technically refers to a block made of dried clay, but it is now frequently used colloquially to refer to various construction blocks that have undergone chemical curing. Bricks can be attached to one another by mortar, adhesives, or by interlocking. Bricks are made in large quantities and come in a wide range of classes, types, materials, and sizes that change depending on the place and the period.
Clay Cores in Dams
The impermeable clay layer in a dam, lake or other structure is referred to as a “clay core” in construction. This layer is intended to prevent water from penetrating and is frequently covered by a semi-permeable shell. Clay is a great material for this purpose since retention dams and ponds need impermeable cores so that water does not just flow out through the porous fill material. Clay can create a watertight seal when properly applied and compacted, despite the fact that it can absorb a tiny quantity of water.
Backfilling
In construction, clay can be used as a backfilling material. Particularly, clay can be used to backfill the outside. If you fill the interior space and there is a water table, there might be some settlement. Therefore, it will be much more appropriate to employ clay for backfilling operations in exterior areas where settlement is not a concern.
There is another application of clay that is a material made from clay.
Tiles
The term “structural clay tile” refers to a group of burned-clay building materials used for both structural and non-structural roofing, wall, and flooring construction, particularly in fireproofing applications. The substance is an extruded clay shape with significant depth that enables it to be put in the same way as other clay or concrete brickwork. It is also known as building tile, structural terra cotta, hollow tile, and clay block. The substance is frequently utilized in partition walls, floor arches, and fireproofing.
Pottery
Clay for pottery can be easily made at home. There are other ways to treat clay, but the simplest and most well-liked method is referred described as “the wet method.”
The wet technique of making pottery clay from dirt or soil involves mixing soil and water in a large container and letting the mixture lie for a while to allow gravity to push larger pebbles and sand to the bottom of the container, leaving just water combined with clay on top. The wet, smooth clay that is left after this water has been filtered using a fine cloth can either be utilized right away or kept for later.
Properties of Clay
Knowing the type of clay is crucial for geotechnical engineering since it has a direct impact on the clay’s key characteristics, including Atterberg’s limits, hydraulic conductivity, swelling shrinkage, settlement (compression), and shear resistance. The link between ground particles and water as well as the status of the soil in reaction to changing water contents are both described by Atterberg’s limits, also referred to as consistency limits.
Hydraulic Conductivity of Clay
It is important to distinguish between the hydraulic conductivity and the flow medium’s intrinsic permeability, also known as permeability.
Natural field soil’s hydraulic conductivity is influenced by factors like cracks, worm holes, root holes, and the stability of the soil particles. With the exception of disturbed soil materials, texture, or the percentage of the main sand, silt, and clay particles, typically has little impact on hydraulic conductivity. The hydraulic conductivity of natural soils ranges from 0.05 m/day for clay to roughly 30 m/day for a silty clay loam. Gravel has a hydraulic conductivity of roughly 600 m/day, while silt and clay have a hydraulic conductivity of only 0.02 m/day.
Swelling-Shrinkage behavior of Clay
In comparison to the first cycle, the swelling or shrinkage potential may dramatically decrease or grow after several wetting-drying cycles. As a result, assessing expansive soils’ in-situ volume change behavior without taking into account cyclic seasonal oscillations produces unreliable results.
After multiple wetting-drying cycles, soils achieve an equilibrium state. The wetting-drying path becomes completely reversible once the equilibrium state is attained, whether it is measured in terms of volumetric strain vs water content or terms of volumetric strain versus suction.
As the wetting-drying cycles continue, there is an accumulation of irreversible swelling or shrinkage before the equilibrium condition is attained. The soil qualities, initial placement circumstances (initial structure), surcharge or confining pressure, swelling-shrinkage pattern, etc. determine whether the accumulated deformation is expansion or shrinkage. Conversely, the magnitude of cumulative expansion reduces with an increase in an applied surcharge or confining pressure. Accumulated shrinkage increases with applied surcharge or confining pressure.
Shear strength behavior of clay
A measured response that assumes no volume change is the shear strength of fine-grained soil under un-drained loading. The un-drained shearing strength and water content for fine-grained soils can be demonstrated as a nonlinear relationship where the classification of soil is determined by two parameters. These variables have to do with the mineral makeup of the soil. In general, more significant characteristics like plasticity, water content, and mineral composition of the soil influence the mechanical properties of cohesive soil. Shear strength may be influenced by variables like the plasticity index, the over-consolidation ratio (OCR) of the mineral composition, and soils loaded under drained conditions.
