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''Soil stabilization'' a general term for any physical, chemical, mechanical, biological, or combined method of changing a natural
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
to meet an engineering purpose. Improvements include increasing the weight bearing capabilities, tensile strength, and overall performance of in-situ
subsoil Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus, and it ...
s, sands, and waste materials in order to strengthen road pavements. Some of the renewable technologies are: enzymes, surfactants,
biopolymer Biopolymers are natural polymers produced by the cells of living organisms. Like other polymers, biopolymers consist of monomeric units that are covalently bonded in chains to form larger molecules. There are three main classes of biopolymers, cl ...
s, synthetic polymers,
co-polymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
based products,
cross-link In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
ing styrene acrylic polymers, tree resins, ionic stabilizers, fiber reinforcement,
calcium chloride Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide. Ca ...
,
calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...
, sodium chloride,
magnesium chloride Magnesium chloride is the family of inorganic compounds with the formula , where x can range from 0 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in natu ...
and more. Some of these new stabilizing techniques create hydrophobic surfaces and mass that prevent road failure from water penetration or heavy frosts by inhibiting the ingress of water into the treated layer. However, recent technology has increased the number of traditional additives used for soil stabilization purposes. Such non-traditional stabilizers include: Polymer based products (e.g. cross-linking water-based styrene acrylic polymers that significantly improves the load-bearing capacity and tensile strength of treated soils), Copolymer Based Products, fiber reinforcement, calcium chloride, and Sodium Chloride. Soil can also be stabilized mechanically with stabilization
geosynthetics Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve civil engineering problems. This includes eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosynt ...
, for example, geogrids or geocells, a 3D mechanical soil stabilization technique. Stabilization is achieved via confinement of particle movement to improve the strength of the entire layer. Confinement in geogrids is by means of interlock between the aggregate and grid (and tensioned membrane), and in geocells, by cell wall confinement (hoop) stress on the aggregate. Traditionally and widely accepted types of soil stabilization techniques use products such as bitumen
emulsion An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although ...
s which can be used as a binding agents for producing a road base. However, bitumen is not environmentally friendly product and becomes brittle when it dries out.
Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th ce ...
has been used as an alternative to soil stabilization. However, this can often be expensive component and is not a very good
Environmentally friendly Environment friendly processes, or environmental-friendly processes (also referred to as eco-friendly, nature-friendly, and green), are sustainability and marketing terms referring to goods and services, laws, guidelines and policies that clai ...
alternative. Cement
fly ash Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired ...
, lime fly ash (separately, or with cement or lime), bitumen, tar, cement kiln dust (CKD), tree resin and ionic stabilizers are all commonly used stabilizing agents. Other stabilization techniques include using on-site materials including sub-soils, sands, mining waste, natural stone industry waste and crushed
construction waste Construction waste or debris is any kind of debris from the construction process. Different government agencies have clear definitions. For example, the United States Environmental Protection Agency EPA defines construction and demolition mater ...
to provide stable, dust free local roads for complete dust control and soil stabilization. Many of the environmentally friendly alternatives have essentially the same formula as soap powders, merely lubricating and realigning the soil with no effective binding property. Many of the new approaches rely on large amounts of clay with its inherent binding properties. Bitumen, tar emulsions, asphalt, cement, lime can be used as a binding agents for producing a road base. The National Society of Professional Engineers (NSPE) has explored newer types of soil stabilization technology, looking for effective and non-harmful alternatives. One of the alternatives utilizes new soil stabilization technology, a process based on cross-linking
styrene Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...
acrylic Acrylic may refer to: Chemicals and materials * Acrylic acid, the simplest acrylic compound * Acrylate polymer, a group of polymers (plastics) noted for transparency and elasticity * Acrylic resin, a group of related thermoplastic or thermosett ...
polymer. Another alternative uses long crystals to create a closed cell formation that is impermeable to water and is frost, acid, and salt resistant. Utilizing new soil stabilization technology, a process of cross-linking within the polymeric formulation can replace traditional road/house construction methods in an
environmentally friendly Environment friendly processes, or environmental-friendly processes (also referred to as eco-friendly, nature-friendly, and green), are sustainability and marketing terms referring to goods and services, laws, guidelines and policies that clai ...
and effective way. There is another soil stabilization method called the Deep Mixing method that is non-destructive and effective at improving load bearing capacity of weak or loose soil strata. This method uses a small, penny-sized injection probe and minimizes debris. This method is ideal for re-compaction and consolidation of weak soil strata, increasing and improving load bearing capacity under structures and the remediation of shallow and deep sinkhole problems. This is particular efficient when there is a need to support deficient public and private infrastructure.


Magnesium chloride

Water absorbing magnesium chloride (deliquescent) attributes include # it starts to absorb water from the air at 32%
relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depen ...
, almost independent of temperature, # treated roads can be regraded and re-compacted with less concern for losing moisture and density. However, limitations include # a minimum humidity level is required to absorb moisture from the air, # it is more suitable in drier climates, # in concentrated solutions it is very
corrosive A corrosive substance is one that will damage or destroy other substances with which it comes into contact by means of a chemical reaction. Etymology The word ''corrosive'' is derived from the Latin verb ''corrodere'', which means ''to gnaw'', ...
, # it attracts moisture thereby prolonging the active period for corrosion, #
rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water fo ...
water tends to leach out highly soluble chlorides, # if there is a high fines content in treated material then the surface may become slippery when wet, # when less than 20% solution it has performance effectiveness similar to water.Dust Palliative Selection and Application Guide
/ref> The use of magnesium chloride on roads remains controversial. Advocates claim (1) Cleaner air, which leads to better health as
fugitive dust Fugitive dust is an environmental air quality term for very small particles suspended in the air, primarily mineral dust that is sourced from the soil of Earth's pedosphere. A significant volume of fugitive dust that is visible from a distance i ...
can cause health problems in the young, elderly and people with respiratory conditions; and (2) Greater safety through improved road conditions, including increased driver visibility and decreased risks caused by loose gravel, soft spots, road roughness and flying rocks. It reduces foreign sediment in nearby surface waters (dust that settles in creeks and streams), helps prevent stunted crop growth caused by clogged pores in plants, and keeps vehicles and property clean. Other studies show the use of salts for road deicing or dust suppressing can contribute substantial amounts of chloride ions to runoff from surface of roads treated with the compounds. The salts MgCl2 (and CaCl2) are very soluble in water and will dissociate. The salts, when used on road surfaces, will dissolve during wet weather and be transported into the groundwater through infiltration and/or runoff into surface water bodies. Groundwater infiltration can be a problem and the chloride ion in drinking water is considered a problem when concentrations exceed 250 mg/L. It is therefore regulated by the U.S. EPA’s drinking water standards. The chloride concentration in the groundwater or surface water depends on several factors including: # application rate, # composition and type of soil, # type, intensity, and amount of precipitation, # the drainage of the road system. In addition, the chloride concentration in the surface water also depends on the size or flow rate of the water body and the resulting dilution achieved. In chloride concentration studies carried out in Wisconsin during a winter deicing period, runoff from roadside drainages were analyzed. All studies indicated that the chloride concentration increased as a result of deicing activities but the levels were still below the MCL of 250 mg/L set by the EPA. Nevertheless, the long-term effect of this exposure is not known. Although the U.S. EPA has set the maximum chloride concentration in water for domestic use at 250 mg/L animals can tolerate higher levels. At excessively high levels, chloride is said to affect the health of animals. As stated by the National Technical Advisory Committee to the Secretary of Interior (1968), “Salinity may have a two-fold effect on wildlife; a direct one affecting the body processes of the species involved and an indirect one altering the environment making living species perpetuation difficult or impossible.” One major problem associated with the use of deicing salt as far as wildlife is concerned is that wildlife are known to have “salt craving” and therefore are attracted to salted highways which can be a traffic hazard to both the animals and motorists. Regarding the accumulation of chloride salts in roadside soils including the adverse effects on roadside plants and vegetation physiology and morphology, documentation dates back to World War II era times and consistently continues forward to present times. As far as plants and vegetation are concerned, the accumulation of salts in the soil adversely affects their physiology and morphology by: increasing the osmotic pressure of the soil solution, by altering the plant’s mineral nutrition, and by accumulating specific ions to toxic concentrations in the plants. Regarding the intentional application of excessive salts: see
Salting the Earth Salting the earth, or sowing with salt, is the ritual of spreading salt on the site of cities razed by conquerers. It originated as a curse on re-inhabitation in the ancient Near East and became a well-established folkloric motif in the Middle ...
. Road departments and private industry may apply liquid or powdered magnesium chloride to control dust and
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
on unimproved (dirt or gravel) roads and dusty job sites such as quarries because it is relatively inexpensive to purchase and apply. Its
hygroscopy Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substanc ...
makes it absorb moisture from the air, limiting the number of smaller particles (silts and clays) that become airborne. The most significant benefit of applying dust control products is the reduction in gravel road maintenance costs. However, recent research and updates indicate biological toxicity in the environment in plants as an ongoing problem. Since 2001, truckers have complained about "Killer Chemicals" on roads and now some states are backing away from using salt products. Also a small percentage of owners of indoor arenas (e.g. for horse riding) may apply magnesium chloride to sand or other "footing" materials to control dust. Although magnesium chloride use in an equestrian (horse) arena environment is generally referred to as a dust suppressant it is technically more accurate to consider it as a water augmentation activity since its performance is based on absorbing moisture from the air and from whatever else comes in contact with it. To control or mitigate dust, chlorides need moisture to work effectively so it works better in humid than arid climates. As the humidity increases the chloride draw moisture out of the air to keep the surface damp and as humidity decreases it diffuses and releases moisture. These naturally occurring equilibrium changes also allow chlorides to also be used as a dehydrating agent including the drying out of and curing and preservation of hides. As a road stabilizer, magnesium chloride binds
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifi ...
and
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay parti ...
particles to keep them from leaving the road. The water-absorbing (hygroscopic) characteristics of magnesium chloride prevent the road from drying out, which keeps gravel on the ground. The road remains continually "wet" as if a water truck had just sprayed the road.{{cite web , url=http://www.soilworks.com/docs/soilworks-army-dust-control-field-handbook-2006.pdf , title=Archived copy , access-date=2013-02-28 , url-status=dead , archive-url=https://web.archive.org/web/20120619104502/http://www.soilworks.com/docs/soilworks-army-dust-control-field-handbook-2006.pdf , archive-date=2012-06-19


See also

*
Cellular confinement Cellular confinement systems (CCS)—also known as geocells—are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth ...
*
Erosion control Erosion control is the practice of preventing or controlling wind or water erosion in agriculture, land development, coastal areas, river banks and construction. Effective erosion controls handle surface runoff and are important techniques in ...
* Post-fire seeding#Soil stabilization *
Land improvement Land development is the alteration of landscape in any number of ways such as: * Changing landforms from a natural or semi-natural state for a purpose such as agriculture or housing * Subdividing real estate into lots, typically for the purpose ...
*
Geopolymer Geopolymers are inorganic, typically ceramic, alumino-silicate forming long-range, covalently bonded, non-crystalline (amorphous) networks. Obsidian (volcanic glass) fragments are a component of some geopolymer blends. Commercially produced geopo ...
*
Geotechnical engineering Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It als ...
*
Mechanically stabilized earth Mechanically stabilized earth (MSE or reinforced soil) is soil constructed with artificial reinforcing. It can be used for retaining walls, bridge abutments, seawalls, and dikes. Although the basic principles of MSE have been used throughout his ...
*
Polymer soil stabilization Polymer soil stabilization refers to the addition of polymers to improve the physical properties of soils, most often for geotechnical engineering, construction, or agricultural projects. Even at very small concentrations within soils, various pol ...


References

Soil science