Uses of bentonite in different fields

Much of bentonite's usefulness in the drilling and geotechnical engineering industry comes from its unique rheological properties. Relatively small quantities of bentonite suspended in water form a viscous, shear thinning material. Most often, bentonite suspensions are also thixotropic. At high enough concentrations (~60 grams of bentonite per liter of suspension), bentonite suspensions begin to take on the characteristics of a gel (a fluid with a minimum yield strength required to make it move). In addition to its rheological and absorbent properties, bentonite has excellent plasticity and lubricity, high dry bonding strength, high shear and compressive strength, good impermeability and low compressibility.  For these reason it is used in the following field of Geo-technical engineering. 

a. In drilling mud

Bentonite is used in horizontal as will as in vertical drilling as a drilling mud.

There are a number of functions, which a drilling mud must perform. This is true regardless of the hole section being drilled, although the emphasis changes in different hole sections, and with different lithologies.

The ten primary functions of a drilling mud are:

1. Control formation pressure

2. Prevent the hole from caving in

3. Seal off permeable formations

4. Carry cuttings from the hole

5. Suspend cuttings when circulation stops

6. Allow for removal of cuttings at surface

7. Cool and lubricate the bit and drill-string

8. Minimize damage to producing formations

9. Allow for easy formation evaluation

10. Minimize corrosion of the drill string.

b.  In horizontal direction drilling

Bentonite is a common component of drilling mud used in horizental direction drilling. Drilling fluid is usually a mixture of freshwater and bentonite. Bentonite is naturally occurring clay that is extremely hydrophilic (i. e., has high swelling characteristics). Certain polymers may also be used that enhance the drilling fluid benefits. HDD is a steer able trench less method of installing underground pipes, conduits and cables in a shallow arc along a prescribed bore path by using a surface launched drilling rig, with minimal impact on the surrounding area. Horizontal directional drilling is done with the help of a drilling fluid, which is a mixture of water and usually, bentonite or polymer. The fluid in continuously pumped to the cutting head or drill bit to facilitate the removal of cuttings, stabilize the bore hole, cool the cutting head, and lubricate the passage of the product pipe. It is the spent fluid, which becomes a liquid waste and must be disposed of in an environmentally safe fashion.

                                               HDD process with the help of bentonite slurry  

Trench less Technologies is economically more profitable in comparison with the traditional method. The explanation of it is the economy of means that were spent on the development of trenches, restoration of pavement, etc. while using the open method of pipe laying. In addition, Trench less Technologies shorten the time of performance of the work and reduce the number of staff, considerably raise the level of works safety (absence of trenches and machinery on the line of laying), and also they don’t harm the environment.

c.  In boring for piles in loose soil

Large diameter bored piles are non-displacement piles used where very large vertical loads or bending moments must be resisted by a single pile.  Bored pile construction techniques depend on ground stability and the amount of free ground water. The shaft is excavated using a rotary drilling rig. Temporary casing, or the use of drilling fluids such as water or bentonite slurry may support the sides of the excavation.

1.Setting up on the pile position, pre-drilling, placing temporary casing.

2. Introducing drilling fluid.

3. Excavation under drilling fluid to the required depth (strata).

4. Cleaning of pile bases, placing reinforcing cage, concreting by tremie. 

5. Concreting to cut-off level plus overpour.

6. Extraction of temporary casing, pile completed. 

                                              Pilling process with the help of bentonite slurry

d.  In Slurry-trenches 

This type of wall, known in North America as "slurry trench", is a cutoff wall made of a mixture of bentonite and aggregates. A fairly wide trench (commonly 5 ft) is excavated under bentonite slurry. Excavated materials (aggregates) are placed in the trench in such a way that the backfilled aggregates form a gentle slope in the opposite direction from ongoing excavation. To ensure an effective cut-off effect, slurry trenches must be rather wide so as to compensate the possible defects due to the simple dumping procedure. 

                                         Excavation process in the presence of bentonite 

Similarly due to the density of bentonite slurry being higher that that of water, bentonite slurry protects a trench from water inflow from outside sources. “Water-soil-bentonite” mixtures inside the trench form a “clay-lock”. Moreover, the walls of the trench dry out over time, and develop a bentonite clay crust, which improves the stability of the trench.

In slurry walls               
Slurry walls are non-structural barriers used to build reinforced-concrete walls. They’re most commonly used on sites where the earth is soft and likely to turn 
water table or those close to open water such as a lake or river are both good candidates for a slurry wall. This technique is common in tunnel-building projects, under and around dams, and for foundations in wet conditions. The slurry wall isn’t really a into soupy mud, which can disrupt the building process. Sites with a high wall at all. It’s actually a trench, usually dug to between one and a half and five feet deep, using a hydraulic excavator. This trench forms a barrier between the concrete work and the ground water. Some special slurry walls may be dug up to 100 feet deep using special cranes and other equipment. Slurry wall trenches should be situated in bedrock, clay, or other low permeability strata, to reduce the chances of leakage.  Once the trench has been dug to the correct depth, workers fill it with bentonite clay and water, which forms a thick barrier on the walls of the trench. Then the trench is refilled with a mixture of dug out soil, dry bentonite clay, and wet bentonite slurry. This material should be mixed to about the same consistency as wet concrete, and should push the previous slurry back out of the trench. This produces the final soil bentonite slurry trench cut off wall.  Instead of using soil bentonite slurry trench cut off wall, it’s also possible to fill the trench with concrete after the bentonite slurry is pumped away for recycling. This produces a solid concrete object underground, usually filled with metal tieback anchors that can be used to support the final concrete wall when the project is finished. This technique was used in the excavation of the World Trade Center site in New York City.

Small-scale slurry

Originally developed in Europe; slurry walls are frequently used for small-scale projects in the United States. This useful technique allows more efficient concrete wall construction in adverse environments, and prevents mud and water from swamping the project.

In seepage control

Bentonite is used in Dams, Water tanks, ponds, swimming pools, canal, culverts and Basement etc for seepage control.

                                                         
History in construction

In the late 1920's bentonite clay was used to seal dams and contain water as a pond liner. One of its earliest noteworthy uses came in the 1930's when it was used, during construction of the Grand Coulee Dam, to seal off water that was preventing construction of a cofferdam. Upon installation, the bentonite clay swelled and filled open water-bearing seams. Water flow was reduced from 30,000 gallons per minute to 250, and work on the Dam was then completed. Bentonite clay soon gained wide acceptance as a liner for lagoons and lake bottoms. It was widely used as an earth stabilizer, as "drilling mud" for removal of tailings during oil well drilling, and as a lubricant for driving pilings and caissons. In the mid-1960's bentonite clay was introduced as a waterproofing membrane for below grade building structures. Its successful performance and low cost led to large waterproofing applications including subways, tunnels, and building foundations etc.

Systems available 

There are several bentonite clay-waterproofing methods presently in use. Over the past 20 years, bentonite has been mixed with other chemicals and containerized in many forms to achieve an economical application. There are basically seven types of systems that use bentonite in some form for waterproofing. They are:

1.    Raw bentonite mixed with soil with or without sand;

2.     Spray bentonite with an asphalt binder in dry format;

3.     Spray polymer enhanced bentonite with binder in dry format;

4.     Bentonite placed in flutes of cardboard panels; 

5.    Bentonite adhered to geotextile in the form of a mat;

6.     Trowel or spray grade bentonite in liquid/gel format; and

7.     Bentonite adhered to high-density polyethylene in sheet and panel form. (Bentonite/HDPE)

a. Raw Bentonite Mixed With or Without Sand

In either powder or granulated form, raw bentonite is inexpensive when compared to other bentonite waterproofing materials. Because of it raw form, it is only usable for horizontal applications such as pond liners. When used, care must be taken to avoid application during high winds or rain. Avoid foot and traffic on the material after application since displacement of bentonite is highly probable. A six to ten polyethylene sheet should be placed over raw bentonite after application. It is very important to eliminate all voids in subsequent layers over the bentonite application. If large voids exist above the bentonite, these areas become avenues for the material to swell and gel into, thus losing its pressurization and seal. It is extremely important to realize that bentonite must be pressurized at all times by a pressure of 30 to 60psf, or more, to effectively seal it. It is best to mix powder and granulated bentonites together when used in the raw form. Granular or powdered bentonite clay, mixed with clean coarse silica-sand, is also used for waterproofing horizontal

surfaces or substrates. Generally a 200 mesh powdered bentonite is mixed in a ratio of 5 to 18 percent bentonite to sand. The sand should approximate 10 to 15 percent moisture content before bentonite is added. Application thickness is usually 2 to 4-inches, with 2-inches being a minimum. The bentonite clay/sand layer should be compacted and covered with a 6-mil polyethylene cover sheet. The advantage of a bentonite clay / sand mixture is that as the bentonite swells and fills the void spaces between the Sand, it forms an effective seal without introducing external movements or pressures to overlying materials. A concern in this type of application is in not getting thorough and proper bentonite clay /sand mix, thus, having intermittent Porous sand pockets that could allow water migration. Another concern with this matrix, when the bentonite content is Low is that large void spaces in the sand matrix could allow for excessive free swelling of the bentonite. When a bentonite clay /sand mixture waterproofing material is installed beneath a concrete slab, quality control must be carefully controlled. The optimum quantity of bentonite will just fill the interstices in the sand when expanded. This percentage is usually about 10 to 13 percent depending upon the sand texture. If the bentonite is mixed with moist sand, some swelling takes place during application, and controlled compaction of the mixture will reduce the formation of porous sand layers. When raw bentonite is placed on or under a substrate, it typically has moisture content in excess of four to eight percent. If raw bentonite is placed on the jobsite substrate drier than two to three percent, uplift problems could occur. During the first one or two molecular layers of water absorption of bentonite, a pressure of over 140,000 psi can be generated. After those first few water layers are built up, water enters by osmosis and pressures generated are very small, perhaps ten psf (0.069 psi) or less. It is important to realize that the stress (pressure) created by swelling bentonite is insignificant when it is compared to the induced strain (movement), generated by expansion, if the confining material is not of proper weight. What this means is that as bentonite swells it conforms into the surrounding soil, rather than creating an added lateral or uplift pressure on the wall or retaining system. Placing very dry bentonite one-inch thick, or more, may require more than a 30 to 60 psf pressure gradient on the material to contain uplift pressures and movements. Other precautions, for the use of raw bentonite with or without sand on horizontal areas, are: avoid wetting the material before it is covered; provide a protective board over it before application of subsequent material layers; and avoid calcium carbonate, chlorides, and other reactive materials from contaminating the sand and neutralizing the sodium montmorillonite. A further consideration against the use of raw bentonite is that without a container, or an adhesive to hold it in place during construction, workmen installing cover sheets, protection board, insulation, or backfill tend to damage and displace it. Raw bentonite has been known to fall through small cracks and joints, while still in its dry state, when

no means is used to bind it together as a membrane. There have been many waterproofing applicators that have created severe problems for themselves by using raw bentonite on vertical walls. The most serious concern arises when water is mixed with bentonite to make it trowelable. This typically requires a nine to one mixture of water to bentonite to make it soft and plastic; it also damages the bentonite's resealing and long-term sealing characteristics. To form a positive seal on a wall it takes two to three-inches, or more. Raw bentonite applications should only be used for pond and lagoon liners, where bentonite clay soil thicknesses are approximately four to six inches thick, and two to four pounds of bentonite per square foot is used. In conclusion, this system is not recommended for residential or commercial waterproofing. It is not actively promoted by any manufacturer, and the description of the system was only included for information.

b. Spray Bentonite with an asphalt binder in dry format

This system is a two-component process in which dry granulated bentonite is blown through a two-inch airline and intermixed with an asphalt emulsion at the end of a spray gun. As the partially asphalt-coated bentonite hits the substrate, it adheres and forms a monolithic-seamless membrane. Thickness can be varied from 1/8 inch for damp proofing to 3/8 inch, or more, for extreme situations where severe hydrostatic conditions may exist. The standard membrane recommended by applicators has an average thickness of1/4 inch, with bentonite clay content of 11/4 to 11/2 pounds per square foot. Permeability tests have shown that this system will perform well at head pressures of 80- feet. The system is sprayed on horizontal substrates at a ratio of 80 to 90 percent bentonite with 20 to 10 percent asphalt emulsion; and a 50/50 mix is used on vertical surfaces. At grade line terminations, where bentonite interacts with the air, a protection material must be placed over the bentonite to insure its pressurization. This system has been used successfully for many years, but it has some drawbacks. Quality control remains essential for its effectiveness. Problems can occur when the asphalt emulsion content is too high and it completely coats the bentonite granules. Water tends to find its way through the asphalt, by passing the bentonite and thus not activating

it. In time the asphalt emulsifies, and exposes the bentonite, which then begins to develop its waterproofing qualities. Another difficulty with this system is that during cold weather the asphalt emulsion has to be heated in order to be properly sprayed. During extremely hot weather the asphalt emulsion tends to creep, which could lead to product fall off or spalling. Another concern with this spray system is the rebound of uncoated bentonite hitting the substrate and dropping to the ground. Many times the bentonite rebound can be left on the footing because it forms a good seal at the construction joint between walls and footings. On horizontal applications no rebound is generated.

This system appears to have the ability to withstand normal field abuse without a costly protective coating. If rainy weather is a concern, the applicator can spray a light asphalt coat over the system to offer some protection. This system is not widely used. It requires the use of specialized application equipment, and there is only one applicator available in the United States. A newer spray bentonite system replaces the asphalt binder with a latex emulsion.

  Many other Uses of Bentonite

1. soletanche bachy

Bentonite can be used in cement, adhesives, ceramic bodies, and cat          litter.

2. Bentonite is also used as a binding agent in the manufacture of taconite pellets as used in the steel making industry.

3. Fuller's earth, an ancient dry cleaning substance, is finely ground bentonite, typically used for purifying transformer oil.

4. Bentonite, in small percentages, is used as an ingredient in commercially designed clay bodies and ceramic glazes.

5. Bentonite clay is also used in pyrotechnics to make end plugs and rocket nozzles.

6. The ionic surface of bentonite has a useful property in making a sticky coating on sand grains. When a small proportion of finely ground bentonite clay is added to hard sand and wetted, the clay binds the sand particles into moldable aggregate known as green sand used for making molds in sand casting.

7. Some river deltas naturally deposit just such a blend of such clay silt and sand, creating a natural source of excellent molding sand that was critical to ancient metal working technology.

 8. Modern chemical processes to modify the ionic surface of bentonite greatly intensify this stickiness, resulting in remarkably dough-like yet strong casting sand mixes that stand up to molten metal temperatures. The same effluvial deposition of bentonite clay onto beaches accounts for the variety of plasticity of sand from place to place for building sand castles.

9. Beach sand consisting of only silica and shell grains does not mold well compared to grains coated with bentonite clay. This is why some beaches are much better for building sand castles than other.

10. The self-stickiness of bentonite allows high-pressure ramming or pressing of the clay in molds to produce hard, refractory shapes, such as model   rocket nozzles.

11. Bentonite also has the interesting property of adsorbing relatively large     amounts of protein molecules from aqueous solutions. It is therefore uniquely useful in the process of winemaking, where it is used to remove excessive amounts of protein from white wines.

12. Were it not for this use of bentonite, many or most white wines would precipitate undesirable flocculent clouds or hazes upon exposure to warmer temperatures, as these proteins denature.

13. It also has the incidental use of inducing more rapid clarification of both red and white wines.

14. Bentonite has been prescribed as a bulk laxative, and it is also used as a base for many dermatologic formulas.

15. Cleansing facial masks to absorb impurities

16. Purification and color reduction of fats, oils, and waxes Bentonite is also 17. Used as long lasting stabilizer for soil.

18. For waste water treatment.

19. Bathing minerals and toxin absorbent.

 20. Small amounts of bentonite are used in the absorption of oils and       greases, in paint, paper industry, cosmetics, insecticides, and in ceramic industries.

 21. Bentonite clay is also used as Healing clay.