Bentonite Slurry

-

Bentonite Slurry in Civil Engineering

Bentonite is a controlled mixture of fullers earth and water which produces a slurry or mud which has thixotrapic properties(ie. as the material is placed under stress to flow). When placed in the borehole it exerts a pressure in excess of earth and hydro-static pressure present on side of excavation.

This also finds its application in the construction of special foundations for digging diaphragm walls and bored piles. Bentonite is implemented for self-hardening mixtures which are then resorted to build cut off walls, grouting mortars, and grouting. Finally, bentonite waterproofing properties are best exploited in environmental engineering, to seal off soil infiltration, and line the base of landfills.

Bentonite is a kind of clay which has an ability to swell and gel when it is dispersed in water. This is used in construction mainly in excavation and foundation works. Bentonite contains more than 85% clay mineral, montmorillonite, and hence it is considered to be high plastic clay. Bentonite also is used in many civil engineering works such as
Bentonite Slurry use in pile foundation
  • foundry sand binding,
  • drilling mud,
  • iron ore palletization and
  • As a water proofing and sealing agent.

Formation

Montmorrillonite-rich clay have formed by weathering and metamorphose of volcanic ashes, tough and basic rock (e.g. basalt). The term bentonite is derived from the first archaeological site near Fort Benton, Wyoming (USA), where plastic clay were found and described for the first time. There are numerous bentonite formations differentiated according to montmorillonite type, kind and location of formation and mineralogical composition.

Preparation of Bentonite Slurry

Bentonite slurry is developed with an aim to attain maximum hydration of the bentonite, hence its powder must be put to the mixing water slowly so as to make sure that all the particles are irrigated and do not get lumped into partially hydrated balls. Potable quality fresh water should be used in the mixing process to obtain the best results. A chemical analysis should be done to ascertain the suitability of the water if there is any doubt. If needed, chemical treatment is given to the water before its usage

The preparation of Bentonite slurry is done either in batches or in a continuous process, which depends on the type of equipment used. The bentonite powder is put in a high shear mixer through a simple venturi-hopper. To assure the dispersion of all the individual bentonite particles in the mixing water, the mixing equipment must generate sufficient shear. The adequate amount of bentonite powder to be added to the mixing water depends on the quality of the bentonite and the required viscosity of the slurry. For most applications, concentrations between 4% and 6% by weight are typical.

Functions and Uses of Bentonite Slurry

  • Supports the excavation by exerting hydro static pressure on its walls i.e. to prevent the collapse or retain an area.
  • Remain in the excavation, and not flow to any great extent into the soil thereby acting as a sealant.
  • Suspend debris and prevent sludgy layers building up at the base of the excavation.
  • Staying non-reactive by clean displacement by concrete, with no significant interference with the bond between reinforcement and set concrete.
  • Cleaning to remove suspended detritus, by passing through screens and hydro cyclones, in preparation for re-use.

Comments

Post a Comment

Popular posts from this blog

Dewatering Methods - Groundwater Control

-
Image
Groundwater Control When rainwater collects in surface depressions, it is called surface water; when it percolates down into the permeable subsoil and collects in tiny soil voids, it is called groundwater; the upper surface of the groundwater is called the water table. Following some problems of water in the subsoil effect the construction work: A high water table could cause flooding during wet periods. Subsoil water can cause problems during excavation work by its natural tendency to flow into the voids create by the excavation activities. It can cause an unacceptable humidity level around finished buildings and structures. Civil engineers are must restrict the major problems of ground water and keep the excavation to safe. Therefore, they introduce many dewatering methods for controlling the ground water.These methods can be classified into two groups: Permanent exclusion of groundwater Temporary exclusion of groundwater Permanent Exclusion of Groundwater This c...
Read more

Basement Construction

-
Image
Basement Construction In the general context of building a basement can be defined as a storey which is below the ground storey and is there for constructed below ground level.  Basements are common in tall buildings as car parks, storage of services and underground shopping centres. The term “basement” has been regarded as synonymous to the term “deep pit”, which applies to excavations over 4.5 m deep. The main purpose of constructing basements are:  to provide additional space,  as a form of buoyancy raft,  in some cases, basements may be needed for reducing net bearing pressure by the removal of the soil. Basement can be classified into three groups: Types of basement Basement can be constructed by following method: Open cut method. Cut and cover method. Top down method. Open Cut Method This is the simplest and most straight forward technique of providing an excavation to the required depth. The sides of the excavation are ...
Read more