rrs unit 3 blo
TRANSCRIPT
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MATERIALS AND TECHNIQUES
FOR REPAIR
T.KARTHIKEYAN, M.E
(SMAFE)
Unit 3
FERRO CEMENT
The term Ferro-cement is most commonly
applied to a mixture of Portland cement and
sand applied over layers of woven or expandedsteel mesh and closely spaced small-diameter
steel rods
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It can be used to form relatively thin,compound curved sheets to make hulls forboats, shell roofs, water tanks, etc.
It has been used in a wide range of otherapplications including sculpture andprefabricated building components. The term
has been applied by extension to othercomposite materials including somecontaining no cement and no ferrousmaterial.
Construction
The desired shape may be built from a multi-layered construction of mesh,supported by an armature, or grid, built with rebar and tied with wire. Foroptimum performance, steel should be rust-treated, (galvanized) orstainless steel.
Over this finished framework, an appropriate mixture (grout or mortar) ofPortland cement, sand and water and/or admixtures is applied to penetratethe mesh.
During hardening, the assembly may be kept moist, to ensure that theconcrete is able to set and harden slowly and to avoid developing cracksthat can weaken the system.
Steps should be taken to avoid trapped air in the internal structure duringthe wet stage of construction as this can also create cracks that will form asit dries.
Trapped air will leave voids that allow water to collect and degrade (rust)the steel. Modern practice often includes spraying the mixture at pressure,(a technique called shotcrete,) or some other method of driving out trappedair.
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Advantages
The advantages of a well built ferro concrete construction are the
low weight, maintenance costs and long lifetime in comparison
with purely steel constructions. Especially with respect to the
cementitious composition and the way in which it is applied in
and on the framework, and how or if the framework has been
treated to resist corrosion.
When a ferro concrete sheet is mechanically overloaded, it will
tend to fold instead of break or crumble like stone or pottery. So
it is not brittle. As a container, it may fail and leak but possiblyhold together. Much depends on techniques used in the
construction.
Skeleton Steel
The skeleton steel comprises of relatively large-diameter (about 3
to 8 mm) steel rods typically spaced at 70 to 100 mm.
It may be tied-reinforcement or welded wire fabric. The welded-
wires normally contain larger diameter wires spaced at 25 mm ormore.
Welded-wire fabrics of 3 to 4 mm diameter wires welded at 80 to
100 mm centre-to-centre have been successfully used for making
skeleton frames for the cylindrical or other ferrocement surfaces
where these meshes can be bent easily.
They provide better and uniform distribution of steel and save time
in fabrication but may cost a little more when compared to mild
steel bar frames.
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Wire Mesh
Wire mesh consisting of galvanized wire of diameter 0.5 to 1.5 mm
spaced at 6 to 20 mm centre-to-centre, is formed by welding, twisting
or weaving.
Specific mesh types include woven or interlocking mesh, woven cloth,
and welded-mesh.
The welded-wire mesh may have either hexagonal or square openings
as shown in. Meshes with hexagonal openings are sometimes referred
to as chicken mesh
Square woven wire mesh
Square welded wire mesh
Hexagonal wire mesh
Expanded metal lath
Mortar or concrete
covering
Usually 1.3 or 1.4 mortar mix is used to cover the
mesh and skeleton steel sometimes aggregate chips
are used to get a good strength.Maximum thickness is not exceed 75mm on both
sides
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FIBRE REINFORCED
CONCRETE
FRC containing fibrous material which increases its
structural integrity.
It contains short discrete fibers that are uniformlydistributed and randomly oriented.
Fibers include steel fibers, glass fibers, synthetic fibers
and natural fibers.
Within these different fibers that character of fiber-
reinforced concrete changes with varying concretes,
fiber materials, geometries, distribution, orientation
and densities.
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Effect of fibres in concrete
Fibers are usually used in concrete to control cracking due to both
plastic shrinkage and drying shrinkage.
They also reduce the permeability of concrete and thus reduce bleeding
of water.
Some types of fibers produce greater impact, abrasion and shatter
resistance in concrete.
Generally fibers do not increase the flexural strength of concrete, and
so cannot replace moment resisting or structural steel reinforcement.
Indeed, some fibers actually reduce the strength of concrete.
The amount of fibers added to a concrete mix is expressed as a
percentage of the total volume of the composite (concrete and fibers),
termed volume fraction (Vf). Vf typically ranges from 0.1 to 3%.
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Polymer concrete
Polymer concrete is part of group of
concretes that use polymers to supplement or
replace cement as a binder. The types includepolymer-impregnated concrete, polymer
concrete, and polymer-Portland-cement
concrete.
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CompositionIn polymer concrete, thermosetting resins are used as the
principal polymer component due to their high thermal
stability and resistance to a wide variety of chemicals.
Polymer concrete is also composed of aggregates that
include silica, quartz, granite, limestone, and other high
quality material.
The aggregate must be of good quality, free of dust and
other debris, and dry. Failure of these criteria can reduce
the bond strength between the polymer binder and the
aggregate.
Uses
Polymer concrete may be used for new construction or
repairing of old concrete.
The adhesion properties of polymer concrete allow patchingfor both polymer and cementitious concretes.
The low permeability of polymer concrete allows it to be used
in swimming pools, sewer pipes, drainage channels,
electrolytic cells for base metal recovery, and other structures
that contain liquids.
It can also be used as a replacement for asphalt pavement, for
higher durability and higher strength.
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Advantages Rapid curing at ambient temperatures
High tensile, flexural, and compressive strengths
Good adhesion to most surfaces
Durability with respect to freeze and thaw cycles
Low permeability to water and aggressive solutions
Good chemical resistance
Good resistance against corrosion Lightweight
Allows use of regular form-release agents
Dielectric
Disadvantages
Some safety issues arise out of the use of polymer
concrete. The monomers can be volatile,
combustible, and toxic.
Initiators, which are used as catalysts, are
combustible and harmful to human skin. The
promoters and accelerators are also dangerous.
Polymer concretes also cost significantly more than
conventional concrete
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RUST ELIMINATORSIn recent years, interest has been shown in the development of
coatings for the steels which could provide a corrosion
resistant surface by interacting with corrosion product(s) of
the steel.There are variety of mechanisms by which these coatings work,
they can be classified as the products that impregnate rust,
convert rust to magnetite, inactivate soluble salts or
convert iron oxides to other products.
The last category is known as rust conversion surface coatings.
Rust conversion coatings are promoted as water-based
products reacting directly with a rusted surface to for an inert,
water insoluble complex that can be top coated.
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The vast majority of commercial rust converters incorporate some type of poly
hydroxylated or tannin like compound.
The transformation of a rusty surface to the blue-black coating which occurs
after the products application has been attributed to the complexation of tennin
resin resulting in the formations of iron oxide and hydroxide in rust and a ferric-
tennate complex.
Two types o f tests were performed while evaluating the performance of rust
RUST ELIMINATORS
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Materials originally tested as organic coatings included
coal-tar enamel, epoxy, asphalt, chlorinated rubber, vinyl,
Phenolic, neoprene and urethane.
In considering the literature most of these were seen to
have significant disadvantages, but the epoxy group
appealed to have the best potential for use.
Despite the fact that epoxy coatings provided excellent,corrosion protection of pre-stressing steel.
Corrosion is caused by the chloride ions from the most
commonly applied de-icing salts, sodium chloride and
calcium chloride.
RUST ELIMINATORS
FOAM CONCRETE
Foam concrete is a cement-bonded material made by blending an extremely
fluid cement paste (slurry), into which is injected a stable, pre-formed foam,
manufactured on site.
Fresh foam concrete has the appearance of a light-grey mousse or milk-shake and it is the volume of slurry to foam which dictates the cast density of
the foam concrete.
The foam is produced using either protein-based foaming agent
PROVOTON, or synthetic additive SYNVOTON, both of which are
manufactured for us exclusively here in the UK.
The physical characteristics of foam concrete are determined by the use of
one of a number of mix designs: Depending upon the application for which
the concrete is required, these mix designs may include the use of Portland
Cement (CEM1), either on its own, or in combination with a percentage of
Pulverized Fly Ash, GGBS, or the inclusion of limestone dust or sand.
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Manufacturing
Low Density High Strength Typical cast densities of foam concrete range between 350 and
1600 kg/m3, giving 28 day compressive strengths of 0.2 to
upwards of 12.0 N/mm2. Due to its low density, foam concrete imposes little vertical
stress on the substructure - a particularly important attribute in
areas sensitive to settlement. Foam concrete is a viable
solution for reducing loading on burden soil and, in its hardened
state, is less susceptible to differential settlement.
Heavier density (1000 kg/m3+) foam concrete is mainly used
for applications where water ingress would be an issue - infilling
cellars, or in the construction of roof slabs for example.
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Dry Pack and Epoxy Bonded Dry Pack.
Dry pack is a combination of Portland cement
and sand passing a No. 16 sieve mixed with
just enough water to hydrate the cement. Dry
pack should be used for filling holes having a
depth equal to, or greater than, the least
surface dimension of the repair area;
Dry pack should not be used for relatively shallow
depressions where lateral restraint cannot be
obtained, for filling behind reinforcement, or for
filling holes that extend completely through a
concrete section.
For the dry pack method of concrete repair, holes
should be sharp and square at the surface edges,
but corners within the holes should be rounded,
especially when water tightness is required.
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(a) Preparation
Application of dry pack mortar should be preceded by a
careful inspection to see that the hole is thoroughly
cleaned and free from mechanically held loose pieces of
aggregate.
One of the three following methods should be used to
ensure good bond of the dry pack repair.
The first method is the application of a stiff mortar or groutbond coat immediately before applying the dry pack
mortar.
The mix for the bonding grout is 1:1 cement and fine sand
mixed with water to a fluid paste consistency.
All surfaces of the hole are thoroughly brushed with the grout,
and dry packing is done quickly before the bonding grout can
dry.
Under no circumstances should the bonding coat be so wet orapplied so heavily that the dry pack material becomes more
than slightly rubbery.
When a grout bond coat is used, the hole to be repaired can
be dry.
Pre-soaking the hole over night with wet rags or burlap prior
to dry packing may sometimes give better results by reducing
the loss of hydration water, but there must be no free surface
water in the hole when the bonding grout is applied
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(b) Materials
Dry pack mortar is usually a mixture (by dry volume or weight) of 1
part cement to 2-1/2 parts sand that will pass a No. 16 screen.
While the mixture is rich in cement, the low water content prevents
excessive shrinkage and gives high strengths.
A dry pack repair is usually darker than the surrounding concrete
unless special precautions are taken to match the colours.
Where uniform colour is important, white cement may be used in
sufficient amount (as determined by trial) to produce uniform
appearance.
For packing cone bolt holes, a leaner mix of 1:3 or 1:3-1/2 will be
sufficiently strong and will blend better with the colour of the wall.
Sufficient water should be used to produce a mortar
that will just stick together while being moulded into a
ball with the hands and will not exude water but will
leave the hands damp.
The proper amount of water will produce a mix at the
point of becoming rubbery when solidly packed.
Any less water will not make a sound, solid pack; any
more will result in excessive shrinkage and a loose
repair.
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(c) Application.
Dry pack mortar should be placed and packed in layers having a
compacted thickness of about 10 mm.
Thicker layers will not be well compacted at the bottom.
The surface of each layer should be scratched to facilitate
bonding with the next layer.
One layer may be placed immediately after another unless an
appreciable rubbery quality develops; if this occurs, work on the
repair should be delayed 30 to 40 minutes.
Under no circumstances should alternate layers of wet and dry
materials be used.
Each layer should be solidly compacted over the entire surface by
striking a hardwood dowel or stick with a hammer.
(d) Curing and Protection.
It is essential that mortar repairs receive a thorough water
cure starting immediately after initial set and continuing for
14 days.
In no event should the mortar be allowed to become dryduring the 14-day period following placement.
Following the 14-day water cure and while the mortar is still
saturated, the surface of the mortar should be coated with
two coats of a wax-base or water-emulsified resin base
curing compound meeting Reclamation specifications.
Additionally, the dry pack repair area should be protected
and not exposed to freezing temperatures for at least 3 days
after application of the curing compound.
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Vacuum concreteVacuum concrete is made by using steam to produce a
vacuum inside a concrete mixing truck to release air bubbles
inside the concrete, is being researched.
The idea is that the steam displaces the air normally over the
concrete.
When the steam condenses into water it will create a low
pressure over the concrete that will pull air from the concrete.This will make the concrete stronger due to there being less air
in the mixture.
A drawback is that the mixing has to be done in a mostly
airtight container.
Vacuum Concrete
This is concrete which includes high water content to allow
sufficient workability to enable it to be placed into
complicated moulds or around extensive reinforcement.The concrete is then subject to a vacuum which removes
significant quantities of water resulting in a stronger concrete
on hardening.
Pumped concrete needs to include higher water content to
improve the flow characteristics.
If a high strength concrete is required then special additives
are use in place of the additional water.
Concrete pumping stations may be static or mobile
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After the requirement of workability is over, this excess water
will eventually evaporate leaving capillary pores in the
concrete.
These pores result into high permeability and less strength in
the concrete.
Therefore, workability and high strength dont go together as
their requirements are contradictory to each other.
Vacuum concreting is the effective technique used to overcome
this contradiction of opposite requirements of workability and
high strength.
With this technique both these are possible at the same time.
In this technique, the excess water after placement and
compaction of concrete is sucked out with the help of
vacuum pumps.This technique is effectively used in industrial floors,
parking lots and deck slabs of bridges etc.
The magnitude of applied vacuum is usually about 0.08
MPa and the water content is reduced by upto 20-25%.
The reduction is effective up to a depth of about 100 to 150
mm only.
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Technique and Equipments
Mainly four components are required in vacuum
dewatering of concrete, which are given below:
Vacuum pump
Water separator
Filtering pad Screed board vibrator
Vacuum pump is a small but strong pump of 5 to 10 H.P. Water is
extracted by vacuum and stored in the water separator.
The mats are placed over fine filter pads, which prevent the removal
of cement with water.
Proper control on the magnitude of the applied pressure is
necessary. The amount of water removed is equal to the contraction
in total volume of concrete.
About 3% reduction in concrete layer depth takes place. Filtering
pad consists of rigid backing sheet, expanded metal, wire gauge or
muslin cloth sheet.
A rubber seal is also fitted around the filtering pad as shown in Fig.
Filtering pad should have minimum dimension of 90 cm x 60 cm.
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AdvantagesDue to dewatering through vacuum, both workability and
high strength are achieved simultaneously.
Reduction in w/c ratio may increase the compressivestrength by 10 to 50% and lowers the permeability.
It enhances the wear resistance of concrete surface.
The surface obtained after vacuum dewatering is plain
and smooth due to reduced shrinkage.
The formwork can be removed early and surface can be
put to use early.
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STRENGTH VS TIME
However, the advantages of vacuum dewatering are more prominent
on the top layer as compared to bottom layer as shown in Fig. The
effect beyond a depth of 150 mm is negligible.
SHOTCRETE
Shotcrete is defined as pneumatically applied
concrete or mortar placed directly onto a surface.The shotcrete shall be composed of water,
cementitious materials, sand, coarse aggregate,
steel fibers (if specified), and admixtures, and
shall be placed by either the dry-mix or wet-mix
process as specified herein.
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dry mix processThe dry-mix process shall consist of thoroughly mixing
the solid materials;
Feeding these materials into a mechanical feeder or
gun;
Carrying the materials by compressed air through a
hose to a special nozzle;
Introducing the water and intimately mixing it with the
other ingredients at the nozzle;
And then jetting the mixture from the nozzle at high
velocity onto the surface to receive the shotcrete.
wet mix process The wet-mix process shall consist of thoroughly
mixing all the ingredients with the exception of the
accelerating admixture, if used;
Feeding the mixture into the delivery equipment;
delivering the mixture by positive displacement or
compressed air to the nozzle;
And then jetting the mixture from the nozzle at high
velocity onto the surface to receive the shotcrete.
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The compressive strength of the shotcrete will be
determined through the medium of tests of 3- by 3-
inch cores or 3-inch cubes. The average compressive
strength of specimens taken from a shotcrete
application shall be not less than:
1. Four thousand pounds per square inch at 28 days'
age.
2. Six hundred pounds per square inch at 8 hours' age.
This will be determined from 3-inch cubes extracted
from test panels.
Materials Portland cement.
Water
Sand and coarse aggregate.
Admixtures
Accelerator
Air-entraining admixture
Steel fibres
Curing compounds
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Application
Mixture proportions
Consistency
Batching
Mixing
Placing
Curing
Shotcrete that is applied where the ambient relative humidity is
85 percent or above will not require measures to control the
evaporation of water during curing.
When the relative humidity is less than 85 percent, the
Contractor shall initiate an approved curing method immediately
after application of the shotcrete.
Curing shall be accomplished by either:
Raising and maintaining the ambient relative humidity above 85 percent,
or
Applying a membrane curing compound as specified in subparagraph
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EPOXY INJECTION one of the most versatile, problem solving
products available in epoxy systems today is
Epoxy Injection Resin.
Structural restoration of concrete by epoxy
injection is very often the only alternative to
complete replacement.
It therefore results in large cost savings.
Injection protects the rebar and stops water
leakage
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Epoxy Injection Resin is a system for welding cracks
back together.
This welding restores the original strength and loading
originally designed into the concrete.
Epoxy injection restores the structural qualities the
concrete design intended.
In other words under most conditions it makes theconcrete as good as new.
It creates an impervious seal to air, water, chemicals,
debris, and other contamination.
PURPOSE Epoxy injection resin has two purposes.
1. It effectively seals the crack to prevent the damaging
moisture entry.
2. It monolithically welds the structure together.
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Most people assume that this welding of the
structure is the most important result of the repair.
Actually what is most important is the sealing.
The sealing property of the injection prevents
premature deterioration of the reinforcing.
This can be of equal, or in some cases greater
importance than the structural welding. It would
theoretically always be desirable to get this welding
effect
Injection Preparation
Proper job preparation is essential to insure
maximum results.
Preparation before injection is even moreimportant.
Once the resin is in the crack, there is no turning
back.
The two most effective systems for setting
injection ports:
Drilling
Surface ports
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Epoxy Resin Properties
For maximum filling of cracks a low viscosity
injection resin must be used.
Any thicker you get poor fill (or you have to
pump at excessive pressure), any thinner
and you get excessive leaks.
Tensile and Bond Strengths are very important, to prevent re-
checking if the structural member injected is put into tension.
In general the Tensile Strength (ASTM D-638) should never
be less than 6,500 p.s.i.
Injection Resin should have a bond strength of 7,000 P.S.I or
greater.
Compressive strength with most epoxies will be close to or inexcess of 10,000 p.s.i.
The resins that we have It is the Epoxy Bonders used to seal
the ports should be:
Grade 1, 2, or 3 may be used on the top side of horizontal
surfaces.
Grade 2, or 3 may be used on walls.
Grade 3 may be used on overhead surfaces.
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injection
Single component caulking guns, pressure pots, or similar
batching equipment are not suitable for injection.
Limit pressures to 40 p.s.i for most applications.
Excessive pressures can create additional stressing of the
crack.
It can also cause hydraulic lifting, rupturing of the crackedsubstrate, or further elongation of the crack.
Low pressures allow gradual resin flow into the crack for
deeper penetration.
On vertical cracks, injection is start at the lowest
point, and continue upward on the crack area.
While injecting the lowest port, resin will flow to
and out of the next higher port.
When pure resin is flowing out the next port cap,plug the current injection port and move to the
next port.
Then injection continues in the port showing
resin flow.
This procedure continues until all ports are full.
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Epoxy Injection Systems is very effective at repairing
concrete cracks, de-laminations, and hollow planes when
used according to manufacturers recommendations. Job analysis and proper preparation are very important to
insuring the maximum performance from the Epoxy
Products, or any other concrete repair products.
The right equipment is critical. Proper setup continuous
mixing epoxy injection machines must always be used
with no exception.
Injection staff and management must have the training
and experience to do the work right the first time.
Epoxy injection has to be done right the first time. There is
no second chance.
So it is critical that your injection work be done by well
trained and equipped, experienced personnel.
In general, underpinning means material ormasonry used to support a structure orfoundation.
underpinning means the rebuilding or deepeningof the foundation of an existing building toprovide additional or improved support
underpinning is the installation of temporary orpermanent support to an existing foundation toprovide either additional depth or an increase inbearing capacity
UNDERPINNING
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Underpinning is the process of strengthening
and stabilizing the foundation of an existing
building or other structure
Foundation underpinning is a means of
transferring loads to deeper soils or bedrock.
To obtain additional foundation capacity
To modify the existing foundation system
To create new foundations through which the existingload may be wholly or partially transferred into
deeper soil
Underpinning is generally used for remedial purposes
To arrest the excessive settlement
To improve the future performance of the existing
foundations
PURPOSE OF UNDERPINNING
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Construction of a new project with deeper foundation adjacent toan existing building.
Change in the use of structure
The properties of the soil supporting the foundation may havechanged or was mischaracterized during planning.
To support a structure which is sinking or tilting due to groundsubsidence or instability of the super structure
As a safe guard against possible settlement of the structure when
excavating close to or below its foundation level. To enable the foundation to be deepened for structural reasons
e.g to construct the basement beneath the building
To increase the width of the foundation to permit heavier loads tobe carried e.g when increasing the story height of the building
WHEN UNDERPINING IS REQUIRED?
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NASTY RESULTS OF POOR FOUNDATIONS
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REQUIREMENT OF AN
UNDERPINNING DESIGN
The art of underpinning requires an engineer
to:-
Analyze the existing structure
Determine the loads
Determine the bearing capacity of the soils
Design an underpinning system to supportthe structure with minimum of settlement
Height of the building
Column spacing
Wall thickness
Type and material of construction
Different loads acting on the building
Condition of the building
CONSIDERATIONS BEFORE
UNDERPINNING
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METHODS USED FOR UNDERPINNING
Pit Underpinning
Push Piers System
Helical Pier System
Pile Underpinning
Other Methods
Chemical Grouting Microfine Grouting
Micropiles
PIT UNDERPINNING
The most common and oldest method of
underpinning
Accomplished by installing piers under astructures foundation, filling them with concrete
and wedging up to transfer the load to the new
piers
Requires careful and skilled work as loss of
ground will cause building settlement
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PIT UNDERPINNING
Columns/ walls above the affected footingshould be braced as much as possible
A pit of 3 wide, 4 long and 5 deep isexcavated in front of the footing to beunderpinned
PIT UNDERPINNING
Pit is extended laterally to reach under the
foundation to be underpinned
The foundation is then deepened to the requireddepth
Vertical formwork is built in the pit and then is
concreted up to the foundation
Dry packing operation is then carried out
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PIT UNDERPINNING
PIT UNDERPINNING
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PIT UNDERPINNING
PIT UNDERPINNING
84
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PIT UNDERPINNING
85
PIT UNDERPINNING
Workable above water table in dryground
Difficult to use below water level
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Push Pier systems utilize high-strength steel pier sections that are
hydraulically driven through heavy-duty steel foundation
brackets to reach deep down to competent load-bearing strata.
The piers have the ability to reach far below the problem soils
and do not rely on friction for capacity.
Foundation Support works Push Piers effectively stabilize settling
foundations and provide the best opportunity to lift your home
back to a level position.
Push pier systems are an easy, economical solution providing
with a long-lasting result. Manufactured with industrial-strength,
galvanized steel, Foundation Support works piers have a high
resistance to corrosion with a 100+ design life in moderate soil
conditions.
Push Pier Advantages:
Piers reach greater depth than other options
Long life span galvanized steel is resistant tocorrosion
Does not require the use of invasive equipment
In most cases can lift foundation back to level
position
Restores Property Value
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Step 1: Footing is exposed and prepared
for the bracket.
PUSH PIER INSTALLATION
Step 2: Foundation Bracket is secured to
the footing.
Step 3: Steel pier sections are hydraulicallydriven through the bracket to competent soil
or bedrock
PUSH PIER INSTALLATION
Step 4: The weight of the home istransferred through the piers to load bearing
strata. Home is lifted back to level if possible.
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Helical piers are used to supportfoundation of existing structures.
Piers are drilled under the affectedfoundations to a specified depth with thehelp of a hydraulic motor attached to abackhoe.
Difficult to use below water level
Damaged
Foundation
Repaired
Foundation
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Excavate down to the footing at eachdesignated pier location
Notch out foundation footing to accommodatesupport bracket
Screw piers into excavated site to a desireddepth using a hydraulic motor attached to abackhoe
Connect bracket to base of foundation andthe top the pier
Backfill all excavated pier locations
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Fast installation
Economical
Can be installed in confined space
Minimum disturbance to site
Immediate loading All weather installation
Applicable for saturated soil conditions99
This technique is used to overcome the
extremely difficult working
circumstances encountered when pitunderpinning action become unsuitable
Piles are often used where water
condition make it difficult to dig below
the footing
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BORED OR DRILLED, CAST IN-SITU
CONCRETE PILES
A series of holes are drilled along the
length of the existing foundation.
Some hand working is done to create a
bearing surface under the old foundation.
Say every second or third one is partly
filled with concrete.
After the concrete in these holes is set a
small but powerful hydraulic jack is used
to lift the existing foundations.
The machine that augers the holes, quite
often has the jack as an accessory and it is
drive by a hose connected to the machine
hydraulic system.
The gap is packed with steel packers and the jack withdrawn and used
again.
When the correct height is reached and the foundation securely packed theyare filled with mass concrete, or with a re-bar cage and concrete
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Perforated pipes are drilled into the ground atspacing and a solution of Sodium Silicate ispressure-injected into the ground and thenCalcium or magnesium chloride is injected asthe pipe is withdrawn.
The two chemicals react to form a gel that bindsthe soil particles into a mass similar to sandstone
If some other method has lifted the structure,then pressure injection of grout into the voidsformed by the lifting process will greatly improvethe repair strength.
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A perforated pipe is drilled into ground
and fluid grout mixture is injected by
pressure
The mixture consist of
- water + Cement- water + cement + fly ash or lime
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Piles with a diameter less than
300 mm are called micropiles.
The first micropiles, Paliradice(root piles), were
invented for underpinning in
1952 in Italy, micropiles
are also called root piles,
pin piles, and minipiles.
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They can be used where there is insufficient
head space for a conventional piling rig
They are applicable to all foundation conditions
if drilling is possible
They can be arbitrarily installed at any angle of
inclinationVibration and noise during construction can be
limited to the minimum extent.
The mechanism of micropiles developing the bearing
capacity is not yet fully understood.
The design method is based on the conventionaldesign method for pile groups.
The contribution of the footing has not been
considered.
Consequently, the effect of interaction between the
footing and micropiles on bearing capacity has not
been considered.
PROBLEMS
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When underpinning is installed to a stratum that is
competent and capable of supporting the structure, it will
stop downward movement of the area of the foundationthat is supported. Underpinning is generally not designed
to keep the foundation from moving upward if the original
support clays swell due to an increase in moisture.
Subsequent upward movement will often occur, which will
result in a distorted foundation and cracking in the
finishes
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Underpinning is only as good as the contact or
connection point between pier/pile and the structure. If
the grade beam, thickened slab, or steel beam support is
faulty, pier support will not be fully transferred to the
foundation and downward movement may occur
What is Corrosion
The chemical or electrochemical reaction
between a material and its environments that
produces a deterioration of the material and
its properties.
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THE CHEMISTRY OF
CORROSION REACTIONS
4Fe + 3O2 + 2H2O 4FeO.OH
4Al + 3O2 2Al2O3
Corrosion reactions are electrochemical in nature. They
involve the transfer of charged ions across the surface
between a metal and the electrolyte solution in which it
is immersed.
There are two types of electrode reaction occurring at
the metal surface: anodic and cathodic , Anodic reactions
involve oxidation: electrons appear on the right hand
side of the equation. For example metallic iron can
produce ferrous ions by the anodic reaction:
Fe Fe2+ + 2e-
In a solution with higher pH, the anodic reaction
produces a surface film of ferric oxide according to
reaction
2Fe + 3H2O Fe2O3 + 6H+ + 6e-
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Cathodic reactions involve electrochemical reduction:
electrons appear on the left hand side of the equation. Incorrosion processes the most common cathodic reaction
is the electrochemical reduction of dissolved oxygen
according to the equation:
O2 + 2H2O + 4e- 4OH-
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Concept Industrial ProcessRemoval of oxidising agent Boiler water treatment
Prevention of surface reaction Cathodic protection - sacrificial anode- impressed current
Anodic protection
Inhibition of surface reaction Chemical inhibitors
pH control
Protective coatings:
a. Organic
b. Metallic
c. Non-metallic
Paint, Claddings, Electroplating,
Galvanising, Metal spraying, Anodising,
Conversion coatings
Modification of the metal Alloys - stainless steel
- cupronickel- high temperature alloys
Modification of surface conditions Maintenance to remove corrosive
agents, Design to avoid crevices
Design to avoid reactive metal
combinations
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Bare Steel Corrosion
Microscopic anodic and cathodic areas exist
on a single piece of steel.
As anodic areas corrode, new material of
different composition is exposed and thus
has a different electrical potential
Forms of Corrosion
General
Identified by uniform formation of corrosion products
that causes a even thinning of the substrate steel Localized
Caused by difference in chemical or physical conditions
between adjoining sites
Galvanic/Dissimilar Metal
Caused when dissimilar metals come in contact, the
difference in electrical potential sets up a corrosion cell
or a bimetallic couple
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Methods of Corrosion Control
Barrier Protection
Provided by a protective coating that acts as a barrier
between corrosive elements and the metal substrate
Cathodic Protection
Employs protecting one metal by connecting it to
another metal that is more anodic, according to the
galvanic series
Corrosion Resistant Materials
Materials inherently resistant to corrosion in certain
environments
Corrosion Inhibitors
Barrier Protection
Paint
Powder Coatings
Galvanizing
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CORROSION PROTECTION
COATING/ PAINTING
Cathodic Protection
Impressed Current
Galvanic Sacrificial Anode
Galvanic Zinc Application
Zinc Metallizing
Zinc-rich Paints
Hot-dip Galvanizing
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Impressed Current
External source of direct current power is
connected (or impressed) between the
structure to be protected and the ground bed
(anode)
Ideal impressed current systems use ground
bed material that can discharge large amounts
of current and yet still have a long life
expectancy.
CATHODIC PROTECTION
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Galvanic Sacrificial Anode
Pieces of an active metal such as magnesium or
zinc are placed in contact with the corrosive
environment and are electrically connected to
the structure to be protected
Example: Docked Naval Ships
Galvanic Zinc Application
Zinc Metallizing (plating)
Feeding zinc into a heated gun, where it is melted
and sprayed on a structure or part using combustion
gases and/or auxiliary compressed air Zinc-rich Paints
Zinc-rich paints contain various amounts of metallic
zinc dust and are applied by brush or spray to
properly prepared steel
Hot-dip Galvanizing
Complete immersion of steel into a kettle/vessel of
molten zinc
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Zinc Metallizing Zinc-rich Paints
Hot-dip Galvanizing Process
Surface Preparation
Galvanizing
Inspection
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Surface Preparation
Zinc-iron metallurgical bond only occurs on clean steel
Degreasing
Removes dirt, oils, organic residue
Pickling
Removes mill scale and oxides
FluxingMild cleaning, provides protective layer
Galvanizing
Steel articles are immersed in a bath of molten
zinc ( 830 F)
> 98% pure zinc, minor elements added for
coating properties (Al, Bi, Ni)
Zinc reacts with iron in the steel to form
galvanized coating.
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Inspection
Steel articles are inspected after galvanizing
to verify conformance to appropriate specs.
Concrete: Rebar Corrosion
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