RRS Unit 3 Blo

8/13/2019 RRS Unit 3 Blo

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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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89

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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96


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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

100


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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

107


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109

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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113

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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Documents

RRS Unit 3 Blo