concrete finishing

8/3/2019 Concrete Finishing

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Submitted by

S.Mohanakrishnan

Engineer, Adit 2


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Concrete Lining

Concrete lining is an effective cover on tunnel ofconcrete mix, that is normally provided for power

tunnels which connect directly to the pressure pipe

line & to run the turbine in power houses.


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Why Concrete lining???

o Reduces head loss in the system

o Prevent leakage of water

o Protect the turbines by preventing loose rock particlesfalling into the water and being carried to the turbines.

o Protect steel ribs from deteriorating.

o Take the part of the internal pressure which is not takenby the rock


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Types of formed surfaces

Formed surfaces of construction joints and other

surfaces which will not be permanently exposed

All permanently exposed formed surfaces.

Formed surfaces which will be exposed to flowing

water


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Finishing of concrete

The quality of the surface shall be inaccordance with the requirements for the particularclass of finish specified hereunder

i)The finished surfaces of concrete shall be free fromareas

o Honeycombs,

o Segregation,

o Loss of cement or fine materials,

o From damage due to stripping of forms,


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Contd

o From bug holes (Excessive amount of entrapped air

voids),

o Abrupt irregularities caused by movement of forms or

components ,

o Loose knots and similar feature,

o Bulges or depressions the general plane or the surface

ii) Only one type of formwork shall be used for all partsof a concrete structure which is visible from any direction

iii) Also the classes of finish shall be as shown on the

construction drawing


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Sealing Work in Concrete Lining of

Underground Structures

Sealing work shall carry out to reduce water inflow and waterlosses through, and to guarantee the normal water-tightness of theconcrete lining of underground structures according to criteria statedhereafter

The work shall consist of

sealing the cold joints,

construction joints,

shrinkage cracks both vertical and horizontal,

honeycombs, and poorly grouted or sealed grout holes.

The work shall be performed intermittently, whenever water inflowsare observed and measured, wide cracks are discovered (especiallyafter performance of tunnel pressure testing), or the futureImpermeability


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Phenomena for undergo sealing works

The sealing work shall be carried out when followingphenomena are encountered:

Water inflow equals or exceed 1 l/min measured at eachsingle inflow source,

Any water inflow from grout holes and through honeycombs isunacceptable,

Cracks or joints, regardless whether they are dry or wet, of

width greater than:- 0.2 mm in tunnels and shafts containing reinforcing steel

- 0.5 mm in unreinforced stretches of tunnels or shafts

Areas of porous concrete (e.g. due to poor vibration) wheredepth of porosity is obviously deeper than superficial.


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Procedure for sealing work execution

The sealing work shall be executed as follows:

Crack or joint 0.2-0.6 mm wide shall be repaired as stipulatedin the Section "Drilling and Grouting".

Crack or joint wider than 0.6 mm shall be repaired as under (1)above, followed by cutting a groove 25x25 mm along the joint orcrack and subsequent filling with an epoxy mortar.

Wet joint may also be sealed by applying the "Oberhasli Method",which consists of cutting a groove as for the dry joint and bycollecting the seepage water into one or several flexible plasticpipes. As soon as the groove is without running water is shall be filledwith a quick-setting mortar and, after its hardening, followed bypumping the cement-bentonite-water slurry through the plastic pipes.


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Contd

Areas of porous concrete shall be grouted under high

pressure (30 bar) with cement grout mix W/C=0.7, by

weight, containing suitable water-reducing air-

entraining admixture. Grout holes shall be drilled at500 mm spacing until the rock. After grouting, the area

shall be repaired with epoxy mortar.

Grout holes filled only with water/cement mix shall beredrilled up to 2/3 of the theoretical lining thickness

and filled with dry-pack mortar.


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Water Leakage Repair

Epoxy injection resins usually fail in stopping active

water leakage because of their slow reaction time

and inability to bond to wet surfaces; this failure is

resolved with a specially formulated PolyurethaneSystem. The actively flowing water will be stopped

by injecting material which reacts quickly with the

water to form an expanding foam.

The Flexible Polyurethane Injection System was

designed with these problems in mind.


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Flexible Polyurethane Injection

Properties:

Low viscosity-enabling penetration into small cracks

Instant reaction with water to stop high pressure

leaks Impervious to water

Hydrostatic pressure resistant

Chemical resistant

Safe and Non-Toxic


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SURFACES AND METHODS OF FINISHES

o Formed surfaces of construction joints and othersurfaces which will not be permanently exposed.

i) The surface will required no treatment after formremoval other than repair of defective concrete.

ii) Specified curing, or

iii) Treatment as specified for construction joints


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Contd

All permanently exposed formed surfaces.

i)

Immediately on the removal of forms all unsightlyridges or fins shall be removed;

ii) all holes of ends of form rods shall be neatly filled

with mortar and surfaces treated to meet requiredtolerances by tooling and rubbing


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Contd

Formed surfaces which will be exposed to flowing water.

i) These surface shall be hard, smooth and dense,

ii) Free from offsets, Pits, Voids, Air holes and

irregularities, and

iii) Shall be chipped, ground and thoroughly cleaned as

necessary to conform to the required tolerances


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Tolerances for surface finishes and other variations

in finishing of concrete

Type of finish General areas of application and method of

forming

Tolerances

(in mm)

Plane ,

CurvedFormed surfaces of construction joints and other

surfaces which will not be permanently exposed.

+25

-10

Plane ,

CurvedAll permanently exposed formed surfaces.

+10

-10

Plane ,

Curved

Formed surfaces which will be exposed to flowing

water

+3

-3


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Curing and protection of concrete

curing Maintaining the humidity and temperature of

freshly placed concrete during some definite period

following, placing, casting or finishing to assure

satisfactory hydration of cementitious materials andproper hardening of concrete

Exposed surfaces shall be kept moist or the

moisture in the concrete shall be prevented from

evaporating for at least 14 days after placing bymeans of continuous sprinkling or spraying with water

Curing shall commence as soon as possible, but no later

than 3 hours after finishing operation have been

completed.


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Tooled finish

There are two basis techniques for obtaining a

tooled finish.

One is knows as Bush hammered and results in a

surface with an over-all rough texture that exposure

the aggregate

The second is called Point tooling, which gives the

pitted effect.


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Bush hammered finish

In bush hammering, the surface layer of concrete isspalled off with a toothed-head hammer

The hammer is held right angles to the wall with one

hand, while the other hand supports the bit tosteady it

Since the hammer is quite heavy, it is advisable towork only a small area of the surface at a time.

Care should be taken to keep the pressure as evenas possible throughout and to see that the hammerdoes not produce any lined effects on the surface.

Small irregularities in the finished surface can be

worked out with further tooling.


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Bush hammer


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Point tooling

In point tooling, the concrete is pitted all over with eithera power or hand operated tool known as a point. Thepoint should be made sufficient close together to removethe entire outer layer of cement paste.

A power-operated point is held at right angles to thewall and pressed against the surface. The size of thepits will depend upon the pressure exerted on the toldand the length of time it is permitted to dig into the

concrete. A hand-operated point works in the same way. It is held

at right angles to the wall and inserted into the concreteby a hammer blow.


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Point tooling


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Repairing works

Grinding

Chipping

Joint repairing by epoxy mortar

Non shrink grout

Epoxy grout


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Grinding

Grinding is the process of

removal of irregularitiescaused by movement offorms or components

The result is a level,smooth, and generallyquieter riding surface

Grinder


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EPOXY REPAIR MORTAR

A concrete repair must replace damaged concrete,restore required structural function, protect itself andpossibly underlying concrete from aggressive

environments, and restore any lost according to userperformance requirements.

Hand-applied techniques are used to place epoxyrepair material on vertical, horizontal and overheadlocations.

The system provides high strength and adhesion to avariety of substrates. Rapid strength developmentallows the repaired area to return to its normalcondition faster.


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Epoxy components

Concresive 1020 special primer

It is in two components

i) Base (B)

ii) Hardener (H)

Mixing ratio by : 7 (B) : 3(H)

Example: In one container Base 700gm and Hardener

300gm. Mix both base and hardener for atleast 1-

2min


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Epoxy components

Concresive ERL special epoxy mortar

It is in three components

i) Base (B)

ii) Hardener (H)iii) Sand (F)

Mixing ratio by weight : 15(B) : 6.2(H) : 78.8(F)

In one container Base 750gm, Hardener 310gm and sand

3940gm.Mix base and hardener in a separate big containermechanically, add sand component and mix thoroughly for2 min to obtain a homogenous mortar.


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PROCEDURE FOR JOINT REPAIRING BY EPOXY MORTAR

Removal of all loose particle from the concrete

surface by wire brush

Apply Concresive 1020 special primer by paint

brush on the cleaned concrete surface and allow

that to set for one hour time

Then apply Concresive ERL special Epoxy mortar bytrowel and finish the surface in required shape.

Epoxy mortar set within 3-4 hours.


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Non shrink grout

Non shrink grout is fast-setting cement products for

general concrete repair, anchoring, industrial

grouting, and formed work.

Non-Shrink Grout is ideal for jobs that requirestrength, durability and low shrinkage.

Non shrink grout consists of carefully graded

aggregates, cements, silica fume, expansive agents,water reducing admixtures and other additives.


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Epoxy grout

One of the most common methods of concrete repairtechniques on vertical, horizontal and, in some cases,overhead locations is the placement of formwork andcasting, formwork and pumping or grouted preplaced

aggregate.

Benefits: Under plate grouting of equipment Turbine and generator base plates Bridge deck expansion joints Fixing anchor bolts and dowel bars Grouting equipment in chemical process areas Structural gap filling


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