METHODOLOGY FOR DIFFERENT TYPE OF REHABILITATION OF OLD STRUCTURES

 DIFFERENT TYPE OF

REHABILITATION OF OLD STRUCTURES

1.  Scope:

~ This work shall consist of giving more strength to existing old structure to full fill the future requirement of road traffic. Part of structure may be Pier, abutments, pier cap, abutment cap, Return wall, and wing wall, deck slab etc.

2.  Reference:

~ Section 2800,1700,900,1000 of MoRT&H specification.

3.  Equipments:

-Chipping tools or small concrete braker, Drilling machine with all size bits ,Hard wire brush, Air compressor with water jets & Air blower, Trowel, Sponge, wooden flat, and plumb bob, scraper, Mortar mixer or Mixing paddle. Hand gloves, & All PPE, Digital weighing machine, Nipples, Grouting pump.

4.  Materials:

-Cement, Fine aggregate, Water, Grouting compound, Corrosion protective chemical, Nitobond or equivalent Polymer, Rush remover chemical, Non shrinkage additive (May be Cebex 100 or equivalent). Water tight shuttering material, Epoxy material.

 

5. Procedure: - Different type of rehabilitation PROCEDURE applicable to different condition of structure.are given below as

A. REPAIR OF SPALLED, LEACHED AND HONEYCOMBED     CONCRETE SURFACE.

       

                Area of repairs to spalled, leached, loose and honey combed concrete area is to                 be treated  and to be repaired by polymer modified cement plaster of average               50 mm thickness in two or more layers with a bond coat of PMC slurry                        between mother concreter and mortar layer.All defective area shall be                          delineated and marked on site in conformity with supervising officer.

a.    Cleaning of the Concrete Surface:

Concrete on the damaged, loose or honey combed area shall be chipped out upto the reinforcement level or upto good parent concrete or upto the point on the reinforcement. Where the reinforcement is affected with corrosion, the chipping of the concrete would be continued to expose the full circumference of the steel and to the further depth of 10 mm as directed by supervising officer.

b.   Cleaning of Reinforcement and applying corrosion protective

                        chemical:

The chipped surface shall be thoroughly cleaned by wire brush to remove loose rust particles then exposed reinforcement shall be cleaned of all rust and millscale by mechanical wire brush, to removal of oil or greasy residues. Applying rust removal chemical (Reebaklens RR of Fosroc) and cleaning of reinforcement with Mechanical wire brush. After that applying one coat of zinc rich coating of Nitozinc Primer of Fosroc).

c.    Bond Coat:

Before commencing the application of concrete repair mortar, the prepared concrete substate shall be thoroughly soaked with water and free water shall be removed before priming.

The Polymer slurry composed of one part of Polymer (Nitobond AR or equivalent) mixed with two parts of cement by weight is of thick paint consistency and can easily be applied to the surfaces were bonding of new cementetious material is required

d.   Polymer Modified Cement Mortar:

The repair of spalled honeycombed concrete shall be done by low permeability polymer modified cementious repair mortar.

e.    Method (Mixing and Applying)

Polymer Modified Cement (PMC) Mortar can be prepared by mixing 100 parts of cement, 300 parts of sand and 10 parts of polymer by weight and 30 parts of water by weight.

To mix PMC it is necessary to have the following items;

a)       A suitable sized non ferrous mixing container preferably plastic.

b)       A high speed drill with mixing paddle.

c)       Promark batching container for measuring out component to be mixed

Step 1: Pour all liquid i.e. water and polymer latex in to mixing container.

Step2: Begin mechanical mixing & while doing so, slowly add the dry component i.e.cement and sand.

Step 3: Mixing for 5minite s until mix shall look uniform, free from lumos and feel creamy. Sand; Local sand Zone II is to be used.

Step 4: Apply PMC mortar in 2 to 3 layer one after other. Another layer should be applied after some time gap for proper bonding between two layers

Step 5: Curing; One day water curing and next three days air curing.

B. REPAIR OF CORRODED REINFORCEMENT.

Repair of corroded reinforcement (where corrosion has reduced diameter of bar by more than 20%), shall be done by providing new reinforcement, which is either welded or firmly secured with the old reinforcement.

The exposed reinforcement showing signs of deterioration by corrosion shall be cleaned by wire brush mechanically and applying rush remover (chemical)

Over this one coat of Zinc based protective cover (Nitozinc Primer) is applied for further protection.

C. POLYMER CEMENT GROUTING.

The work shall be done in accordance with MoSRT specification 2806. Method:

Step 1: Drilling of holes

16 mm or 20 mm dia holes would be drill at a distance not more than 500 mm with mechanical drill. Depth of whole would depend on the size of the structure in which grouting has to be done

Step2: Fixing of nipples

Nipple is fixed with polymer modified cement mortar

Step 3: Preparing of Grout

12% by weight of cement Polymer along with 0.45% non shrinkage additive (chemical) by weight of cement i.e., 220gms of cebex 100 will be added to the cement grout as per manufacturer^·s specification.

Step4: Carrying out Grouting

The grouting shall be done by grout pump with compressed air pressure of 3 kg / sq. cm. to 5 kg / sq. cm.

Wrapping

a)       Removal of old repair works

b)       Sealing of crack with epoxy mortar and filling by injection grouting of low viscosity epoxy grout

c)       Applying PMC mortar test wherever it is required

d)       Grouting the girder with Polymer modified cement grout

e)       Surface preparation

f)      Applying primer coat

g)     Applying saturant coat

h)    Fixing of glass fibre wrap

D.   REPAIR OF DAMAGED CONCRETE BY MICROCONCRETE.

Cleaning of the Concrete Surface:

Concrete on the damaged or loose area shall be chipped / removed. And dust particles from opened area shall be removed by air blower.

Microconcrete:

Flowable mix of 1part by weight of Microconcrete power, 1 part by weight of grit (upto 10mm) and necessary water required for workability. The mix shall be mixed thoroughly by mechanical stirred for about 3 mins.

Applying

After providing necessary water tight shuttering, the flowable mix should be poured and there is no need for compaction as it is flowable and self compacting mix.

E.   METHODOLGY OF EPOXY INJECTION GROUTING.

1.    Mapping of Cracks: Identification, locating (span wise & girder wise) and measurement (length) of crack

  2.    Preparation:

Surface adjacent to the crack shall be cleaned of dirt, dust, oil efflorescence by air blower a mechanical wire brush.

V groove of 20mm by 20mm along the surface of the crack is to be cut. Loose particle is blowned apart by air blower. For fixing nipple, hole of 12 mm dia and 200 mm depth is to be drill along the crack at intervals of not more than the thickness of concrete at the location. 10 mm dia metal nipple of 120 mm length is to be fixed in hole with PMC mortar. The crack is also sealed with

PMC mortar. Prior to sealing of crack with PMC mortar, cleaning of crack is to be done by air and applying of primer (bond coat) is to be done

 

Surface sealing by PMC shall be applied to the face of the crack between entry ports. For through cracks surface seal shall be applied to both faces

 Before proceeding with the injection the surface sealed with PMC mortar is given time to gain adequate strength to resist injection grouting pressure

3.    Equipment for Injection:

Compressed air operated epoxy injection gun is to be utilized for epoxy grouting. Constant pressure of air may be 3 kg/cm2. Gun may be of capacity 2.5 to 3 litre with stop cock regulation.

4.    Material:

The material for injection shall be low viscosity two component epoxy (Lapox B47 & K 46 of Atul Ltd.) in ratio of 2 resin and 1 harder (by volume), having following, bonding characteristics with concrete and have good compressive strength, flexural strength and tensile strength

Technical Data:

		Lapox® B-47	Hardener K-46
Commercial form		Liquid	Liquid
Viscosity at 25oC	m Pas	450-650	10000-15000
Epoxy Equivalent	g/ equiv	182-192	-
Epoxy Content	val/kg	5.2-5.5	-

Amine Value	val/kg	-	6.6 -7.5
Amine number	mg KOH/g	-	370-410
Colour	Gardner	4	12
Density at 25oC	g/cm	1.15
Shelf life		12 months at least	12 months at least

 

5.     Injection of Epoxy:

It shall be begin at lowest entry port and continue until there is an appearance of epoxy at the next port. On appearance of epoxy either at the next entry port or reverse flow of epoxy from the same port the grouting should be discontinued or entry port shall be sealed. Thereafter epoxy grouting is to be carried out in adjacent entry port where epoxy has appeared. At max 2 kg grout per nipple would be done and after grouting 2 kg grouting would be stop for next 1-2 hours

For through cracks if grout is coming out from other side then nipple of other side would be sealing and further grouting would be carried out

6.     Test:

a.    Pot Life: Actual pot life is identified before epoxy grouting by conducting a test on site mixing 100 ml resin and 50 ml hardener. A record of mixing time and completion of individual mix batch is kept by maintaining full record along with time

b.    Compressive strength test: Material for 3rd party testing will be provided for testing per lot of procurement

1.    Electric Motor (1.5 HP)

2.    Air Compressor

3.   Portable compressor unit^·s tank

4.    Pressure gauge

5.    Stop cock

6.    Flexible 20 mm dia high pressure pipe (upto 15 kg/cm2 )

7.    Stop cork

8.    Epoxy gun (capacity of 3 litre) made of PVC/G.I pipe

9.    Pipe cylinder epoxy gun.

7

Arrangement for Epoxy Grouting by Compressed Air

F.  REINFORCEMENT ANCHOR FIXING FOR CRASH BARRIERS AND PARAPET WALL.

• a.    16mm holes will be drilled to accommodate 12mm reinforcement, spacing of reinforcement will be as per approved crash barrier drawing.
• b.    After drilling ,Holes will be cleaned with air blower
• c.    Crash barrier reinforcement will be inserted into the hole and it will be grouted with Hilti HY 150 or GP2 or any other equivalent compound.

G.   DRAINAGE SPOUTS.

Existing drainage spouts will be cleaned and made to usable condition, if downtake of spout is found shorter than deck slab, the pipe will be extended below slab by means of welding extra length pipe or and buy providing connector.

Damaged drainage spouts will be removed and replaced .

H.   REPAIRING OF RR MASONRY.

a.    Damaged masonry stones will be removed and replaced with new stones.

b.    New RR masonry will be laid with CM 1:6.

c.    After Repairing the portion will be cured for 3 days.

I. REPAIRING OF MASONRY POINTING.

a. Damaged pointing will be removed by means of chisel and hammer.

b. The same area will be repointed with CM 1:3

c. The surface will be kept wet for 3 days.

 

6. Safety Precautions:

~       All workmen at work area shall wear PPE^·s and reflective jackets.

~      It shall be ensured that the safety belts were wore, tied and anchored                 properly while Working at heights.

~       All working platforms shall be tied at the both ends firmly.

~       Wherever required, Flagman shall be provided.

~       Experienced personnel shall be deployed.