Figure-1: Cracks treatment with epoxy pressure grout.

Procedures For Maintenance And Rehabilitation Of Bridges:

Procedure for Crack repairs: 

The following steps shall be followed to treat cracks:

1. In case of Hairline cracks or fine cracks or surface cracks, low viscosity epoxy resin shall be applied. Tell-tale glass shall be fixed over some cracks to observe the propagation of cracks in the future.

2. Minor / Major Cracks repairs through Epoxy Injection Grouting: 

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

B. Surface Preparation: The surface adjacent to the crack shall be cleaned of dirt, dust, oil, efflorescence by an 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 blown apart by an air blower. For fixing the nipple, a hole of 12 mm diameter and 100 mm to 150 mm depth is to be drilled along the crack at intervals of not more than the thickness of concrete at the location. 10 mm diameter metal nipple of 120 mm length is to be fixed in the 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 primer (bond coat) is to be done. 

C. Surface Seal:  Surface Sealing by PMC needs to be applied to the face of the crack between entry ports. For through cracks, a surface seal needs to 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.

D. Equipment for Injection: Compressed air-operated epoxy injection gun is to be utilized for epoxy grouting. The constant pressure of air may be 3 kg/cm2. Gun may be of capacity 2.5 to 3 liters with stop cock regulation.

E. Material: The material for injection shall be low viscosity, two-component epoxy (Lapox B47 & Hardner K 6) in a ratio of 10 resin and 1 harder (by weight), having the following, bonding characteristics with concrete and have good compressive strength, flexural strength, and tensile strength. 

F. Injection of Epoxy: It shall be begin at the lowest entry port and continue until there is an appearance of epoxy at the next port. The 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 the adjacent entry port where the epoxy has appeared. At max 2 kg grout per nipple would be done and after grouting 2 kg grouting would be stopping for next 1-2 hours. For through the cracks if grout is coming out from the other side, then nipple of other side would be sealed and further grouting would be carried out.

G. Test:

i. 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 a full record along with time.

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

Procedure For Repair of Spalled, Leached and Honeycombed Concrete Surfaces:

The following stepwise treatment is to be followed:

A. Area of repairs to spalled, leached, loose and the honeycombed concrete area is to be treated and to be repaired by polymer modified cement plaster of up to 40 mm thickness in two or more layers with a bond coat of PMC slurry between mother concrete and mortar layer. 

B. Cleaning of the Concrete Surface: Concrete on the damaged, loose or honey combed area shall be chipped out up to the reinforcement level or up to good parent concrete or up to the point on the reinforcement.

C. 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 remove oily or greasy residues. Applying rust removal chemical (Reebaklens RR of Fosroc or equivalent product of BASF or Sika) and cleaning of reinforcement with a mechanical wire brush. After that applying one coat of zinc rich coating of Nitozinc Primer of Fosroc or equivalent product of BASF or Sika).

D. Bond Coat: Before commencing the application of concrete repair mortar, the prepared concrete substrate 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 product of BASF or Sika) and one part of Water mixed with three parts of cement by weight is of thick paint consistency and can easily be applied to the surfaces were bonding of new cementitious material is required.

E. Polymer Modified Cement Mortar: The repair of spalled honeycombed concrete shall be done by low permeability polymer modified cementitious repair mortar.

F. Method (Mixing and Applying) Polymer Modified Cement Mortar can be prepared by mixing 100 parts of cement, 300 parts of sand and 10 parts of polymer by weight of cement, 1 part of corrosion inhibitor by weight of cement and 30 parts of water by weight of cement. To mix PMC it is necessary to have the following items;

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

ii) A high speed drill with a mixing paddle.

iii) Promark batching container for measuring out component to be mixed.

G. Following Steps to be followed for repairs:

i) Step 1: Pour all liquid i.e. Water and polymer latex into mixing container.

ii) Step 2: Begin mechanical mixing & while doing so, slowly add the dry component i.e., cement and sand.

iii) Step 3: Mixing for 5 minutes until mix shall look uniform, free from lumps and feel creamy. Local wash sand is to be used after cleaning.

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

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

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