REPAIR, REHABILITATION AND RETROFITTING

Repair
Repair is the process of improving something that is inferior in quality or damaged to get in  good condition.

Repairs are strengthen the old buildings or chemically affected structures or cracks having structure.


Rehabilitation
Rehabilitation is the process of restoring the structure and enhance its service level for further use.

It consists the upgrading or altering the foundation or other element according to desired goal, use and regulatory requirement.

Retrofitting
Retrofitting is process of strengthen the elements of structure which are affected to distress and prevent further distress.


Repair techniques are used due to deterioration of concrete structure.
The main causes of deterioration are given below.

1. Deterioration due to corrosion 
The damage to the concrete due to corrosion of reinforcement is considered to be one of the most serious problem. Deterioration occurs due to corrosion are given below.
 Spalling of concrete cover
 Cracks parallel to the reinforcement
 Spalling at edges
 Swelling of concrete
 Dislocation

 Internal cracking and reduction in area of steel reinforcement.

2. Environmental effects 
Micro-cracks present in the concrete and permeability of concrete are very affected by environment effects like oxidation and carbonation procedure. These defects ingress of moisture into concrete from environment which directly attack the reinforcement and various ingredients of concrete and reactions take place.

3. Poor quality material used 
Quality of materials, to be used in construction, should be ensured by means various tests as
specified in the IS codes. Alkali-aggregate reaction and sulphate attack results in early deterioration.
Clayey materials in the fine aggregates weaken the mortar aggregate bond and reduce the strength.

Salinity causes corrosion of reinforcing bars as well as deterioration of concrete. 

4. Quality of supervision
Construction work should be carried out as per the laid down specification. Adherence to
specified water-cement ratio controls strength, permeability durability of concrete. Insufficient vibration

may result in porous and honey combined concrete, whereas excess vibration may cause segregation. 

5. Poor construction practices
A wide variety of poor construction practices can result in cracking in concrete structures. few of these are below.
  • Common practice of adding water to concrete to improve workability
  • Lack of curing
  • Inadequate formwork supports
  • Inadequate compaction
  • Placement of construction joints at joints of high stress

Objectives of repair of concrete structures
1. To improve strength of structure.
2. To increase or restore stiffness
3. To provide water tightness
4. To improve durability
5. To improve functional performance
6. To improve appearance of concrete surface
7. To prevent corrosion of reinforcement

  • The main reason for deterioration of concrete is crack developed in concrete.
  • Causes of cracks in concrete are given below.
1. Temperature and plastic shrinkage 
Plastic shrinkage cracking occurs when subjected to a very rapid loss of moisture caused by high temperature and low humidity in atmosphere. When the moisture reduced in concrete, It develop tensile stress and concrete become stiff and weak. It results in shallow cracks of varring depth which may be random.

2. Drying shrinkage
Drying shrinkage occur by the loss of moisture from cement paste constituent which can shrink the concrete by 1%. It restraint by aggregate that reduce drying shrinkage by 0.6 %. 

3. Chemical reaction
When the aggregates used in concrete contains active silica and alkalies react with cement paste and create swelling of gel which cause local expansion accompanied by stresses and eventually the structure get deterioration. 

4. Weathering
The weathering processes that can cause cracking include freezing and thawing, wetting, drying, heating and cooling. 

5. Construction overloads
Loads included during construction can generate sever conditions because in early age of concrete, it is very susceptible to damage and they often results in permanent cracks.



  • Various methods are used to repair cracks
1. Repair by Epoxy injection grouting
2. Repair by Routing and sealing
3. Repair by stitching
4. Drilling and plugging
5. Providing additional reinforcement
6. Repair by prestressing steel


Classification of material used for repair and rehabilitation

1. Patch repair material
  • Cementitious Mortar / Concrete
  • Polymer modified mortar / concrete
  • Polymer mortar / concrete
  • Quick setting compounds
2. Injection grout
  • Cementitious grout
  • Polymer grout
  • Epoxy grout
3. Bonding materials
  • Polymer emulsion type
  • Polymer resin type
4. Resurfacing material
  • Protective coating and memberane
  • Guinting
  • Shotcrete
  • Overlays
5. Sealing materials
  • Thermoplastic elastomers. 
  • Thermoplastic elastomers belong to the elastomer-family of materials. 
  • Elastomers (rubbers) are materials that can be highly expanded by exerting relatively little power. 
  • PTFE-based thermoplastics. 
  • Oil & Gas - Elastomers. 
  • High Perfomance Plastics. 
  • Engineering Plastics.

6. Waterproofing materials
  • Latex based waterproof chemicals
  • Acrylic based waterproof chemicals
  • Polymer based waterproof chemicals
7.Corrosion resistance material


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