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The building structure once built is subjected to weathering actions and structural loadings due to which it looses its serviceability.Deterioration to building is not uncommon in India and also anywhere in the world.Deterioration of building takes place due to improper repair and maintainance.Factors like:Environmental pollution, thermal stresses, chemical and biological effects lower the life of structure and its durability.

The important factor influencing the building deterioration specially in India is lack of maintainance culture.Economic considerations and time constraints have made it compulsory to go for repair and rehabilitation of the damaged building structures rather than their total replacement.Thus the repair materials are intended to protect and maintain the original form and serviceability of buildings for longer periods.Proper repair materials at proper time brings maximum economic benefit by optimizing the serviceable life of the building structure.

The repair materials for cement concrete/mortar shall be easy to apply and require no attention after the application of repair materials to repair.The essential parameters for selection of repair materials are as follows:Low shrinkage propertiesSetting and hardening propertiesWorkabilityGood bond strength with existing substrateCompatible coefficient of thermal expansionCompatible mechanical and strength properties than substrate

Should allow relative movements particularly in case of sealing of cracks and dealing with expansion jointsMinimum or no curing requirementAlkaline characterLow air and water permeabilityAesthetics to match with surroundingsCostDurable, non degradable or non biodegradable Non hazardous and non polluting.

The basic construction materials like cement, sand, aggregate, steel, bricks, concrete/mortar, timber, paints can all be used as a repair materials.Following are the types of repair materials depending upon requirements, properties and use are as follows:Anti corrosion coatingsAdhesives/Bonding aidsRepair mortarsCuring compoundsJoints SealantsGroutsWaterproofing systems for roofs

Special concretesMigratory corrosion inhibitorsProtective coatingsFibre reinforced polymersAramid fibre reinforced polymersCarbon fibre reinforced polymersGlass fibre reinforced polymersEpoxysMaterials for special applications

A good repair material should have the best combination of following properties:

Mechanical properties as close to the base materials as possibleGood adhesion in dry, damp or wet conditionsLow shrinkage (during curing and long term)

Sealants (as the name)-it is a repair material that seals the pores and gaps.In building and construction industry-the term sealant is defined as a material used for sealing of expansion joints and gaps between dis-simmilar building materials.In construction practices, building materials like steel, concrete, plastics, aluminium and glass are used which essentially consists of joints or cracks and these get widened due to differential thermal coefficients of materials used.A sealant in any material intended to maintain a seal or act as a barrier between two sides of a joint/crack which may be subjected to some degree of movement.Thus the sealant is required to seal the inner portion from the external environments like wind, rain, pollution, air borne dust, micro-organisms, insects, water, heat and sunlight.

Accommodate continuous changes in size of a jointAccommodate movement of various elementsExclude rain, snow and wind from interior of buildingResist freeze/thaw effectsResist abrasion and water flow through jointsPrevent the entry of materials which cause movements and damagesExclude chemical and biological contiminants from joints to protect from damage and maintain hygienic conditionsProvide sound insulation

Ease of mixing and application over practical temperature rangeAdhesion to faces of jointsNo undue shrinkageFreedom fromCreep, slump or cold flow bleeding, and regular maintainanceAdequate cohesive propertiesResistance to chemicalsResistance to weathering agenciesAdequate hardness of abrasion resistanceCapability of being repaired and resealed

Oleo resinous masticsBitumen and rubber/bitumen-based sealantsAcrylic resin sealantsFlexible epoxide sealantsPolysulphide sealantsPolyurethane sealantsSealing stripsSilicone sealantsHot poured sealants

Epoxies come in category of polymersIn case of epoxies, polymerization process takes place when two materials called, epoxy resin and hardener come in contact by thorough mixing in specified proportionThe epoxy resin material have:A good mechanical strengthChemical resistanceEase of work

Epoxies are used in civil engineering for

High performance coatings

Adhesives

Injection grouting

High performance systems

Industrial flooring or grouting etc

Epoxies are generally toxic in nature, thus it requires a lot of care in their handling

Special care required during mixing and applications of epoxies are:

They should not come in contact with skin, hence to be used with rubber gloves

The utensils/equipments used for mixing resin and hardener should be immediately cleaned after its use

The pot life of the mixed epoxy is generally very limited-1 to 2 hours

Thus it should be finally applied as an adhesive within the pot life period

The epoxies are generally used as an adhesives to act as a bond coat between the old concrete and repaired concrete

The epoxies have a glass transition range at temperatures at 60 to 80 deg-Cel depending upon type of epoxy thus they should not be used in exposed environments

Epoxies have much higher bond strength than other polymers, but at the same time, epoxies are costlier.

Anti corrosive and water proofing protective coatingsFussion bonded epoxy powder coatings-used for protection to reinforcing bars against corrosion in RCC structures in highly aggressive environmentsIPN coatings-used as surface coatings to arrest carbonation of concrete cover or other chemical attack by sealing their surface against environmental elementsEpoxy coating along with epoxy grouting-used to render leaking roofs, toilets, bathrooms as impervious. Epoxies should not be used exposed to sunlightsPolyurethane coatings-used as surface coatings on exposed RCC structures as they have excellent UV resistance, good elasticity and abrasion resistance.

Bond coats (structural adhesives) and grouts-Epoxies are used as bond coats and grouts due to their excellent adhesive qualities on cementatious and metallic surfaces

Structural repairs to concrete-due to excellent mechanical properties and bond characteristics of epoxy mortars/concretes are use to repair the damages of the structures.

Fibre reinforced polymers are the materials made from aramid, carbon, glass or any other high performance materials embedded in polymeric matrices in the form of bars, tendons, and strands are produced and used in construction

High strength in the direction of fibresIt is anisotropicImpervious to chloride ions and chemical attackTensile strength is greater than steel the weight of steelTransparent to magnetic fields and radar frequenciesNon conductive both electrically and thermallyGood resistance towards corrosionEasy to handleGood resistance to damping and fatigue behaviourConvenient to use for repairing structures

High cost

Low shear strength

Low ductility

Susceptibility to stress rupture effect

The need to repair is dictated by the severity and root causes of the deterioration as determined from the diagnosis.The success of repair of damage depends upon the correct assessment of the root cause, the right choice of repair materials and the quality or workmanship in its execution.The damages in many cases can be effectively repaired and rectified with the use of new materials in confirmity with modern construction technology.

Building repair and maintainance management by P.S.Gahlot, Sanjay Sharma.

Handbook on repair and rehabilitation of RCC buildings by C.P.W.D.

The repair on concrete structures by R.T.L.Allen.

American composites manufacturers association.

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