The document discusses selection of repair materials and techniques for concrete structures. It provides guidelines for selecting materials based on properties like low shrinkage, bond strength, compatible properties, and durability. Common repair materials mentioned include premixed cement, polymer modified mortars, epoxies, and chemicals. Repair techniques are categorized for cracking versus spalling/disintegration. Specific techniques discussed include additional reinforcement, autogenous healing, concrete placement, drypacking, jacketing, and shotcrete. Surface preparation is emphasized as critical for repair success.

1. Repair materials
&
Repair techniques
Sourav Acharya

2. Repair materials - selection
• Selection of repair material is one of the most important tasks for ensuring
durable and trust worthy repair.
– Understand the process of deterioration of repair material under service
condition
– Ensure availability of material
– Skilled manpower
– Necessary equipment

3. Repair materials - durability

4. Repair materials – essential parameters
• The essential parameters for deciding upon a repair material for concrete are
– Low shrinkage properties
– Requisite setting/hardening properties
– Workability
– Good bond strength with existing substrate
– Compatible coefficient of thermal expansion
– Compatible mechanical properties and strength to that of the substrate
– Should allow relative movement, if expected, particularly in case of sealing of cracks or dealing with
expansion joints.
– Minimal or no curing requirement
– Alkaline character
– Low air and water permeability
– Aesthetics to match with surroundings
– Cost
– Durable, non degradable or non-biodegradable due to various forms of energy, life, UV rays, heat etc
– Non-hazardous/non-polluting

5. Low shrinkage
• Cementitious repair materials shrink with passage of time
• Cementitious repair material in its original form, if used for repair to concrete/
mortar, is likely to get either
– delaminated due to de-bonding or
– develop shrinkage cracks on its surface due to shrinkage strains and stresses.
• It is, therefore, essential that the low shrinkage property of repair material shall be
looked for while selecting a material for concrete repair

6. Bond with the substrate
• The bond strength of repair patch with the substrate is essential to have a
successful repair system.
• If it is felt that the bond strength of the repair material with the base material is
inadequate or less than the strength of the base material, then some other suitable
means could be explored to improve bond strength between repair material and
substrate.
– Adhesive,
– Surface interlocking system, and/or
– Mechanical bonding

7. Compatible properties
• The hardened material shall have compatible mechanical properties or rather slightly better
strength than that of base material.
• This property is desirable to ensure uniform flow of stresses and strains in loaded structures.
• It is well known that the elastic modulus of two concretes would be different for different
crushing strength . So if repair concrete is having strength much different than the base, it
could lead to non-uniform flow of stresses and may result in an early failure of the repair patch.
• For example, if M-20 grade of concrete has been used in original construction, the grade of the
repair material shall neither be less than M-20 nor higher than M-25.

8. Durability & Bio-non degradability
• The repair material selected should be durable under its
exposure conditions during the service life against
– chemical attack,
– resistant to any form of energy like ultra violet rays, infra red rays,
heat etc and
– should be bio non-degradable

9. Materials for repair
• Wide range of materials are available for concrete repair. Their application are
– Materials for Surface Preparation
– Chemical Rust removers for corroded reinforcement
– Passivators for reinforcement protection
– Bonding Agents
– Structural Repair Materials,
– Non-structural Repair Materials,
– Injection grouts,
– Joint sealants,
– Surface coatings for protection of RCC

10. Materials for repair
• Though available under different brand names, they can be classified as
follows:
– Premixed Cement concrete/mortars (modified with non-polymeric
admixtures/additives).
– Polymers/latex modified cement additives for mortars/concrete/cement slurry
[styrene butadiene rubber (SBR) latex, Poly (Vinylidene Chloride-Vinyl
Chloride) (PVDC), acrylics and modified acrylics)]
– Epoxy resins
– Chemicals for corrosion inhibitor, removal of rust

11. Premixed cement concrete/mortars
• cement concrete and mortars are most
natural repair materials for carrying out the
repairs to RCC
• Yet they are not favored because of
– drying shrinkage, slow setting, low workability,
prolonged curing requirement, permeability, etc

12. • Cements
– OPC
– Rapid hardening cement
– Portland slag cement
– Shrinkage compensating expansive cements
• Mineral additives
– Silica fume
– GGBS
– Fly Ash
• Admixtures
– Retarding admixtures
– Water reducing admixtures
– Air entraining admixtures, and
– Super-plasticising admixtures

13. Polymer modified mortar/concrete
• The technology of making the latex-modified mortar
and concrete is similar to that of the conventional
binding systems.
• Most polymers, such as latexes, are in the dispersed
form. These are initially mixed in water in required
proportion and then added to the cement mortar or
concrete.
• The latex-modified mortar or concrete, are placed
similar to normal concreting and cured under
optimum conditions.

14. Epoxies
• Epoxies also come in the category of polymers but in the case of epoxies, the
polymerisation process takes place when two materials called the epoxy resin and
hardener come in contact by thoroughly mixing in specified proportion.
• The epoxy resin materials have good mechanical strength, chemical resistance and
ease of working. These are being used in civil engineering for high performance
coatings, adhesives, injection grouting, high performance systems, industrial
flooring or grouting etc.

15. Repair techniques
• Repair technique should be selected prioritizing the following
– Repair of structural defects to ensure safety of the structure and
– Protection of the structure from further deterioration.
• The selected method of repair should achieve one or more of the following
objectives:
– Reinstate the structural integrity of the member by restoring or increasing its strength &
stiffness.
– Prevent the ingress of distress promoting agents such as moisture, chlorides and
carbon dioxide to improve durability.
– Maintaining the aesthetics/appearance of concrete surface.

16. • For ease of selecting repair methods and materials, it is
helpful to divide the possible approaches into two
general categories:
– those more suited for cracking
– those more suited for spalling and disintegration.
Repair techniques

17. Selection of repair method - active
cracks

18. Selection of repair method – dormant
cracks

19. Repair of spalling & disintegration
• Spalling and disintegration are only symptoms of many types of concrete distress.
• There is no single repair method that will always apply.
• Following have to be considered
– What is the nature of damage?
– What is the cause of damage?
– Is the cause of damage likely to remain active
– What is the extent of damage?

20. Repair of spalling & disintegration

21. Repair of spalling & disintegration

22. Concrete removal & surface
preparation
• Most repair projects involve removal of distressed or deteriorated concrete.
• The care with which deteriorated concrete is removed and a concrete
surface is prepared will determine the success of a repair project
• Repair techniques requiring no concrete removal should be considered for
situations where the deteriorated and damaged concrete does not threaten
the integrity of the member or structure.

23. • Concrete removal methods are classified into
– blasting,
– crushing,
– cutting,
– impacting,
– milling, and
– presplitting.

25. Preparation for repair
• One of the most important steps in the repair or rehabilitation of a concrete structure is the
preparation of the surface to be repaired. For reinforced concrete, repairs must include
proper preparation of the reinforcing steel to develop bond with the replacement concrete to
ensure desired behavior in the structure.
• Methods of surface preparation for concrete surfaces
– Chemical cleaning
– Mechanical cleaning
– Shot blasting
– Blast cleaning
– Acid etching
– Bonding agents

26. Repair techniques
• Repair techniques could be
– Provide additional reinforcement
– Autogenous healing
– Conventional concrete placement
– Drilling & plugging
– Drypacking
– Using FRP
– Flexible sealing
– Chemical grouting
– Cement grouting
– High strength concrete
– Jacketing
– Polymer overlays
– Polymer coatings
– Polymer concrete
– Routing and sealing
– Stiching
– Guniting (Shotcrete)
– Cathodic protection

27. Provision of additional reinforcement
• Provision of additional reinforcing
steel, either conventional
reinforcement or prestressing steel,
to repair a cracked concrete
section. In either case, the steel
that is added is to carry the tensile
forces that have caused cracking in
the concrete.

28. Autogenous healing
• Autogenous healing is a natural process of crack repair that can occur in the presence of
moisture and the absence of tensile stress.
• Autogenous healing has practical application for closing dormant cracks in a moist
environment. Healing will not occur if the crack is active and is subjected to movement
during the healing period
• Healing occurs through the carbonation of calcium hydroxide in the cement paste by carbon
dioxide, which is present in the surrounding air and water. Calcium carbonate and calcium
hydroxide crystals precipitate, accumulate, and grow within the cracks. The crystals interlace
and twine, producing a mechanical bonding effect, which is supplemented by chemical
bonding between adjacent crystals and between the crystals and the surfaces of the paste
and the aggregate. As a result, some of the tensile strength of the concrete is restored
across the cracked section, and the crack may become sealed.

29. Conventional concrete placement
• Replacing defective concrete with a new conventional concrete mixture of suitable
proportions that will become an integral part of the base concrete.
• The concrete mixture proportions must provide for good workability, strength, and durability.
• If the defects in the structure go entirely through a wall or if the defects go beyond the
reinforcement and if the defective area is large, then concrete replacement is the desired
method.
• Should not be used for replacement in areas where an aggressive factor which has caused
the deterioration of the concrete being replaced still exists.

30. Drilling & plugging
• Drilling and plugging a crack consists of
drilling down the length of the crack and
grouting it to form a key.
• This technique is applicable only where
cracks run in reasonably straight lines and
are accessible at one end.
• This method is most often used to repair
vertical cracks in walls.

31. Dry packing
• Process of ramming or tamping into a confined area a low water‐content mortar.
Because of the low w/c material, there is little shrinkage, and the patch remains
tight and is of good quality with respect to durability, strength, and water tightness.
• This technique has an advantage in that no special equipment is required.
However, the method does require that the craftsman making the repair be skilled
in this particular type of work.
• Drypacking can be used for patching rock pockets, form tie holes, and small holes
with a relatively high ratio of depth to area. It should not be used for patching
shallow depressions where lateral restraint cannot be obtained
• Drypacking can also be used for filling narrow slots cut for the repair of dormant
cracks. The use of drypack is not recommended for filling or repairing active cracks.

32. Fiber reinforced concrete
• Fiber‐reinforced concrete is composed of conventional
portland‐cement concrete containing discontinuous discrete fibers.
The fibers are added to the concrete in the mixer.
• Fibers are made from steel, plastic, glass, and other natural
materials.

33. Fiber reinforced concrete
• Carbon fiber reinforced plastic has over the past two decades become an increasingly notable
material used in structural engineering applications. It has proved itself cost‐effective in a
number of field applications strengthening concrete, masonry, steel and timber structures.
• Due to the incredible stiffness of CFRP, it can be used underneath bridge spans to help prevent
excessive deflections, or wrapped around beams to limit shear stresses. When used as a
replacement for steel, CFRP bars are used to reinforce concrete structures. More commonly
they are used as prestressing materials due to their high stiffness and strength.
• The advantages of CFRP over steel as a prestressing material, namely its light weight and
corrosion resistance, enable the material to be used for niche applications such as in offshore
environments.

34. Flexible sealing
• Flexible sealing involves routing and cleaning the crack and filling it with a suitable field
molded flexible sealant.
• This technique differs from routing and sealing in that, in this case, an actual joint is
constructed, rather than a crack simply being filled.
• Flexible sealing may be used to repair major, active cracks. It has been successfully used in
situations in which there is a limited water head on the crack.
• This repair technique does not increase the structural capacity of the cracked section.

35. Chemical grouting
• Chemical grouts consist of solutions of two or more chemicals that react to form a gel or
solid precipitate as opposed to cement grouts that consist of suspensions of solid particles in
a fluid.
• Cracks in concrete as narrow as 0.05 mm (0.002 in.) have been filled with chemical grout.
• The advantages of chemical grouts include
– their applicability in moist environments,
– wide limits of control of gel time, and
– their application in very fine fractures.
• Disadvantages are the
– high degree of skill needed for satisfactory use,
– their lack of strength, and,
– for some grouts, the requirement that the grout not dry out in service.

36. Cement grouting
• Hydraulic‐cement grouting is simply the use of a grout that depends upon the hydration of
portland cement, portland cement plus slag, or pozzolans such as fly ash for strength gain.
• These grouts may be sanded or unsanded (neat) as required by the particular application.
Various chemical admixtures are typically included in the grout.
• Hydraulic‐cement grouts may be used to seal dormant cracks, to bond subsequent lifts of
concrete that are being used as a repair material, or to fill voids around and under concrete
structures. Hydraulic‐cement grouts are generally less expensive than chemical grouts and
are better suited for large volume applications.
• Hydraulic cement grout has a tendency to separate under pressure and thus prevent 100
percent filling of the crack. Normally the crack width at the point of introduction should be at
least 3 mm.

37. High strength concrete
• This method is similar to an extension of the conventional concrete
placement method. Chemical admixtures such as water‐reducing
admixtures (WRA’s) are usually required to achieve lower w/c and
subsequently higher compressive strengths. Mineral admixtures are also
frequently used.
• High‐strength concrete for concrete repair is used to provide a concrete with
improved resistance to chemical attack, better abrasion resistance,
improved resistance to freezing and thawing, and reduced permeability.

38. Jacketing
• Jacketing consists of restoring or increasing the section of an existing member (principally a
compression member) by encasing it in new concrete. The original member need not be
concrete; steel and timber sections can be jacketed.
• When properly applied, jacketing will strengthen the repaired member as well as provide
some degree of protection against further deterioration.
• The removal of the existing damaged concrete or other material is usually necessary to
ensure that the repair material bonds well to the original material that is left in place. If a
significant amount of removal is necessary, temporary support may have to be provided to
the structure during the jacketing process.

39. Jacketing
• Any suitable form material may be used. A steel reinforcement cage may be
constructed around the damaged section.
• Once the form is in place, it may be filled with any suitable material.
• Choice of the filling material should be based upon the environment in which it will
serve as well as a knowledge of what caused the original material to fail.
• Filling may be accomplished by pumping, by tremie placement, by preplaced
aggregate techniques, or by conventional concrete placement.

40. Jacketing