This document discusses repair and retrofitting techniques for masonry structures. It begins by outlining objectives and definitions of repairs and retrofitting. It then describes various causes of damage in masonry structures, including aging effects, construction errors, and maintenance issues. The document outlines different types of cracks seen in masonry structures and general causes. It discusses evaluation and various repair techniques like mortars, grouts, coatings, and mechanical anchors. Retrofitting techniques including surface treatments like ferrocement, reinforced plaster, and shotcrete are covered. The document provides details on methods like grout injection, post-tensioning, and confining masonry with reinforced concrete columns.

1. REPAIR AND RETROFITTING OF
MASONRY STRUCTURES
EFFORTS BY:
ABHISHEK BHATT (0506)
ANTARA MASHRUWALA (1706)
DISHITA SHAH (3006)
RAVI SONI (5207)

2. Objective:
To study different repair materials and techniques to be
adopted in various situation to repair defective structures of brick
and stone masonry.
Repairs: Process to replace or correct deteriorated/damaged
materials and components of a building.
Retrofitting: Upgrading of structural and non-structural systems to
provide a higher level of resistance than existed before .

3. HOW DAMAGE OCCURS IN BRICK-MASONRY STRUCTURES:
Effect of Aging on Brick-Work:
Rain Exposure
Temperature
Moisture Absorption
Chemical Alteration
Continuous Exposure to Chemicals
 Construction Error:
Eccentrically Loaded Walls gives overturning effect (Decorative Panels on one
side, Support of Working platforms on one side)
Usage of Poor quality of materials
Error due to saving in economy

4. Maintenance:
Common maintenance to brick is to white wash or to paint them at regular
intervals, preferably every 2 years.
To maintain all sanitary installation in a good condition, any leakage notice
anywhere should be intended to immediately, since a small leakage from nani-
trap would lead to a major damage in due course.
Any cracking wherever noticed should be attended immediately either by
sealing the joints with cement mortar or by strengthening the cracks with
reinforced bands.

5. TYPES OF CRACKS IN MASONRY STRUCTURES:
1.Vertical cracks in sidewalls at corner
2.Vertical cracks around balconies
3.Vertical cracks below the openings in line with the window jambs.
4.Vertical cracks at the junction of RCC column and masonry wall.
5. Vertical cracks in the top most stories at corners of structures having RCC slab.
6.Horizontal cracks at window lintel or sill level in the top most story.
7.Horizontal cracks in the top most story below the RCC slab level.
8. Horizontal cracks at eaves level in the buildings having pitched roof with wooden
joists and purlins.
9. Random cracks in all directions involving both external and internal walls.
10. Diagonal cracks over RCC lintels spanning large openings.
11. Shrinkage cracks.

6. TYPES OF CRACKS IN MASONRY STRUCTURES:
Typical Earthquake Typical Earthquake Wall Cracking above the
Damage - Wall Corner Damage: In-Plane Wall Door Opening (1993
Failure (1993 Killari Cracking Killari Earthquake)
Earthquake)

7. GENERAL CAUSES TO DEVELOP THE CRACKS:
Poor quality of bricks.
For masonry work,use the porous stones.
Absence of grading in before the use of fine aggregate fine mortar.
If percentage of clay and silt in fine aggregate exceed 3 percent.
Due to the excessive amount of soluble sulphate.
Plumb alignment.
The position of the element in the structure.
Differential loading.
Weak mortar.
Insufficient bond.
Improper curing.
Entered dampness from ground, roof and exterior faces.
High daily temperature variations.
Atmospheric pollutions.
Lack of strength at corner and at junction of walls.
Improper binding of thick walls.

8. REPAIR TECHNIQUES
Sand / Cement Mortar:
It is the most simplest and basic repair method. It is highly reliable but may fail
under severe drying conditions.
Thus cracks will appear as a result of shrinkage in the plastic state of mortar.
Due to this shrinkage, debonding and delaminating frequently occurs.
Due to high water cement, ratio strength decreases.
High density of pores and capillaries allow water and acidic vapours to more easily
penetrate the repair and attack to the reinforcement bars.
Polymer modified cementations mortars:
Polymer modified cementitious mortars are factory controlled blend of specially
graded fillers, cement and admixtures to control strength development in set time. To
reduce the shrinkage they contain polymers to improve the low permeability, quality
and to enhance adhesion.
The thermal expansion properties are similar to normal concrete.
Heat development is low so much larger volume repairs can be undertaken.
Low impermeability can prevent ingress chlorides.

9. Epoxy resin mortars:
Epoxy technology is based on the mixing of two liquid resins which
react together to form a hard solid if aggregates are added the resin system
acts to bind them together to create mortar.
Achieves compressive strength of 60-80 N/mm2 and very heavy high
flexural strength.
Due to good adhesion repair will never fail along correctly prepared
bond line.
More strength gain occurs in one day in normal atmospheric conditions.
Properly compact mortar is impermeable to water.
Most epoxy mortar requires primer.

10. Epoxy injection:
Narrow cracks of 0.05 mm cracks are repaired by this method.
High strength, highly viscous material can be achieved.
In this, holes are drilled at closer interval repairs are done under external force
through pumps or greasing guns.
Normal pressure should be of 1 kg/cm2.We should not apply too much
pressure which propagates the cracks.
High degree of skills and executions are required to repair these types of
cracks.

11. Crack stitching:
This method involves drilling holes on both sides of crack and grouting in
stitching dogs.
Stitching may be used when the tensile strength must be re-established
across major cracks.
Stitching a crack tends to stiffen the structure, causing the concrete to
crack elsewhere. therefore it may be necessary to strengthen the adjacent
section with external reinforcement.

12. METHOD FOR ADVANCE RETROFIT TECHNIQUE WITH
HELICAL REINFORCEMENT
Firstly slots are cut with cutter machine of length 500 mm on each side of crack.
1.
The depth of slot is 10 mm but it also depends on the plaster surfaces.
Clear loose detritus from slots ensuring exposed brick surfaces are cleaned of
2.
mortar and flush thoroughly with water, or treated with a suitable primer.
3. Now fill the slot with grout with pressure.
Push Helical 6mm reinforcement crack stitching tie into grout to approximately
4.
two thirds of slot depth.
Finish the surface and repair the crack on the wall with appropriate filler /grout
5.
chemical.

13. Tuck pointing:
 Defective joints can usually be repaired by tuck-pointing with Portland cement
mortar, with the help of skilled stonemason
 In this method, all joints, vertical and horizontal, in the face of the wall should be
tuck-pointed.
 This procedure requires removing and replacing all mortar to a depth of at least
16mm throughout every joint. each joint is raked to a depth not greater than
26mm unless the old mortar is so defective then it is necessary to remove the
mortar up to greater depth.
 The depth of old mortar is removed first so that sound mortar acts as a base for
new mortar.
 All dust and dirt within the raked joints should be washed out.
 The mortar is mixed at least 1 hour prior to use to ensure pre-hydration which
stabilizes the plasticity and workability of mortar and minimizes any tendency to
shrink after insertion into the joint opening.
 The sand/cement ratio should be about 3 to 1 by volume.

14. TUCK POINTING

15. Grouting (cement mortar):
Masonry structures can be sealed effectively with less cost by using grout
provided the cement-base stabilizing mixture contains an intrusion aid.
The consistency of intrusion mixture is that of smooth slurry.
Before the intrusion, grout is pumped, the holes are tested by pumping
water to see the drilling is adequate and to determine correct consistency
for the slurry repairs.
Firstly plaster is removed near the cracks from inside and outside of
walls and clean the cracks thoroughly with airjet and water.
Wet the cracks ,if dry ,by sprinkling water.
This mixture is pumped into holes previously drilled at various interval
to various depths without damaging the integrity of structure.
Pumping the grout simultaneously into multiple series of drill holes
ensures good penetration into any fissures within the structure and for
making masonry structures watertight.

16. Grouting (chemical):
 Chemical grouts consist of solution of two or more chemicals (such as
urethanes, sodium silicate) that react to form a gel. This grout opposed
to cement grouts that consist of suspension of solid particles in a fluid.
 Advantages of chemical grout include applicability in moist
environment and their ability to be applied in very fine facture.
 Disadvantage is high degree of skill needed for satisfactory use and their
lack of strength.
 Crack as narrow as 0.05 mm can been filled with chemical grout.

17. Polymer coating:
 Polymer coating is use for the job condition and can be an
effective protective coating if properly applied.
 Polymer coating should be selected from the material specifically
for the intended application.
 Some formulation will adhere to damp surfaces and even under
water but may required a completely dry surface.
 Mixing and applying polymers below 16 degree and above 32
degree Celsius will require special caution and procedure.
 Moisture passing through the sub grade backfill or from
rainwater can accumulate under the coating, which will be
interrupted by freezing and thawing.

18. REPAIR MATERIALS
Epoxy resins
 Epoxy resins are excellent binding agents with high tensile strength. The
epoxy components are mixed just prior to application. The product is of low
vis­cosity and can be injected in small cracks too.
 The higher viscosity epoxy resin can be used for surface coating or filling
larger cracks or holes.
Epoxy mortar
 Epoxy resins when combined, with sand aggregate it forms epoxy mortar.
Epoxy mortar mixture has higher compressive strength, higher tensile
strength and a lower modulus of elasticity than Portland cement concrete.
Quick-setting cement mortar
 It is a non-hydrous magnesium phosphate cement with two components, a
liquid and a dry, which can be mixed in a manner similar to portland cement
concrete.
Gypsum cement mortar
 It has lowest strength at fail­ure among these three materials. So it is used in
minor repair works in structural application.
Mechanical anchors
 Mechanical anchors provide both shear and ten­sion resistance. Such anchors
are manu­factured to give sufficient strength.

20. RETROFIT:
Post earthquake improvement of the seismic resistance of
a structure including repair of damage . Upgrading of structural
and non-structural systems to provide a higher level of resistance
than existed before the earthquake.
SURFACE TREATMENT:
Surface treatment is a common method, which has largely
developed through experience.
Surface treatment incorporates different techniques such as
ferrocement, reinforced plaster, and shotcrete.

21. FERROCEMENT:
Ferrocement consists of closely spaced multiple layers of hardware
mesh of fine rods
(Figure 1 (a)) with reinforcement ratio of 3-8% completely embedded
in a high strength (15-30 MPa) cement mortar layer (10- 50 mm
thickness).
The mortar is troweled on through the mesh with covering thickness
of 1-5 mm.
Typical mortar mix consists of 1 part cement: 1.5-3 parts sand with
approximately 0.4 w/c ratio.

22. REINFORCED PLASTER:
A thin layer of cement plaster applied over high strength steel reinforcement
can be used for retrofitting.
The steel can be arranged as diagonal bars or as a vertical and horizontal
mesh.
In diagonal tension test and static cyclic tests, the technique was able to
improve the improvement in strength depends on the strengthening layer
thickness, the cement mortar strength, the reinforcement quantity and the
means of its bonding with the retrofitted wall, and the degree of masonry
damage.

23. SHOTCRETE:
 Shotcrete overlays are sprayed onto the surface of a masonry wall over a mesh
of reinforcing bars.
 In shotcrete the size of coarse aggregate is limited to 6mm.
 With thorough mixing of aggregates and adjustment of pressure at the nozzle
should be controlled otherwise a large proportion of coarse aggregate is lost in
rebound.
 Due to greater wear of nozzles during shotcrete there is a tendency to reduce the
proportion or even eliminate coarse aggregates.
 Certain additives are available which can reduce wear and tear of nozzles.
 After shotcreting proper curing is essential.
 In situation where heavy construction machinery can not be moved or is not
economically viable, manual shotcreting can also be resorted too.
 In manual method layers of concrete can not exceed 35-40 mm in thickness
when laid.
 Mason should be trained properly to move the trowel applying vibrations and
simultaneously for compacting effect on each layer.
 Non destructive testing of shotcrete repair work should be carried out.

24. GROUT AND EPOXY INJECTION:
 PROCESS :
 The crack or joint should be widen wherever the injection work is to be carried out
(approximately 15 mm wide x 15 mm depth)
 Drill holes of about 13 mm dia upto 150 mm deep at 500 mm @ c/c.
 Use compressed air to clean the hole, as well as crack to remove dust, dirt, loose
materials etc.
 Use 12 mm dia specially threaded injection nipples and fix them into the holes
provided. Seal the entire surface around the nipple with putty.
 Seal the surface of the crack with putty so as to ensure that the injected grout does
not leak from the gaps & from cracked surface.
 The surface now is ready for injection.
 Prepare the injection grout and load it into the injection gun.

25. EXTERNAL REINFORCEMENT:
A steel plates or tubes can be used as external reinforcement for existing
Unreinforced Masonry(URM) buildings.
Steel system is attached directly to the existing diaphragm or wall.
Two vertical members (via pin connections), which are placed next to the
existing wall (i.e. creating in-fill panel) can be used.

26. CONFINING URM USING R.C. COLUMNS:
 Confined masonry with R.C., weak frame represents one of the most widely
used masonry construction system in Asia and Latin America.
 In China, they used such confinement in new masonry buildings as well as it is
used as retrofitting for existing URM buildings.
 The basic feature of confined masonry structures is the vertical R.C. or
reinforced masonry tie columns, which confine the walls at all corners and wall
intersections as well as the vertical borders of doors and windows openings.
 In order to be effective, tie columns should connect with a tie beam along the
walls at floors levels.

27. POST TENSIONING:
Post-tensioning involves a compressive force applied to masonry wall; this force
counteracts the tensile stresses resulting from lateral loads.
There has been little application of this technique; post-tensioning is mainly used
to retrofit structures characterized as monuments.
This is due in part to lack of knowledge about the behavior of post-tensioning
masonry.
In addition, the codification of post-tensioning masonry has only begun recently.

28. (Contd…..)POST TENSIONING:
Post-tensioning tendons are usually in the form of alloy steel thread bars.
Bars typically show higher relaxation losses (2-3 times strand losses) and much
lower strength/weight ratio (VSL 1990); in addition, a major drawback for using of
steel bars is corrosion. Fiber reinforced plastic presents a promising solution for this
problem
Tendons are placed inside steel tube (duct) either within holes drilled along the
midplane of the wall or along groves symmetrically cut on both surfaces of the wall.
Holes are cement grouted and external grooves are filled with shotcrete.

29. GROUT OR EPOXY INJECTION IN
CRACKS
1 - Plaster removed
2 - Cracks sealed after cleaning
3 - Grout ports
Strengthening of existing
masonry
1 - Brick or block wall
2 - Injection holes
3 - Grout mixture

30. STRENGTHENING WITH WIRE MESH AND MORTAR
STRENGTHENING WITH WIRE MESH
Two steel meshes (welded wire fabric with an elementary mesh of approximately 50 x 50 mm)
are placed on the two sides of the wall, they are connected by passing steel each 500 to 750 mm
apart, A 20 to 40 mm thick cement mortar or micro concrete layer is then applied on the two
networks thus giving rise to two interconnected vertical plates. This system can also be used to
improve connection of orthogonal walls.
1 - Welded wire mesh - 50 mm x 50 mm
2 - Mortar or micro-concrete rendering
3 - Concrete roof band
4 - Cross ties at 500 to 750 mm apart
5 - Corner bar diameter 8 mm
3
CORNER REINFORCEMENT

31. For Large cracks and crushed concrete
For cracks wider than about 6 mm or for regions in which the concrete or masonry has crushed, a
treatment other than injection is indicated. The following procedure may be adopted.
The loose material is removed and replaced with any of the materials mentioned earlier, i.e., expansive
cement mortar, quick setting cement or gypsum cement mortar.
Strengthening of existing
masonry
1 - Wire mesh on front face
2 – Clamps
3 - Wire mesh on back face
4 - Cement plaster
5 - Crack in wall

32. Splint and bandage strengthening technique
The technique of covering
the wall with steel mesh
and mortar or micro-
concrete may be used only
on the outside surface of
external walls but
maintaining continuity of
steel at the corners. This
would strengthen the walls
as well as bind them
together. As a variation and
for economy in the use of
materials, the covering
may be in the form of
vertical splints between
openings and horizontal
bandages over spandrel
walls at suitable number of
points.

33. Splint and bandage strengthening technique

34. NEGLIGENCE AFTER REPAIRS AND RETROFITTING
No. Negligence Reasons
1 Hair cracks are found on lack of curing after 4 hours from the application
the all ready strengthened of cement mortar.
brick masonry walls.
2 Weld mesh are soon on the improper thickness of the cement mortar
brick masonry walls after
finishing coat.
3 Uneven plaster surface are works are going on without preparing proper
found on the wall. level markers.
4 Different shades are found Improper mixing of cement with other
on plastered surface. materials and improper curing

35. CASE STUDY : JABALPUR EARTHQUAKE
• PHOTOGRAPHS OF DAMAGE DUE TO EARTHQUAKE
• STRENGTHNING OF EXISTING CONSTRUCTION
• STRENGTHNING OF NEW CONSTRUCTION
• PHOTOGRAPHS OF NEW CONSTRUCTION AFTER
EARTHQUAKE

36. JABALPUR EARTHQUAKE DAMAGED NUILDINGS
Partial Building Collapse in the Faillure of Brick Masonry Walls in
1997 Jabalpur Earthquake the 1997 Jabalpur Earthquake

37. STRENGTHENING OF EXISTING CONSTRUCTION
Description of Seismic Strengthening provisions
Seismic Deficiency
used
Lack of integrity (box-type action) Installation of seismic belt (bandage) at the lintel level; it
consists of welded wire mesh installed above the lintel
level and anchored to the wall. The mesh is covered with
a thin cement plaster overlay (see Figure a)
Cracks in the walls In case of small cracks, pressure injection of epoxy
grout; in case of large cracks, filling the gaps with
cement grout and jacketing with reinforced cement
overlay.
Inadequate wall resistance (shear and tensile) Reinforced concrete jacketing. Difficult to find skilled
labor and materials for welded wire mesh in rural areas
Flexible floor/roof diaphragm (Corrugated metal Installation of RC roof band (bond beam). Provision of
sheets/timber) roof band is expected to enhance the overall intergrity
and improve torsional resistance of building
Cracking/damage of wall corners (due to improper Corner strengthening of wall corners - installation of
interlocking of cross walls) welded wire mesh anchored to the walls with steel
dowels and covered with a thin cement plaster overlay ,
see Figure b.

38. FIGURE A FIGURE B

39. STRENGTHENING OF NEW CONSTRUCTION
Description of Seismic
Seismic Deficiency
Strengthening provisions used
Reinforced concrete roof band; provision of roof band
Roof
results in an improved overall integrity and torsional
resistance of the building.
RCC lintel band; very effective, however skilled labour
Wall
and materials may not be available, see Figures 7D, 7E
and 7F
Improved quality of masonry (bricks and mortar) use of
Wall
better quality bricks will drastically improve the wall
seismic resistance; use or richer cement/sand mortar will
improve wall shear resistance.
Provision of vertical reinforcement at wall corners and
Wall
intersections, see Figure 7G (Source: IAEE 1986)

40. 7D-An Example of New Construction with 7E-Construction of RC lintel
Seismic Features (note RC lintel band) band
7F-Construction of RC Lintel Band - Pouring of
Concrete Completed

41. 7G-Provision of Vertical
Reinforcement at Wall
Corners and
Intersections

42. CONCLUSION
 Cost effective and safer approach will be to carry out appropriate repair and
retrofitting of the building.
 It will offer the advantage of carrying out the work part by part or room by room
so that the occupants may continue to live in the building during the repair and
retrofitting work .
 By doing so the cost of repair and retrofitting came to only 8 % of the estimated
cost of reconstruction.

43. REFERENCES:
 Civil Engineering & Construction Review (Vol.14 Dec.2001)
 Structural Consolidation & Strengthening of masonry (Department of
Civil Engineering, Belgium)
 13th International Brick & Block masonry Conference
 Deterioration & Damages in Buildings, Department of Civil
Engineering, IIT, Kharagpur
 Jabalpur & Killari earthquake Damage reports & Retrofitting Method,
Department of Civil engineering, IIT, Kanpur

44. QUESTION FROM OUR PRESENTATION
 Why cracks or deteriorations occurs in brick masonry
structures? State any 6 techniques by which it can be
repaired? Explain any one in detail with neat sketches.