Distress of concrete structures & their repair techniques
DISTRESS OF CONCRETE
STRUCTURES & THEIR
CONSTRUCTION & MATERIALS –III
PRESENTED BY: MOHAMMAD ZAID & MOHAMMAD FARZAN
PRESENTED TO : AR. KHALID HASAN
If a building has given about 25v to 30 years of service without much
maintenance or repair then it is reasonable to expect that it would need
some repair sooner or later.
CATEGORIES OF REASONS DISTRESS OF CONCRETE STRUCTURES
3. ENVIRONMENTAL EFFECTS
4. INADEQUATE MAINTENANCE
5. POOR DESIGNING AND CONSTRUCTION QUALITY
6. CHANGE OF LOADING PATTERN OR NON CONVENTIONAL LOADING ON
7. WATER LEAKAGE LEADING TO CORROSION OF CONCRETE STRUCTURE
PERFORMANCE OF CONCRETE STRUCTURE DEPENDS UPON:
1. QUALITY OF CONCRETE
2. AMBIENT CONDITIONS
EXPECTED SERVICE LIFE OF STRUCTURES
Life span of RCC is generally taken as 100 years
EXPECTED CONVENTION ABOUT DESIGN LIFE SPAN
Monumental structure like temple ,mosque or church is 500 to 1000 yrs.
Steel bridges ,steel buildings or similar structures is 100 to 150 yrs.
Concrete bridges or hign rise buildings or stone bridges is 100 yrs.
A house or general building is 60 to 80 yrs.
Highways :concrete pavement for about 30 to 35 yrs and bituminous
pavements for about 8 to 10 yrs.
COMMON FAILURE MODES OF R.C.C.
Cracks, potholes and erosion of the top layer of concrete,
rusting of reinforcement, splitting etc.
Cracking is the most common phenomenon in concrete
Cracking of concrete section cannot be prevented but size
and location of the cracks can be limited & controlled by
reinforcement, placement of control joint, and better
concreting and curing
Poor workmanship : untrained man power and bad quality of
Inadequate cover to reinforcement.
Loosely fitted joints.
Excessive water cement ratio
The IS: 456:2000 has laid down upper limits for water cement
ratio, normally it need about 15 to 18 lts. Of water per 50kg bag of
With this quantity of water concrete will be stiff and uncompact able so
we mix additional water for workability. This extra water after
evaporation leaves out minute capillary pores which lead to corrosion 0f
CAUSES OF EARLY DETERIORATION OF
Inadequate concrete cover
Bars are not bent accurately or may not be effectively fixed to
ensure that specified gap is left between bars and form work
while often not only bars touch formwork but also the binding
wires loose ends and the steel bars are seen at the surface of
In that case, they are prone to moisture.
Honey comb or Un vibrated concrete
Porous concrete is a major source of weakness in concrete.
Un-compacted concrete results in honey combing which gives
low compressive strength and permits moisture to enter,
resulting in corrosion of steel bars.
Cold joints or bad construction joints
A cold joint is a joint where fresh concrete is placed against a
previous un-compacted concrete which has already hardened
due to lapses of time that is more than concrete setting time.
Many a contractor does not put enough reinforcement in
concrete structural member s and hence it fails under tension.
Wrong placing of reinforcement
Many times contractors do not know the correct location of
reinforcement in structural member so it is not placed at
Inadequate cement quantity
IS: 456:2000 has laid down the minimum quantity in concrete.
Minimum quantity of cement is needed not only to coat the
fine and coarse aggregate particles but also to fill the voids
between the aggregate particles and to provide a thicker fill of
cement grout for easy workability.
Congested reinforcement bars
Too many steel bars in narrow and slender RCC columns, walls
or beams results in NO room for having cover in concrete nor
for inserting a needle vibrator to ensure full compaction
leading to honey combed concrete.
Initially rust steel bars
Alkali – aggregate reactivity
Under most conditions the reaction causes excessive
expansion and cracking of concrete after few months or year.
Effect of weather and water leakage
Weather causes structure to delay.
Prolong exposure to polluted environ,ent and acid rain can
give weathered concrete anfd corrode metal ties and
Porous cover blocks
Having incorrect mix proportions and water cement ratio.
These are usually fixed to the steel bars at about one meter
centers and if they are porous they become the starting
source of decay as they permit the ingress of moisture.
EFFECTS OF CRACKING ON LIFE OR
DURABILIY OF STRUCTURE
Understanding of cracks in concrete will help us to avpoid failures of
concrete on one hand, avoidable worries and expenditure on other
Reduce loading capacity of structure
Loss of appearance
• Apprehension of failure in mind
Better concrete mix design
Friendly environment condition at the time of concreting at
Have dense concrete
• Use low heat of pozzolanic cement in mass concreting.
IDENTIFICATION OF DISTRESSED
LOCATIONS ON STRUCTURES
Carry out a preliminary inspection possibly with some testing in order to get
characterize the nature of problem and to plan the detailed investigations.
Checking the strength of concrete
Chemical analysis on concrete
Conclusion from investigation
In majority of cases ,the cause of damage can be tracked to the following singly
or in combination:
Low cover to steel
• High chloride levels
Repair refers to modification of structure, damaged in its
appearance or serviceability, to restore, partly or wholly,
the pre-existing characteristics of serviceability, load-
bearing capacity and if necessary, to improve its durability.
Repair techniques are used to restore the structural
integrity and shape of a concrete element and generally
include removal of damaged concrete and replacement of
GENERAL REPAIR PROCEDURE
Surface preparation and protection of reinforcement
Chipping of defective or deteriorated concrete should be done till all
defective concrete is removed.
During repairs structural load carrying members must be supported.
Remove all rust from steel bars if it is reinforced member. In concrete
rust is like cancer.
The old concrete of masonry surface should be made rough to give
proper mechanical bond.
Wash and clean the entire surface before taking up repairs
Bonding material / epoxy should be applied between old and new
Spraying of water at regular intervals on inclined or vertical members
or we may also apply curing compound.
MATERIALS AND METHODS FOR CRACK
Repair materials can be of following types:
Polymer cement bound
Resin hardener bound(epoxy)
Following materials are generally used in crack repair:
1. Low viscosity epoxy materials
2. Epoxy modified mortar
3. Polyurethane based coating over epoxy mortar
4. Elastomeric concrete
5. Fiber reinforced concrete
6. Ferro cement
Low viscosity epoxy material
Designed for grouting gaps of low width of about 0.5 to 10mm. Epoxy
compound like RESICRETE of SWC or CONVEXTRA EP10 of FORSROC
which is normally supplied as two component product consisting of base
and hardener that is filler and polymer can be used.
Epoxy modified mortar
Epoxy mortar is a common material used for repair of concrete surfaces
in general. It cannot be used in open surfaces as it is non UV resistant
Polyurethane based coating over epoxy mortar
As epoxy mortars are non UV resistors ,but still have good strength so
they can be used with a coating of this material.
An epoxy material used in repairs not only in slabs and roads but also in
structures and concrete surface.
Fiber reinforced concrete
It is a concrete with small sized aggregates, cement sand mortar and
some type of hair .Various types of hair can be:
Generally polypropylene fiber is used.
Term Ferro cement is applied to a mixture of Portland cement and sand
reinforced with layers of woven or expanded steel mesh and closely
spaced small diameter steel rods. Construction made with this is more
resistant to earthquakes.
SOME SPECIFIC REPAIR TECHNIQUE FOR
1. Cracking of concrete surface up to certain depth:
a) Cracks up to depth of 0 to 20 mm –category A
b) Cracks between depth of 20 to 50-category B
c) Cracks to depth of more than 50mm-category C
1. Weather effects on concrete or rusting of reinforcement –category D
2. Blowholes and streak marks on concrete-category E
3. Honeycombing in concrete –category F
4. Holes in concrete or potholes or holes in road –category G
Repair methods-anyone of the above materials can be used with following
Application by hand
Casting into formwork fixed into existing concrete surface
Spraying through purposely designed equipment.
ASSESMENT OF QUALITY OF STRUCTURE
SOON AFTER ITS CONSTRUCTION
As the repair of structural element of building is over, it is desirable
hat soundness of structure is assed with the help of non-destructive
testing technique. Some NDTs which are available are:
Pulse velocity measurement method (PVM)
Rebound hammer or similar methods
Core cutting and testing of critical spots
Through these methods the strength of concrete, depth of
cover, cracks, voids, if any can be found.
REQUIREMENT FOR TRAINING FOR CONCRETE
REPAIR AND CONCRETE WORKERS
To achieve good quality of work it is necessary to have skilled
workers at site.
Like masons know the importance of water, right placement of
reinforcement, mixing ingredients etc. Training should look that
construction workers are trained for correct process and quality
procedure with practical sessions and hands on work.