REPAIR AND REHABILITATION
OF CRACKS IN CONCRETE
ABSTRACT
Deterioration Of A Reinforced Concrete Structure Is Frequently Caused By A Combination Of Various Factors.
It Can Result From Physical Damage, Chemical Attack, And
Structural Movement And From Material Degradation On Exposure To Severe Environment
Since Time And Money Get Wasted In The Process Of Replacing New Structure its Better We Repair Them For Extending The Life Of The Structure And Help It To Function It As It Was Before.
The Project Deals With The Case Study On The Deterioration And Damages in Concrete Structure With Suitable measures For
Rehabilitation.
The Deteriorated Structure Chosen For Our Investigation Is
INTRODUCTION
Every structure is vulnerable to Deterioration and Damage. The structure is designed to meet the
structural demands and design loads, coming up on the building.
Destroying a previling structures and constructing a new one is not economical and needs lots of fund and loss of energy.
Hence there is an urgent need for rehabilitation of concrete structures.
Rehabilitation is the process of renewing the old
structure by using special material and suitable methods so that the structure will serve the purpose to our needs
DETERIORATION OF STRUCTURE
AND THEIR CAUSES
Distress in building are common. A building component develops cracks whenever stress in the component
exceed its limit stress in a structural member of a building can be caused by external forces.
Distress can be broadly classified as: Structural
Non structural
TYPES OF CRACKS
Intrinsic cracks
Flexural and shear cracks
Temperature cracks
Manufacturing and shipment cracks
Structural and Non-Structural cracks
Torsion cracks
Tensile cracks
Compression cracks
CLASSIFICATION OF CRACKS
Classification of cracks based on their width.
Fine : Width less then 0.1mm
Thin : Width 0.1mm to 0.3mm
Medium : Width 0.3mm to 0.7mm
Wide : Width 0.7mm to 2.0mm
Very wide : Width greater than 2mm
Cracks may be only at the surface or may extend to
more than one layer of materials. Occurrence of closely spaced fine cracks at surface of a material is called
CAUSES OF CRACKS
Structural cracks
Cracks due to Shrinkage
Cracks due to Foundation settlement
Construction Cracks
Cracks due to Quality of materials
Cracks due to construction error
Natural Cracks
Cracks due to Vegetation
Cracks due to Earth Quake
CRACKS DUE TO SHRINKAGE :-
EFFECTS OF SHRINKAGE:-
Vertical Cracks around balconies
Diagonal Cracks over RCC lintel’s sparrey large
openings. This is due to shrinkage of concrete
Very fine Cracks of map pattern known as Crazing on concrete
REMEDIAL MEASURES :-
Shrinkage Cracks in masonry could be minimized by avoiding are of rich cement mortar in masonry.
To reduce the Cracking tendency due to shrinkage, using adequate and properly
CRACKS DUE TO FOUNDATION
SETTLEMENT
EFFECTS DUE TO FOUNDATION SETTLEMENT :-
Diagonal Cracks across the corners of the
building affecting two adjacent walls there Cracks due to shrinkage of soil below foundation.
REMEDIAL MEASURES :-
To avoid the settlement of soil by taking the foundation 3.5m deep.
By avoiding the planting of trees near the building.
CRACKS DUE TO POOR QUALITY
MATERIALS :-
EFFECTS :-
When using poor quality cement the strength and durability of the plastering in affected.
The cement used in mortar shrinking occur due to temperature which causes Cracks in walls
REMEDIAL MEASURE :-
During construction, the sand having no impellers live mud, clay, salt and shed chips reduce the
Crack in building.
Water due from salt and other chemical reducer the Crack.
CRACKS DUE TO VEGETATION :-
Effects :-
Existence of vegetation, such as fast growing tress in the compound walls some time causes the cracks in the walls due to expansive action of roots growing under the foundation
Remedial Measures :-
Fast growing frees should not be planted near the compound wall.
If old trees exist done to an old building there threes should not be removed all at once
operation. The removal of trees should be done in stages.
MATERIALS FOR REPAIR AND
REHABILITATION
WATER PROOFERS
These chemicals are added to concrete or mortar at the time of preparation to make the structure waterproof .
They react with the lime contained cement to form
inorganic salts which block the pores and capillaries thereby reducing moisture penetration
The water proofers may be obtained in powder or liquid form and consist of pore filling or water repellent materials.
Materials in water repellant class are soda and potash soaps to which lime, alkaline and silicate are sometimes added.
Chemically inactive materials in the water repellant class are calcium soaps, resins, vegetable oils, fats, waxes, bitumen and coal tar.
CORROSION INHIBITING CHEMICALS
corrosion inhibiting chemicals – They resist
corrosion of reinforcement. Generally alkalinity of concrete in adequate protection for steel.
However in adverse environment sodium
benzoate, calcium lingo sulphonate and sodium nitrate have shown good results
ANTIFUNGUS ADMIXTURES
Antifungus admixtures – These are added to
control and inhibit growth of bacteria or fungus in surfaces expressed to moisture Polyhalogenated phenol, Dieldrin emulsion and copper compounds are some of the chemicals used for this.
POLYMER COMPOSITES
These are produced using polymers with cement, sand and or aggregate. The addition of polymers to concrete have been shown to improve.
Compressive strength
Resistant to wear and tear
Fatigue resistance
Impact resistance
Impermeability
Durability
EPOXY RESINS FOR STRUCTURAL
REPAIRS AND REHABILITATION
Amongst the synthetic resins such as epoxy, polyester, acrylic, polyurethane etc. epoxy resins posses very
high mechanical and adhesive strength properties most desirable for Civil Engineering applications. Epoxy
resins when cured with different hardeners offer a wide range of properties:
High adhesive strength to almost too all materials.
Low shrinkage drying, curing.
Exceptional dimensional stability.
Natural gap filling properties
Thermosetting (Does not melt)
EPOXIES FOR CRACK REPAIRS
The most approximate method of crack repair depends on whether the crack is still actively moving or not.
Active cracks may be de to inadequate provision of movement joints in the structure.
The repair process involves converting the crack into a movement joint, by the se of a suitable sealant, the
injection of a low – viscosity epoxy is a possible repair method for cracks between 0.02 mm to 6mm in width.
For epoxy injection to be effective the cracks must be free of dirt, grease, etc. Before injection can being, the crack where it appears on the surface of the member must be sealed.
ASSESSMENT OF DAMAGES AND
TESTING TECHNIQUES
INTRODUCTION
The 400 KVA Electrical substation at salem
comprises various columns and column braced frames on which electrical equipments are
mounted. Minor cracks where also noticed in some of the other columns and braces.
Observations
The following are the physical observations
Wide cracks along the main reinforcing steel were observed in the cover concrete in majority of the RC columns .
The cover concrete in most of the columns was found to have delaminated when examined with hammer test
PHYSICAL OBSERVATIONS AND INFERANCES
The present distress is essentially due to corrosion of reinforcing steel bars in the RC column
The wide cracks of cover concrete in RC members is a direct results or corrosion
Recommendation
– The repairs scheme essentially comprises the following stages
Identification of members to be repaired
Surface preparation of both concrete substract and reinforcement steel for treatment
Providing treatment for existing reinforcement
steel with anti corrosive zinc rich primer to
combat further corrosion.
Reinstatement of spalled concrete using
polymer modifier mortar for isolated patches
and free flow micro concrete by encasement
technique.
Providing protective coatings to all exposed
concrete surfaces to protect it from further
attack
MEASURING INSTRUMENTS
Measuring Magnifier - Proceq CRACKSCOPE –
REPAIR TECHNIQUES OF
CRACKS
The Following Techniques are Available for
Repairing Cracks.
Routing and sealing
Stitching Grouting Blanketing Overlays External stressing Autogenous healing
Routing and sealing
This method involves enlarging the cracks along its exposed surface, filling and finally sealing it with a suitable material
This is the simplest and most common technique for sealing cracks and is applicable for sealing both fine pattern cracks and larger isolated defects.
The cracks should be dormant unless they are opened up enough to put in a substantial patch in which case the repair may be more property termed as “
Stitching
Precautions to be followed
Stitching the crack will tend to cause its migration
else where in the structure. For this reason
strengthening the adjacent areas of cracks have to be made to take care of additional stresses. More over the stitching dogs should be of variable length, orientage and so located that the tension transmitted across the crack does not devolve on a single plane of the section but is spread over an area.
Strengthening of the adjacent sections of concrete may consist of external reinforcement embedded in a suitable overlay material.
Where there is a (leakage of ) water problem, the
crack should be sealed as well as stitched so that stitches are not corroded
Grouting
Grouting can be performed in a similar manner
as the injection of an epoxy. However the use of
an epoxy is the better solution except where
considerations for fire resistance or cold
weather prevent such use, in which case
grouting is the comparable alternative.
An alternative and better method is to drill down
the length of the crack and grout it so as to form
a key. This is applicable only when the crack
runs approximately in a straight line and are
accessible at one end
.REHABILITATION TECHNIQUES
Present day technology has sophisticated testing equipment to determine the extent of damages and suggest repair techniques.
The plan of action for repair is different in each case with respect to the selection of material however: the basic concepts of repair remain the same.
To remove the week zones and replace them with stronger materials so that transfer of stresses is unaffected
To prevent further action of deteriorating agent from the external environment.
DETAIS OF TYPES OF REPAIR
TREATMENT
The cracks are chipped clearly and grouted with epoxy based compound, in high pressure technique.
The rust on the corroded bars be removed out by sand blasting or by scrapping with wire brush.
The reinforcement bars are coated with Anti-corrosive agent.
Grouting of surface by cement based material.
Guiniting using concrete mix of higher grade.
Finally, Plastering might be done by mixing water proof admixture with mortar.
TREATMENT METHODS FOR
CASE STUDY
Identification of the members for repair
Surface preparation
Provision of additional reinforcement
Provision of shear connectors
Priming the reinforced steel
Reinstatement of spalled cover concrete at isolated locations
Curing
CONCLUTION
The cause of cracks and corrosion leading to the
deterioration of the structure has been studied in detail. The remedial measures suggested in this context are highly effective and also economical. The materials recommended for the rehabilitation works of concrete structures are at a reasonable cost and are available in all places.
Due to umpteen reasons mentioned earlier, reinforced concrete structures are prone to damaged before the expiry of their designed life which normally varies from 60 to 120 years.