Guided By:-

TYPES OF CRACKS IN MASONRY STRUCTURES

1. Vertical cracks in sidewalls at corner

2. Vertical cracks around balconies

3. Vertical cracks below the opening 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. Random cracks in all directions involving both external and internal walls.

9. Diagonal cracks over RCC lintels spanning large openings.

10. Shrinkage 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 sulphete. Plumb alignment. The position of the element in the structure. Differential loading. Weak mortar. Insufficient bond. Improper curing. High daily temperature variations. Atmospheric pollutions. Lack of strength at corner and at junction of wall. Improper binding of thick walls.

GENERAL CAUSES OF CRACKS:

Plastic Shrinkage Cracking

Plastic Settlement Cracking

Drying Shrinkage Crack

Long Term Shrinkage Cracking

Concrete Crazing

Thermal Cracking

Cracking due to Chemical Reaction

Steel Corrosion induced Cracking

Errors in Design and Detailing

Improper Construction Joint

Causes of cracks in concrete structure

1.Plastic Shrinkage Cracking: It occurs within 1 to 8 hours after placing, when subjected to a

very rapid loss of moisture caused by a combination of factors, which include air and concrete temperatures, relative humidity and wind velocity at the surface of the concrete. These factors can combine to cause high rates of surface evaporation in either hot or cold weather.

2. Plastic Settlement Cracking: After initial placement, vibration and finishing concrete has

tendency to continue to consolidate. During this period, the plastic concrete may be locally restrained by reinforcing steel, earlier placed hardened concrete or formwork. This local restraint Fig a, Settlement Crack at Surface . Fig 4b, Settlement Causing Crack & Void.

3.Drying Shrinkage Crack: When associated with reinforcing steel, settlement cracking

increases with increasing bar size, increasing slump and decreasing cover. The degree of settlement may increase with insufficient vibration, lack of compaction at top layers of concrete, or by the use of leaking or highly flexible forms. This is more of a problem with high bleed concrete particularly in winter when the cooler temperatures provide longer time to initial set and therefore a higher amount of bleed (Fig.a)

Fig a Drying Shrinkage Cracks in slab

4.Concrete Crazing: Crazing is the development of a network of fine random cracks

or fissures on the surface of concrete caused by shrinkage of the surface layer. These cracks are rarely more than 3mm deep, and are more noticeable on over floated or steel-troweled surfaces. The irregular hexagonal areas enclosed by the cracks are typically no more than 40mm wide and may be as small as 10mm in unusual instances (Fig a & b).

Fig a, Crazing Fig b, Crazing pattern

5.Steel Corrosion induced Cracking: Corrosion of the steel produces iron oxides and

hydroxides, which have a volume much greater than the volume of the original metallic iron. This increase in volume causes high radial bursting stresses around reinforcing bars and results in local radial cracks.

Fig, Corrosion Induced Cracking

1. EPOXY INJECTION

2. CRACK STITCHING

3. SEALING OF CRACKS

4. PROVIDING ADDITIONAL REINFORCEMENT

5. COLUMN JACKETING

6. BEAM JACKETING

CRACK REPAIR METHODS

1.EPOXY INJECTION:

PURPOSE: To provide guidance on use of epoxy injection to repair cracks in concrete.

DESCRIPTION: This method can be used to repair cracks as narrow as 0.002 in. The method generally consists of drilling holes at close intervals along the cracks, in some cases installing entry ports, and injecting the epoxy under pressure. For massive structures, an alternative procedure consists of drilling a series of holes, usually 7/8 in. in diameter, that intercept the crack at a number of locations. Typically, holes are spaced at 5-ft intervals

EQUIPMENT, TOOLS, AND PERSONNEL REQUIREMENTS: A concrete drill, an epoxy injection system, a means of cleaning holes and cracks, and normal hand tools are required. One man can repair cracks using this method, but a two- or three-man operation is more efficient. Epoxy injection requires personnel with a high degree of skill for satisfactory execution.

Epoxy injection fig

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 crack from inside and outside of wall and clean the crack thoroughly with inject and water.

Wet the crack , if dry ,by sprinkling water. This mixture is pumped into holes previously drilled at various

interval to various depth without damaging the integrity of structure.

Pumping the grout simultaneously into multiple series of holes ensures good penetration into any fissures within the structure and for making masonry structures watertight

Grouting(cement mortar):

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.

Grouting (chemical):

BEFORE AFTER

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 to strengthen the adjacent section with external reinforcement

CRACK STITCHING:

In concrete structure repairing of cracks is very important.

Because it reflects the harmful gases entering the concrete.

Before sealing the cracks its length side is made wide.

Which is known as routing.

SEALING OF CRACKS

After routing cracks is sealed by using cement.

Before pasting cement the edge should be clean and the edge should be dry.

1. Cement slurry2. Cement mortar3. Epoxy resins4. Poly vinyl acetate5. Polymer resins6. Acrylics7. Fibber8. Parma bond(bonding agent)9. Parma master bond-base(epoxy concrete bonding agent)10. Parma crack fill(crack repair)

Crack repair Material

Causes of cracks at junction of masonry and concrete

Temperature Changes

Final setting time of cement is 600min.as this time

Fine cement and fine aggregate

Increased W/C ratio

Failure to resist tension

Poor Workmanship

Inadequate structural supports

CASE STUDYcracks at junction of masonry and

concrete

1. Temperature Changes

Temperature change is a major cause of cracks in large concrete applications. This is because of the temperature variations between concrete that is poured first and subsequent layers of concrete. These temperature variations can cause some portions of the slab to expand while others are shrinking, which leads to cracks. The more extreme the difference in temperature, the more dramatic and deep the cracking will be.

2.FINAL SETTING TIME OF CEMENT IS 600MIN.AS SOON AS THIS TIME :

Curing is required to meet with the hydration temperature during setting of cement. But in High strength concretes like M50 or more there will be minor cracks on the surface. To avoid this immediately sprinkle (spray) the water on the surface even within half an hour of casting, So that this immediate cracks can be avoided.

3. Increased W/C ratio Increase in water content and less cement content

will allow Bleeding. And hence the accumulated water will lead to....

But exactly i think the gases such as CO2, SO2, SO3, etc. from atmosphere react with the water and initially making it ACIDIC and then used for mixing mortar ultimately results in CRACKS.

In other words also shrinkage, creep, modulus of elasticity, etc. many other factors lead to formation of CRACKS

4. Failure to resist tension

Concrete by character is to crack when there is unadjusted tension. However out of other reasons, a rich cement, poor detailing of reinforcement, inadequate cover to reinforcement, variable load conditions etc. also responsible for cracking of concrete.

5.Poor Workmanship There are many reasons why concrete cracks....my

experience shows that the major reasons are poor curing, imbalanced water cement ratio, poor compacting of concrete, water used for concrete mix, leaving steel elements like binding wires, nails, links exposed, using rusted steel.......yes and other material characteristics... different contraction and expansion values.

Recron 3s methodRole of Recron 3s Controls cracking

Recron 3S prevents the micro shrinkage cracks developedduring hydration, making the structure/plaster/componentinherently stronger. Further, when the loads imposed onconcrete approach that of failure, Cracks will propagate,sometimes rapidly. Addition of Recron 3 s to concrete andplaster arrests cracking caused by volume change (expansionand contraction), simply because 1 kg of Recron 3s offersmillions of fibres which support mortar/concrete in alldirections.

Method for repair cracks at junction of masonry and concrete

Concrete:

Use 12mm Recron 3s @ 900 gms/cubic meter.

Plaster:

Use 6mm recron 3s @ 125 gms/bag of cement of 50 kgs. In 1:4 cement send ratio. Dosage rate can be altered as per requirement.

DOSAGE RATE:

Applications

Recron 3s fibres can be used in concrete elements such as RC and PC lintel, beam, column, flooring and wall plastering; foundations, tanks, manhole cover and tiles; plastering; roads and pavements; hollow blocks and precasts.

MIXER:

Sprinkle Recron 3s in the rotating site mixer with 2-3liters of water/add chips/sand/cement and balance water and rotate as usual.

MANUAI MIXING:

For best results, use one pouch of Recron 3s (appx 100 gms) with one bag of cement. Empty content of pouch in a bucket (15litres) of water and mix well. Pour content of the bucket in the pond of cement and sand and mix thoroughly for few minutes.

Direction for use

Reliance recron 3s fibre

CHICKEN MESH PLASTER

1) METAL MESH

TECHNICAL DATA:

Width: 700 mm

Length: 2500 mm

Pack Quantity: 1 Pk.

Material: Galvanized Steel

Size: 2500 x 700 mm

Type: Metal Mesh

Fiberglass mesh

First of all this technique is used in cracks between column and masonry.

Above these it is also used in cracks between homogenous material.

Use for chicken mesh plaster:

First of all the surface of the wall should be made clean. And then water is sprayed on wall. Then the height from plinth to slab is measured and then chicken mesh of that size is being cut and then chicken mesh is kept on wall and then keeping washer and then chicken mesh is filleted by bolt. If necessary then for bolt should be provided and then water of cement is being prepared and the water is being sprayed on the wall. So that the strength between wall and plaster should be strong and then plaster work is done on the wall by skilled mason. That plaster should always be done of double coat. In this way plaster is done than the cracks between walls and columns can be stopped and then the life span of structure is also increased.

HOW TO USE:

CHICKEN MESH PLASTER SITE PHOTOS

In our project we studied different types of cracksin construction work, its causes and remedialmeasures.

We carried out case study on cracks occursbetween masonry and concrete work and find outfield solution to minimise this type of cracks.

CONCLUSION