Cracks - Types Of Defects In Buildings 6a5s4h

VARIOUS TYPES OF DEFECTS IN BUILDINGS CRACKS.

Presented By;

Various reasons of Cracks and their preventive measures are:

1) Elastic Deformation : foundation movements and settling of buildings 2) Thermal Movement : changes in temperature and climate. 3) Chemical Reaction : chemical reactions in construction materials 4)

Shrinkage : environmental stresses like nearby trains, earth quakes etc

5) Excessive Fine materials 6) Foundation Movement and Settlement of Soil

Note: Faulty design, bad quality materials, wrong method of construction, weather effects and lots of wear and tear can

1.

Elastic Deformation •

When the walls are unevenly loaded, due to variation in stresses in different parts of wall the cracks are formed in walls.

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When two materials having wide different elastic properties are built together under the effect of load, different shear stresses in these materials create cracks at the junction

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Dead and live loads cause elastic deformation in structural components of a building.

The Prevention of Elastic Deformation: •

Create slip ts under the of RCC slab on walls.

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Masonry work on RCC slabs and beams should not be started before drying RCC slab and beam.

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Provide horizontal movement ts between the top of brick and RCC beam/slab.

2. Thermal Movement: •

All materials expand on heat and contract on cool.

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Thermal movement in components of structure creates cracks due to tensile of shear stresses.

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It is one of the most potent causes of cracking in buildings and needs attention.

Prevention (i)

Construct ts such as construction ts, expansion ts, control ts and slip ts.

(ii)

The ts should be planned at the time of design and be constructed carefully.

3. Chemical Reaction: •

Chemical reactions in building materials increase their volume and internal stress causes cracks.

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The components of structure also weaken due to chemical reactions.

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Some common instances of chemical reactions are following : i. Sulphate attack on cement products ii. Carbonation in cement based materials iii. Corrosion of reinforcement in concrete iv. Alkali aggregate reaction

Prevention of Chemical Reaction: (i) concrete

Use dense and good quality concrete i.e. richer mix of cement 1:1.5:3 to prevent cracks.

(ii) Repair corrosive cement concrete surface by ‘guniting’/ injecting technique after removing all loose and damaged concrete and (iii)

cleaning reinforcement from all rust also.  

• • •

Most building materials expend when they absorb moisture from atmosphere and shrink when they are dry. Cement made materials shrink due to drying up of the moisture used in their construction. The factors causing shrinkage in cement concrete and cement mortar and their preventions are following : a. Excessive Water : The quantity of water used in the mortar mix can cause shrinkage. Vibrated concrete has less quantity of water and lesser shrinkage than manually compacted concrete.  

Prevention: • Use minimum quantity of water required for mixing cement concrete or cements mortar according to water cement ratio. • Never allow cement concrete work without mechanical mix and vibrator. •

b. Quantity of Cement : As a general rule, the richer the mix is, the greater the shrinkage/drying will be.

Prevention: •

Do not use excessive cement in the mortar mix

• •

Aggregate can cause shrinkage also. If un-graded and fine material/aggregate is used in cement concrete and cement mortar which requires more water and can cause greater shrinkage. 

Prevention • Use largest possible aggregate and ensure good grading of materials. • The use of water according to required workability has less shrinkage because of reduction in the porosity of hardened concrete. d. Curing : • After laying cement concrete mix, the hardening of cement takes place, causes reduction in moisture and creates shrinkage. • This causes cracks in concrete work. Prevention • Proper curing should be started as soon as initial setting has taken place and be continued for at least seven to ten days.  • When hardening of concrete takes place under moist environment, the shrinkage due to drying is comparatively less.

5.

Excessive Fine materials: • Fine materials take more surface area and require more water for mix. • The use of excessive fine materials i.e. silts; clay and dust in aggregate create more shrinkage.

Prevention: • Do not use fine materials containing silt, clay and dust. • Use coarse sand/fine aggregate in cement concrete and cement mortar mix which has silt and clay less than 4%. • Use coarse aggregate and fine aggregate after washing to reduce silt contents.   6. Foundation Movement and Settlement of Soil • Shear cracks occur in buildings when there is large differential settlement of foundation due to any of following causes : (i) Unequal bearing pressure under different parts of the structure (ii) Bearing pressure being in excess of safe bearing strength of the soil (iii) Low factor of safety in the design of foundations (iv) Local variation in the nature of ing soil •

Prevention

7.

Earth Quake •

Crack may occur due to sudden shift in lower layer of

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The voids in the earth might have suddenly collapsed with soil from the above.

and be filled

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Many geological events can trigger earth movements continuous movement. This results in cracks.   

but is

the earth.

  Prevention •

Construct the foundation of buildings on firm ground construction.

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Tie up the building with connecting beams at level and roof level. 

while doing

foundation level, door

CRACKING IN BRICKWORK • The role of a pre-purchase building inspector is to identify defects in the property and make recommendations that will enable the purchaser to make informed decisions about whether to buy this particular property or not. • When the building inspector finds significant cracks in the brickwork or rendered surfaces, or other cracks that may appear to the building inspector to be significant, then the purchaser needs to be informed of how significant the cracks appear to be. • The prolonged drought in Australia has caused a significant increase in the incidence of cracked buildings, particularly housing, due to the drying out of foundation soil. CRACKING IN BRICKWORK RELATED TO REACTIVE SOILS • The movement of the footings and foundations is rarely even over the whole of the building site. • Therefore, differential movement under different parts of the footings creates stresses in the walls resulting in cracks. • Foundations are usually classified as either reactive or nonreactive to changes in their moisture content. • Reactive soils are typically soils that have a high clay content. • These types of soils are referred to as plastic soils, expanding and contracting over time as their moisture content increases or decreases. • For example, reactive clays may swell and retain moisture when

CRACKING IN BRICKWORK RELATED TO TREES • Contrary to popular belief, it is rarely the growth or uplift of the tap roots of big trees which damage the footings and foundations. • The damage is more often caused by the tree roots extracting considerable quantities of moisture from the soil. • This can cause footings and foundations to subside and cracks in the masonry to appear. • This phenomenon is known as tree drying settlement. NOTE: A commonly accepted formula is that a tree’s root system will extend for a horizontal distance equal to its height. A large healthy tree can extract up to 300 litres of moisture from the per day. CRACKING IN BRICKWORK RELATED TO POOR SITE DRAINAGE • The provision of an adequate storm water drainage system to carry all roof water away from the footings and foundations is essential to avoid subsidence, rising damp, cracking and the eventual failure of the structure. • Down pipes should be connected to a storm water drainage system or water conservation tank to avoid failure of footing and foundations.

CRACKING IN BRICKWORK RELATED TO LINTELS • Cracking in brickwork can often be associated with settlement, subsidence, poor drainage, inadequate footings, reactive soils and brick growth. • • •

Cracking can also be a result of other forms of destructive processes, such as corroding steel lintels or arch bars. The expansion of the steel can be destructive to brickwork. We recommend that corroding steel lintels be replaced with galvanised steel to avoid further destruction of the brickwork.

CRACKING RESULTING FROM BRICK GROWTH   • Fired clay products expand exponentially over time, and it is an inherent phenomenon of all natural clay products fired at relatively high temperatures. •

This includes most clay bricks, pavers and ceramic (clay) tiles.

•

Much of the growth takes place in the first few months and may become evident as long vertical cracking.

ESSENTIAL ADVICE TO ASSIST IN REDUCING FURTHER CRACKING IN BRICKWORK I. II. III. IV. V.

Ensure that all down pipes are placed into a storm water drain or water retention tank Keep ground levels at least 3 bricks below the damp course Keep tree roots at least 5 metres from the footings and foundations Replace corroding lintels with galvanised steel Keep mortar ts in good repair

 

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Inadequate structural resistance, which results into typical diagonal shear cracking and disintegration of walls and, consequently, partial or total collapse of buildings

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Typical diagonal shear cracks in the walls of a stone-masonry building indicate story mechanism of seismic behavior. In some cases, inadequate structural layout was the reason for partial and/or total collapse, whereas in the other cases, an inadequate foundation system and /or foundation soil caused partial settlements, sinking, sliding, tilting, and/or overturning of buildings.

Figure . Vertical cracks in the wall due to out-ofplane vibration because of poor connection between the walls and floors.

Figure 15. Building D: In 2004, severe damage occurred to the non strengthened stone masonry walls on the ground floor. No damage has been observed in the walls of the upper story.

CRACK MEASURING : • Cracks occur in most buildings and civil engineering structures. • Monitoring the changes in crack width is an important diagnostic technique for determining the cause and specifying the remedial work.

• Quick and easy measurement. • Supplied in an ever ready case. • Manufactured in rigid durable acrylic. • Calibrated to edge scale which simplifies crack measurement in corners and awkward locations.

Crack Width Gauge • THE CRACK WIDTH GAUGE IS SPECIFICALLY DESIGNED TO ASSIST THOSE WHO SURVEY AND REPORT ON DAMAGED BUILDINGS

Tell-Tale PLUS Crack Monitor

•

• a

Internal or external use. Monitors the opening or closing of

crack to an accuracy of 1.0mm. • Capable of monitoring vertical as well as horizontal movement. • Crack record cards supplied with each Tell-Tale simplifies Monitoring.

Tell-Tale Crack Monitor

PLUS

• Monitoring Spigots incorporated in the Tell-Tale enable exact measurements to ±0.1mm with calipers. • Increased horizontal monitoring range to ±25mm. • Manufactured in vandal resistant polycarbonate. • Fixing slots and "extra grip" surface.

Corner Tell-Tale Plus • MONITORS CRACKS IN CORNERS • USE SINGLY TO MONITOR TWO DIMENSIONAL MOVEMENT • USE IN PAIRS TO MONITOR THREE DIMENSIONAL MOVEMENT • MAY BE USED IN INTERNAL OR EXTERNAL CORNERS • THE TEL-TALE IS HINGED ENABLING IT TO BE USED IN INTERNAL CORNERS WITH ANGLES FROM 70 TO 180 DEGREES

Corner Tell-Tale Plus

COMMON METHODS OF CRACK REPAIR: i. Epoxy injection • Preparation of the crack. • Drilling Hole • Surface sealing of crack • Fixing of injection ports or nipples in the holes • Mixing of resin • Injection of resin • Removal of nipples and plugging the hole • Removal of sealing material and finishing the surface. ii.

Grooving and Sealing

iii.

Stitching a. Stitching Dogs. b. Interlocking of plates c. Dowel Bars.

iv.

Adding Reinforcement

vi.

Dry packing

viii

v. vii.

Overlays and surface treatment Autogenous healing.

Grouting Polymer Impregnation ix.