Causes of cracks.pptx

8/19/2019 Causes of cracks.pptx

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“Causes and repair methods of cracks in concretPrepared By:

Bhavik patel

Enrollment No. 140670720016

Semester: III, M.E. (I!I"#

S$" instit%te o& 'ehnolo)* an+ En)ineerin) esearh

Gujarat Technological University

SAL Institute of Technology & Engineering Research


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OUTLI!OUTLI!

Introduction

Cracks Classi"cation

Cause of cracking

#ethods of crack repair


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IT$O%UCTIOIT$O%UCTIO

Cracks in the concrete structures are early signs

distress which have to be diagnosed properly.

Cracks may aect appearance only, or they mayindicate signicance structural distress or a lackdurability.

Eorts should be made to prevent the occuranccracks.

Cracks are analogous to ‘CACE!" for !.C.Cstructures # their presence may not only deterithe !.C.C structures but also makes it unsafe to

inhabit.


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Cracks Classi"cati


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C&U'! O( C$&C)IG

*+ Cracking of plastic concrete,

A. Plastic shrinkage cracking:

$ig. %.%& 'ypical (lastic shrinkage cracking


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When moisture evaporates from the surface of freshly placeconcrete faster than it is replaced by bleed water, the surfa

concrete shrinks. Due to the restraint provided by the concrete the drying surface layer, tensile stresses develop in the wea

stiening plastic concrete. This results in shallow cracks of va

depths that may form a random, polygonal pattern, or be esseparallel to one another (ig. !.!".


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#. Settlement cracking:

$ig. %.)& Crack formed due toobstructed settlement


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$oncrete has a tendency to continue to consolidate after iniplacement, vibration, and %nishing. During this period, the placoncrete may be locally restrained by reinforcing steel, a prevconcrete placement, or formwork. This local restraint may res

voids, cracks, or both, ad&acent to the restraining element(ig.


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-+ Cracking of hardened concrete,

A. Drying shrinkage cracking:

$ig. %.*& +hrinkage crack inrestrained and unrestrained

drying


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A common cause of cracking in concrete is restrained dryinshrinkage. Drying shrinkage is caused by the loss of moisture

the cement paste constituent. f the shrinkage of concrete coulplace without restraint, the concrete would not crack. t is t

combination of shrinkage and restraint that causes tensile stres

develop. When the tensile strength of the material is e)ceedconcrete will crack.


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#. Thermal stresses:

Temperature dierences within a concrete structure may be caby portions of the structure losing heat of hydration at dierent

or by the weather conditions cooling or heating one portion ostructure to a dierent degree or at a dierent rate than anot

portion of the structure. These temperature dierences resudierential volume changes. When the tensile stresses due todierential volume changes e)ceed the tensile strength, concre

crack.


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C. Chemical Reaction:

$oncrete may crack with time as the result of slowly develope)pansive reactions between aggregate containing active silicalkalis derived from cement hydration, admi)tures. When the ain cement react with susceptible aggregate particles, a reactio

of alkali*silica gel is formed around the aggregate. f this gee)posed to moisture, it e)pands, causing an increase in volumthe concrete mass that will result in cracking and may eventu

result in the complete deterioration of the structure.


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D. Weathering:

$ig. %.& Crack in concrete dueto weathering


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The weathering processes that can cause cracking include freeand thawing, wetting and drying, and heating and cooling. Dam

from free+ing and thawing is the most common weather*relaphysical deterioration. $oncrete may be damaged by free+in

water in the paste, in the aggregate, or in both . Damage ihardened cement paste from free+ing is caused by the movem

water to free+ing sites and, for water in larger voids, by hydra

pressure generated by the growth of ice crystals .


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F. Poor construction practice:

$ig. %.-& Crack in basementwall due to poor construction

practice


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oremost among these is the common practice of adding watconcrete to increase workability. Added water has the eectreducing strength, increasing settlement, and increasing dry

shrinkage. An increase in water content will also mean an increthe temperature dierential between the interior and e)ter

portions of the structure, resulting in increased thermal stressepossible cracking.


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G. Error in design and detailing:

$ig. %.& 'ypical crack patternsat re&entrant corners


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rrors in design and detailing that may result in unacceptabcracking include use of poorly detailed re*entrant corners in w

precast members, and slabs- improper selection or detailingreinforcement, or both- restraint of members sub&ected to volchanges caused by variations in temperature and moisture- laadeuate contraction &oints- and improper design of foundati

resulting in dierential movement within the structure .


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#!T.O% O( C$&C) $!/&

!. po)y in&ection/

$ig. %.%%& Epo/y 0n1ection in progress


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'. 0outing and sealing/

$ig. %.%%& !epair of crack byrouting and sealing


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1. 2ear*surface reinforcing and pinnin

$ig. %.%)& !epair of crack bynear surface mountedreinforcement


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3. $ement 4routing/

$ig. %.%*& Cement grouting

machine


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Thank 0ou

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Causes of cracks.pptx