Cracks in concrete

Cracks in Concrete

Dr.P.Rama Mohan RaoAssociate Professor

Centre for Disaster Mitigation and ManagementVIT University, Vellore , TamilNadu

Introduction Concrete as material has high adaptability to

satisfy many aspects functionally needs

Economy and maintenance Protection against fire and Environment Resistance to cyclic loading Explosive resistance and better control over

deflection

RCC structures extensively used for 50 -60 years.Deterioration of RCC is natural phenomenonIt needs to maintain the functional condition of the structure.

The distress in the concrete structures due to • faulty designs and detailing• use of inferior and substandard materials• defects in construction • extreme loading conditions like severe Earthquakes or

cyclonic storms• lack of maintenance of the structure etc.,

Concrete structures that are deficient in quality will reflection its durabilityReinforcement corrosion will be faster and resistance to accidental fire will be reduced to a very great extent.

Introduction ..,

Defects in concrete structures

Cracking of concrete

a)Before concrete hardens plastic shrinkage cracks plastic settlement cracks cracks caused by movement of the formwork.

b) After concrete hardens

SpallingHoneycombingDustingCrazingRain damageEfflorescenceBlisteringCorrosion of reinforcing bars

Visual inspection Sketches of types of cracks

Sketch of exposed aggregate. Sketch of exposed aggregate.

when concrete has been mixed for too long or the time of transport has been too long cracking due to sinking of timbering

Cracks……differential settlement of central column

Rusting of reinforcing bars

Rusting of reinforcing bars insufficient reinforcement

Cracks..

High temperature Abnormal set of concrete

Sinking of concrete Earthquake

CAUSES OF DISTRESS OF MALFUNCTIONING

The distress in old concrete structure could be due to one or more of the following reasons

•Corrosion of the reinforcing bars due to ingress of corrosion promoting chemicals or due to carbonation of relatively porous concrete•Distress caused in the structure due to attack of chemicals in chemical factories.•Crack formation due to alkali aggregate reaction, drying shrinkages or u earthquake damage or uneven settlements.•Due to impact damage or due to continuous erosion by water, liquids or solids•Due to the effect of aerobic and anaerobic bacteria in sewage disposal or treatment systems.

Fire damage of structures

CAUSES OF DISTRESS OF MALFUNCTIONING

•Damage due to the use of poor quality ingredients, poor workmanship or improper design.

•Change of use of structures, such asa)Residential to commercial useb)Increased axial load beyond capacity of columns.c) Modification of structure for increasing space/accommodation.

•Structures may also require major repair after their normal constructional lifespan.

•Sometimes buildings are required to be given a new architectural look to fit in the surrounding

Structural malfunction Causes •Foundation settlement•Weak and friable concrete•Overloading•Design deficiencies

Effects•Structurally significant cracks•Excessive deflection in beams•Spalling and cracking of cover due to delamination from the confined core