REPAIRS AND REHABILITATION OF STRUCTURESUNIT – II

SERVISIBILITY AND DURABILITY OF CONCRETE

Syllabus: Quality assurance for concrete construction concrete properties- strength, permeability, thermal properties and cracking. - Effects due to climate, temperature, chemicals, corrosion –design and construction errors - Effects of cover thickness and cracking

Quality Strength:• Strengthening measures are required in structures when they are required to accommodate increased loads.• This leads to a redistribution of forces and the need for local reinforcement.• In addition, structural strengthening may become necessary owing to wear deterioration arising from normal usage or environment factors.

Need for strengthening:• Load increases due to higher live loads, increased wheel loads, installations of heavy machinery, or vibrations.• Damage to structural parts due to aging of construction materials or fire damage, corrosion of the steel reinforcement, and impact of vehicles.• Improvements in suability for use due to limitation of deflection, reduction of stress in steel reinforcement and reduction of crack widths.• Modification of structural system due to the elimination of walls /columns and opening cut through slabs.• Errors in planning or construction due to insufficient design dimensions and insufficient reinforcing steel.

Construction Errors•Failure to follow specified procedures and

good practice or outright carelessness may lead to a number of conditions that may be grouped together as construction errors.•Typically, most of these errors do not lead

directly to failure or deterioration of concrete• Instead, they enhance the adverse impacts

of other mechanisms.

•Each error will be briefly described below along with preventive methods.

•In general, the best preventive measure is a

thorough knowledge of these construction errors are plus an aggressive inspection program

CRACKING:•Load – induced tensile stresses may result cracks tensile forces. •Flexural and either sustained or repetitive loading.

A well – distributed reinforcing arrangement offers the best protection against undesirable cracking.

DESIGN ERRORS:

•resulting from in adequate structural design and those resulting from lack of attention to relatively minor design details.

The two types of design errors.·Inadequate structural design.· Poor design details.

Chemical Attack on Concrete • Acid attack• Alkali attack•Carbonation•Chloride attack•Leaching•Salt attack•Sulphate attack

Acid attack

CORROSION The nature of reinforcement corrosion mechanism can be attributed to three predominant process, namely Chemical Electro chemical and Physical.

CORROSION INFLUENCING FACTOR • The cover thickness.• The quality of concrete in the cover region, especially in terms of permeability and diffusivity.• Environmental conditions• pH value in concrete• Chloride level in concrete and presence of cracks etc.

CORROSION PROTECTION TECHNIQUES 1. Coating to reinforcement

2. Galvanized reinforcement 3. Improving metallurgical by addition of certain elements.