(SEM VI) THEORY EXAMINATION 2021-22 REPAIR AND REHABILITATION OF STRUCTURES

REPAIR AND REHABILITATION OF STRUCTURES (KCE063)

Section-wise Detailed Answers – B.Tech Semester VI

SECTION A

(Attempt all questions – brief but explanatory answers)

(a) Difference between repair and rehabilitation

Repair refers to the process of restoring damaged or deteriorated components of a structure to their original condition so that the structure can perform its intended function. It generally involves local treatment of defects such as cracks, spalling, or corrosion. Rehabilitation, on the other hand, is a broader concept that aims at improving the overall performance, strength, durability, and service life of a structure. Rehabilitation may include repair, strengthening, retrofitting, or modification to meet present and future requirements.

(b) Physical inspection of damaged structure

Physical inspection of a damaged structure is carried out by visual examination and simple non-destructive methods. It involves identifying visible signs of distress such as cracks, deflection, corrosion stains, spalling of concrete, leakage, and settlement. Measurements of crack width, alignment, and deformation are taken, and photographs are recorded. This inspection helps in preliminary assessment and deciding the need for detailed investigation.

(c) Judging durability of concrete structures

Durability of concrete structures can be judged by evaluating resistance to environmental actions such as moisture, chemicals, temperature variation, and corrosion. Tests such as permeability test, carbonation depth measurement, chloride content analysis, and cover thickness assessment help in determining durability. Visual condition, service life performance, and maintenance history also indicate durability.

(d) Difference between thermal conductivity and thermal diffusivity

Thermal conductivity is the ability of concrete to conduct heat and is expressed as heat flow per unit area per unit temperature gradient. Thermal diffusivity represents how quickly heat spreads through concrete and is the ratio of thermal conductivity to heat capacity. While conductivity indicates heat transfer ability, diffusivity indicates rate of temperature change within the material.

(e) Role of accelerators and retarders in concrete

Accelerators are admixtures that increase the rate of hydration of cement, resulting in faster setting and early strength gain. They are useful in cold weather concreting and emergency repairs. Retarders delay the setting time of concrete, allowing sufficient time for placing and finishing in hot weather or large pours. Both admixtures help control setting behavior based on construction requirements.

(f) Dry pack

Dry pack is a repair technique using a stiff mixture of cement and sand with very little water. The mix is placed and compacted forcefully into cracks, holes, or recesses. Dry pack repairs are dense, strong, and have low shrinkage, making them suitable for small repairs in concrete structures.

(g) Jacketing

Jacketing is a strengthening technique in which an existing structural member such as a column, beam, or pier is enclosed with additional material like reinforced concrete, steel, or fiber-reinforced polymer. The jacket increases load-carrying capacity, stiffness, and ductility. It is commonly used for seismic strengthening and rehabilitation of distressed members.

(h) Applications of bacterial concrete

Bacterial concrete is used for self-healing of cracks, improvement of durability, and reduction of permeability. It is applied in bridges, tunnels, marine structures, and water-retaining structures where crack control and durability are critical. The bacteria produce calcium carbonate, which seals cracks automatically.

(i) Steps during demolition of a structure

Demolition involves preliminary inspection, planning, safety measures, disconnection of utilities, removal of hazardous materials, controlled dismantling, debris handling, and disposal. Proper sequencing ensures safety of workers, nearby structures, and environment.

(j) Role of sensors in construction industry

Sensors are used to monitor structural health, strain, vibration, temperature, corrosion, and load behavior. They help in early detection of damage, performance evaluation, and maintenance planning. Sensors play a crucial role in structural health monitoring systems for safety and longevity.

SECTION B

(Attempt any three – detailed answers)

(a) Defects in structures, causes, and precautions

Structural defects such as cracks, honeycombing, corrosion, and settlement arise due to poor material quality, improper construction practices, inadequate curing, design errors, and environmental exposure. Precautions include proper mix design, quality control, skilled workmanship, adequate curing, and regular inspection during construction.

(b) Need of quality assurance for structures

Quality assurance ensures that structures meet design specifications, safety standards, and durability requirements. It involves material testing, workmanship inspection, supervision, documentation, and compliance with codes. Quality assurance prevents premature failure, reduces maintenance cost, and enhances service life of buildings.

(c) Special mortars

Special mortars include polymer-modified mortar, epoxy mortar, fiber-reinforced mortar, and shrinkage-compensated mortar. These mortars offer improved strength, adhesion, durability, and crack resistance. They are widely used in repair, rehabilitation, and protective applications.

(d) Improving load-carrying capacity of beams

Load-carrying capacity of beams can be improved by jacketing, adding external reinforcement, bonding steel plates, or using fiber-reinforced polymer laminates. These methods increase flexural strength, shear capacity, and stiffness, restoring structural safety.

(e) Techniques of demolition

Demolition techniques include manual demolition, mechanical demolition, controlled blasting, and implosion. The method depends on structure type, location, safety considerations, and environmental impact. Proper planning ensures safe and efficient demolition.

SECTION C

3(a) Stages of condition survey

Condition survey involves preliminary inspection, detailed investigation, material testing, structural assessment, and diagnosis of distress. The survey helps identify causes of damage, severity, and suitable repair techniques. It forms the basis for repair and rehabilitation planning.

3(b) Maintenance and classification

Maintenance is the process of preserving a structure in safe and serviceable condition. It is classified into routine maintenance, preventive maintenance, corrective maintenance, and emergency maintenance. Proper maintenance reduces deterioration and extends service life.

4(a) Mechanism of corrosion with chemical equations

Corrosion in reinforced concrete occurs due to electrochemical reactions. At anodic regions, iron loses electrons forming ferrous ions, while at cathodic regions oxygen reacts with water and electrons forming hydroxyl ions. These reactions produce rust, which expands and causes cracking and spalling of concrete.

4(b) Effect of permeability on concrete structures

High permeability allows ingress of water, chlorides, and aggressive chemicals into concrete. This accelerates corrosion and reduces durability. Low permeability concrete improves resistance to environmental attack and enhances service life.

5(a) Ferrocement

Ferrocement is a thin composite of cement mortar reinforced with closely spaced wire mesh. Materials used include cement, sand, water, wire mesh, and skeletal steel. Ferrocement exhibits high tensile strength, crack resistance, and durability. It is used in roofing, water tanks, boats, and repair works.

5(b) Epoxy injection for crack repair

Epoxy injection involves cleaning cracks, sealing surfaces, inserting injection ports, and injecting epoxy resin under pressure. The resin fills cracks and restores structural continuity and strength.

6(a) Effect of marine exposure and fire

Marine exposure causes chloride-induced corrosion, sulfate attack, and surface erosion. Fire exposure leads to loss of strength, cracking, and spalling due to high temperature. Both require specialized repair and protection techniques.

6(b) Repair evaluation procedure

Repair evaluation involves inspection, testing, damage classification, selection of repair strategy, execution, and performance monitoring. A systematic approach ensures effective rehabilitation.

7(a) Sensors and their role in structures

Sensors measure strain, vibration, temperature, displacement, and corrosion activity. They enable real-time monitoring, early warning, and performance assessment of structures.

7(b) Hurdles in health monitoring techniques

Challenges include high cost, data interpretation complexity, sensor durability, installation difficulty, and lack of skilled personnel. Despite hurdles, health monitoring improves safety and maintenance planning.