Intro

Repair and Rehabilitation of structures course consists of seven lecture series each lecture series is about 10 to 15 minutes.

1. introduction to repair and rehabilitation of structures
2. special concrete lecture series
3. non-destructive testing techniques
4. epoxy injection and lecture series
5. corrosion protection techniques
6. strengthening of structural elements a
7. is demolition techniques

the contents for the lecture series are

1. maintenance and repair strategies
2. special concretes
3. techniques for repair
4. repair rehabilitation and retrofitting of structures

Maintenance and Repair Strategies

So now we are going to see the maintenance and repair strategies so in which the basic definitions include maintenance repair rehabilitation strengthening or retrofitting.

DefinitionsClaude

Maintenance → Before damage occurs (proactive)

Maintenance is preventive and routine in nature, encompassing systematic inspection, monitoring, and minor interventions designed to preserve a structure's intended functions and sustain its original design standard of service throughout its anticipated lifespan. This includes activities such as cleaning drainage systems, repainting protective coatings, sealing minor cracks, and replacing worn components before failure occurs.

Repair → After damage occurs (reactive, localized)

Repair addresses the technical restoration of structural integrity and functionality. It involves the modification, replacement, or treatment of damaged, deteriorated, or deficient structural elements to restore their load-carrying capacity, durability, appearance, or serviceability to acceptable levels. Repair may be localized (addressing specific defects) or widespread, and typically returns the structure to its pre-damage condition without necessarily enhancing its original design capacity.

Rehabilitation → After extensive deterioration (comprehensive restoration)

Rehabilitation is a comprehensive intervention that restores a structure to a serviceable condition—one it possessed previously but has since lost due to deterioration, damage, or obsolescence. Rehabilitation often involves multiple repair activities combined with upgrades to meet current codes, standards, or functional requirements. It may include structural modifications to accommodate changed loading conditions or usage patterns while preserving the structure's essential character.

Strengthening → When you need more than original (enhancement)

Strengthening/Retrofitting involves strategic interventions to enhance a structure's performance beyond its original design intent. This includes increasing load-carrying capacity, improving seismic resistance, enhancing durability, or adapting the structure for new functions. Strengthening typically targets undamaged or previously repaired areas and may involve adding new structural elements, upgrading connections, or incorporating advanced materials. Retrofitting specifically refers to implementing modern performance standards (particularly seismic or blast resistance) into existing structures.

Key Distinctions to Emphasize
These definitions would benefit from clarifying the hierarchy: Maintenance prevents the need for repair; repair addresses existing damage; rehabilitation combines repair with functional restoration; and strengthening/retrofitting enhances beyond original capacity. Understanding these distinctions helps engineers select appropriate intervention strategies based on structural condition assessments and performance objectives.

Basic defects

Categories of basic defects:

1. cracking
2. spalling (1)
3. physical damage of concrete
4. increased porosity of the concrete
5. corrosion of the reinforcing steel due to moisture or other chemical reagents
6. excessive deflection and misalignment of the structure

1. Spalling refers to the flaking, chipping, or breaking away of the concrete surface in fragments or layers. It typically happens when:

   - Moisture gets into the concrete and reaches the steel reinforcement bars (rebar), causing them to rust and expand - The expansion creates internal pressure that causes pieces of concrete to pop off or flake away - Freeze-thaw cycles cause water in the concrete to expand and contract - The concrete surface is exposed to fire or extreme heat

   Spalling usually appears as shallow craters, depressions, or areas where chunks of concrete have broken off, often exposing the reinforcement beneath.

   Cracking and spalling are related but different:

   - Cracking is linear breaks or fissures in the concrete

   - Spalling is the actual loss of concrete material from the surface

   In fact, cracking often precedes spalling—water can enter through cracks, corrode the rebar, and eventually cause spalling. So your instructor was likely describing a progression or two different types of concrete deterioration that engineers need to watch for.

Delamination

Concrete delamination results from various deterioration mechanisms that compromise the bond between concrete layers. Corrosion is the most prevalent cause—when reinforcement steel corrodes, the rust products occupy greater volume than the original steel, generating internal pressure that forces the concrete apart. Chemical attacks, including alkali-aggregate reaction (where reactive aggregates expand in the presence of alkalis) and sulfate attack (which forms expansive compounds), also induce delamination. These processes create subsurface voids and horizontal fractures. Progressive deterioration leads to spalling, where chunks of concrete break away and leave the reinforcement exposed and vulnerable to accelerated corrosion.

Alkali-Aggregate Reaction

classclaude

So next is alkali aggregate reaction so in which the alkalis in the aggregate react with the silica present in the cement. so which causes the reaction and the reactive products will get settled in the voids of the concrete. so these voids keep on expanding when the chemical reaction takes place and these voids create the micro cracks and due to which the concrete cracks and the spalling delamination and other care other process of defects takes place aggressively.

Alkali-Aggregate Reaction (AAR)

What It Is

A harmful chemical reaction between alkalis in cement (sodium/potassium hydroxides) and reactive silica in aggregates.

How It Works

1. Alkalis + reactive silica + moisture → alkali-silica gel
2. Gel absorbs water and expands
3. Expansion fills voids, then creates internal pressure
4. Micro-cracks form and propagate
5. Visible surface cracks appear (map-cracking pattern)

Key Effects

• Progressive cracking and expansion
• Spalling and delamination
• Loss of structural strength
• Increased permeability

Required Conditions

• Reactive silica in aggregates
• High alkali content in cement
• Moisture presence
• Time (slow, progressive process)

Prevention

• Use low-alkali cement, non-reactive aggregates, or supplementary cementitious materials (fly ash, slag) to reduce alkali levels.

Sulphate Attack

classclaude

in sulphate attack the waterborne sulphate gets accumulated inside the concrete in the voids of the concrete. These sulfates get reacted with the silica present in the concrete and it affects the foundation. so these sulfates get accumulated and it creates the compression or tension and creates micro cracks and further the crack develops when this sulphate ingress into the concrete. and the cracks when developed it creates see delamination and that's why the foundation is mainly affected due to this sulfate attack. the reaction in the sulphate attack is the sulphate ions get mixed with the cement matrix treats and it founds the gypsum plus ettringite .so these cement and and the sulfate gives the gypsum and a ettrignite which accumulates and forms the micro cracks and it further causes the delamination. these gypsum content get expanding in its volume. These expansion creates the stress due to this stress the concrete gets cracked. So these cracks further developed when further sulphate gets ingress into the concrete.. so that the sulphate attack caused some defects.

Sulphate Attack - Technical Summary

Mechanism
Waterborne sulphate ions penetrate concrete voids and react with cement matrix components, forming two expansive products: - Gypsum (calcium sulphate) - Ettringite (calcium sulfoaluminate hydrate)

Damage Process
1. Sulphate accumulation in concrete pores 2. Chemical reaction with cement compounds 3. Formation of gypsum and ettringite (both undergo volumetric expansion) 4. Internal expansion generates tensile/compressive stresses 5. Micro-cracks initiate and propagate 6. Progressive crack widening as more sulphate ingresses 7. Delamination (separation of concrete layers) 8. Foundation deterioration

Visual Example
Imagine a concrete foundation pier in groundwater containing dissolved sulphates (common in coastal areas or soils with gypsum deposits). The sulphate ions slowly migrate into the concrete's pore network. Inside, they react with calcium aluminate in the cement, producing ettringite crystals that occupy 2-3 times more volume than the original compounds. This is like ice forming in rock crevices—the expansion creates internal pressure, forcing micro-cracks to form radially from reaction sites. As cracks open, more sulphate-laden water enters, accelerating the cycle until surface layers delaminate like peeling paint.

Related Concepts
- Alkali-Silica Reaction (ASR): Similar expansion-based degradation from aggregate reaction - Chloride attack: Corrosion of reinforcement steel - Carbonation: pH reduction enabling steel corrosion - Protective measures: Sulphate-resistant cement, low permeability concrete, protective coatings

Chloride Attack

classclaude

so next we are going to see about the chloride attack. so in chloride attack the chloride ions penetrate through the voids of the concrete through moisture content. so these moisture content carries the chloride ions and these chloride ions will get penetrated into the concrete through its voids. so when these voids it's expanding and once it reaches the surface of the steel these chloride ions start reacting with the iron content in the steel. so these chloride ions and the iron content that will that is CN-, Fe+, react and the further it forms the rust. so these just particles will get accumulated in the voids of the concrete. so when it is get accumulated in the voids of the concrete so the voids of the concrete has get filled with the rust. so these rusts keeps on expand that is the volume gets increased. the void volume get increased and these volume creates the tension stress in the concrete. these tension stress causes the further development of the crack. so the crack when it further develops the concrete get spalled. and then it is delaminated and the surface of the steel reinforcement is exposed. and this is how the fluoride attack takes place.

Chloride Attack in Reinforced Concrete: Technical Summary

Process Overview

Chloride Ion Penetration

• Chloride ions (Cl⁻) penetrate concrete through voids via moisture
• Moisture acts as a transport medium carrying ions deeper into the structure

Corrosion Initiation

• Upon reaching steel reinforcement surface, chloride ions react with iron (Fe⁺) in the steel
• Chemical reaction: Cl⁻ + Fe⁺ → iron chloride compounds → rust (iron oxide)

Deterioration Mechanism

1. Rust particles accumulate in concrete voids
2. Rust occupies 2-6 times more volume than original iron
3. Volumetric expansion creates internal tensile stress
4. Tensile stress exceeds concrete's tensile capacity
5. Cracks develop and propagate
6. Concrete spalling (flaking/breaking away) occurs
7. Delamination exposes steel reinforcement
8. Accelerated corrosion continues

Visual Example

Scenario: Marine bridge pier with chloride exposure from seawater spray

• Seawater containing dissolved chlorides penetrates through microscopic pores in concrete column
• After months/years, chlorides reach steel rebar 50mm below surface
• Rust forms at steel-concrete interface, expanding like ice forming in a crack
• Expanding rust acts like a wedge, creating radial pressure (~15 MPa)
• Vertical cracks appear on pier surface, eventually causing concrete cover to break away
• Exposed corroded rebar shows characteristic orange-brown rust and reduced cross-section

Related Concepts

• Carbonation-induced corrosion (pH reduction breaking down passive layer)
• Passivation layer breakdown (protective oxide film on steel)
• Concrete cover thickness (primary defense against chloride ingress)
• Chloride threshold concentration (~0.4% by cement weight)
• Depassivation of steel reinforcement

Freeze Thaw Disintegration

classclaude

so next we are going to say about the freezing and thawing effect of the concrete. so we need to when the concrete is freezed the moisture content inside the content it gets expanding in its volume. so these expansion causes the capillary reaction in which this expansion creates a tension and the concrete get cracked. so next is thawing so in this thawing the when the moisture content is expelling out of the concrete and the concreate get shrinked in its volume. soa these continuous shrinking and expansion causes cracks in the concrete. so the corrosion inhibitors and the cathodic protection techniques can be used to prevent the steel or concrete corrosion.

Freeze-Thaw Deterioration in Concrete

Core Mechanism

Freezing Phase: - Moisture inside concrete freezes and expands in volume - Expansion generates capillary pressure/tension - Results in internal cracking

Thawing Phase: - Frozen moisture melts and exits the concrete - Concrete shrinks as moisture leaves - Volume contracts

Cumulative Damage: - Repeated freeze-thaw cycles cause progressive cracking through alternating expansion and contraction

Visual Example

Imagine a concrete bridge deck in winter climates: - Night: Temperature drops to -10°C, water in pores freezes and expands by ~9%, creating internal pressure like ice cracking a bottle - Day: Temperature rises to 5°C, ice melts and drains out, concrete contracts - After 50+ cycles over one winter: visible surface scaling and internal microcracking accumulate

Protection Methods

• Corrosion inhibitors: Chemical additives to protect embedded steel
• Cathodic protection: Electrochemical technique to prevent steel/concrete corrosion

Related Concepts

• Air entrainment (intentional micro-bubbles to accommodate ice expansion)
• Permeability and porosity control
• Concrete carbonation
• Salt scaling damage (when combined with de-icing salts)

Preventive Measures

classclaude

so the preventive measures that should be followed during construction is list outed in this slide.

Design aspects:

1. Low w/c ratio
2. High concrete strength
3. Higher minimum cement content
4. Higher concrete cover
5. Proper detailing of reinforcement
6. Moderate stress levels

Construction aspects:

1. Adequate compaction of concrete
2. Effective curing
3. Production of impervious concrete
4. Effective grouting of prestressed tendons
5. Periodical maintenance

so the it consists of two major categories: so which is design aspect and construction aspect.

so under design I expect we have to consider:

1. the low water cement ratio
2. high concrete strength
3. higher minimum cement content
4. high concrete cover proper detailing of the reinforcement
5. moderate stress levels

so these are the strategies which should be kept in mind during design aspects. so in construction aspects adequate compaction and adequate curing and protection of impervious concrete and it needs remedy a progressive maintenance and in case of pre-stressed and prefabricated structures the grouting of the pre-stressed concrete should be done and it should be maintained regularly.

Preventive Measures in Construction: Design & Construction Aspects

Design Aspects

Key strategies to implement during design phase:

1. Low water-cement (w/c) ratio - Reduces porosity and permeability
2. High concrete strength - Improves durability and load-bearing capacity
3. Higher minimum cement content - Ensures adequate binder for durability
4. Increased concrete cover - Provides better protection for reinforcement against corrosion
5. Proper reinforcement detailing - Ensures structural integrity and prevents cracking
6. Moderate stress levels - Prevents premature failure and excessive deformation

Construction Aspects

Critical practices during construction:

1. Adequate compaction - Eliminates air voids, increases density
2. Effective curing - Maintains moisture for proper hydration and strength development
3. Impervious concrete production - Reduces water penetration and chemical attack
4. Effective grouting of prestressed tendons - (For prestressed structures) Protects tendons from corrosion
5. Periodic maintenance - Regular inspections and timely interventions

Visual Example

Scenario: Bridge deck construction in a coastal environment

• Design phase: Engineer specifies w/c ratio of 0.40 (instead of 0.50), concrete cover of 50mm (instead of 30mm), and Grade M40 concrete (instead of M30) to resist chloride penetration from sea spray
• Construction phase: Workers ensure vibration compaction for 30 seconds per layer, apply wet burlap curing for 14 days, and for prestressed girders, inject epoxy-cement grout into ducts housing post-tensioned cables to prevent corrosion

Result: The bridge resists environmental attack and maintains structural integrity for its design life of 75-100 years.

Related Concepts

• Durability design: Service life prediction, exposure classification
• Corrosion protection: Cathodic protection, corrosion inhibitors, protective coatings
• Quality control: Material testing, construction monitoring, acceptance criteria
• Life-cycle cost analysis: Balancing initial investment vs. long-term maintenance costs

Preventive measures for different distress

next we are going to see about the preventive measures for different distress so the different distress may include movement of the formwork and erosion etc. so the movement of the former is mainly due to the absorption of the moisture from the fresh concrete so these leads to the micro cracks or swelling of the concrete. so this can be prevented by giving a coating layer to the former so next is erosion. so the erosion can be prevented by using some high-strength concrete.

Various aspects of Inspection

so now we are going to see about the next topic which is inspection. so the inspection in the sense we have to inspect the repair or the structure to be repaired or the structure that is a distressed or damaged. the various stages of inspect includes you have to observe:

1. the nature of the distressed
2. type of the distress
3. extent of the damage
4. its classification

so the major courses for the distress and you have to prepare a document and after that you have to collect some samples samples for laboratory analysis and you have to plan the in-situ testing and then the special environmental effects that should be considered and also the information of the load acting on the structure should also be collected during inspection period and the preventive measure to stop the further distress should be planned.

Flow chart

so next we are going to see the various aspects of inspection so which is given in the flow chart so these flow chart consists of the various strategies that should be followed by the inspecting so the first thing is you have to do a conditional survey so in conditional survey how to take a visual inspection of the building so next you have to give a non-restrictive testing destructive testing so based on these types we have to give a soil investigation structure investigation and preliminary investigation these things should be carried out. so next is demolition or demolish or may aware of noises for the threat of life so next you have to decide immediate repair that is a repair in the sense you have to strengthen or retrofit the structure and the selection of the rehabilitation system you how to process so after that you have to do these structures re- analysis of the structure and rehabilitation system which should be followed for building the structure or renovate the structure. next you how to give a cost-benefit analysis and then you have to execute the rehabilitation work so the habitation work may include the repair or retrofit measures that should be carried out in a structure.

Classification of Distresses

so next we have to do a general assessment so in this general assessment you how to give the description of the number of stories and dimension of the building so next is structural system we have to describe the structural system based on the load resisting system flows diaphragms basements foundation system etcetera. and next tests you have to give the non structural mentor the description so which may include the building type performance level resistant region of seismic city, soil type building occupancy, etcetera so these should be considered by doing your conditional survey.

Visual Inspection

so next we are going to see the visual inspection so in which our detailed plan showing the architecture and structure layout so which indicates the modifications done should be done if any so next is the plan should be checked out for its damages and the individual structural elements like slabs beams column stairs and a shear wall what tanks in fist non structural element everything electrical wiring plumbing so each and everything should be clearly analyzed. so next is you have to note the crackings, deterioration or damage or distress in a structure and you have to note the dead load and live load that is acting in the building. so next the horizontal and vertical movements of the building should be clearly checked out. and the types of during the type of construction what materials they have used and every each and everything should be photographed.

NonDestructive Testing

After visual inspection you how to do a non-destructive testing. so in that you have to locate the weakness. so based on the weakness you how to do the non destructive testing at those points. so these non-destructive testing includes the compressive strength of the concrete uniformity of the concrete homogeneity of the concrete, presence of cracks voids deflection depth everything should be clearly tested using a non-destructive testing. So next is you have to determine the in-situ compressive strength of the structure at the current compressive strength of the structure and a small course of the chemical tests can also be carried out to determine the chloride and sulfate content in the concrete. So next you have detecting carbonation depth and define the crack tip and next you how to locate the reinforcement and diameter of the bars at present detecting the corrosion activity and how to map the corrosion.

Soil Investigation

So in soil investigation you have to do the various process like drilling of bore holes a borehole report can be prepared and you have to collect these samples both disturbed and undisturbed samples can be collected. and you have to connect the standard penetration depth test to know down depth of the water table.

Based on the samples collected from the field you have to carry out the following laboratory investigation:

which includes bulk density and moisture content for the collected samples grain size analysis of the soil index properties of the soil. shear test should be carried out the shear test mainly includes tri-axial shear test consolidation test unconfined compression test can also be carried out for the collected samples.

Report

so based on the conditional surveying and the visual inspection field investigation and the laboratory investigation you should prepare a detailed report so the reports may include the test results and drainage property of the soil physical property and strength of the soil and allowable beginning capacity and possibility of liquefaction etc and the detailed report can be provided. And in case of super structures the reports can be modified based on the plan and the distressed or damaged cracks delamination and then a deflection cracking everything should be considered during preparing a report. And a suitable repair and rehabilitation can be given. Now let me conclude this that you have understood about the various causes for distress or damaged engine structure and various aspects of inspection and based on this inspection you might have able to know how to prepare a report and then in our next session we'll be carrying out the special concretes.

Comments