Repair, Rehabilitation and Strengthening Materials

Introduction

Existing concrete and masonry infrastructure rarely fails because of a single material deficiency. Deterioration usually results from interacting actions: moisture and ion transport, carbonation, chloride-induced corrosion, sulfate attack, alkali–silica reaction, freeze–thaw cycling, abrasion, overloading, fire, poor original construction, and inadequate maintenance. The engineering task is therefore not simply to replace damaged concrete. It is to diagnose the mechanism, establish the required performance, select compatible materials, detail the intervention, and verify its effectiveness over the intended service life.

Repair, rehabilitation and strengthening have distinct meanings. Repair restores damaged or defective material, generally without substantially increasing the original load capacity. Rehabilitation returns a structure to an acceptable level of service, durability and safety, often through several coordinated interventions. Strengthening increases resistance, stiffness, ductility or fatigue capacity beyond the existing condition. A durable intervention must address both symptoms and causes; patching chloride-contaminated concrete without controlling corrosion, for example, may accelerate damage at the repair boundary.

This chapter presents a materials-centred framework for condition assessment and intervention design. It considers repair mortars and concretes, grouts, surface coatings, crack-injection systems, cathodic protection, and steel- and fibre-reinforced-polymer (FRP) strengthening. The discussion is consistent with the principles found in international concrete repair and strengthening standards; project-specific design must nevertheless follow the governing national code, specification and safety regulations.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Diagnose common deterioration mechanisms and distinguish active from dormant damage.

2. Plan a condition assessment using inspection, testing and structural appraisal.

3. Select repair mortars, grouts, coatings and crack-injection materials for compatibility and service performance.

4. Explain the operating principles and limitations of cathodic protection.

5. Select and conceptually design FRP or steel strengthening systems.

6. Develop a staged, quality-controlled intervention and evaluate life-cycle risks.

7. Critically assess sustainability, monitoring, constructability and ethical responsibilities in repair decisions.

1. Diagnosis Before Material Selection

1.1 The deterioration model

A useful diagnosis links four elements: cause, transport or reaction mechanism, observed manifestation, and structural consequence. For example:

• Carbonation lowers concrete alkalinity. If the carbonation front reaches reinforcement, the passive film may be destroyed and corrosion can initiate.
• Chloride ions may enter from marine exposure or de-icing salts. When the chloride concentration at reinforcement exceeds a critical, environment-dependent threshold, localized corrosion can develop.
• Sulfate reactions may produce expansive products and loss of cohesion, especially where moisture is continuously available.
• Alkali–silica reaction can cause gel swelling, map cracking and loss of stiffness; removing surface concrete alone does not remove the reactive aggregate.
• Freeze–thaw damage requires water-filled pores and repeated freezing; air entrainment and drainage are preventive measures, whereas a dense, non-air-entrained patch may be vulnerable.
• Mechanical damage, impact, fatigue and overload may produce cracks that are structurally significant even when the concrete appears sound.

The same visual symptom can have different causes. Rust staining may indicate active reinforcement corrosion, but it may also be residual staining from an earlier event. A crack may be shrinkage-related, thermal, settlement-induced, flexural, shear-related, corrosion-induced or caused by foundation movement. Material selection without diagnosis is therefore a high-risk practice.

1.2 Condition assessment sequence

A professional assessment normally proceeds through the following sequence:

Document review. Collect drawings, design calculations, construction records, exposure history, previous repairs, change of use, load records and inspection reports.

Preliminary survey. Map cracking, delamination, spalling, leakage, staining, deflection, joint deterioration and exposed reinforcement. Record location, width, length, orientation and apparent activity. Photographs should include scale and orientation.

Structural appraisal. Establish the present load path and assess whether damage affects flexure, shear, compression, anchorage, stability, fire resistance or robustness. Temporary propping or load restriction may be required before intrusive testing.

Material and environmental testing. Typical tests include cover-depth measurement, half-cell potential mapping, concrete resistivity, carbonation depth, chloride profiling, petrography, pull-off strength, core compressive strength, absorption, moisture measurement and corrosion-rate estimation. Tests must be selected to answer decisions, not performed merely to produce data.

Cause and extent assessment. Delamination surveys, radar, impact echo, ultrasonic methods and targeted opening-up can identify hidden deterioration. Results should be interpreted with environmental exposure and structural analysis.

Intervention design and verification. Define performance requirements, repair boundaries, compatibility criteria, execution controls, acceptance tests and monitoring provisions.

No individual nondestructive test proves corrosion or structural safety. Half-cell potential indicates the probability of corrosion under suitable moisture and electrical continuity conditions; it does not directly measure corrosion rate. Resistivity is influenced by moisture, temperature, ionic content and concrete composition. Core strength represents sampled locations and may not describe the whole member. Engineering judgment and multiple lines of evidence are essential.

1.3 Compatibility requirements

A repair material should be compatible with the substrate in:

• Mechanical behaviour: compressive and tensile strength, modulus, creep, shrinkage and thermal expansion.
• Dimensional behaviour: drying shrinkage, restrained expansion and movement accommodation.
• Transport properties: permeability, sorptivity, vapour transmission and chloride diffusivity.
• Chemical behaviour: alkalinity, sulfate resistance, alkali sensitivity and interaction with reinforcement.
• Electrochemical behaviour: electrical resistivity and the possibility of creating anodic or cathodic regions around a patch.
• Durability and fire performance: resistance to the actual environment and required fire rating.
• Constructability: access, thickness, curing, temperature, overhead application and tolerance for substrate moisture.

Higher strength is not automatically better. A very stiff patch placed beside weaker, cracked concrete may attract stress and promote debonding. Conversely, a strengthening overlay must possess sufficient stiffness and bond to participate in the intended load path. Compatibility is a system property, not merely a product property.

2. Repair Mortars and Concrete Repair Systems

2.1 Material classes

Repair materials include cementitious mortars, polymer-modified cementitious mortars, expansive or shrinkage-compensated grouts, epoxy mortars, polymer concretes and high-performance cementitious concretes. Selection depends on repair volume, orientation, substrate condition, exposure, required strength gain, moisture, access and fire requirements.

Conventional cementitious repair concrete is appropriate for large-volume replacement where formwork and curing are possible. Its advantages include familiar behaviour, alkalinity compatible with steel reinforcement and good fire resistance. Drying shrinkage and inadequate curing are common causes of failure.

Polymer-modified cementitious mortars improve adhesion, tensile capacity and resistance to water ingress. They are widely used for thin repairs and overhead work. They may have different vapour transmission, thermal movement and fire characteristics from the substrate.

Shrinkage-compensated materials use expansive mechanisms, generally controlled by admixtures and restraint, to reduce net shrinkage. Their performance depends on moisture, restraint and curing; “non-shrink” should not be interpreted as zero dimensional change under all conditions.

Epoxy mortars and polymer concretes provide high bond and chemical resistance and can cure at relatively low thickness. They are vulnerable to high substrate moisture, elevated temperature, ultraviolet exposure and differential thermal movement unless specifically formulated. They may also have lower fire resistance than mineral systems.

Sprayed concrete or mortar is useful for large, irregular or overhead surfaces. Nozzle operation, rebound control, substrate preparation, reinforcement encasement, thickness control and curing govern quality.

2.2 Surface preparation and placement

Successful repair generally requires removal of unsound concrete to a sound, clean substrate. Edges should be cut to a defined profile rather than feathered to a thin edge. Reinforcement should be exposed sufficiently to remove corrosion products around its circumference, but unnecessary damage or bending of bars must be avoided. Steel loss should be measured before deciding whether replacement or supplementation is required.

The substrate must be free of dust, laitance, oil, loose rust and standing water. Cementitious materials commonly require a saturated-surface-dry condition, whereas some resins require a dry surface. Bond coats must not be allowed to dry unless the system specifically requires it. Repairs should be placed in lifts within the manufacturer’s and specification’s limits, compacted without segregation, and cured against premature drying, thermal shock and freezing.

Quality control should include batch identification, mixing water or resin ratio, temperature, pot life, placement records, thickness checks, compressive or tensile tests where specified, and bond testing. A pull-off test is useful for assessing near-surface tensile bond, but the result is affected by substrate failure, test location and moisture; it is not a complete prediction of long-term durability.

2.3 Electrochemical consequences of patch repair

When a small chloride-contaminated region is removed and replaced with low-chloride material, surrounding contaminated concrete may remain electrically connected to reinforcement. The new patch can become relatively cathodic while adjacent chloride-contaminated steel becomes anodic, producing incipient anode or halo-effect corrosion around the repair. Mitigation may involve extending removal to the chloride-contaminated zone, using electrochemical chloride extraction, applying a surface treatment, installing galvanic anodes, or using impressed-current cathodic protection. The choice depends on chloride distribution, corrosion activity and service-life objectives.

3. Grouts and Void-Filling Materials

Grouts transfer load, fill voids, seal water paths or anchor embedded components. Their required properties differ according to use.

Cementitious precision grout is used beneath base plates, bearings and machinery. It should have controlled flow, adequate early and ultimate strength, low bleeding, dimensional stability, and compatibility with the support. Flowable grout must not segregate or wash out.

Microfine cement grout can penetrate finer cracks and pores than ordinary cement grout, but penetration depends strongly on particle-size distribution, pressure, crack geometry and water movement. It is not a universal substitute for resin injection.

Chemical grouts, including polyurethane and acrylate systems, are selected for water cut-off, flexible sealing or very fine fissures. Some react with water and expand; others require dry conditions. Their reaction time, expansion pressure, leachability, toxicity and long-term stability must be verified.

Epoxy grout provides strong adhesion and chemical resistance but generally requires clean, sufficiently dry conditions and may be brittle relative to moving joints.

For grouting, define the objective first: structural load transfer, rigid crack bonding, flexible water sealing, soil improvement or void filling. Pressure should be controlled to avoid hydraulic jacking, delamination or unintended migration. Injection ports, refusal criteria and post-injection verification should be specified.

4. Surface Coatings and Waterproofing Systems

Coatings may reduce ingress, protect against carbonation and chlorides, provide chemical resistance, or improve appearance. They do not restore lost structural capacity.

Hydrophobic impregnation reduces capillary water absorption while allowing vapour movement; silane systems are commonly used for chloride-exposed concrete when the substrate is sufficiently sound and accessible.

Pore-blocking and mineral coatings can reduce water penetration while retaining relatively mineral compatibility. Film-forming acrylic, epoxy and polyurethane coatings provide a more continuous barrier, but their adhesion, vapour permeability, ultraviolet resistance and crack-bridging capacity must match exposure.

The required carbonation resistance of a coating is commonly assessed through its equivalent air-layer thickness, while chloride protection is evaluated through appropriate diffusion or absorption tests. These are system performance concepts, not guarantees based solely on nominal thickness. Coatings require sound substrate, correct moisture condition, adequate surface profile, compatible primers and controlled application temperature.

A coating that blocks outward vapour movement over a persistently wet substrate may blister or debond. Crack-bridging claims must be related to crack width, temperature, cycling and substrate movement. Coatings should therefore be integrated with drainage, joint repair and crack treatment rather than used as cosmetic concealment.

5. Crack-Injection and Crack-Sealing Systems

Crack treatment begins by classifying cracks according to width, depth, activity, moisture condition, contamination and structural significance. A dormant crack with dry faces may be bonded with a rigid epoxy. A moving crack requires flexible sealing or a designed joint; injecting a rigid resin into an active movement crack is likely to fail.

Epoxy injection can restore continuity and transfer tensile stress across suitable, relatively dry, dormant cracks in structural concrete. It is not appropriate where cracks are contaminated, continuously wet, actively moving or caused by unresolved settlement.

Polyurethane injection is useful for water stopping and flexible sealing. Hydrophilic products absorb water and may remain flexible; hydrophobic products generally expand through gas or chemical reaction and may require different moisture conditions. Water sealing does not necessarily restore structural continuity.

Cementitious and microfine cement injection is compatible with mineral substrates and may be appropriate for larger cracks, voids or masonry, but penetration and bond are limited by particle size and water flow.

A typical injection procedure includes crack mapping, cleaning, port installation, surface sealing, low-pressure injection from one end to the other, recording material consumption and pressure, curing, port removal and verification. Pressure must be sufficient for controlled penetration but low enough to avoid widening cracks or forcing resin into unintended spaces. The specification should define acceptance by filled length, bond, leakage reduction or structural test, as appropriate.

6. Cathodic Protection

Cathodic protection reduces reinforcement corrosion by making the reinforcing steel act as the cathode of an electrochemical cell. It can be delivered by:

• Galvanic systems, in which a more active sacrificial anode supplies protective current.
• Impressed-current systems, in which an external power source drives current from durable anodes to the reinforcement.

The basic current relationship is

\[

I = iA

\]

where \(I\) is protective current in amperes, \(i\) is design current density in amperes per square metre of steel, and \(A\) is the electrically connected steel area in square metres. This relationship is a sizing identity, not a complete design equation. The selected current density must be based on corrosion condition, concrete resistivity, temperature, exposure, system type and applicable standards. Excessive current can cause acidification at the anode, hydrogen-related damage in susceptible steels, coating debondment and alkaline reactions.

Cathodic protection requires electrical continuity of the reinforcement, suitable anode distribution, monitoring reference electrodes and safe control of current. Impressed-current systems require power, control equipment and maintenance. Galvanic systems are simpler but provide limited current and may require anodes to be replaced. Verification commonly uses potential shift, depolarization criteria, current output and reference-electrode measurements, interpreted according to the governing standard.

Cathodic protection is especially valuable where chloride contamination is widespread and complete concrete removal would be uneconomic or destructive. It does not replace structural repair of delaminated concrete, and it does not by itself restore section loss or bond. Damaged concrete must still be repaired, and electrical isolation from unintended metallic components must be considered.

7. Strengthening with Steel and FRP

7.1 Design philosophy

Strengthening begins with a revised structural analysis. The engineer must establish existing capacity, load history, residual material properties, failure modes, ductility, load redistribution and construction-stage effects. Strengthening should not create a brittle failure mode elsewhere. For example, increasing flexural capacity of a beam without checking shear may shift failure from ductile flexure to brittle shear.

The strengthening system must be activated by an appropriate load-transfer mechanism. Bonded plates or FRP depend on interface shear and anchorage; external post-tensioning depends on deviators and anchorages; section enlargement depends on shear transfer across the interface and reinforcement development.

7.2 Steel plates, sections and jackets

Steel plates can increase flexural or shear capacity, while steel angles, channels and jackets can improve confinement or axial resistance. Advantages include high modulus, ductility, established design practice and inspectability. Limitations include corrosion, heavy handling, site welding, fire protection, stress concentrations and demanding surface preparation.

Steel strengthening should include checks for plate yielding, local buckling, connection or adhesive capacity, fatigue, corrosion protection, fire resistance and load introduction. Bolted systems may be preferable where wet adhesive conditions or future removability are important. Welded work on existing reinforcement or prestressing steel requires strict control because heat can damage materials or create residual stress.

7.3 FRP systems

FRP composites consist of fibres embedded in a polymer matrix. Carbon FRP has high tensile strength and modulus with low density and good corrosion resistance. Glass FRP is less expensive but generally has lower modulus and greater sensitivity to moisture and alkali unless appropriately protected. Aramid FRP has useful toughness but may have environmental and ultraviolet limitations.

FRP is efficient for flexural, shear and confinement applications where corrosion resistance, low added weight and rapid installation are valuable. It is anisotropic and generally linear-elastic until rupture. The design must account for debonding, concrete cover separation, end peeling, anchorage, fire and environmental reduction factors. FRP does not provide the same ductile yielding mechanism as steel.

For a rectangular reinforced-concrete beam strengthened with externally bonded FRP, the conceptual strain compatibility approach is:

\[

\varepsilon_f = \varepsilon_{cu}\frac{d_f-c}{c}-\varepsilon_{bi}

\]

where \(\varepsilon_f\) is the effective FRP strain, \(\varepsilon_{cu}\) is the assumed ultimate concrete compression strain, \(d_f\) is the distance from the compression face to the FRP centroid, \(c\) is neutral-axis depth, and \(\varepsilon_{bi}\) is the existing strain in the concrete at installation. The equation assumes plane sections remain plane and requires consistent strain reference and sign convention. The usable FRP strain is the lesser of the strain permitted by rupture and the strain permitted by debonding and code limits. The tensile force is approximately

\[

T_f = A_f E_f\varepsilon_f

\]

where \(A_f\) is FRP area and \(E_f\) is its elastic modulus. The associated moment contribution depends on the internal force resultants and their lever arms; it should not be calculated as \(T_f d_f\) without accounting for compression and steel forces. Actual design requires an equilibrium solution, existing strain state, reduced material properties and the applicable FRP guideline.

For confinement of columns, FRP wraps provide lateral restraint. Their effectiveness depends on fibre orientation, corner radius, continuity, concrete strength, dilation and rupture strain. Poorly rounded corners can cut fibres and cause premature rupture. FRP is combustible or loses resin properties at elevated temperature, so fire protection may be essential.

7.4 Interface preparation and installation

The concrete surface must be sound, clean and sufficiently strong for the specified bond. Weak laitance, coatings and contaminants are removed; corners are rounded for wraps; voids are repaired; moisture and temperature are controlled. Resin mixing, fibre alignment, overlap, consolidation and cure are recorded. Adhesion tests, visual inspection, fibre orientation checks, tap testing and monitoring of environmental conditions form part of quality assurance.

8. Integrated Intervention Planning

A durable repair project should be expressed as a performance specification. It should state the required service life, exposure, water tightness, structural capacity, crack tolerance, fire performance, appearance, maintainability and inspection provisions. Product names alone are inadequate.

A practical decision sequence is:

1. Make the structure safe and control immediate hazards.

2. Identify the deterioration mechanism and its spatial extent.

3. Decide whether the objective is preservation, repair, rehabilitation or strengthening.

4. Remove or control the cause where feasible.

5. Select a compatible material system and define preparation and curing.

6. Design load transfer, interfaces, joints and drainage.

7. Plan access, sequencing, temporary works and protection of occupants.

8. Establish inspection and testing hold points.

9. Verify performance after completion and monitor critical locations.

Life-cycle evaluation should compare initial cost, disruption, energy and carbon, maintenance frequency, replacement risk and consequences of failure. A low-cost patch with a short life may be inferior to a more expensive electrochemical or protective system when traffic closure or failure consequences are high.

9. Illustrative Case: Chloride-Damaged Parking-Garage Beam

Background

This illustrative case concerns a 25-year-old reinforced-concrete parking garage in a region using de-icing salts. A beam over an entrance ramp shows longitudinal cracks, rust staining and local spalling at its soffit. The owner requires continued service for at least 20 years with minimal closure.

Problem and assessment

The inspection team maps cracks and delaminated areas, measures cover, opens selected locations, tests carbonation depth and obtains chloride profiles at several depths. Half-cell mapping indicates a high probability of active corrosion over much of the beam. Concrete cores show adequate compressive strength in sound regions, but reinforcement has measurable section loss near the soffit. The beam is checked for current gravity loads and revised loads from a proposed change in parking arrangement. Flexural capacity is marginal after section loss, while shear capacity remains adequate but must be checked after strengthening.

The diagnosis is chloride-induced corrosion, not merely defective cover. Chloride contamination extends beyond the visibly spalled zones, and a patch-only solution would leave active corrosion around the repair.

Approach

The intervention consists of temporary load restriction, removal of delaminated and chloride-contaminated concrete to defined boundaries, cleaning and measurement of reinforcement, replacement of severely reduced bars where required, and repair with a compatible polymer-modified cementitious material. Because chloride contamination is widespread and closure is difficult, a monitored impressed-current cathodic-protection system is installed after continuity testing. A silane treatment is applied to exposed horizontal surfaces and leakage paths are repaired.

Independent structural analysis identifies insufficient flexural reserve under the revised loading. A carbon-FRP plate is therefore bonded to the beam soffit, with end anchorage and fire protection designed according to the applicable strengthening guideline. The substrate is moisture-tested, prepared, repaired and pull-off tested before installation. FRP installation is scheduled only within the resin manufacturer’s temperature and humidity limits.

Outcome and learning points

Acceptance records show repair-bond results exceeding the project requirement, continuous electrical reinforcement continuity, stable cathodic-protection monitoring values and satisfactory FRP inspection. The garage reopens in stages. The owner receives a maintenance plan involving annual visual inspection, periodic corrosion monitoring and renewal of the water-repellent treatment when performance declines.

The case demonstrates five principles: visible damage underestimates chloride extent; patch repair alone may cause halo corrosion; strengthening must follow diagnosis and revised load analysis; electrochemical systems require monitoring; and surface protection and drainage are essential complements to structural repair.

10. Limitations, Governance and Emerging Practice

Repair decisions contain uncertainty because hidden damage, variable workmanship and future exposure cannot be known perfectly. Probabilistic deterioration modelling and reliability-based assessment can improve decisions, but model results depend on representative inspection data. Owners should be informed of assumptions, residual risks and inspection obligations rather than being promised an unconditional service life.

Ethically, engineers must not conceal unsafe conditions through cosmetic coatings or accept test results outside their valid application range. Records should preserve traceability of materials, batch numbers, environmental conditions, test results and deviations. Local regulations govern worker exposure to solvents, resins, dust, confined spaces, electrical systems and traffic interfaces. Cathodic-protection installations require electrical safety, and resin systems require control of volatile compounds and skin sensitizers.

Digital photogrammetry, drones, infrared imaging, ground-penetrating radar and sensor networks can improve mapping and trend analysis. Artificial intelligence can assist crack segmentation, anomaly detection and prioritization, but it should not replace engineering diagnosis. Training-data bias, false positives, poor lighting and lack of causal interpretation remain important limitations. AI-supported decisions should retain human review, audit trails and calibrated uncertainty.

Contemporary research is developing low-carbon repair binders, geopolymer and alkali-activated systems, recycled aggregates, self-healing cementitious materials, durable bio-based coatings, nano-modified grouts, distributed corrosion sensors and digital twins. These technologies should be evaluated through verified performance, whole-life assessment, compatibility and maintainability—not novelty alone.

Best-Practice Checklist

• Diagnose the cause before specifying the product.
• Map damage and define repair boundaries from evidence.
• Consider mechanical, dimensional, transport, chemical and electrochemical compatibility.
• Remove or control the deterioration mechanism where possible.
• Design interfaces, drainage, joints, anchorage and construction stages.
• Use mock-ups for complex repairs and strengthening systems.
• Control substrate condition, mixing, placement, curing and environmental limits.
• Include acceptance testing and independent inspection at hold points.
• Reassess adjacent failure modes after strengthening.
• Provide monitoring, maintenance and clear residual-risk documentation.

Chapter Summary

Durable intervention in existing structures is a diagnosis-and-design process rather than a material-shopping exercise. Condition assessment combines records, visual mapping, structural appraisal, targeted testing and environmental interpretation. Repair materials must be compatible with the substrate in mechanical, dimensional, transport, chemical, electrochemical and fire behaviour. Cementitious and polymer-modified mortars, grouts, coatings and injection systems each serve distinct purposes and have specific moisture, movement and preparation requirements.

Cathodic protection controls reinforcement corrosion by supplying protective current, but it requires continuity, monitoring and continued repair of physically damaged concrete. Steel and FRP can restore or increase capacity, yet their effectiveness depends on load-path design, anchorage, interface quality, failure-mode checks, fire protection and construction control. Life-cycle planning, ethical reporting, regulatory compliance and monitoring are integral to successful rehabilitation. Emerging digital and low-carbon technologies are valuable when supported by verified evidence and professional judgment.

Key Terms

Condition assessment: Systematic evaluation of a structure’s physical condition, causes of damage and performance.

Compatibility: Suitability of a repair material’s mechanical, dimensional, chemical and transport properties relative to the substrate.

Carbonation: Reaction that lowers concrete alkalinity as atmospheric carbon dioxide penetrates concrete.

Chloride-induced corrosion: Reinforcement corrosion initiated when chlorides disrupt steel passivity.

Delamination: Separation of a near-surface concrete layer, often caused by corrosion or freezing.

Repair mortar: Mortar formulated to replace defective or missing concrete.

Grout: Flowable material used to fill voids, transfer load or seal cracks and openings.

Hydrophobic impregnation: Treatment that reduces capillary water absorption without forming a continuous surface film.

Crack injection: Introduction of a fluid material into a crack to bond, seal or fill it.

Halo effect: Corrosion developing adjacent to a repaired patch because contaminated concrete remains beside a relatively clean region.

Cathodic protection: Electrochemical method that reduces corrosion by making reinforcement cathodic.

Galvanic anode: Sacrificial anode that supplies protective current without an external power source.

Impressed-current system: Cathodic-protection system using an external power supply.

FRP: Fibre-reinforced polymer composite used for repair, strengthening or confinement.

Debonding: Loss of adhesion or interface failure between strengthening material and substrate.

Strain compatibility: Assumption or method relating strains in bonded components through their deformation geometry.

Load path: Route by which forces are transferred through structural members, connections and supports.

Incipient anode: Localized corrosion region formed near a repaired area due to electrochemical changes.

Life-cycle assessment: Evaluation of impacts and resources over construction, use, maintenance and disposal stages.

Review Questions

Short Answer Questions

1. Distinguish repair, rehabilitation and strengthening.

2. Why is visual inspection alone insufficient for diagnosing reinforcement corrosion?

3. State three compatibility requirements for a concrete repair material.

4. What is the principal difference between galvanic and impressed-current cathodic protection?

5. Why may rigid epoxy injection be unsuitable for an active crack?

Long Answer Questions

1. Explain a complete condition-assessment sequence for a deteriorated reinforced-concrete member.

2. Compare cementitious, polymer-modified, epoxy and shrinkage-compensated repair materials.

3. Describe the mechanisms, benefits and limitations of cathodic protection.

4. Discuss the design and construction considerations for externally bonded FRP strengthening.

5. Develop a life-cycle intervention strategy for a chloride-exposed concrete structure.

Analytical / Application Questions

1. A beam has widespread chloride contamination, local spalling and limited allowable closure time. Compare patch repair alone, cathodic protection with repair, and complete concrete removal. Recommend a strategy and justify it using technical and life-cycle criteria.

2. An externally bonded FRP plate is proposed for a beam whose shear capacity is uncertain. Explain the checks required before installation and the possible consequences of increasing flexural capacity without verifying shear.

3. A crack is wet and shows seasonal width changes. Select an appropriate crack-treatment approach, identify unsuitable materials, and propose verification and monitoring measures.

Multiple Choice Questions with Answers

Question 1

Which observation most strongly indicates that patch repair alone may be inadequate in a chloride-damaged member?

A. The repair area has a smooth finish

B. Chloride contamination extends beyond visible spalling

C. The concrete has adequate compressive strength

D. The member is located indoors

Correct Answer: B. Chloride contamination extends beyond visible spalling

Question 2

What is the principal function of cathodic protection?

A. Increase concrete compressive strength

B. Seal all surface cracks

C. Reduce reinforcement corrosion by making steel cathodic

D. Replace lost reinforcing steel

Correct Answer: C. Reduce reinforcement corrosion by making steel cathodic

Question 3

Which material is generally most suitable for bonding a dormant, dry structural crack?

A. Rigid epoxy injection

B. Hydrophilic polyurethane only

C. Loose sand-cement fill

D. Uncured acrylic paint

Correct Answer: A. Rigid epoxy injection

Question 4

What does the relation I = iA represent in cathodic-protection planning?

A. Concrete strength from area

B. Protective current from current density and steel area

C. FRP stress from strain

D. Water absorption from coating thickness

Correct Answer: B. Protective current from current density and steel area

Question 5

Which property is especially important when selecting a repair material beside weaker existing concrete?

A. Only maximum compressive strength

B. Mechanical and dimensional compatibility

C. Colour difference

D. Maximum resin pot life regardless of exposure

Correct Answer: B. Mechanical and dimensional compatibility

Question 6

A hydrophobic impregnation primarily functions by:

A. Increasing capillary water absorption

B. Reducing capillary water absorption while generally allowing vapour movement

C. Adding flexural reinforcement

D. Replacing delaminated concrete

Correct Answer: B. Reducing capillary water absorption while generally allowing vapour movement

Question 7

A major limitation of FRP compared with steel strengthening is that FRP generally:

A. Has no tensile capacity

B. Is heavier and more corrosion-prone

C. Does not provide the same ductile yielding mechanism

D. Cannot be bonded to concrete

Correct Answer: C. Does not provide the same ductile yielding mechanism

Question 8

Which condition is most likely to cause failure of an epoxy repair system?

A. Correctly prepared dry substrate

B. Unresolved active crack movement

C. Controlled curing temperature

D. Sound concrete substrate

Correct Answer: B. Unresolved active crack movement

Question 9

Why must shear be checked after flexural strengthening of a beam?

A. Flexural strengthening can shift failure toward a brittle shear mode

B. Shear is unrelated to flexural capacity

C. FRP eliminates all shear forces

D. Steel reinforcement cannot resist shear

Correct Answer: A. Flexural strengthening can shift failure toward a brittle shear mode

Question 10

Which statement about half-cell potential measurements is correct?

A. They directly measure reinforcement diameter loss

B. They indicate corrosion probability under suitable conditions

C. They measure concrete compressive strength

D. They prove that no corrosion exists when values are uniform

Correct Answer: B. They indicate corrosion probability under suitable conditions