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Assessment Of Defects In Concrete Structures And Evaluation Of Safety Of Concrete
Infrastructure Training3rd Day
Rehabilitation Strategies, Design and Materials
By:MAHMOUD ABUFOUDA
MSc Civil Engineer
Course Content Introduction •Background•Current Repair Practice•Repair Management•Distress identification
Review of Causes of Damages• Intrinsic •Extrinsic
Rehabilitation Assessment Process•Condition Survey
Rehabilitation/Repair Strategies
Selecting Rehabilitation Techniques
Material Requirements and Selection
Analysis and Design for Selected Repair
RC structures are expected to give a trouble free service throughout its intended design
life.
RC Structure
s
Structural deficiencies
Unanticipated over-loadings
Physical damages
(fire, explosion
etc.)
Material deterioratio
n
Regular restoration
and maintenance (functional requirement
s)
Harsh environmen
t
Concept Difference Repair
Repair techniques generally include removal of damaged parts and placement of new parts in its place. Repair methods, however, do little to address the cause of assist.
Rehabilitation Includes work to restore the original capacity to meet typical service loads
and conditions experienced by the structure. For example, patching a bridge deck, or replacing spalled concrete are part of rehabilitation.
Retrofitting Retrofitting reduces the vulnerability of damage of an existing structure
during a future earthquake. It aims to strengthen a structure to satisfy the requirements of the current codes for seismic design.
Current Repair Practice
RC construction activities have a massive and geometrical growth. This growth doesn’t match the increase in availability of quality input
in terms of materials and skilled workmanship. The gap between quality planned and quality achieved has become
wider.
Current Repair Practice
Specification is not enough.
They are adequate to maintain quality.
Misunderstood of their significance by the field engineers.
Standard Cube Test Vs the casted concrete quality.
Current Repair Practice Concrete Structures need regular
maintenance.
The repair procedure are not followed or maintained.
Buildings remain for several years without getting due attention.
Periodic Inspections
Damage Documentation
Regular Maintenance
Current Repair Practice
Some cases, only visual inspection is carried out for preparing the maintenance budget estimates.
This exercise is often left to engineers who have no experience of such problems.
Current Repair Practice
The treatment of symptoms instead of dealing with the real cause and effect phenomenon.
Such of approach may offer a quick action with minimum inconvenience to the real cause.
Leads the source of damage to be unknown and continue to cause problem even after repairing.
Current Repair Practice This fashion is like
DAMAGES MASKED WITH FINISHES
Repair Management A rational approach to any repair and rehabilitation work is to
consider the source of the problem and the symptoms together. Three stages for managing repair job:
Documentation of Damages
• Type • Degree• Diagnosis of Cause Phenomenon
• Selection of Consultant
Preparation Of Repair Documents
• Detailed Drawings
• Guidelines (practical and flexible)
• Material lists• Work Specifications
• Tender Documents
Execution of Repair
• Supervise by qualified Engineer
• Monitor Effectiveness of repair
• Selection of Repair Material and Technique
Distress Identification It is necessary to have a planned
approach to investigate the condition of concrete and reinforcement.
Sometimes, the causes are straightforward but it may not be in so many cases.
Particularly difficult cases in which the cause and effect phenomenon cannot be readily explained.
Review of Causes of Distress (Intrinsic)
Ref: CPWD Handbook on Repairs and Rehabilitation of RCC Building (2002)
Review of Causes of Distress (Intrinsic)
Ref: CPWD Handbook on Repairs and Rehabilitation of RCC Building (2002)
Review of Causes of Damages (Extrinsic)
Ref: CPWD Handbook on Repairs and Rehabilitation of RCC Building (2002)
Rehabilitation Assessment Process The steps of RC repair assessment process are;
Seeing an EFFECT
Determining the CAUSE
Deciding whether the problem needs to be repaired
Conducting some form of condition survey to quantify problems
Dealing with repair analysis and engineering issues in the repairDetermine repair strategies that includes methods, techniques and repair materials
Finally, accomplishing the repair
Condition Survey Condition survey is an examination of concrete for the purpose of identifying
and defining area of distress. Condition survey objectives:
a) To identify: Causes of distress, The sources of distress.
b) To assess: The extent of distress occurred due to corrosion, fire, earthquake or another reasons, The residual strength of the structure, The rehabilitability.
c) To prioritize the distress elements according to seriousness for repairs.d) To select and plan the effective remedy (repair).
Condition Survey (Stages)
Preliminary
Inspection
PlanningVisual
Inspection
Field and Laboratory Testing
Condition Survey- Preliminary Inspection Objectives
1. to assess and collect following necessary information Background history from the owner or the occupants of the building Notes or records of earlier repairs, if carried out. All possible relevant data and information. Practical site restrictions and how to overcome them. The safety requirements. Site preparation such scaffolding, working platforms etc. The time of survey. The requirement of field testing equipment and the tools for sampling.
2. To advise the owner in regard of immediate safety measures to avert any accidents endangering life and structure.
3. To define the scope of work of field investigations with the owner.4. Provide photographic records.
Condition Survey- Planning The planning stage involves;
Preparation of Field
Documents
•Survey objectives•Scope of work•Method of survey•The field and laboratory testing requirements
•Field equipment and tools required
•List of tasks and their sequence
•Required drawings •As built drawings •Worksheets and tables for recording in a logical manner
•Previous conditions survey results, if any
•Maintenance and repair records
Grouping of Structural Members
•Structural members shall be grouped according to their type and based on the similarity of exposure.
Classification of
Damages
•Based on the preliminary data collected and site visit, the rehabilitation engineer should freeze the interpretation rules and subdivide the repair classification into five classes
•Class 0•Class 1•Class 2•Class 3•Class 4
Condition Survey- Planning
Ref: CPWD Handbook on Repairs and Rehabilitation of RCC Building (2002)
Condition Survey- Visual Inspection The most effective qualitative method of
evaluation. For an experienced engineer, it provides
valuable information. Gives quick scan of the structure to assess its
state. It is essential for preparation of realistic bill of
quantities. Experienced engineers shall carry out this work. Simple tools and instrument like camera with
flash, magnifying glass, gauges for cracks width measurement, chisel and hammer are needed
Condition Survey- Visual Inspection What to look For ?
Ref: CPWD Handbook on Repairs and Rehabilitation of RCC Building (2002)
Condition Survey- Field/Lab Testing It should be based on the findings of visual inspection. It is important to select the appropriate Non Destructive Evaluation
(NDE) techniques and location of investigation. It may neither feasible nor practical to conduct field/lab testing on
every structural member. Representative samples should be selected from each of the
structural groups which are based on the exposure conditions. A single technique may not be adequate Sometimes, combination of techniques has to be adopted to get a
truly representative data on the condition of the building.
Condition Survey- Final Report The condition survey report shall include the following considerations;1. Identification of the cause of the problem and its source. (critical
success criteria).2. To achieve an effective and economical solution, systematic
documentations of all observations is essential.3. Available space and accessibility are constraints for the selections of
repair methods.4. The prioritization of repairs and their sequencing.5. Safety measures to prevent any immediate major accidents.6. Safety measures to be adopted during the execution of Repairs.
Rehabilitation/Repair Strategies
Rehabilitation/Repair Strategies
Stress reductions
Strengthening of Structural
elements
Improving the strength of concrete.
Stabilization: repairing cracks,
settlement and joints
Improving the masonry structure
Provide protective
covers against the aggressive
chemicals
Water-proofing
Rehabilitation/Repair Strategies1. Stress Reduction (Live and/or Dead Load Reduction) As a rehabilitation strategy, reduction of stress provide a solution for
the distress of the structure It can be achieved by
Reducing dead and live load. Replacing heavy solid partitions with lightweight partitions. Enlarging the openings by removing filler walls. Reducing numbers of stories. Changing the building use to lower classification of loading. Span reduction of beams by providing struts.
Rehabilitation/Repair Strategies2. Strengthening of structural elements Like beams, columns, slabs, etc. Will be covered next lecture
Rehabilitation/Repair Strategies3. Improving the strength of concrete The concrete strength can be enhanced by impregnation with specific
polymers like;1. Methacrylate (MMA) 2. Vinyl Ester Gel
Benefits of using these material are their strong mechanical properties and shorter time to apply and hardening.
Rehabilitation/Repair Strategies4. Stabilization By repairing Cracks, Deferential Settlements and Joints. Also by adding propping and supports Cracks indicate a tensile failure of the material Cracks can be
Inactive (nonmoving) can be solved by adding plaster layers or grouting with non-shrinkage repair materials.
Active (moving) the source of cracking should be identified and treated accordingly.
https://www.youtube.com/watch?v=uBAkNeNw-yQ
Rehabilitation/Repair Strategies5. Improving the masonry Structure The masonry may be required to be strengthened for resisting
bearing loads to support the structural elements.
Selecting Rehabilitation Techniques
After conducting the condition survey, the decision shall be made for the selection of:
1. Method of repair, and2. Repair material.
The priority of selecting the method of repair should be assigned to:1. Ensuring safety of the structure, and 2. Protection of the structure from further deterioration.
Selecting Rehabilitation Techniques
The selected method of repair should achieve one or more of the following objectives: Restore the structural integrity of the member by restoring or increasing
its strength and stiffness. Prevent the effects of damage promoting agents such as moisture,
chlorides and carbon dioxide to improve durability. Maintaining the aesthetics/appearance of concrete surface.
Performance Requirements of Repair
Performance
Requirement
Strength, Serviceabilit
y and Durability
Protection of steel
Bond with parent surface
Dimensional stability
Resistance to
environmentally induced
damage
Ease of application
Appearance
Important factors for Repair Selection
Important Factors
for Repair
Selection
Type and degree of damage
Location of damage
Environmental
exposure
Availability of skill
Availability of time
and access for
repairs
Appearance
Cost
Material Requirements and Selection One of the most important tasks for ensuring durable and trustworthy
repair is the selection of material. Understanding the cause of damages is essential to select the repair
materials. Availability of materials of relevance, equipment and skilled labor
have to be explored before deciding upon the repair material.
Essential factors for Selecting material
1. Low shrinkage properties.2. Requisite setting/hardening properties.3. Workability.4. Good bond strength with existing sub-strata.5. Compatible coefficient of thermal expansion.6. Compatible mechanical properties and strength to that of the sub-strata.7. Should allow relative movement, if expected, particularly in case of sealing of
cracks or dealing with expansion joints.8. Minimal or no curing requirement.9. Alkaline character.10. Low air and water permeability.11. Aesthetics to match with surroundings.12. Cost.13. Durable, non-degradable or non-biodegradable due to various forms of energy, life.14. Non-hazardous/non-polluting.
Analysis and Design for Selected Repair
After selection of repair method based on the information from the condition survey report, the analysis and design of the repairing method are conducted.
According to the type of deterioration, the analysis and design of the repair will differ.
The analysis and design shall take the followings into consideration:1. Structural sizes and material properties established based on the investigation.2. The reduction in member dimensions.3. Changes in end conditions.4. Sequence of construction and subsequence changes.5. In modeling the structure for analysis, all geometric and material
characteristics shall be realistic.
Analysis and Design for Selected Repair
6. Comparing between the theoretical model and actual observations. 7. The structural safety and load transfer shall be ensured at all stages of
repair. The removal of concrete during the repair may reduce the effective size of
structural member and affect its stiffness. The stability of the structure maybe endangered due to the transfer of loads to
adjoining members. Removal of structural members may increase the effective length of a
compression members. In case of indeterminate beams or slab, it is advisable to assume the member as
a simply supported in the design.
Repair Stages As long as the analysis and design of the selected rehabilitation
technique is ready, the repairing stage can be started. According to the type of repairing techniques, Repair Stages may
differ The Genera Stages of Repair involves
Site Preparation
Concrete removal and
surface preparation
Bonding/ passivating
coat and repair
application
Repair Stages- Site Preparation This stage involves
Mobilization
• Offices• Equipment and tools • Materials
Submittals
• Condition Survey Report, Specifications, Guidelines, Tender documents, BOQ, Drawings, etc.
• QC/QA plans• Safety Plan• Testing Program and Testing Plans
Prior-Repairing
• Cleaning Working Site• Insuring Safety • Propping and supporting• Installing scaffolding
Site Preparation (Falsework) Propping and supporting (Falsework Installation) Falsework consists of temporary structures used in construction to
support spanning or arched structures in order to hold the component in place until its construction is sufficiently advanced to support itself.
The purpose is to provide relief in stresses and strains of structural members.
Also to provide support for the whole structure. Need a structural analysis and design to be constructed.
Site Preparation (Scaffolding) Scaffold is a temporary structure on the outside of a building, made
of wooden planks and metal poles, used by workmen while building, repairing, or cleaning the building.
Scaffolding types
Fixed Scaffoldi
ng
Supported
Scaffolding
Suspended
Scaffolding
Mobile Scaffoldi
ng
Aerial Lifts
Concrete Removal & Surface Preparation
According to the recommendation provided in the rehabilitation assessment report, damaged concrete removal and surface preparation are conducted.
Types of mechanical damaged concrete and surface preparation techniques;
Removing of plaster manually by hammer and chisel
Chipping of unsound concrete using power driven tools (Hammer Drills or Jackhammer)
Cleaning unsound surfaces by water or sand blasting
Concrete Removal & Surface Preparation Essential points to take into considerations
Exposed reinforcement shall be inspected for access clearance, cross sectional area and location.
Reinforcing bars should be further exposed if the remaining concrete is not bonded with reinforcing steel.
Corroded reinforcement shall be cleaned with wire brush and treated with epoxy prior to cast it with mortars or concrete.
In some cases, additional reinforcement is needed to be installed in the repaired elements
To improve the ponding between the old and the new layers of concrete, steel mesh, anchors, fasteners and epoxy are applied prior to casting.
Applying Repair Application (Formwork)
After surface preparation of damaged members, formwork can be conducted to cast the new layers of concrete.
Formwork is a mold including all supporting structures, used to shape and support the concrete until it attains sufficient strength to carry its own weight. It should be capable of carrying all imposed dead and live loads apart from its own weight.
Types of Formwork;1. Timber Formwork 2. Hardboard Forms (wood fiber)3. Aluminum forms 4. Plastic forms5. Steel Forms
Applying Repair Application This step can be done according to the repair method Various options are available such as;
Filling the cracks with cement and resin based grout. Injecting grout into a mass of dry aggregates. Poured concrete. Dry packing Sprayed concrete (shotcrete)
These options will be covered briefly next lecture.
Thank you …Any Questions ?