3rd day - mahmoud abufouda

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.


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


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.


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 Damages (Extrinsic)


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


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 ?


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.



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

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.


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.


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.


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.


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 ?