INTRODUCTION TO REPAIR AND

REHABILITATION OF STRUCTURES

Prepared By:Assistant Professor Ankit Patel

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Since 1950s, the construction activity in India has been increasing geometrically without matching increase in the availability of quality inputs, in terms of materials and skilled workmen. The gap between the quality planned and the quality achieved continues to become wider. The factors contributing to damages/distresses in buildings have, thus, become intrinsic right from the construction stage. Construction documents contain adequate specifications and instructions required to execute quality works. However, they remain as written document without achieving the desired level of results, because of lack of understanding of their significance by the field engineers. Standard cube test results are taken as a measure of quality in the construction.

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Whereas the factors such as method of placing, compaction and curing of concrete, which have significant influence on the quality achieved in the hardened concrete, are given scant attention. Many a times, the quality of concrete as placed and hardened in position has no correlation to the cube test results, which are used for quality control measures. Procedures, mandatory or otherwise, for periodic inspection of buildings and documenting defects in logical manner, and recording of structural repairs already carried out, are generally not followed or maintained.

The word ‘repair’ normally conveys small and ordinary repairs, which are not of structural significance. But the aim of rehabilitation is to restore a distressed structure back to its original durability.

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Repair, Rehabilitation and Maintenance

• Repair: Repair is the process of restoring something is damaged or deteriorated or broken, to good condition.

• Rehabilitation: Rehabilitation is the process of returning a building or an area to its previous good conditions.

• Maintenance: Maintenance is the act of keeping something in good condition by checking or repairing it regularly.

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CHAPTER-1 REPAIR STRATEGIES

Prepared By:Assistant Professor Ankit Patel

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Distress In Structures:Distress in Structure: Damage in Structure

Concrete may suffer distress or damage during its life period due to number of reasons. Because of varying conditions under which it is produced at various locations, the quality of concrete suffers occasionally either during production or during service conditions resulting in distress.

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Causes of Distress(Damage) in Concrete

• Structural causes ie (Externally applied loads, Environmental loads, Accidents)

• Construction Errors & Design Errors

• Poor Construction Practices

• Construction Overloads

• Drying Shrinkage

• Thermal Stress

• Chemical Reactions

• Weathering

• Corrosion

• Acid attack

• Chemical Reactions• Acid attack• Aggressive-water attack• Alkali-carbonate rock reaction• Alkali-silica reaction• Sulfate attack• Corrosion of Embedded Metals• Inadequate structural design• Poor design details

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Causes of Distress(Damage) in Concrete

For Plastic Concrete Distress:

Plastic Shrinkage

Early Removal Formwork

Improper design of formwork

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Defects, Causes, & Precautions

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Defects, Causes, & Precautions

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Causes of Distress(Damage) in Concrete

Voids in concreteRust Stain

Drying Shrinkage Plastic Shrinkage

scaling

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Blow holes in concreteBlow holes are individual, generally rounded, cavities on vertical surfaces of concrete, generally less than 10 mm across. They are caused by air in the concrete being trapped against the form face, sometimes due to insufficient vibration. Some blow holes are almost inevitable unless a permeable formwork material is used. The occurrence of blow holes can be minimized by the use of a suitable release agent on the surface of the formwork and the use of adequate vibration. In addition the concrete should have adequate workability. Blow holes are a cosmetic problem only and will not affect the long-term performance of the concrete structure

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Plucked Surface in concrete• This appears as surface material lost upon striking the formwork

• Normally occurs when the concrete surface is not of sufficient strength when striking the formwork.  Could be due to cold weather, retarded surface, high cement replacement or a combination thereof.

• Allowing the concrete to gain sufficient strength reduces the risk of its occurrence and is generally accepted as being 5MPa.

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Distress(Damage) in Concrete

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Construction Errors and Design Deficiencies:Poor construction practices and negligence can cause defects that lead to the cracking and concrete deterioration. These include: Scaling, Dusting of concrete Improper alignment of formwork Movement of formwork Improper location of reinforcing steel Improper curingErrors made during construction such as adding improper amounts of water to the concrete mix, improper curing cause distress and deterioration of the concrete. Proper mix design , placement and curing of the concrete, as well as an experienced contractor are essential to prevent constructing errors from occurring. Construction errors can lead to some of the problem such as scaling and cracking. Honeycombing and bug holes can be observed after construction. Honeycombing can be recognized by expose coarse aggregate on the surface without any mortar covering or surrounding the aggregate particles. The honeycombing may extend deep into the concrete. Honeycombing can be caused by a poorly graded concrete mix, by too large of aggregates, or insufficient vibration at the time of placement .

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Construction Errors and Design Deficiencies:Bug holes is the term used to describe small holes that are noticeable on the surface of the concrete. Bug holes are generally caused by too much sand in a mix, a mix that is too lean or excessive amplitude of vibration during placement. Bug holes may cause durability problems with the concrete should be monitors.Design Errors:It is broadly divided into two parts1. Inadequate structural design:The failure mechanism is due to over stressing of concrete beyond its capacity. These defects will me manifested in the concrete either by cracking or spalling. If the concrete experience high compressive stresses then spalling will occur. If concrete expose to high torsional or shearing stresses then spalling or cracking may occur and high tensile stresses will cause the concrete to crack. Such defects will be present in the areas where high stresses are expected. Through visual inspection engineer should decide weather to proceed for detail analysis. These problems can be prevented with a careful review of design calculations and detailing.

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Construction Errors and Design Deficiencies:2. Poor Design Detail:An adequate design does not guarantee a satisfactory function without including design detailing. Detailing is an important component of structural design. Poor detailing may or may not directly lead to a structural failure but it may contribute to the deterioration of the concrete. In order to fix a detailing defect it is necessary to correct the detailing and not to respond to the symptoms only. Some of the design and detailing defects include:1. Abrupt Changes in the section2. Insufficient reinforcement at corners and openings3. Inadequate provision of drainage4. Inadequate expansion joint5. Material incompatibility

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Condition SurveyCondition Survey is an examination of concrete for the purpose of identifying and defining area of distress. While it is referred in connection with survey of concrete and embedded reinforcement that is showing some degree of distress, its application is recommended for all buildings and structures. The system is designed to be used for recording the history of the project from its inception to completion and subsequent life.

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Objectives of Condition Survey• The objective of Condition Survey of a building structure is

• To identify Causes of distress and Their sources;

• To assess The extent of distress occurred due to corrosion, fire, earthquake or anyother reason, The residual strength of the structure and Its rehabilitability;

• To prioritise the distressed elements according to seriousness for repairs and

• To select and plan the effective remedy.

• “Find the cause, the remedy will suggest itself”. Sometimes, the source of the cause of distress is different than what is apparently seen. It is, therefore, essential that the engineers conducting condition survey determine the source(s) of cause so as to effectively deal with it and minimize their effects by proper treatment.

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Stages of Condition SurveyStages for carrying out Condition Survey largely depend on field conditions, user habits, maintenance, etc. Condition Survey of a building/structure is generally undertaken in four different stages to identify the actual problem so as to ensure that a fruitful outcome is achieved with minimum efforts & at the least cost. The four stages of Condition Survey described are:Preliminary Inspection,Planning,Visual Inspection,Field and Laboratory testing

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1. Preliminary InspectionA. The primary objective of the preliminary inspection is:1. To assess and collect following necessary information for a thoughtful planning before a condition survey is physically undertaken: Background history of the distressed structure From the

Owners/Clients From the occupants of building, general public, etc based on personal enquiries;

Notes and records of earlier repairs, if carried out, All possible relevant data and information; The safety requirements for condition survey team; Necessary site preparations including access scaffolds, working

platforms, etc, if any; The approx. time required for survey;

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1. Preliminary Inspection The extent and quantum of survey work; The requirement of field-testing equipment's, Tools for sampling. 2. To advise the client/owner of the building in regard to take immediate safety measures.

3. To define the scope of work of field investigations with the Clients/Owners.

B. Basic Information Gathering: A programme has to be evolved to obtain as much information as possible about the distressed structure at reasonable cost and in a reasonable time. Accordingly, the information required from the owner/client has to be listed out. Even though; many construction details and other related information may not be available with the owners/clients, yet as much as information and details as possible be gathered during the Preliminary Site Visit. Before undertaking a Condition Survey of a building/structure, the following essential information is required and be obtained from the clients/owners:

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1. Preliminary Inspection Period of construction; Construction details including architectural, structural and as built

drawings; Exposure conditions of structure; Present use of structure; Previous changes in use, if any; Record of structural changes made, if any; Record of first occurrence of deterioration, if any; Details of repairs, if carried out in the past; Reports of previous investigations/condition surveys, if any; Photographs of distressed portions of structure.BITS Edu Campus

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1. Preliminary Inspection

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1. Preliminary Inspection

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1. Preliminary Inspection

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1. Preliminary InspectionC. Photographic Record: It is always necessary to carry a camera with flash during such ‘Preliminary inspection’ and take necessary photographs of the distressed structure and its members. Preliminary Inspection and collection of data would be helpful in planning, the Condition Survey for field investigations. This allows a reasonably sufficient understanding of the cause of distress for an experienced Rehabilitation Engineer.

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General approach for pre-repair evaluation of distress concrete

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2. Planning StagePlanning stage involves preparation of field documents, grouping of structural members and classification of damage as under:

• Preparation of Field Documents:

• For condition survey, the following are required to be prepared: Survey objective; Scope of work; Method of survey; The field and laboratory testing requirements and field

equipment's & tools required for the same; Maintenance and repair records.

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2. Planning Stage Required number of photo copy of available drawings; Floor plans based on field measurements; Work sheets and tables for recording in a logical manner all

information, test results including field data gathered; Previous Condition Survey results and Investigation Reports, if

any; Maintenance and repair records.

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2. Planning StageGrouping of the Structural members:Soon after the preliminary site visit and on obtaining of building plans, the structural members shall be grouped as per their type and based on similarity of exposure conditions for proper appreciation of the cause of distress. For example in a building subjected to normal environmental attack, the grouping could be done as under: External columns/beams would be subjected to more severe

environmental attack than the internal structural members of a building and could be grouped in two broad groups.

Even from amongst the external columns, those at corners or projected out are likely to be exposed more due to adjacent faces being exposed than those not at corners or un-projected columns. Hence to be grouped separately.

• .

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2. Planning Stage The members subjected to dampness/wetting/drying located in or

around the toilet shafts are likely to undergo similar class of distress and be grouped separately.

Structural members with different protective finishes have to be grouped separately.

• Classification of Damage:

• Based on the preliminary data collected and site visit, the rehabilitation engineer should interpret rules and subdivide the repair classification broadly in to five classes as ‘Class 0’ to ‘Class 4’ named as Cosmetic Repair, Superficial Repair, Patch, Repair, Principal Repair and Major Repair.

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Classification of Damage

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Classification of Damage

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3. Visual Inspection1. Visual Inspection and observations:

Visual examination of a structure is the most effective qualitative method of evaluation of structural soundness and identifying the typical distress symptoms together with the associated problems. This provides valuable information to an experienced engineer in

regard to its workmanship, structural serviceability and material deterioration mechanism.

It is meant to give a quick scan of the structure to assess its state of general health.

The record of visual inspection is an essential requirement for preparation of realistic bill of quantities of various repair items.

Experienced engineers should carry out this work as these forms the basis for detailing out the plan of action to complete the diagnosis of problems and to quantify the extent of distress.BITS Edu Campus

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3. Visual Inspection Simple tools and Instruments like camera with flash, magnifying

glass, binoculars, and gauge for crack width measurement, chisel and hammer are usually needed. Occasionally, a light platform/scaffold tower can be used for access to advantage.

The study of crack pattern leads to the primary cause of damage. The mesh pattern generally suggests that the distress in a structure could be due to drying shrinkage, frost action or alkali aggregate reaction.

The cracking along the reinforcement indicates that the damage could be due to corrosion of reinforcement.

The study of colour and texture of the concrete and condition of fixtures is very much useful in investigation of fire damage structure.

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3. Visual Inspection2. Questioning of personnel/Scrutiny of field data and records:The questioning of personnel and the scrutiny of field data and records is carried out for the following: Grade of concrete adopted Cube test results Type of materials and sources Construction details Environmental conditions

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3. Visual InspectionCommonly

Observed Order

Location of RCC component

Deterioration of RCC Building

First Wet / water stagnating areas with RCC elements located on external

direct exposed walls/slabs and frequented with alternate wetting/drying

cycle.

Second Thin exposed non structural RCC elements e.g. chhajjas, railings etc.

Third Terrace RCC slab with ineffective insulation, water proofing and

drainage systems

Fourth Wet areas with RCC elements located on inner unexposed walls and

frequented with alternate wetting/drying cycle

Fifth Beams/columns with one face exposed direct to sun and rain and the

other face unexposed.

Sixth Beams/Columns exposed to rain and sun from all sides.

Last Beams/Columns/Slabs located in the interior of building.BITS Edu Campus

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3. Visual InspectionTypes of cracks in concrete structures: Structural cracks. Non Structural Cracks.Structural Cracks• Structural cracks are those which result from incorrect design, faulty

construction or overloading and these may endanger the safety of a building and their inmates.

Non Structural Cracks.• Non Structural cracks occur mostly due to internally induced stresses

in building materials. These cracks normally do not endanger the safety but may look unsightly, create an impression of faulty work or give a feeling of instability.

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3. Visual InspectionDefects in Concrete:• Concrete defects can be broadly classified into two categories :• 1. Macro Defects:• If these defects are present, concrete has low strength and will rapidly

deteriorate due to easy ingress of water and other chemicals. Invariably, structure will require repairs within a few years of its construction. Causes will have to be analysed and defects removed before doing any additional protective treatment. Often, waterproofing of concrete slabs is carried out superficially and it fails to give the desired benefit because the defective concrete below this waterproofing layer has not been treated to seal the macro/micro defects which existed within the concrete slab. The main causes of these defects are generally due to inadequacies in design and / or construction practices.BITS Edu Campus

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3. Visual Inspection• 2 Micro Defects:• These defects are not visible to the naked eye. They are usually very

fine voids caused by large capillary pores resulting from the use of low grades (strength) of concrete with high water to cement ratio.

• They could also occur due to addition of excess water or high water to cement ratio of concrete mix. Fine cracks are generally present in concrete and can occur due to various reasons. They do not pose a serious threat to concrete deterioration initially as they are generally not deep and are discontinuous. With lapse of time due to variations in temperatures, changes in weather conditions, changes in loading conditions they increase in depth, length and width and combine with other fine cracks to create continuous passage for moisture, chlorides, sulphates and other chemicals from the environment to enter and start corrosion of steel in concrete and other deleterious reactions.

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3. Visual InspectionTo conclude, macro defects and micro defects in concrete are both harmful to the health of buildings and can cause deterioration of concrete depending on the extent of their presence, environmental conditions around the building and maintenance done during its life cycle. However macro defects by virtue of being larger can cause faster deterioration and more damage to the structure than the micro defects

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3. Visual InspectionObstructions to visual inspection: Recently done paints, patch work of replaster, false ceiling etc. are

likely to create obstructions to visual inspection. Carefully analyze such areas

Insufficient light inside the building. The access height from within and from outside during visual

inspection could also be a major problem.Types of cracks and their pattern: It is generally easy to differentiate various types of cracks and relate

them with the cause of distress. The location of cracks and their pattern give the first indication of the problem.

Cracking and spalling, or rust staning are visual indication of the corrosion of steel in concrete. Corrosion cracks run along the reinforcement location.

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3. Visual Inspection A mesh pattern of cracks suggests drying shrinkage, alkali aggregate

reaction or frost attack, Cracks at right angle to main reinforcement are generally associated

with structural deficiency. Cracking along the bar can be an important indication that the

reinforcements are subjected to corrosion.

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3. Visual Inspection.

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3. Visual InspectionWorksheetThe visual inspection shall largely cover:• Recording of Areas of high distress;• Cracks & their location;• Excessive deflection;• Exposure conditions of various distressed areas;• Moisture, leakage/ seepage & dampness locations;• Abnormal vibrations in structure, if any;• Algae, fungus growth and/or efflorescence etc and their locations;• Photographic records,Visual inspection is, therefore, the best way of qualitative assessment of any structure. BITS Edu Campus

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4. Field/laboratory Testing Stage• Objective: It may neither be feasible nor is the practice to conduct field/laboratory

testing on every structural member in an existing distressed building. The field/laboratory testing of structural concrete and reinforcement is to

be undertaken, basically for validating the findings of visual inspection. These may be undertaken on selective basis on representative structural

members from each of the various groups based on exposure conditions as explained in the preceding sections.

The programme of such testing has to be chalked out based on the record of visual inspection.

After identification of weak zones in a structure, detailed assessment of insitu quality of material is done. A number of test have been developed for different properties of concrete.

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Considerations for Repair StrategyIn the Condition Survey Report, before arriving at the Repair Strategy, it

shall include the following considerations: Identification of the cause of problem and its source is the fundamental

to the success or failure of the repair. A lack of attention at this point can put at risk the whole job.

For arriving at an effective and economical solution, systematic documentation of all observations is essential.

Available space and accessibility will determine the selection of repair method and repair strategy.

Depending upon the scope and scale of repairs, the repair strategy has to suit the on-going activities in the building.

The prioritization of repairs and their sequencing are important components for deciding the repair strategy.

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Considerations for Repair Strategy Major repair procedure may demand propping the structural members to

relieve a part or full component of the load acting on the member. If the building requires extensive propping, vacating the building may become the pre-requisite.

Safety measures to prevent any immediate major mishap shall be prescribed without loosing further time.

The report should also include requirements on safety measures to be adopted during execution of repair jobs.

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NON DESTRUCTIVE EVALUATION TESTSA number of non-destructive evaluation (NDE) tests for concrete members are available to determine in-situ strength and quality of concrete. Some of these tests are very useful in assessment of damage to RCC structures subjected to corrosion, chemical attack, and fire and due to other reasons. The term ‘non destructive’ is used to indicate that it does not impair the intended performance of the structural member being tested/investigated. The non-destructive evaluation has been broadly classified under two broad categories via ‘in-situ field test’ and ‘laboratory test’. These tests have been put under four categories depending on the purpose of test as under:

In-situ Concrete Strength

Chemical Attack

Corrosion Activity

Fire DamageBITS Edu Campus

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Concrete Strength AssessmentA. Objective: Generally, in-situ non-destructive evaluation of concrete is to have an

overall idea of the quality of concrete. In some cases, a sufficiently accurate estimate of quantitative value of

concrete strength is required for assessment of load carrying capacity of a structural member. The need for such an estimate may arise during evaluation of change in usage of structure, modification or extension of the original structure or damage due to fire, earthquake, etc

B. Limitations: The accuracy is not very high as most of the non-destructive methods of

evaluation of concrete strength are based on indirect measurement of concrete strength.

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Rebound Hammer Test The operation of Rebound Hammer (also called Schmidt’s Hammer)

is illustrated in Figure When the plunger of rebound hammer is pressed against the surface of concrete, a spring controlled mass with a constant energy is made to hit concrete surface to rebound back. This test is conducted to assess the relative strength of concrete based on the hardness at or near its exposed surface and to identify relative surface weaknesses in cover concrete and also can be used to determine the relative compressive strength of concrete. Locations possessing very low rebound numbers will be identified as weak surface concrete and such locations will be identified for further investigations like corrosion distress, fire damage and/or any other reason including original construction defects of concrete. The extent of rebound, which is a measure of surface hardness, is measured on a graduated scale. This measured value is designated as Rebound Number (a rebound index). A concrete with low strength and low stiffness will absorb more energy to yield in a lower rebound value.

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Rebound Hammer Test• The results are significantly affected by the following factors: a. Mix characteristics: i. Cement type, ii. Cement Content, iii. Course aggregate type: b. Angle of Inclination of direction of hammer with reference to

horizontal c. Member Characteristics, ii. Compaction, iii. Surface type, iv. Age, rate of hardening and curing type, v. Surface carbonation, vi. Moisture Condition,

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Rebound Hammer TestAverage Rebound Quality of Concrete

>40 Very Good

30-40 Good

20-30 Fair

<20 Poor and/or delaminated

0 Very Poor and/or delaminated

 

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Rebound Hammer Test

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Ultrasonic Pulse Velocity Test The ultrasonic pulse velocity method basically involves the

measurement of velocity electronics pulses passing through concrete from a transmitting transducer to a receiving transducer. The density and elastic properties are in turn related to the quality and the strength of material. The pulse velocities ranges from about 3 to 5 km/s.

An Ultrasonic pulse apparatus consists of a transmitter and a receiver which are held again two faces of concrete. The apparatus generates pulses of ultrasonic frequency which are transmitted through concrete by the transmitter. On the other face, the receiver receives the pulses and the apparatus records them. The time of travel between initial onset and the reception of the pulse is measured electronically. The path length between the transducer and the receiver, divided by the time of travel gives the average velocity of wave propagation. The velocity of pulses is correlated to the strength of concrete. Higher the velocity of pulses greater the strength of concrete.

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Ultrasonic Pulse Velocity TestPulse Velocity Concrete quality

> 4.0 km/s Very good to excellent 

3.5-4.0 km/s Good to very good, slight porosity may exist.

3.0- 3.5 km/s Satisfactory but loss of integrity is suspected

<3.0 km/s Poor and loss of integrity exist

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Penetration Resistance (‘Windsor Probe’ and ‘PNR Tester’)

The determination of the resistance of concrete to penetration by a steel rode or probe, driven by a fixed amount of energy can be assess the compressive strength of concrete. The Principal is that, the depth of penetration is inversely proportional to the compressive strength. The relation between strength of concrete and the depth of penetration greatly depends on the hardness of the aggregate because the coarse aggregate particles become fractured in the penetration tests.

This technique offers a means of determining relative strengths of concrete in the same structure or relative strength of different structures. Because of the nature of equipment, it can not, and should not be expected to yield absolute values of strength. ‘Windsor Probe’, as commercially known, is penetration resistance measurement equipment, which consists of a gun powder actuated driver, hardened alloy rod probe, loaded cartridges, a depth gauge and other related accessories.

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Penetration Resistance (‘Windsor Probe’ and ‘PNR Tester’)

In this technique, a gunpowder-actuated drivers used to fire a hardened alloy probe into the concrete. During testing, it is the exposed length of probe, which is measured by a calibration depth gauge.. Being a low energy device, sensitivity is reduced at higher strengths. Hence, it is not recommended for testing concrete having strength above 28 N/sqmm. The penetration of pin creates a small indentation (or hole) on the surface of concrete. The pin is removed from the hole, the hole is cleaned with an air jet and the whole depth is measured with a suitable depth gauge. Each time a new pin is required as the pin gets blunted after use. The strength properties of both mortar and stone aggregate influence the penetration depth of the probe in a concrete. It is claimed an average coefficient of variation for a series of groups of three readings on similar concrete of the order of 4% may be expected.BITS Edu Campus

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Penetration Resistance (‘Windsor Probe’ and ‘PNR Tester’)

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Pull out Testing

As the name suggests, this method involves the measurement of the force required to pull out a specially shaped steel rod or some similar device from a concrete surface. There two basic categories one which involves an insert having to be cast into the concrete is called cast-in method and another where the insert is fixed into a hole drilling into hardened concrete is called drilled hole method and it is more appropriate for field survey of hardened concrete.1. Cast-in Method (LOK Test):The main aim of this technique is to measure the tensile force required to pull-out the a metal insert which has been cast into the fresh concrete. This test is commercially known as LOK-test. In this system the insert is directly attached to the formwork. The basic geometry of insert contains 25mm diameter disc attach to a removable steam which locates the disc 25mm below the concrete surface. To prevent the disc rotating when the stem is being removed a 15mm notch is provided on one side of the disc.

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Pull out Testing

The load is applied to the disc through a removable pull-bolt using a hydraulic jack which has a constant loading rate. From the peak tensile load recorded by the jack the cube compressive strength is estimated.

2. Drilled-hole method (CAPO Test):It is observed that one of the main limitations of the cast-in method was that the inserts needed to be place before or at least during concreting process. To overcome this problem another type of pull out test was developed which would be completed on existing structures. The basic geometry of this is same as the cast-in method. The main advantage of this method is extremely valuable for in situ strength assessment. The CAPO is based on the expression cut and pull out. The basic procedure for this test consists of drilling a 45mm deep, 18mm dia hole after which a 25mm dia groove is cut at a depth of 25mm using portable reaming machine.

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Pull out Testing

An expanding ring is than placed and expanded into grove using a pull bolt assembly. The convenient LOK Test pulling equipment is then attach to the pull bolt continues until the cone of concrete is removed to allow retrieval of the pull bolt.

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Chemical Test

Some of the chemical test are as follows: Depth of carbonation Chloride content Cement content Sulphate content Alkali content1. Depth of carbonation:This test is carried out to determine the depth of concrete affected due to combines attack of atmospheric carbon dioxide and moisture causing g a reduction level of alkanity of concrete.A spray of 0.2% solution of phenolphthalein is used as pH indicator of concrete. The change of color of concrete to pink indicates that the concrete is in a good health, where no change in color takes place, it is suggestive of carbonation affected concrete.

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Chemical Test

The i-situ test is conducted by drilling a hole on the concrete surface upto cover concrete thickness, removing dust by air blowing spraying 0.2% solution of phenolphthalein with physician’s injection syringe and needle on such freshly drilled concrete and observing the color change.2. Chloride content:It is important to know the level of chloride near the steel concrete interface. Chloride present in concrete are fixed as well as free. Though it is free chloride ions which are importance from corrosion risk point of view. Chloride contents are determined and compared with the limiting values specified for the concrete to assess the rise of corrosion in concrete.As per IS code the test consists of obtaining powdered samples by drilling and collecting from different depths ie 5mm and mixing the sample with a special chloride extraction liquid and measuring the electrical potential of the liquid by chloride ion sensitive electrode.

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Corrosion Assessment (test)

1. Cover meter survey:The main purpose of providing concrete cover to reinforcement is to protect it from corrosion. A Cover thickness survey is useful to determine existing cover thickness in a specific location where a damage has been identified and elsewhere for comparison on same structure. A cover meter is use to measure the thickness of cover, dia of rebar and spacing of rebars.2. Half cell potential survey:The corrosion of steel in concrete is an electrochemical process. Depending on the corrosion activity the electrode potential of steel rebar undergoes changes with reference to a standard electrode. By making measurements on well defined grid points over the whole surface, a distinction can be made between corroding and non-corroding locations.

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Corrosion Assessment (test)

The various standard electrodes used are:Copper-copper sulphate electrodeSilver-silver chloride electrodeA reference electrode is connected to the rebar and voltage difference is measured between the rebar and the reference electrode. Generally, the voltage potential becomes more and more negative as the corrosion becomes more and more active.

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Fire Damage Assessment

The current practice is to assess fire rating of building rather than fire resistance of materials although fire resistance has a significant contribution to fire rating.Generally fire resistance of a material or fire rating of an element depends on: Properties of materials Temperatures generated during fire Duration of fire exposure Concrete can resist fire up to about 200-300 degree Celsius. It is non combustible material and does not give out smoke or fumes when expose to fire.

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Fire Damage Assessment

The factor affecting the fire resistance of concrete are:1. Type of aggregate: Igneous stone aggregate will be more stable

against fire. Light weight aggregates offer vary good fire resistance.2. Lean Concrete: Lean concrete having low cement content show

better resistance to fire.3. Admixtures: Concrete with admixtures like fly ash, ground furnace

slag also have better fire resistance.4. Moisture content in concrete: Moist concrete disintegrates faster

than dry concrete.

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Prof. Ankit Patel

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Fire Damage Assessment

DTA- Differential Thermal Analysis:This technique is use to study the physical and chemical changes that occur in a material when it is heated. It is concerned with the rate of change of temperature of a sample as it is heated at a constant rate of heat flow. Its principle is based on “when a material is slowly heated its temperature rises but when the material undergoes any endothermic reaction ie losing water, losing carbon dioxide its temperature remains constant.” In DTA study the sample and an inert material are heated separately and the difference of temp between the two is recorded by means of thermocouples which generated an electrical signal whenever there is temp differences between the reference and the sample. When there is no endothermic reaction in the sample there would not be any differences of temp between the reference and the sample and hence no electrical signal would occur.

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Prof. Ankit Patel

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Fire Damage Assessment

The results of DTA are presented in the form of DTA curves. The occurrence of any pulse appears as a peak in the DTA curve which is a plot of temp versus electrical signal generated. Qualitative composition of the sample can be judged by measuring the size of the peak in the DTA curve. The peak size is directly related with the amount of heat involved in the transition.

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Prof. Ankit Patel

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