Crack Guid Line

 

  Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

 J apan apan  C oncrete oncrete   I nstitute nstitute  

 

  Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Japan Concrete Institute All rights reserved. No part of this work may be reproduced, transcribed or used in any form of by any means-graphic, electronic, or mechanical, including photocopying, recording, typing, W Web eb distribution, or information storage and/ or systems-without the prior written permission of the Japan Concrete Institute.

 

 

Preface

 In spite spi te of numerous efforts to eliminate elimina te cracks crack s from concrete structures, there are still many cracked concrete structures. Some cracks are very harmful and should be repaired as soon as possible, while other cracks are almost harmless. Therefore, a good guideline on how to deal with cracks in concrete structures has long been needed. JCI  published “Practical Guideline Guidelin e for Investigation and Repair of Concrete Structures” in 1980, a second version followed in 1987, and a third version was followed in 2003 and 2009. In this third and fourth version, English edition was also published. A fifth version was published in Japanese in 2013. This volume, titled “Practical Guideline for  Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-“ is the  English edition of this latest version. It is believed that this guideline will be much use when cracks are detected in existing concrete structures, both in Japan and overseas. 

 

Contents Chapter 1 General

1

1.1 Scope and Objective 1.2 Procedure from Investigation to Repair and Strengthening 1.3 Terms Terms and Definitions

Chapter 2 Investigation

11

2.1 General 2.2 Standard Investigation 2.3 Detailed Investigation

Chapter 3 Cause Estimation

44

3.1 General 3.2 Cause of Cracking  Cracking  3.3 Cause Estimation Based on Standard Investigation 3.4 Cause Estimation Based on Detailed Investigation In vestigation

Chapter 4 Evaluation of Cracks

79

4.1 General 4.2 Evaluation-I (Applied for Cracks due to Drying Shrinkage, etc.) 4.3 Evaluation-II (Applied for Cracks due to Carbonation and Chloride Attack, etc.) 4.4 Evaluation-III (Applied for Cracks due to Combined Deterioration, etc.)

Chapter 5 Judgment of Necessity of Repair and Strengthening

96

5.1 General 5.2 Methods of Judgment

Chapter 6 Repair and Str Strengthening engthening 6.1 General 6.2 Design of Repair and Strengthening 6.3 Repair Methods  6.4 Strengthening Methods 6.5 Repair and Strengthening Strengthening Materials 6.6 Repair and Strengthening Works 6.7 Inspection 6.8 Records and Interim Observations

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Chapter 1 General 1.1 Scope and Objective

(1) This Guideline covers the practicable investigations of cracked concrete members or structures, cause estimation, evaluation, judgment of the necessity of repair or strengthening, selection of the most effective repair and strengthening method, and the case studies. This Guideline applies mainly to cast-in-situ concrete structures. (2) This Guideline covers the cracks generated in a concrete member or structure after casting and during the service life. (3) The main users of this guideline are the owners including managers of the concerned structures as well as engineers who are working for investigation, cause estimation, evaluation, judgment and repair or strengthening of cracked concrete structures. [Comments] (1) and (2) 1) Targeted concrete members or structures This Guideline mainly covers the common cast-in-situ reinforced concrete and prestressed concrete structures which include buildings, bridges, pavements, concrete dams, etc. This Guideline does not cover the precast reinforced concrete structures. However, it can be used for such structures with certain limitations and restrictions. 2) Targeted cracks This Guideline covers the cracks which are developed in concrete members or structures after casting of concrete. Although countermeasures in advance can be adopted during the design stage of concrete members or structures, this Guideline does not cover the countermeasures. In this Guideline, the normally recommended items and methods for investigation of cracking, cause estimation, evaluation,  judgment on the necessity for repair and strengthening and appropriate technical methods for repair and strengthening are explained. The causes of cracking covered by this Guideline are summarized in Table 3.1. This Guideline does not deal with all conditions such as various types and importance of structures, exposure conditions, etc. This Guideline can be used as a basic tool to conduct investigation, cause estimation, evaluation, judgment, selection of repair and strengthening methods for cracked concrete structures in normal conditions. Therefore, when this Guideline is applied, it is necessary to plan  practical countermeasures taking into consideration of the various conditions of target cracked structures such as its own unique environment, service loads, etc. 3) Technical contents The main users of this Guideline are from a beginner to a middle career engineer who is in-charge of a structure for maintenance and taking actions if there are cracks in the structures or concrete members. Therefore, this Guideline is prepared in a simple way for easy learning and application of the learned knowledge in concerned structures. This Guideline systematically describes the process of investigation (Chapter 2), cause estimation (Chapter 3), evaluation (Chapter 4), judgment (Chapter 5) and repair and strengthening (Chapter 6). Moreover, examples are compiled in this Guideline that can be used as useful references by the engineers with a little professional experience in this field. 4) Necessity for re-investigation Crack widths generally fluctuate with service loads, seasonal change such as temperature and humidity, etc. and age of the structure. Therefore, judgment may differ based on the time of evaluation. Even if a structure is judged not to do repair based on the result of investigation of the present condition of the structure, re-investigation is necessary in the future and appropriate measures may be adopted based on the future investigation. Therefore, a periodical investigation is to be suggested for the important concrete members or structures even though any repair actions are not necessary at the present condition. In such a case, it is wise to suggest re-investigation, evaluation, judgment and selection of a repair and a

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

strengthening method based on the evaluation and the judgment in future. (3) 1) The main users of this Guideline The intended users of this Guideline are owners, managers, and beginner to mid-level engineers who are assigned for examining the structure or concrete members. Therefore, this Guideline is prepared in a simple way so that the users can gain the knowledge of the subject and apply the learned knowledge in practice. If a user cannot understand some parts or has some doubts, he/she should ask expert engineers for help. This Guideline assumes that the beginner is a person who does not have practical experiences regarding crack-related problems of concrete, such as a resident who discovers cracks in concrete members in his/her apartment building and a municipality official who is just nominated as a maintenance engineer of concrete structures. 2) Limit of this Guideline As stated earlier, this Guideline is prepared in a simple and understandable way for a series of acts from the investigation to the selection of the repair and strengthening of a crack so that the beginner to the mid-level engineers who are engaged with the maintenance of concrete structures can easily use it. But, when it is not possible to deal only by this Guideline, the judgment of an expert engineer who has advanced knowledge and the experience in investigation, repair, and strengthening of concrete structures is needed. 1.2 Procedure from Investigation to Repair and Strengthening

A flow diagram of the general procedure from investigation to repair and strengthening of concrete structures with cracks is shown in Fig. 1.2.1. Identification of crack 

Standard investigation for cause estimation (2.2)

Detailed investigation for cause estimation (2.3)

Can it be estimated the cause of cracking?

 No

Yes The cause estimation (3.3) ［When detailed investigation was conducted (3.4 ）］

Selection of type of estimation (4.1) Investigation for evaluation （When it is necessary） Evaluation (4.2)(4.3)(4.4)*

Judgement (5)*

Repair and strengthen strengthening ing (6)

Additional investigation for repair and strengthening （6.2.3） （Mainly, investigation such as construction environment, amount and range, etc.）

 Note1) A parenthesis ( ) in the flow means number of chapter or section.  Note2) An asterisk * in the flow means that the evaluation and judgment method are different  by the selection of Evaluation-I, Evaluation-II and Evaluation-III.

Fig. 1.2.1 Procedure from the investigation of cracks to the application of repair or strengthening

[Comments]

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

The procedure from investigation to repair and strengthening in this Guideline is shown in Fig. 1.2.1. Strictly, this procedure could not correspond to some cracks while this flow diagram shows a standard  procedure that can correspond to most of the cracks. When cause estimation, evaluation, judgment and selection of repair and strengthening methods are difficult, it is preferable to receive advice from  professional engineers engineers who have advanced advanced knowledge and and experiences. 1) Identification of the crack A series of repair and strengthening begins upon identification of cracks in a structure. Thus, the identification of crack shown in Fig. 1.2.1i  s defined when some actions are intended to consider against the crack. 2) Standard investigation and detailed investigation The investigation is classified into “a. investigation for cause estimation” as a principal objective of investigation and “b. additional investigation for evaluation and repair/strengthening design.” The methods and the principles of standard investigation and detailed investigation are described in 2.2  and 2.3, respectively. a. Investigation for cause estimation After crack identification, standard investigation for cause estimation of the crack is executed first. Sometimes the cause estimation might be possible only by the result of standard investigation. However, when the information obtained from standard investigation is insufficient, detailed investigation including nondestructive tests, minor destructive tests, coring, destructive tests, laboratory test, etc. is required. When a crack is estimated to be caused by alkali aggregate reaction, frost damage and chemical attack, detailed investigation for evaluation might become necessary in order to obtain further information on degradation of a concrete member or structure. b. Investigation for repair/strengthening design Sometimes all the information necessary for repair/strengthening design might be able to be covered by a. However, additional investigation is often needed to specify the environment at site and amounts of the repair/strengthening. repair/strengthening.

3) Cause estimation In this Guideline, first of all, the cause of cracking is estimated from the result of standard st andard investigation. When it is judged that the information collected by standard investigation is insufficient for cause estimation, detailed investigation is carried out for adding further information for precise estimation. When the causes are still unclear, advice from expert engineers may support the estimation. 4) Evaluation After completing the cause estimation, the influence of cracking on structural performance of a concrete evaluated. and Thatthe is,estimated the evaluation thisthis Guideline  member based on or thestructure result of is investigation causes.inFor purpose,istheobjectively evaluationconducted should be done taking into account the influences of cracks on required performance of a member or structure at  present and in the future. Therefore, in this Guideline, proper methods of evaluation should be selected  based on the estimated causes of cracking. The classification of the evaluation methods is described in 4.1. 5) Judgment Judgment is conducted in consideration of the result of evaluation, economical conditions, social importance of structure, etc. When judgment is made according to this Guideline, the owner or the manager of the structure is required appropriately to specify required performance of the structure or member at present and in the future, an expected remaining service life by the owner, social importance,  budget allocation for repair repair and strengthening, etc. For instance, repair or strengthening is not necessary if the cause of cracking is clearly estimated and the evaluation results indicate that structural performance might not be degraded over a long period of time (compared with the expected remaining service life). Conversely, if evaluation results conclude that structural performance would be degraded below the required levels within a short term (in the near

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

future from the identification of the crack), repair or strengthening is necessary. In case of budget restriction, some countermeasures might be selected, such as an increase in frequencies of investigation, repair for aesthetic purposes, limitation of services, change in use, demolition/removal, etc. 6) Repair and strengthening Design and execution of repair and strengthening are done in consideration of the estimated cause of cracking, the evaluation and judgment results, etc. Repair and strengthening methods are preferably selected based on the life-cycle assessment, asset management as well as the prediction of future deterioration of concrete member or structure. 1.3 Terms and Definitions

The technical terms used in this Guideline are defined as follows: (1) Investigation: action to grasp grasp the current state of concrete members (structures) and to collect the definite data on concrete members (structures) and cracks. (2) Evaluation: action to objectively objectively grasp the influence influence of the targeted targeted cracks on the performance performance of concrete members (structures) at the present and in the future. (3) Judgment: action to decide the necessity necessity of repair and strengthening according to the influence of the targeted cracks on the performance of concrete members (structures) as well as special limitation, such as importance of structure, which is obtained as the results of evaluation. (4) Repair: action taken for recovering recovering the performance performance of degraded (deteriorated (deteriorated and/or damaged) damaged) structures by cracks. The main objectives of repair are to reduce water and air permeability, to control the rate of corrosion, to improve the aesthetic view, etc. Strengthening of concrete or structural members is not covered in repair. (5) Strengthening: improvement improvement of structural pe performance rformance such as as the load carrying capacity capacity etc. to a desired safe level. (6) Crack width: opening opening width on the surface of the structure normal normal to the direction direction of the crack. (7) Initial defect: cracks, cracks, honeycomb, cold joint, etc etc.. generated during construction. construction. These are th thee construction defects. (8) Deterioration: changes changes in material performance performance with time after after hardening of concrete concrete due to the some changes in concrete itself or by cracks due to corrosion of steel in concrete. (9) Damage: cracks or spalling generated generated on the surface of concrete caused caused by an earthquake earthquake or impact for a short period of time. (10) Degradation: a term that covers initial defect, damage and deterioration. (11) Expert engineer: An engineer having advanced knowledge and experience on concrete technology and diagnosis of damaged concrete structure. In Japan, “concrete inspectors” and “professional concrete engineers” are certified by the Japan Concrete Institute (JCI). (12) Owner: owner or manager of the structure. (13) Residual period: residual period that the concrete member or structure could satisfy the required  performance from the time of investigation of the crack, evaluation, judgment, repair and strengthening. (14) Remaining service life: residual life to reach the design service life from the time of investigation of the crack, evaluation, judgment, and repair and strengthening. (15) Expected remaining service life: residual life which is expected by the owner to use the concrete member or structure from the time of investigation of the crack, evaluation, judgment or repair and strengthening.

[Comments] In this Guideline, the following technical terms are defined. The other technical terms used in a  particular section are are defined there accordingly. accordingly. (1) In this Guideline, “investigation” is defined as a technical action and “inspection” as an

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

administrative action. That is, investigation includes technical contents, such as what tests should be  performed and what should be measured, etc, while inspection includes administrative and businesslike contents, such as who is the person in charge and what items should be inspected, etc. Since the inspection of this Guideline is defined as the action to grasp the current state of concrete members or structures and generic term of the action to investigate whether there are some defects or not in the targeted structure, sometimes investigation is included in inspection. (2) In this Guideline, “evaluation” is defined as an objective action to grasp the influence of cracking on the performance of concrete members or structures at the present and in the future by using the results of investigation and cause estimation in order to perform the technical judgment from the cause estimation of cracking to the judgment of the necessity of repair and strengthening. Moreover, the evaluation methods can be classified into the following three types: 1) Evaluation-I (applied for cracks due to drying-shrinkage, etc.) Evaluation-I is applicable to the cracks that stop spreading within several years after casting, such as drying-shrinkage cracks and thermal cracks etc. The evaluation can be conducted by investigating the documents and also investigating the current state of concrete members or structures. In general, this evaluation is applicable to a case when the structural performance is able to keep over requirements by repair during the remaining service life or the expected remaining service life by the owner. When Evaluation-I is applied, a crack width at the time of investigation or repair can be evaluated taking into account durability against corrosion of steel bar, water tightness and environmental conditions, etc. The criteria of the crack width for Evaluation-I are specified in 4.2. 2) Evaluation-II (applied for cracks due to chloride attack, carbonation, etc.) Evaluation-II should be applied for the cracks which progress with time, such as the cracks due to chloride attack and carbonation. Furthermore, evaluation for these cracks can be conducted with the results of detailed investigation as well as the investigation of documents and visual observation of the concrete members or structures. st ructures. These kinds of cracks are often discovered at several years or decades after construction. Therefore, it may possible that the performance degradation has already been induced at the time of investigation or repair. Moreover, since the mechanisms and the factors of the cracks are different depending on the causes, these kinds of cracks should be evaluated by understanding the performance degradation at the time of investigation, repair or strengthening, and considering the remaining service life or the expected remaining service life by the owner. The standard evaluation criteria are specified in 4.3  according to the causes of cracking. 3) Evaluation-III (applied for cracks due to combined deterioration, etc.) Evaluation-III is applied for the cracks when Evaluation-I or Evaluation-II is not applicable because the cause of crack is due to the combined deterioration or when the verification of structural performance of concrete member or structures is needed. This evaluation should be conducted by an expert engineer who has the license for concrete inspection. This evaluation is applied when a long-term (more than 20 years) remaining service life or a long-term expected remaining service life by the owner is required. Moreover a crack caused by the mechanical reasons such as changes in support or loading condition should be evaluated by Evaluation-III. (3) In this Guideline, judgment is conducted by considering the restrictions, such as social importance of concrete member or structure, budget of the owner and the scenario of maintenance including the remaining service life or the expected remaining service life, life cycle assessment and asset management. Therefore, the judgment includes the increase in frequencies of inspection, repair for aesthetic purpose, limitation of service, change of use, demolition etc. (4) Cracks in concrete will degrade structural performance such as safety, influences on the third party, serviceability, durability, etc. Repair is defined as an action to recover and improve the performance except the load carrying capacity to their required levels (generally at least the level of the performance without any cracks).

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

(5) Repair is performed against a crack itself in order to improve the performance such as waterproofness, while strengthening is performed against the concrete members or the structures. In this Guideline, strengthening is defined as an action to recover and improve degraded structural performance caused by the cross-sectional loss of steel bar and degradation of bond between steel bar and concrete due to corrosion. Structural performance after strengthening should definitely satisfy the required  performance; for example either load carrying capacity against current load actions or load carrying capacity due to more loads in future. Furthermore, strengthening may enhance structural performance compared to the originally designed level. There are two types of members in a concrete structure. One is a member to support loads acting on the structure, which is called as a structural member, while the other is that to satisfy the non-mechanical  performance, such as fire resistance, heat heat insulation, water tightness, air tigh tightness, tness, sound insulation, etc., which is called as a non-structural member. Since an unexpected crack may cause performance degradation of a concrete member or structure, examination for repair is necessary for both structural and non-structural members. Moreover, examination for strengthening is sometimes necessary for a structural member in addition to that for repair. When strengthening is judged to be necessary, a repair work may be added depending on the cause of crack and the applied strengthening method. In this Guideline, when a crack is initiated in structurally unimportant directions even in a structural member, the same treatment as for a non-structural member may be applied. (6) A crack width is defined as the surface opening perpendicular to the crack path. Generally, rapid degradation is observed for a wider crack. Contrary, degradation may not be so significant during the service life of structure for a narrower crack. Therefore, the width of crack is an important factor for  judgment on the necessity of repair and strengthening as well as selection of a suitable repair and strengthening method. Additional notes related to the crack width are given below: (i) The surface crack width generally varies with the depth inside concrete. A larger width is observed on the surface and it gradually reduces with depth. The surface crack width also greatly depends on the location of steel bar in concrete. A larger cover depth will lead to increase the crack width on the surface. Therefore, degradation rate cannot be generalized with respect to the crack width. (ii) Dimensional change such as shrinkage and expansion of concrete structures occurs with the variation of temperature as well as moisture content and imposed service load over the structure. It indicates that the crack width is not necessarily a constant value. (iii) Multidirectional cracks can be generated on the concrete surface, therefore it may be difficult to fix a particular direction for measuring the crack width. (iv) The crack width may vary along the crack path. For these reasons, it is necessary to specify the time of measurement, position, and the method of measurement of crack width, which will be utilized to judge the present condition of the structure, causes of cracking, and possible necessary countermeasures. In addition, the crack width for Evaluation-I related to steel bar corrosion is the maximum on the surface of concrete at the position of steel bar. (7) Defects are generated in a structure during construction as well as after construction of a structure. Defects that are generated during construction, such as cracks, honeycomb, cold joint, etc. are  particularly called as “initial “initial defect”. 3 .1o In addition, a crack caused by "A9: drying shrinkage" presented in Table 3.1   ccurs after the removal of formwork or during curing. There is a case that this kind of crack occurs during construction (several days to several months) or several years after the start of service. Therefore, in this Guideline, the former are classified as “initial defect” because a crack due to drying shrinkage based on the former tends to generate due to the early removal of formwork and the insufficient curing period. (8) In this Guideline, “deterioration” is defined as a process which adversely affects the structural

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

 performance, such as steel corrosion due to chloride attack and carbonation and change in properties of concrete itself due to alkali aggregate reaction, frost damage, etc. Moreover, as mentioned in comment (7), the cracks that occur several years after the start of service by “A9: drying shrinkage” are classified as “deterioration” because it tends to generate when the concrete member or structure is always exposed to drying condition and when the relative humidity around the structure drastically decreases by weather change. (9) In this Guideline, degradation that occurs in a short term and does not change with time, such as a crack or peeling of concrete generated by earthquake, impact, etc. is defined as “damage”. (10) Degradation is defined as a general term including initial defect, damage and deterioration. (11) Judgment on the necessity of repair is comparatively easy when the cause of crack is clear and the degradation of the structure can be observed with the naked eye, such as water leakage, deformation, and spoiled appearance. However, a crack generated in a real structure may come in different form and it may be difficult to find out the exact causes of cracking even after detailed investigation. In some cases, judgment on the necessity for repair and strengthening is difficult even though degradation is clearly observed over the surface. Therefore, in this case, judgment as to the cause of crack, the necessity for repair/strengthening, and repair/strengthening methods, if required, must be made by an engineer who is familiar with the subject matter and has extensive experiences in this area. In Japan, a “concrete inspector” and a “professional concrete engineers” have been certified by the Japan Concrete Institute since 2001 and 1971, respectively. Both categories are registered as concrete experts. The concrete inspector is certified as having advanced engineering ability for investigation, diagnosis, and selection of repair and strengthening strategies for the deteriorated concrete structures. A  professional concrete engineer is mainly certified certified as having advanced advanced knowledge in concrete concrete technology and the ability to supervise the construction by ready-mix concrete and in-situ casting of concrete. Here, the term “expert engineer” as used in this Guideline also includes persons with advanced knowledge of concrete technology. A first-class architect and a building engineer are also included in this category. A  person with engineering knowledge and experience experience equal to or greater than that of concrete inspector or  professional concrete engineer can also be considered as an “expert engineer”. An engineer is always responsible for all his/her judgments related to repair and strengthening, and must keep him/herself up to date with the present state of the art. (12) The owner in this Guideline is an owner or a manager of a concerned concrete structure. It is indicated the person who can actually decide the importance of structure, budget, and necessity of repair and strengthening. For instance, it corresponds to the management society of an apartment house or the municipality that manages buildings, RC bridges, and so on. Here, a consulting engineer who is given the authority of judgment and decision of technical point by the owner is also called as the owner for descriptive purposes. (13) Generally, the durable period of a concrete structure is set as the period that maintains the required  performance during the design service life at the planning and design stages. Therefore, it is common that the design and construction of concrete structure are executed in such a way so that the durable  period is longer than the design service life. However, However, when a crack occurs due to some causes that were not considered in the design stage and the performance of the concrete member or structure is degraded, there is a case that is compelled to evaluate as the durable period shorter than the design service life even if repair and strengthening is performed. Therefore, in this Guideline, the technical term as the “residual period” is defined as the period during which the required performance of structure can be maintained after the execution of investigation, evaluation, judgment, and repair and strengthening. (14) There are three concepts about the service life; one is the “design service life” that is set based on how many years the owner wants to use the structure in consideration of the amortization period of the structure and social importance. The second is the “elapsed service life” that is the period for which a

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

structure has been actually used after construction. The third is the “remaining service life” that is the  period from the present present to the design service life. life. In this Guideline, the remaining service life is defined based on the judgment of the necessity of repair or strengthening and the execution of repair or strengthening design considering the “residual period” after investigation, evaluation, judgment, and repair and strengthening. (15) In the other guidelines, the technical terms, such as the design service life and the residual period are often used. Moreover, there are many descriptions assuming that the service life and the residual  period can be determined easily. easily. However, in many cases, the inhabitants of an apartment or the owner of a structure which was constructed a long time ago do not know the design service life at the design stage and therefore cannot set the remaining service life. In addition, there are also cases that an owner wants to use the structure over a design service life or make an alternation to the structure for a shorter  period than that set at design by the change of the social importance of the structure and economic circumstances. In other words, it can be concluded that judgment and design of repair and strengthening are performed based on the owners’ intention how long he/she wants to use the structure in the future. Therefore, in this Guideline, the expected remaining service life is newly introduced as the period when an owner expects to use the structure at the time of investigation of cracking, evaluation, judgment, repair or strengthening (it is included neither the repair nor the strengthening work). It is described to  perform the judgment of necessity of repair repair and strengthening and the repair and strengthe strengthening ning based on the expected remaining service life by the owner. When the remaining service life can be set by using the design service life at the design stage, in the  judgment and the designing of repair and strengthening, it is necessary to choose either of the expected remaining service life by the owner or the remaining service life. In this case, it is decided to conduct the judgment and the design of repair and strengthening based on a period by the judgment of the owner. The concepts of repair and strengthening designs are shown in Figs. C.1.3.1 and C.1.3.2, respectively. It is very important for design of repair and strengthening to define the level of performance, such as safety,, serviceability and durability necessary for the structure, to grasp the performance of the structure safety at the time of investigation of crack and adequately to decide the level of performance to recover by repair and strengthening and the duration of the effects of repair and strengthening. In addition, considering the lifecycle of the structure, it is important to conduct sufficient examination considering that it is possible to conduct the reasonable maintenance not only by one time of repair but also by multiple repair.

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

The Investigation, evaluation evaluation,,  judgment or execution o off repair  Service start Design service life Remaining service life Elapsed service life

Expected remaining service life

Residual period on serviceability etc. when a repair is executed. Repair *  Serviceability etc. When a repair is executed one time

When crack occurs and repair is not executed. Required level of  performance erformance Residual period on serviceability serviceab ility etc. when a repair is not executed.

Elapsed year

Residual period on the safety performance when repair is executed.

Safety performance

Required level of  performance erformance 

Repair *  When a repair is executed one time

When crack occurs and repair is not executed. Residual period on the safety performance when a repair is not executed.

Elapsed year

* When repair is executed, the performance such as waterproof or the aesthetic can be recovered or improved, while the safety performance such as the load carrying capacity cannot be recovered or improved. However, the period that the concrete member could satisfy the various performances can be extended (the durability is recovered or improved).

Fig. C.1.3.1 Concepts of design for repair (only one repair during a life time) 

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Service start

The Investigatio Investigation, n, evaluation evaluation,,  judgment udgment or execution of strengthening (repair) Design service life Remaining service life

Elapsed service life

Expected remaining service life Residual period on serviceability etc. when a strengthening (including repair) is executed.

Strengthening * 

When a strengthening (including repair) is executed one time.

Serviceability etc. 

Required level of  performance erformance 

When crack occurs and strengthening (or repair) is not executed. Residual period on serviceability, etc when a strengthening (or repair) is not executed.

Elapsed year

Residual period on the safety performance when strengthening (including repair) is executed. Strengthening *  Safety performance

Required level of  performance erformance 

When a strengthening (including repair) is executed one time.

When crack occurs and strengthening (or repair) is not executed. Residual period on the safety performance when a strengthening (or repair) is not executed.

Elapsed year

* When strengthening is executed, the mechanical performance such as load carrying capacity can  be recovered or improved, and the performa performance nce such as water tightness, the aesthetic can be also recovered or improved by a combination with suitable repair repair.. Besides, the period which the concrete member could satisfy the various performances can be extended (the durability can be recovered or improved).

Fig. C.1.3.2 Concepts of design for strengthening

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Chapter 2 Investigation 2.1 General

(1) The main objective of investigation is to collect data for the estimation of the causes of cracking of a structure or its members. These data are also necessary for subsequent evaluation of cracks,  judgment of the necessity of of repair and strengthening. strengthening. (2) There are two types of investigation, such as standard investigation and detailed investigation. [Comments] (1) Investigation described in this chapter is the beginning step for cause estimation, evaluation of cracks and a selection of repair and strengthening. Information based on the appropriate investigation enables not only to predict the causes of cracking but also to select suitable methods of repair and strengthening. This Guideline recommends identifying the causes of cracking before selection of a repair and strengthening method. Hence, cause estimation of cracking plays a significant role in this Guideline. Furthermore, the investigations proposed in this chapter are useful for evaluation of cause of cracks, repair and strengthening. (2) In this chapter, "investigation" is divided into two steps, such as "standard investigation" and "detailed investigation." Standard investigation must be carried out as the preliminary investigation. The detailed investigation should be carried out in the case that cause estimation of cracking, repair and strengthening cannot be performed based on the standard investigation. Table C.2.1.1  shows a list of investigation methods proposed in this Guideline. The applicable grades of each testing method are classified as ,  and f  or the cause estimation, evaluation of cracks, repair and strengthening. 2.2 Standard Investigation

(1) Standard investigation is carried out by investigating the documents and visual inspection of structures. (2) Investigations of documents and observation of structures should include the following items: 1) Investigation of documents a. Engineering drawings, design reports reports and specifications (drawings, steel bar arrangement, arrangement, structural calculation results, etc.)  b. Construction record such as materials used, mixture proportion, placing, curing method, construction schedule, sub-soil investigation report, formwork, weather condition during  placement of concrete concrete c. History of the past investigation, repair and strengthening strengthening (maintenance record record of structure, records of repair and strengthening, renovation, claim, etc.) d. Service load condition (conditions at at design and at present) e. Climate condition (temperature, relative humidity, humidity, wind veloc velocity, ity, wind direction, direction, height of wave, direction of wave, air pressure, etc.) f. Geological condition (distance from the sea, existence of harmful agents, such as de-icing agents, snow melting agents, etc.) g. Ground condition (vertical distance distance to the adjacent structures, co conditions nditions of retaining wall, foundation, etc.) 2) Visual observation of structures a. Investigation of the condition of the cracks (such as crack crack width, crack length, crack area, area, crack pattern, existence of penetrating crack, etc.)  b. Investigation of other phenomena occurred due to the cracks (peeling of concrete cover and finishing materials, honeycomb, pop out, efflorescence, efflorescence, etc.) c. Investigation of inconveniences due to cracks (moisture leakage, leakage, corrosion of steel bars, deflection of structural members, appearance, etc.) d. Investigation of unusual unusual vibration (a (att driving and aatt walking)

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

[Comments] (1) Standard investigation is carried out in the preliminary stage before estimating the causes of cracking followed by the repair and strengthening plan, as outlined in the flow diagram related to the approach to the investigation, repair and strengthening in Fig. C.1.2.1. The standard investigation includes investigation of documents and observation of the structures. The investigation of documents is carried out to estimate the cause of cracking of the member (structures) by collecting the information of the structures, geological ground condition with and/or simple tools. any The standard investigation is condition limited toand basic investigations that naked can beeye done veryusing quickly without experiments or long-term observation. In some cases, drying shrinkage cracks will be estimated by the standard investigation. In this case, drying shrinkage cracks can be evaluated as Evaluation-I defined in 4.1, which can be followed by an easy judgment of repair and strengthening. (2) The investigation of documents includes the investigation of engineering drawings, design report and specification, construction record, history of past investigation, repair and strengthening, service load condition, climate condition, geographical condition, ground condition, etc.. The observation of structures includes the investigation of the situation of cracks, inconvenience due to cracks, other  phenomenon such as peeling of concrete, unusual vibration, etc. 1) Investigation of documents Investigation of documents is carried out to collect the information of the structures through reviewing engineering drawings, design report and specification, construction record, history of past investigation, history of past repair and strengthening, service load condition, climate condition, geographical condition, and to ground condition. items from a. to g. areplan, introduced as follows. is recommended record the data The on ainvestigation general construction plan, ground stereoscopic plan, Itetc. (refer to Table C.2.2.1). a. Engineering drawings, design report and specification Engineering drawings includes all structural drawings, design reports, steel bar arrangement, etc. An engineering drawing provides very basic information about the structure and is necessary to grasp the general scale and shape of the targeted structure. The steel bar layout drawing is necessary to examine the relation between the direction of cracks with the direction of steel bars, the relation between the interval of cracks with the interval of steel bars, etc. The design report is necessary to examine the stress of the concrete and steel bar at the cross section where cracks are generated. Furthermore, the construction specification provides important information that cannot be found in engineering drawings and is useful to understand the actual conditions and sequence of construction. b. Construction record It is very difficult to get construction records of the structure whose age exceeds 10 years. However, recent standards of ISO 9000 series etc. promote contractor and/or owner to storage the construction

records for a while (5 to 10 years). Some ready-mixed concrete plants permanently store the test results of aggregate of ASR. These records are useful to estimate the cause of cracks. (i) Materials used The details of this investigation are given in Table C.2.2.2 

16

 

Table C2.2.1 （ｂ） Example of Fill Up Papers for Standard Investigation（Civil Engineering Structure） 1. General Information

6. Materials Used 

3. Environment of Structure

1.1 Date of Investigation:

3.1 Location  

Organization in Charge: 1.2  Name of Organization 1.3 Address of Organiz Organization: ation:

 

〒

 

1.4 Telephone Number and   

Mailing Address

 

□Cold ， ，□ □Mild ， ，□ □Subtropical

6.1 Concrete

 

□Country・Suburb，□Urban，□Industrial Area

6.2 C Ceement

 

□Spa，

Ｔｅｌ

3.2 Vibra Vibration tion

Ｅ-mail

3.3 Chemical Substance

1.5 Name of Person in Charge:

 

□Mountainous Area，□Ma rrii n nee E En nv viir o on nm meen t

□Ordinary，□Light，□Others □Ordinary，□Early Hardening，□Others

6 ..3 3 Coa rrsse A Ag gg grr eeg g aatt e  □River Gravel，□Crushed Stone（Rock Type：

）,   □ No，□Unclear 

 

□Yes（

）,   □ No，□Unclear

6.4 F Fiine Aggregate   □River Sand ，□ ，□Mountain Sand ，□ ，□Sea Sand ， ，□ □Crushed Sand 

3.4 Heat (High or Low Temperature Environment)   □Yes（

）℃, □ No，□Unclear 

 

 

3.5 Distance from the Sea

 

3.6 Surface Facing Facing the Sea

 

□Others □Others

□0ｍ，□0～100ｍ，□0.1～1ｋｍ

6.5 Mine Mineral ral Admixture □Yes（

□1～10ｋｍ，□more than 10ｋｍ  inland

6.6 C Ch hemical Admixtur □   Yes（

□East，□South，□West，□ North

6.7 Design Strength Strength  

），□ No，□Unclear  ），□ No，□Unclear  2

kgf/cm ，

 

3.8 Average Wind Ve Velocity locity

ｍ/ｓ

□Factory Product，□Unclear  6.9 Casting Season   □Spring（Location： ），□Summer （Location： □Autumn（Location：

4. Book Record 

2.1 Name

4.1 General Drawing

2.2 Location 2.3 Application

4.2 Engineering Drawing 4.3 Design Calculation Book  

2.4 Date of Completion 2.5 2.5 Age Age

2.8 Found Foundation ation

   

Year(s)    

□Unclear

2.10 Superviso Supervisor r 

 

□Yes，□ No，□Partially，□Unclear 

 

(mainly)

 

 

 

5.1 Application Change 5.2 Ex E xtension and Reconstruction

□Unclear

5.3 Repair  

2.11 Construction Company

 

□Unclear

5.4 R Reeinforcement

2.12 Maintenance Company

 

□Unclear

5.5 Disaster  

 

   

□Yes（  

 

）

） ）

7. Special Matters Related to Maintenace and Management

Date of Completion Completion

5. History of Structure

□Unclear

）

□Yes，□ No，□Partially，□Unclear  □Yes，□ No，□Partially，□Unclear 

4.6 Previous Instivation Instivation Data Data

Indoor（  

□Direct Foundation，□Pile Foundation □Independent Foundation，□Others

2.9 Designer  Designer 

）

□Yes，□ No，□Partially，□Unclear 

 

4.5 Specification

□ＲＣ，□ＳＲＣ，□ＰＣ，□Others（

6.10 F Fiinishing Material Outdoor（ 

□Yes，□ No，□Partially，□Unclear  

），□Winter （Location：

□Unclear 

□Yes，□ No，□Partially，□Unclear  

4.4 Construction Record  

 

2.6 Structura Structurall Type 2.7 Geometries

2

 N/mm ，□Unclear 

6.8 Concrete Type   □Ready-Mixed Concrete，□Cast-in-Place Concrete

3.7 Annual Main Wind Direction

2. Outline of Structure

）

□Yes（

），□ No，□Unclear 

□Yes（

），□ No，□Unclear 

□Yes（

），□ No，□Unclear 

□Yes（

），□ No，□Unclear 

□Yes（

），□ No，□Unclear 

18

 

Age

8. Others

 

Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Table C.2.2.2I  nvestigation on Used Materials

Materials Cement

Example of Investigated Items Type, Brand, Quality, Physical Properties ,Chemical Composition

Aggregate

Type, Rock Type, Maximum Size, Quality, Grading Distribution, Density, Absorption, etc, Impurities (Amount of Clay, Amount of Particulates, Organic Impurities, Chloride Amount, etc), , Alkali-Aggregate Reactivity, etc

Admixture

Type (Classification), Brand, Dosage, Quality, Quality,

Water

Type, Quality Qualit y

(ii) Mixture proportions of concrete Investigate the designed mixture proportions with the actual mixture proportions at the site. (iii) Placing and curing Investigate the mixing time of the concrete, transportation time, waiting time, placing time, placing quantity,, placing method, placing direction, placing order, compaction method, finishing method, curing quantity method, and so on. It is recommended to investigate not only the placing order of concrete of one block in a day but also the nearby blocks are to be considered in the whole process to identify the causes of cracking. Furthermore, it is advisable to obtain the records on other factors that affect the quality of the concrete, such as whether the mixture proportions were adjusted at the site or not, the occurrence of rain or snow, freezing, curing temperature, water tightness of the formworks, etc. (iv) Experimental data of quality control Investigate the experimental data on quality control, such as slump, air content, compressive strength, etc. For strength, it is necessary to take into account the relation between the curing condition of specimens and the environmental condition of the actual structure. (v) Ground condition It is necessary to examine settlement of support, differential settlement, and displacement of a structure. For an underground structure, the back filling period and changes in the ground water level are points of concern. (vi) Types of formworks Records of formworks, supports, type and interval of spacers, deformation due to the weight of concrete during placing of concrete, and heat of hydration must be investigated. (vii) Environmental conditions Records of weather, temperature and humidity during placing of the concrete at the site must be investigated. In special cases, it is also necessary to investigate wind speed, wind direction, amount of rain and snow, etc. c. History of past investigation Items a. and b. are carried out to collect the information of design and construction of member (structure). This section deals with the investigation of maintenance records of the structures on service. The maintenance record includes daily inspection and routine inspection. The daily inspection may includes the information on the date of crack occurrence, the crack propagation, claim from resident, etc.

The routine inspection may include the information on initial detect, deterioration and damage of

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

concrete which are difficult to obtain by the daily inspection. This information is useful to estimate the cause of cracking. History of the past inspection is very valuable for this purpose. Some old structures may experience repair, strengthening and renovation and, of course, this information will contribute the effective investigation. Also, records on experienced disasters (earthquake and fire damage) are important.

d. Service load condition The design load on structure and its effect on structural behavior can be found in the design report. The design load must be compared with the service load. If the service load is higher than the design load, there is a possibility of cracking due to overload. e. Climate condition Investigation of the climate condition includes investigations of t  emperature and relative humidity humidity,,   wind velocity and directions and  wave height, directions and atmospheric pressure. The information can be obtained from meteorological agencies and/or oceanographic observatories. Furthermore, a visit to the site and asking questions to the people on the required data are useful for this investigation. Although, the amounts of CO2  and chloride are very important information to estimate the cause of cracks, the standard investigation only covers the collection of past records as well as the past detailed investigation which are described later. f. Geological condition There exists a strong correlation between geological condition and cause of cracking. For example, a

structure which locates near to sea shore will suffer chloride induced steel bar corrosion. Structure which locates at cold region will suffer frost damage as well as de-icing agent, snow melting agent induced steel bar corrosion. A structure which locates near to the spring area and acid river may suffer chemical attack induced steel bar corrosion. The structures constructed for sewerage facilities, chemical  plant, and food processing plant may also suffer chemical corrosion. It should be noticed that the geological condition provides us the significant information for cause estimation of cracking. The investigation items should include the information of the distance from sea, existence of de-icing agent, snow melting agent in winter, and existence of other chemical agents. The methods of investigation include investigation of drawings, maps, observation with naked eyes, hearing from the third party, etc. g. Ground condition Ground condition may cause crack in the structure. In the case that the structure locates near to the hillside or to sea bank or with an elevation compared to the nearby structures, conditions of retaining wall should be investigated. In the case that the influences of eccentric earth pressure or differential settlements are significant, type of foundations and investigation records of foundation should be collected. These information will be covered within the investigation of the documents described in “a”.

2) Visual inspection of structures This section deals with the items of visual inspection of structures. a. Situation of crack Crack widths, crack lengths, location of crack, area of crack, crack pattern, existence of penetrating crack, etc. are carried out on the targeted cracks. The locations of the tips of cracks are essential to estimate the state of stress in concrete. Therefore, it is necessary to perform visual observation until the tips of cracks can no longer be observed and recording of the observed data accordingly. Making lattice marks on the surface of the structure and writing on the engineering drawing in correspondence to these marks is useful for improving the accuracy (Fig. C.2.2.1). Recently, technology has been developed to automatically trace crack patterns on the concrete surface from the digital Photographs of the surface of the structure.

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

(b) Example of cracks on floors of building

Fig. C.2.2.1E   xample of sketch of cracks (Part1)

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Fig. C.2.2.1E   xample of sketch of cracks (Part2)

Method with microscope

Measured crack width 0.1mm

Crack scale

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Photo. C.2.2.1M   ethods for measurement of crack width a-1 Crack width The crack width is a parameter closely related to the effect of cracks on the structure. Fluctuation in crack widths is also an essential criterion for the estimation of the causes of cracking and the selection of repair and strengthening methods. Therefore, it is recommended to carry out the investigation of crack widths and fluctuation of crack widths carefully. carefully. The crack width is defined in 1.3(  6) as the t he width measured on the surface of the structure perpendicular to the direction of the crack.  Normally the width of a continuous crack varies over the path of the crack. This raises the issue of how to define and indicate the width of a crack. If the crack width is used as a data for judging the necessity of repair and strengthening, recording of the maximum crack width is sufficient. However, in the crack  path, if the length of the maximum maximum crack width is very very short compared to the total total length of the crack, or if the concrete at the edge of the crack is partially chipped and making the crack width of that part abnormally wide compared to the other parts, in such cases recording of the maximum crack width will lead to an excessive repair work. Therefore, it is necessary not only to record the maximum crack width  but also to record the crack crack width at several several locations on the crack crack path. Measurement of crack width as explained in Photo. C.2.2.1  is carried out using a crack scale and a magnifying lens. Fluctuation in crack width can be measured by using a pi-type displacement gage or an electric dial gage. Such fluctuation can also be measured using a contact gage between gage marks. To investigate fluctuation in crack widths at a particular location, it is necessary to record the crack widths

at a particular interval of time at the targeted location using the methods explained earlier. The recorded initial crack width is compared with the crack width measured at other times. In this Guideline, crack width is defined as the width perpendicular to the direction of the crack path. However, it is necessary to note that crack width is strongly influenced by the presence of steel bars as well as the bar diameter, spacing of the bars, cover concrete, etc. a-2 Crack length Generally, length of a crack is not directly related to the evaluation and judgment of cracks. However, the length of a crack indicates whether that crack has been generated by a local cause or a widespread cause. The length of a crack is important for understanding the scale of repair and strengthening and also to calculate the construction cost. The repair of cracks is considered when the crack width exceeds 0.05 mm, as noted in Table C.4.2.2. Therefore, it is at least necessary to measure and record the length of cracks having widths exceeding 0.05 mm. The repair and non-repair parts of a crack must also be defined. It is recommended to measure as many crack widths and crack paths as possible through visual observation. The length of a crack is measured along the crack using an ordinary scale. It is not necessary to measure  precisely along the curvature of a crack. Considering the amount of work required for actual measurement and repair work, it is recommended to measure the crack length by adding up direct distances measured at adequately selected intervals. a-3 Location of crack Location of cracks is closely related to the cause of cracking. For example, diagonal crack at the corner of an opening and cracks around pipe are often caused by the drying shrinkage of concrete. Crack under a parapet wall of building is caused by the expansion due to temperature rise of protective concrete layer under water proofing. Hence, the location of crack provides important information for the cause of cracking. Locations of crack and steel bar will be an indicator of the cause of cracking. Hence, investigation of the crack location based on the location of steel bar (same position to steel bar, parallel to steel bar or perpendicular to steel bar) is also significant. a-4 Area of crack Area of crack, whether the crack occurs at a local or in a wide area, provides information for the cause

estimation of cracking. Length and width of the area of crack is significant for the cause estimation of cracking.

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

a-5 Crack pattern The crack pattern (refer to Fig. C.3.3.1) is closely related to the cause of cracking. Therefore, it is necessary to carry out the investigation of crack patterns very carefully. For example, for RC wall with openings, diagonal cracks at the corner of the openings is typical crack due to drying shrinkage of C.2.2.2of concrete (refer to Fig. ). steel Shrinkage expansion cracks, aasparticular well as pattern. cracks due to the alkali-silica reaction, corrosion bars incracks, concrete, etc. also follows Therefore, crack patterns must be recorded accurately accurately..

Fig. C.2.2.2T   ypical ypical crack pattern due to drying shrinkage a-6 Existence of penetrating p enetrating crack Cracks that penetrate through a structural member are closely related to the degree of serviceability failure (inconvenience) due to cracks. Therefore, during investigation, it is necessary to confirm whether cracks penetrate throughout the members of the structure. Water and air can easily pass through  penetrating cracks. Therefore, Therefore, the existence of this kind of cracks can be judged by observing water and air permeability. It is also possible to observe a similar crack path on the opposite surface of a member in the case of a penetrating crack. ASR often causes a difference in level between the cracks due to the expansion of concrete. In this case, information of the difference in levels is also useful for the cause estimation. b. Investigation of other phenomena induced by cracks Peeling of concrete cover and finishing materials, honeycomb, pop out, efflorescence, etc. will be included in this section. This information is significant for the judgment and selection of repair and strengthening. In the case that peeling of concrete was found, steel bar corrosion may progress seriously. Peeling of finishing materials closely relates the carbonation progress of concrete. Honeycomb due to  poor construction results in the defect of concrete which may a cause of cracking. The moisture condition (dry or wet) of the surface not only indicates the generation of cracks due to drying shrinkage, alkali aggregate reaction, etc., but is also closely related to the sselection election of the repair method. Therefore, it is necessary to carefully investigate and record the moisture condition at the vicinity of cracks. Further, it is desirable to investigate and record rust, efflorescence, deposit on the concrete surface, and discoloration of the concrete at the vicinity of cracks. Fouling of the concrete surface is not only related to the appearance of the structure but also indicates micro cracking in the surface region, which can be easily overlooked during the investigation of cracks by visual observation. Therefore, it is recommended to pay careful attention to this matter. matter. Visual observation and use of a test hammer will be useful to detect the peeling of concrete and finishing. c. Investigation of inconvenience due to cracks   Investigation of serviceability failures (inconveniences), such as water leakage, exposure of steel bar, excessive deflection, etc., is carried out by visual observation. All serviceability failures (inconveniences) are to be recorded on the drawing. In the t he case of serviceability failure (inconvenience)

related to appearance, careful attention should be paid to micro-cracks, rust, and efflorescence, and the

24

 

Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

information is to be recorded on the drawing. d. Investigation of unusual vibration  Deflection, inclination, vibration and other unusual problems of fittings such as sliding doors of architectural buildings. Unusual sound and vibration are observed in civil structures if there are some  problems at joint of viaduct during passing a car or a train over it. In this case, the location and area

should be investigated. 2.3 Detailed Investigation

(1) Detailed investigation is carried out in cases when the estimation of the causes of cracking is not  possible within the scope of standard investigation. (2) The detailed investigation is divided into on-site investigation and laboratory test. The items of investigation are as follows: 1) The items of on-site investigation a. Investigation of materials used in the structure st ructure a-1. Non-destructive, minor destructive test and test with core specimen (i) Investigation of concrete (progress of cracks, location of peeling of concrete cover and finishing, depth of defect, area of defect, evaluation of strength, quality and homogeneity of concrete, size and thickness of member, member, internal crack, existence of void, crack depth, etc.) (ii) Investigation of steel bars (cover thickness, location and arrangement of bars, diameter, state corrosion, corrosion rate, etc) (iii)ofInvestigation of PC tendon (grouting) (iv) Other investigations (water leakage) a-2. Destructive test (i) Investigation of steel bars (corrosion rate, diameter, types of steel bars, condition of bend locations of the steel bars, cover thickness, etc.) (ii) Investigation of concrete (carbonation depth, margin from cover depth to carbonation depth, crack depth, deposition, depth of chemical corrosion, etc.) (iii) Investigation of aggregate (types of aggregate, existence of shell, maximum size, reaction rim, crack in aggregate, etc.) (iv) Other investigations (water leakage, ingredient)  b. Investigation of loading and and environmental conditions conditions of structure c. Investigation of subsurface conditions d. Investigation of structural performance and deformation e. Investigation of vibration of structure 2) The items of laboratory test a. Investigation according to test methods (i) Physical test (ii) Chemical Chemical composition analysis (iii) Analysis of microstructure (iv) Accelerated test (v) Petrology test  b. Investigation according according to types of deteriorations deteriorations (i) Quality of concrete concrete (ii) Carbonation (iii)Chloride attack (iv) Frost damage (v) Alkali-aggregate reaction (vi) Chemical attack [Comments]

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

(1) Detailed investigation should be carried out according to the flow chart shown in Fig. C.1.2.1 in the case that the cause of cracking is difficult to estimate based on the results of the standard investigation. The detailed investigation is performed with special equipment while the standard investigation is done  by simple tools. The detailed investigation is more expensive and needs longer period than the standard investigation. Hence, the purpose of the detailed investigation must be fixed before planning the detailed investigation and also the number of the specimens is to be tested must be fixed as per the  budget and also time constraint. constraint. (2) Detailed investigation is divided into on-site investigation and laboratory investigation. On-site investigation includes investigations of materials used in the structure, loadings on the structure, environmental conditions of the structure, foundation condition, structural performance, deformation and vibration of the structure. On the other hand, laboratory investigation is performed based on the symptoms of deterioration. The detailed investigation should be carried out on some selected items and hence will not be covered all items described in this section. The results of laboratory investigation will contribute significantly to the judgment of an expert engineer. Hence, the items to be investigated in the laboratory should be discussed with an expert engineer prior to the laboratory investigation. The items of investigations are as follows: 1) The items of on-site investigation a. Investigation of materials used in the structure The materials used in a structure are investigated by non-destructive test, minor destructive test, test of

cored and test.and Thearrangement overall quality of understood crack, typesfrom and qualityconcrete of steelsamples, bar, state ofdestructive deterioration of of theconcrete, steel bardetails can be non-destructive or minor destructive tests. These tests need special equipments and the results must be analyzed by an expert engineer. By the destructive test, direct observation of the condition of the concrete and steel bars is made by removal of the concrete cover locally. Although this test damages the structure, it helps the general engineer to easily grasp the useful information and also to take the samples for laboratory test at the same time. a-1 Non-destructive, minor destructive test, and test of core concre concrete te specimen By these tests, concrete, steel bar, and PC tendon are investigated. Table C.2.3.1  shows items of investigation and the methods (equipments) of investigation. Testing of the representative specimens through proper sampling is very important to get the accurate results. If the sampling of the specimen is not appropriate, it may mislead the cause estimation of cracking. Basic requirements for the sampling are as follows:

•  Obtain representative sample Take equal number of samples from each member. Take samples from appropriate location taking into account the direction as well as the height of the structure. •  Avoid factors affecting the test results In the case of core drilling for the compressive strength test of concrete, defective areas, such cold joint, cracks, etc. should be avoided. In the case of core drilling from a vertical member, samples should be collected from the same height (say 1.3 to 1.5 m) of the member to avoid variation of strength with respect to the height. Wet core boring is often adopted to obtain the concrete samples to measure chloride content of concrete for simplicity compared to the dry core drilling in spite of washing out of some chlorides from the sample. Therefore, careful analysis of data is necessary based on the method of collecting samples. •   Number and amount of samples In the case of core strength test, the number of core specimens should be 3 or more for each storey of architectural structure while 3 for 1 pear of a bridge structure. In the case of chemical analysis, the amount of weight of sample taken should be 4 to 8 times of the amount of sample necessary for testing. It should be noted that too much quantity of sample is not reasonable from the view point of economy

26

 

Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

as well as structural safety. •  Time between sample collection and testing of samples at laboratory Cored concrete specimens will be carbonated if it is stored in air. If the samples are not tested rapidly after collection of the samples, prevention against carbonation of the samples should be needed. Rapid completion of the laboratory test or storage of the samples in an airtight container is needed due to the loss of moisture and chloride from the samples by evaporation. •  Take samples not only from the cracked area but also from the t he sound zone Based on the purpose of the investigation, the samples are to be collected from a cracked zone or a sound zone. However, it is recommended to take samples from the both zones to grasp the progress of deterioration and to judge whether the deterioration is occurred locally or not. The destructive test results of the same area are to be compared with the results of non-destructive and minor destructive test. The main items of investigation, the method of investigation and the equipment to be used for the investigation are explained below: Table C.2.3.1 Test items and methods with Non-destructive, minor destructive test and test with core specimen Types

Items

Test methods (Equipment)

Concrete

Visual inspection, crack scale, microscope,

-type displacement

π

Crack progress

gauge, contact type gauge, digital camera, acoustic emission, laser method

Position, depth and area of  peeling and flaking of concrete cover and finishings

Sampling of core and thermographic method

Estimation strength

of

quality

and

Strength test by rebound hammer method, ultrasonic method,  pull-out method, method, impact elastic wave m method ethod and with small core ultrasonic method, impact elastic wave method Thermographic method and ultra sonic method

Steel

Size and thickness of member

impact elastic wave method , radar method and ultra sonic method

Internal crack and voids

ultrasonic method, impact elastic wave method, thermographic method, test hammer

Crack depth

Sampling of core and ultra sonic method

Cover thickness

Radar method, impact elastic wave method and ultrasonic method

Position

PC tendon Others

of

steel

bar,

bar

Radar method, electro magnetic reasonance method, ulutrasonic

arrangement and bar diameter Corrosion rate

method,X-ray transmission method half-cell potential

Corosion velocity

polarization resistance

Insufficient grouting Water leakage

X-ray transmission method, impact elastic wave method, CCD camera Tracer method, thermographic method (visual inspection is impossible ） 

(i) Investigation of concrete P   rogress of crack Whether new cracks are developed after detection of the cracks, and whether there are any fluctuations in crack width over time are very important factors for cause estimation and the selection of repair and strengthening methods. The tracking methods are shown in Fig. C.2.3.1, (a) a method by inserting a tapered pin into the crack, (b) a method by recording the tips of cracks, (c) a method by inserting a thin layer of paste, and (d) a method by which the changes in crack width are measured using a pi-type displacement gage,with etc.a digital Recently, technology to intervals investigate of It cracks based tooncarry the Photographs taken camera at periodic wasthe alsoprogress developed. is desirable

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

out these measurements for 1 month or more, if possible. Recording of the deformation of the structure, the loading conditions, the environmental conditions, etc., are to be recorded together for accurate  judgment. Crack widths vary according to the temperature and humidity. Therefore, to measure fluctuation in crack width, it is desirable to perform measurements under the same temperature and humidity conditions as close as possible. Since the temperature varies with the time of a day, measurements should outtemperature at the same of time as close as possible. Since the temperature at 10atam corresponds roughlybe tocarried the mean a day, it is recommended to measure crack widths around 10 am. In the case of structures, such as walls, roof floors, etc., which are directly exposed to rain, it is recommended to perform measurements measurements at least 3 days after the last rain. If the crack width of a crack fluctuates due to a cyclic load or a moving load, it is hard to confirm it by visual observation, however, however, it may possible to detect the fluctuation of a crack width by placing fingers on the crack plane. It is also possible to monitor the crack location and crack progress by using acoustic 1) emission (AE) method , which measures the elastic wave produced due to the generation of a crack or crack movement. For the investigation of cracks, a digital camera or a laser is also used in addition to the usual visual 2) inspection. For example, in the method using a laser  , cracks are detected by measuring variations in the reflection intensity of the laser applied to the concrete surface ( Photo C.2.3.1). It is possible to record information on cracks by a digital data. The analysis of crack patterns can be done easily by image processing after the investigation.

(d)

Fig. C.2.3.1 Methods of measurement of crack progress

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Photo. C.2.3.1E   xamples of measurement of crack with laser 

L   ocation peeling of concrete cover and often finishing Progress of of steel corrosion induced cracks causes peeling of concrete and finishing. Location of  peeling of concrete cover and finishing, depth and area are useful information for the estimation of cause of crack, judgment of repair and strengthening and finally the selection of a method for repair or strengthening. Although visual inspection is possible for the case of peeling, but it will not be possible for the case of flaking of concrete and finishing. It is possible to roughly estimate the range of flaking  by listening to the sound from the surface of the concrete while hitting it softly by a hammer. hammer. By 3) thermographic method   it is also possible to estimate the area of flaking from the temperature distribution of the surface of concrete. A high temperature is generally found in the flaking area. The advantage of this method is that it is possible to efficiently investigate a wide range without any contact with the structure. This method is suiTable for rough estimation of the existence of flaking. However, depth of peeling and flaking is difficult to be detected by non-destructive or minor destructive test methods, and hence, core sampling should be needed in this case. Photo C.2.3.2  shows an example of investigation of flaking of the external wall of a building. The red zone in the Figure represents a high-temperature area, which is considered to be the location of flaking.

Steel bar corrosion will progress seriously in the case of peeling and flaking of concrete and finishing. Hence, detail investigation of area of peeling and steel bar should be needed. In the case that the peeling and flaking of concrete and finishing are dangerous to the third parties, immediate counter measures must be needed.

flaking

Visual image

Thermographic image

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Photo C.2.3.2  Investigation of flak flaking ing of external wall with with thermographic thermographic method E   stimation

of concrete strength Strength of concrete is the most basic information for cause estimation of cracking, judgment of necessity of repair and strengthening and selection of repair and strengthening. Hence, accurate investigation on concrete strength in a wide area is required. Non-destructive and minor destructive test methods are useful to grasp the variation of concrete strength in a wide area. Tests used for the evaluation of concrete strength are as follows: 4)5)

•  Rebound hammer method   Rebound hammer is used to estimate the strength of concrete by counting the number of vibration after hitting by the Rebound hammer on the surface of concrete. The strength is varied based on the hardness of concrete surface. This test method is useful to estimate the variation of concrete strength in a wide area. A relationship between rebound number and compressive strength is to be established prior to the test. 6)7)

•  Ultrasonic method   The velocity of the elastic wave is measured in ultrasonic method. The elastic wave is created by an oscillator having wave frequency over 20 kHz and the wave is received by a receptor. The travel time from the oscillator to the receptor is recorded. The strength of concrete can be estimated using arrival time, shape, frequency, frequency, and phase of the wave. 8)

•  Impact elastic wave method   The principle of impact elastic wave is similar to the ultrasonic method. In this method, the elastic wave is created by a hammer. The impact of a hammer produces a wave having frequency lower than 20 kHz. Concrete strength, member thickness, internal defect and distance to the defect from the surface can be detected by analyzing reflected echo, frequency, frequency, and phase. 4)

•  Pull out method   A steel disk is adhered on the surface of concrete and a tensile load is applied to the disk until the failure of concrete. Compressive strength of concrete is estimated based on the maximum load at failure. 9) 10) Broken off specimens by splitting (BOSS) test  and strength test using small core specimens  from 25 to 50 mm in diameter are also used. Generally, correlations between measured compressive strength and in-situ compressive strength are used in non-destructive and minor destructive tests. Hence, to improve the accuracy, correlation equation or calibration coefficient should be obtained based on the type and quality of concrete. Verification by using core specimen is also preferable prior to these investigations. Pull-out test is classified as a minor destructive test. Q   uality and homogeneity of concrete The purpose of this investigation is to grasp the variation of quality of concrete in a wide area. It can be done by the ultrasonic method or the impact elastic wave. A thermographic method can be used to investigate the homogeneity of concrete. S   ize

and thickness of member Verification of size and thickness of member is very important for cause estimation of cracking,  judgment of repair and strengthening and selection of repair and strengthening. In some cases, it is  possible to measure the size and thickness of a member directly, directly, but in many cases, it is difficult to measure them directly. Non-destructive method such as the impact elastic wave method and radar method can be used for these cases. I  nternal crack

The purpose of this investigation is to grasp the existence of internal crack and voids due to peeling and flaking. It is possible to roughly estimate the range of flaking or peeling by listening to the sound from the surface the concrete whilethe hitting it softly with aor hammer. Further, it isofpossible to detect location of flaking peeling more precisely by using the following

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

non-destructive test methods: •  •  •  • 

11)

Impact-echo method b   y microphone measurement 12) Ultrasonic wave method   13) Impact elastic wave method   14) Thermographic method  

In method microphone measurement, flakingoforthe peeling their level are evaluated theimpact-echo characteristic valuesby (amplitude, frequency distribution) wave and of the impact-echo captured by by the microphone. It is an easier method compared to the method using the human auditory sense. Moreover,, using this method, quantitative evaluation is possible (Fig. C.2.3.2). Moreover In ultrasonic wave method, it is possible to estimate the depth from the surface of the concrete to the flaking position, using the time to receive the reflected ultrasonic wave from the flaking position ( Fig. C.2.3.3). By the impact elastic wave method, it is possible to estimate the depth from the surface of the concrete to the flaking position by measuring the resonant frequency of the elastic wave generated by the impact, which reflects repeatedly between the surface of the concrete and the flaking plane (Fig. C.2.3.4). In the thermographic method, it is possible to estimate flaking and its range from the temperature distribution of the surface of the concrete. A flaking area shows a higher temperature. By this method it is possible to efficiently investigate a wide range of area without any contact with the structure.

Fig. C.2.3.2O   utline of impact method with measurement with microphone

Fig. C.2.3.3O   utline of ultrasonic method

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Fig.  C.2.3.4O   utline of impact elastic wave method C   rack

depth

The depth of a crack can be estimated by using the following methods: 14) •  Ultrasonic wave method   •  Core drilling To estimate the crack depth quantitatively, ultrasonic wave method can be used. The method is described in Fig. C.2.3.5, where 2ai  s the distance between the receiver and the transmitter t ransmitter.. The crack is  placed at the middle location between the transmitter and receiver receiver.. In this method, the propagation time of the ultrasonic wave diffracted at the tip of the crack is measured. Using this time, ti me, the crack depth can  be calculated. If t c  is the propagation time in cracked concrete and t o  is the propagation time in sound concrete, crack depth d (  cm) can be calculated by using the following equation: d 





a  t c t 0

2





1

12

 

Investigation of the surface of cored samples can be used to confirm the depth of crack. It is recommended to inject red ink into the cracks before investigation. In some cases, it is possible to estimate the types of stress applied at the fractured surface of the concrete by careful observation of cracks, which is useful for the evaluation of the causes of cracking. In the case of direct tensile stress or flexural tensile stress, bond failure often occurs at the interface  between the coarse aggregate and mortar. On the other hand, in the case of shearing stress, some cracks  penetrate through coarse aggregates. Cracks generated by shear stress are shown in Fig. C.2.3.6, (a) shows a crack generated due to the shearing deformation, and (b) shows a crack generated outside the shearing face. In case (b), it is possible to find out the slippage between the two sides separated by the crack by placing fingers on the crack plane.

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Fig. C.2.3.5  Ultrasonioc method (TC.T0)

Fig. C.2.3.6  Example of crack due to shear deformation

(ii) Investigation of steel bar The cover thickness and the position of the steel bars can be determined using a device called cover 15) meter  . The possibility of corrosion can be judged by the natural potential (half-cell potential) of the 16) steel bars . However, careful attention is needed because the reliability of these tests varies depending on various conditions. Although, in the case of thin concrete cover, correct measurement is possible, in the case of thick cover or rough surface, it is difficult to measure the depths correctly. An example is shown in Fig. C.2.3.7. There are many standards for evaluating the corrosion conditions of steel bars based on the measurement of half-cell potential. The Japan Society of Civil Engineers proposes JSCE-E 601-2000, "Test method of half-cell potentials of uncoated steel bars in concrete structures." An example of measurement of half-cell potential is shown in Photo C.2.3.3. Generally, the probability of corrosion is  judged based on ASTM C 876, as explained in Fig. C.2.3.8 and Fig. C.2.3.9. Theoretical background of this method is not explained here but can be obtained from a book of electrochemistry. Measured value

○  electro magnetic wave metho method d △ electro magnetic reasonance method x Ultrasonic method --- ±5mm

Cover thickness

Fig. C.2.3.7  Example of measurements of cover thickness t hickness with various equipment

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Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-

Ag/Cl Unit mV

Counter of half-cell potential

Expression as absolute value

Photo C.2.3.3  Example of measurement of half-cell potential Ecorr (Cu/CuSO4)* >-0.20V -0.35 to -0.20V