Chapter 1 INTRODUCTION
- General Introduction
Over recent years in construction, vast changes in the operation of projects has occurred. Complex designs of building are introduced to suit modern architecture and so, newer materials such as steel are used for many applications to increase effectiveness. Such alternative may ultimately entail higher maintenance costs.
Concrete as an element has good durability ; otherwise concrete could not have become the most abundantly used building material in the world. In addition, the requirement of steel reinforcement is considered to maximise the strength of the structural integrity, to increase its suitability of certain applications. Existing concrete structures are required to be maintained to its highest level, where the correct use of remedial and repair works is applied to ensure the overall structural value, and its design life.
This dissertation provides an review by a given evaluation of defects, and its available repairs to enhance the structural performance of concrete buildings. It is aimed to provide such information to building surveyors, engineers, designers and local authorities on what works can be observed to construct concrete structures with reference to the use of code of practice. In order to do this, modern day practice through the use of superior technology and regular inspections is expected to be carried out. This is done to monitor, and guide engineers on what maintenance can be practical to enhance the appearance of concrete structures if there are presence of defects. This will eventually show that the vunrability can be be minimised by preparing for the worst-case scenario.
Furthermore, main points of concrete distress will be discussed and focused on, outlining aspects with respect to its cause, where several site inspections of various locations will be carried out to identify and evaluate this point of discussion.
The context of this thesis will assess the problems associated with concrete buildings, to determine why reinforced concrete structures should not be considered as ‘maintenance free’. Generic approaches will be suggested on what repair should be considered, and how conservation can increase the structural performance and show somewhat wider difference.
With reference to the Institution of Civil Engineers; durability of existing infrastructures in the UK has become a major concern (ICE June Report, 2014). The route of poor maintenance has led to number of factors arising. The lack of care and correct monitoring procedures of concrete deterioration are not accounted, where remedial works for repair and critical inspections on concrete defects are not well acknowledged, leading the concrete corrosion to weaken the structural stability and performance of buildings.
In the same report, it is also mentioned that the strength and durability of concrete structures has affected thorugh number of factors; this may be a result of:
- Mix Design
- Poor Construction
- Environmental Exposure / Chemical Attack
- Mechanical Overloading
- Impact Damage
- Historical Background
For many years, different approaches have been proposed on how concrete structures should be designed. However, the scientific synthesis through construction process has affected many areas of buildings. It is understood that majority of concrete defects are associated with corrosion of steel reinforcement. De-icing salts, lack of concrete cover, and Alkali Silica reaction all associate with this problem. Over time, the right recommendation of repair strategies has been made to alter such problems, but is not as effective.
Concrete structures such as Bridges and Multi-storey Carparks have good design life, and with regular maintenance it is expected to remain serviceable over time. The working life of the structures may be reduced where extensive maintenance of steel that are subject to corrosion may be required however, very cost effective. With evidence of this type of damage, many concrete structures have suffered severe deterioration within 20 or 30 years of its service life. [Wallbank, 1989- Vassie, 1984].
In 1950s, Alkaline Silica Reaction (ASR) had received considerable attention in the UK. The reaction occasionally resulted in expansion and cracking in high quality concrete with presense of high alkali conent however, the structural performance was sometimes referred as overly exaggerated. [pp 2 ,D.W.Hobbs, 1988].
Between 1960s and 1970s, the preferable construction approach included ‘Magnesite’ , a chloride-rich carbonate monotal was used for level surfacing and as floor screed. The chemical content had reacted with moisture, producing a weak hydrochloric acid. In higher contents, the chloride breaks down the protective passive film in localised areas of reinforced concrete structures (RC) affecting the reinforcement.
It was not until 1976, that the Institution of Structural Engineers and of Highways and Transportation published the first authoritative guide to multi-storey car park design. The guide did not give comprehensive detailed advice on structural design, waterproofing or on the deleterious effects of de-icing salt on the reinforcements.
Evidence showed the presence of early deterioration within the first few years of design life. This increasing concern of chemical effect had been recognised by the Institution of Civil Engineers, where corrosion management started to be exercised more rigorously and issuing new design recommendation in the UK in the 1980s , as a result of the requirement of maintenance.
1.2 Problem Statement
The problems that are required to be investigated are essential to assess the durability of concrete structures by identifying the defects and its cause. An analyitical assessment can be prepared accordingly to recognise how its value is still relevant today.
Although the main problems are well acknowledged in the past, structural engineers should realise that modern approach are being considered, where low standard of maintenance are applied to existing structures.
In doing so, structural engineers requires sufficient knowledge on relevant code of practice to familiarise the potential risks that could occur if there was inadequacy within the design, and what degree of damage that can produce in terms of safety.
Reinforced concrete structures have proven to be acceptable about its strength, but many of them have had durability faults; over 99% of concrete structures that are built between the 1960s and 1990s attribute to durability faults [Wood, 1996]. Signs of premature deterioration through construction faults do not meet current serviceability requirements.
As pointed by (Shamsad Ahmad, 2003), the three main causes of concrete structures include:
- Alkali-Silica Reaction (ASR)
- Chloride Attack
Other defect such as shrinkage, honeycombing, freeze-thawing , poor quality of detailing, poor workmanship may have furthur worsened the situation.
1.3 Aim and Objectives
The aim of this project is to critically analyse defects by detecting and quantify deterioration of existing concrete structures. Suitable guidance can then be given to the local authorities to assess the level of maintenance they should consider to, when repair works are being acknowledged for future assets.
- Explain defects associated with Reinforced Concrete structures. (Chapter 2) and Chapter 4 will discuss by detailing the crucial factors affecting concrete with reference to the obtained information from the different literature.
- To carry out three visual surveys on concrete buildings, recording any defects with evidence supported by site reports and photographs:
- Two Multi – Storey Car Parks
- London Bridge
- Harlow Linkway Carpark: Harlow
- Precast Concrete Culvert – River Ching: Epping Forest
- To provide an analytical approach of concrete defects by recommending appropriate repairs. (Chapter 6) will discuss the relevant repair strategies regarding the site inspections carried out.
- To compare and review two site reports of the same building type; past and present. (Chapter 5)
1.4 Overview of Design and Content
The outlined objectives for this dissertation will be addressed in separate chapters (Chapters 2-6) supported with current research, each including a discussion where the findings will be synthesised in Chapters 6 and 7 of the conclusion with given evaluations.
Chapter 2 LITERATURE REVIEW
2. 1 Introduction
The deterioration in the 20th century of reinforced concrete buildings has become a significant problem. The visual signs of these concrete deterioration are shrinkage cracks from drying, cracks due to wear, thermal cracks , rust stains, leaching, and spalls.
However, these small problems have been associated further with corrosion of reinforcement. A densely imbedded protected layer, known as passive film within the reinforcement prevents further corrosion of the steel. Although the passive film is stable during its whole service life, there are still factors affecting it by destroying the layer, exceeding the depth of the concrete cover, placing the reinforcement at risk of corrosion. This may be due to the lack of cover depth associated with poor design, or lack of effective waterproof membrane. It is important to determine the cause of the deterioration through careful analysis and the likely consequences, before deciding what scale of remedial works are required. [Raupach, 1996- Shamsad Ahmad, 2003]
The two mechanisms related to this problem are:
- General corrosion associated with carbonation
- Chloride Intrusion
Open concrete structures, especially highway structures and bridges are subjected to wetting events due to harsh weather conditions . Under these conditions, chloride penetration can occur [Hong & Hooton, 1999] . However, there is still lack in understanding of the processes involved to tackle this problem, to comprehend how chloride ions are transported through concrete elements.
Therefore, this chapter will review and evaluate the literature relevant to the assessment of defects, causes and repair regarding concrete structures.
2.2 General Literature on Concrete and Defects
For a student, wishing to gain an insight into ‘concrete defect and its available repairs’, P.H.Perkins (1997) provides a comprhensice understanding of the topic as a whole. The third edited publication from the author provides not only literature on the history of concrete, but the types of defects and the structural types associated with it. The author continious to present research on all the possible defects that can occur in existing concrete buildings if the generl maintenance is not well considered.
The book also illustrates several concrete repair strategies that can be acknowledged structurally and non- structurally. The types of monitoring and testing methods are identified, to define the purpose of internal examinations of reinforced elements which certainly requires greater attention on the potential causes that is subjected to. Mehta (2010) and Dellate (2009) both provide a structural appraisal to define the purpose of the Life Care plan of new and exitising concrete buildings.
Dellate (2009) expands the process of understanding of the failure mechanisms that links with the general defects of reinforced structural elments. In comparison, Ferraris (1997) in ‘Creep, Shrinkage and Durability Mechanics of Concrete’ provides a unique explanation on the effect of load durability classifying general , and major defects associated with corrosion. Hanley-Wood,(1976) expands their points with a greater evaluation on the overall durability prfomance.
The requirement of waterproof membrane of open deck structures to protect and prevent from corrosion of reinforcement, due to chemical attack are also explained. Cathodic protection of the steel to reduce water penetration, and the diffusion of carbon dioxide in existing structures are also mentioned.
For literature on the strength and the behaviour of Concrete as an element , Mehta and Monterio, (1993) provides great knowledge on the background of Concrete as a material where certain construction techniques such as , ‘Slump Test’ and design properties are mentioned to evaluate the test procedures before direct application during construction.
- Non-Destructive Evaluation
The methods implied to assess concrete defects can be valuable to carry out to allow further investigations to successfully identify, and with supported evidence to prevent it from occurring over time. Mailvaganam, N.P (1992) focuses his points on the repair and protection of concrete structures, but to achieve this, he provides a general guidance by considering a proper repair strategy to address the concrete problems by understanding the actual ‘cause’, to allow adequate approach for repair of concrete structures. The idea of Non-destructive tests (NDT) involves visual determination. The assessment allows engineers to produce a clear understanding to evaluate structures. The diagram provided by [Hoła et al, (2015)] shows a synthesis of NDT methods and techniques that can be used to critically appraise structural defects.
Figure 2.1 – NDT Methods & Techniques (Hoła et al, 2015)
Hoła et al (2015) also defines that further tests on concrete elements shall be only done after observing its actual cause to allow successful laboratory testing for repetition and greater accuracy in determining properties and characteristics of concrete, in which the overall specification can be altered upon this to ensure good form of construction, and applied techniques.
- Visual Inspections
To successfully carry out a survey on the performance of concrete structures, principle knowledge of optical methods through visual inspection to assess the structural geometry is required. Visual inspection is the common method of inspection, even though it is the most subjective [Schabowiczs, 2013]. The author mainly discusses their points on the methods available however, visual inspection provides valuable information which can be easily missed if only other NDT methods were applied which are highly dependent on the interpretation of the data.
The inspection period per building asset will depend on the inspector and the life-care plan. Only trained engineers can make correct conclusions without the necessity of carrying out systematic tests [International Atomic Energy Agency, 2002]. Depending on the level of experience and expertise, the correct determination on the state of the structure can be made [The Federal Highway Administration (FHWA), 2006]. The limitations of performing visual inspection practices can lead to variable results, and the subjectivity of this process can become difficult to advance consistent condition assessment [Bickley and ENGINEERS, 1986] .
Furthermore, by introducing remote sensing techniques through superior technology into the current inspection practices to assess the mechanical parameters, such as thermal mapping and Light Detection and Ranging (LiDAR) can reduce the variability [Falkner 1995].
Perkins’ (1997) book ‘Repair, Protection and Waterproofing of Concrete Structures’ , pp69, indicates the preliminary inspections methods, which suggests that depending on the type of structure and the alleged defects, the engineer should take with them binoculars, a rebound hammer, a good camera , an electromagnetic cover meter, and a spray bottle containing phenolphthalein for the detection of depth of carbonation , simple means for accuracy and approximate measurements.
- Locating Deliminated Concrete
There are number of various methods that apply to locate such defects that cannot be adapted by a human eye. If Visual Inspection reveals signs of concrete distress, further investigation is necessary to complete the overall objectives. Low cost and quite simple methods to detect delamination into concrete is by using hammers or chain dragging sounds and through thermal mapping , which sends transverse waves across the elemetn to locate small defects. However, the methods are generally insufficient to derive a detailed layout required for reconstruction [Emmons and Emmons 1993].
Figure 2.2 – NDT Methods Summary (Courard et al. 2006)
- Code of Practice
- Concrete Strength
To gain insight into the structural assessment of concrete as an element, the most important property is the strength. For the engineer to able to predict with reasonable accuracy of the load-carrying capacity of various structural elements , and to determine the overall performance of the structure , it is essential to recognise design codes, BS 0089: Assessment of Concrete Strength in existing structures and BS1881: Part 120 (Cube strength), as it is the basic requirement of structural design for a structure to sustain live and dead loads, and to have adequate structural resistance which will arise from any proposed alterations.
- Multi-Storey Car Parks.
The structural performance of Multi- Storey Carparks, design codes apply for the impact loading on edge barriers due to road vehicles as published in the British Standard Code of Practice Cp3: Chapter V:1972. The publication of this was an add on to the 1967 CP3, as it was understood that the requirement of edge barriers involves the understanding of impact, due to the acceleration in place of causing further distress to the concrete elements [Institute of Structural Engineers, London, 2002]. As of 1997, study on the edge barriers had proposed some changes to the specified design requirements in BS 6399: Part 1 as building were designed to the normal building standards.
- General Code of Practice
Factors attributing with concrete strength include design and construction errors, may relate to the standard code of practice used by structural engineer in the assessment of concrete loading that are BS6399, CP 3, CP114 Chapter 5, Pt 1, EC2 and BS EN 1992-1-2:2004, and for Cathodic Protection BS 7361 applies.
Concrete Durability and Cracks– Reinforced Concrete
- Problem Statement
The durability of low strength graded reinforced concrete structures, have been affected by few factors that has altered the whole process of maintenance (BS 8210) , limiting the serviceability where further attention is required on the design life for performance purposes. The purpose of durability design is defined as its “The ability to resist weathering action, chemical attack, abrasion or any other process of deterioration. Durable concrete will retain its original form, quality and serviceability when exposed to the environment.” [ACI 201.2 R92].
- Water Ingress – Chemical and Corrosion Defects
Concrete is a mixture of cement, aggregates and water, where the cement portion of the concrete makes up 25% of the volume, determines all the physical properties in durability and strength areas. Concrete is a porous material, allowing water and air to penetrate through. A good example of water ingress defect is freeze thawing, allowing water to seep through existing cracks and with its repeated effect, water expands on freezing, increasing the volume by 10% , delaminating the surface layer of concrete by forming popouts. Ferraris (1997) discusses his points associated with the penetration of water through concrete and mortars which can allow chloride and sulphates resulting in corrosion [ Marty’s and Ferraris, 1997]. As pointed out by Mehta et al (1992), water is “at the heart of most of the physical and chemical causes underlying the deterioration of concrete structures”. Among other effects, moisture levels determine the risk of corrosion attack occurring on steel reinforcement and the rate of deleterious mechanisms such as alkali-aggregate reaction (AAR). At the same time long-term ageing effect caused by a combination of dry and wet concrete will be evident and the result will be reduced strength, which may cause differential shrinkage, leading to cracks to appear.
- Cracking of concrete due to reinforcement corrosion
Clear (1976), ‘Time-to-Corrosion of Reinforcing Steel in Concrete Slabs’, is a standard Federal Highway Administration Publication report on reinforcement corrosion. Clear (1973) adds specific points on spalling of concrete cover and mortar due to corrosion.
The author discusses the effects of expansion of corrosion with the build up of rust within the reinforcement, which may relate to pitting corrosion. Hay (1973), acknowledges these similar problems and states that., “ due to the expansion, tensile stresses are created, eventually causing cracking and spalling of the concrete cover; depending on the concrete design quality, and depth ratio of cover to the steel”.
Figure 2.2 – Expansion of corroding steel ,Hay (1973).
- Chloride ions: De-icer Scaling – Corrosion of Steel
Premature Deterioration of reinforced concrete structures is a worldwide problem. A survey of 200 concrete highway bridges prior to 1969 [Wallbank, 1989] confirmed that chloride contamination is a widespread, where old specification for design was considered during the time.
The chloride level is mentioned by various authors as the threshold value for corrosion [Ann et al, 2006]. Upon Wallbanks’ (1989) survey on concrete highway bridges, he had added that the main causes of the bridge deterioration was alkali-silica reaction (ASR), high alumina cement (HAC) ,chloride attack, carbonation, frost action and sulphate attack.
Mobile free chloride ions derived from de-icing salts progressively penetrates concrete, and with presence of oxygen and moisture can cause corrosion [Corrosion in Steel and Concrete. BRE Digest 444, February]. As mentioned before, the level of coating and depth of concrete cover is essential for this purpose. The effect of de-icing salts has had a major impact on the structural durability depending on the environmental exposure [Hanley-Wood,1976].
In car park structures, the protection is likely to be lost because of the chlorides being present. Chloride contamination generally occurs through de-icing salts imported into the car park on vehicles or manually spread onto carpark deck during wintery periods [Pitchard, 1992- Mays, 1992]. The similar effect may result due to the buildings being located nearer to the sea ,where exposure to seawater can cause this type of corrosion.
Pitchard’s (1992) , ‘bridge design for economy and durability’, also includes a diagram illustrating the process of concrete deterioration.
Figure 2.3 – General Process of Deterioration Pritchard (1992)
In addition, Pritchard (1992) details on the surface decks based on his experience; he notes that the surfaces of substructures ( example of Multi-storey Carparks) are rarely waterproofed and are sheltered from rain however, it is the most vulnerable element to chloride induced corrosion.
- Carbonation: Corrosion of Steel
The effect of carbonation on existing concrete buildings can also affect the steel reinforcement. The problems are confined to buildings prior to 1960s that were constructed under old specifications with relatively porous concrete. Currie’s (1986) report , ‘Carbonatation Depths in Structural Quality Concrete, p.19’ is prominent in the literature on this section, as great deal has been written on the subject of the carbonation of concrete and its effect on the rust ions in rebars.
The process of carbonation is relatively slow depending on the type of concrete. The deteroation through this process has a great effect on the rebar as carbonation occurs with the presence of carbon dioxide in the atmosphere ,reacting with hydroxides to form carbonates. With constant environmental changes and the level of carbon content has affected the overall appearance.
Verbeck (1958) mentions that, when the concrete cover to the rebar is carbonated, it leaves the steel vulnerable to corrosion. Mehta (2000) and Perkins (1997) both analyses the effects of carbonation with a discussion of their views. As pointed out by Mehta (2000), carbonation will proceed at a rate up to 1mm per year. Perkins (1997) elaborates his opinions on the change in rate of carbonation in concrete , due to the water-to-cement ratio, low cement content, loss in strength, short curing period during construction and the use high permeable cement paste.
As mentioned previously on the expansion of reinforcements, Currie (1986) goes into great detail with relation to this, suggesting new design techniques that will support further investigations into the cover depth to evaluate the problem.
Figure 2.4 – Corrosion of reinforcement around window frame due to Chloride Intrusion. Morton (2000)
- Research Perspectives – Reports
Several papers on concrete defects are relevant to this dissertation where further will be reviewed in detail in Chapter 5 to support the content on findings from the survey.
- NDT (Thermal Imaging)
Bhalla’s, Tuli’s, and Arora’s (2010) research into defect detection of concrete involves Non-Destructive evaluation. Their study includes the detection of general concrete defects as small as 50mm in width using thermal imaging technique. The specimen tested in their investigation involves a concrete block measuring 500mm x 100mm x 100mm, where ultrasonic pulses are sent across the beam to detect and locate small cracks. Their research progresses into in-depth evaluation of possible affects that could have cause these cracks to occur. The outcome of their study proves that ultrasonic technique provides only a qualitative identification defects, on the other hand and in comparison, captures visual interpretation of the defects.
- Deterioration of Concrete Buildings in the 20th Century
Morton’s (2000) research into the deterioration process of historical buildings shows a detail insight on how it is affecting the latest development of maintenance management. As a Building Surveyor , his investigation involves inspection of various RC Buildings, in which he points out that the visual signs of serious concrete deterioration are cracks, rust stains and spalls. He reports on the values of inspections and how it is important to apply this method to determine the causes. A survey conducted on a 19th Century historical property in the British Islands showed presence of reinforcement corrosion. Although the building would have been neglected and destroyed by the local authorities if this survey was not considered, further study into this led Morton (2000) to discover the problems and recommend adequate maintenance and repair strategies such as, Patch Repair, Desalination, and Re-Alkalisation and considered that this should have been not neglected as an unsafe building as it did not deteriorate to a point where it would be very expensive for repair. Significance in protecting building indicates that there are techniques available for repair to improve the serviceability life if a building is of sufficient historic interest.
The research article written by Ware (2013) in the Journal of Building Survey, Appraisal and Valuation Vol .1, gives and in depth review on the techniques involved in diagnosing and repairing carbonation in concrete structures.
The process of carbonation is well recognised with detail analytical explanation and annotation of the breakdown of carbonation, and how it can affect the passive layer embedded in steel reinforced concrete construction. The information provided is to educate engineers to gather a general knowledge, and with expert advice provided in the report the application of redesign can be introduced . the report also includes sections on for Precast Viaducts and Car-Park Structures.
Figure 2.5 – Carbonation Process, Ware (2013)
In addition to the main problem behind carbonation, Alternative technique in terms of innovative concrete technology are mentioned to enhance the overall lifespan of future builds.
In comparison to this, Broomfield’s (2015) research, ‘Determining and Extending the Remaining Service Life of Reinforced Concrete Structures’, is by far the most detailed written piece out of the four research articles that applies with concrete deterioration. The written piece outlines all the chemical elements associated with the production of concrete such as the level of permeability percentage due to difference in water/cement ratio, PH values of alkalinity and general defects. Slika (Annual Report-2005) lists all the major defects and its repair of reinforced concrete in a tabulated form .
Broomfield expands these points and notes that the carbonation and chloride diffusion processes takes many years to reach the steel reinforcement to corrode, and that the non-corroding areas are cathodically protected.
|Concrete Damage due to Reinforcement Corrosion|
|Carbonation||Corrosive Contaminations- Chlorides|
Table 2.1 : Concrete Damage associated with Corrosion, provided by Slika’s Annual Report (2005)
|General Concrete Damage and Defects|
Table 2.2 : General Concrete Damage , provided by Slika’s Annual Report (2005)
- Case Studies
Recent case studies have shown…
2.8 Guidance Manuals
This form of literature evaluates the points that should be followed under standard procedures which supports the code of practice , but not published by the British Standards. The manuals within this section will support the subjects that will be discussed in the remaining chapters.
Both Perkins (1992) and Hobbs (1998) recognises section BA.52/94 (part of the Design Manual for Road Bridges) published by the Department of Transport ; configures the attributes behind Alkali-Silica Reaction, and the factors from the analysis of relevant research. Publication BA.52/94 makes the following comment:
“Recent research has shown that ASR has much less effect on strength than would be imagined from the appearance of the affected members; indeed, some tests have identified some increase in strength due to ASR”.
A Guide to Design and Management is currently it its second edition, Mills (1996). The current edition supports BS 8210: Guide to Building Maintenance Management and BS 7543: Guide to the Durability of Buildings. Standard’s (2004) Guide to Repair of Concrete Structures to EN 1504 mainly concentrates on corrosion repair and supports the Code of Practice – B7361: Cathodic Protection.
Critchell’s (1958) book, ‘Joints and Cracks in Concrete’, addresses on the defects in joints in concrete structures, both in-situ and precast due to unsatisfactory performance. It supports BS 6093 : Code of Practice for design of joints and for minor repair is a continuous description on BS 6231 : Guide to selection of Sealants.
The coalation of reference journels, books make up the ‘Recomendation for the Inspection, maintenance and Management of Car park Strutures’, provided by the Institute of Civil Engineers (ICE). The maual supports, CP3 and ‘BS8110 : Part 1 “Structural Use of concrete 1997, BSI. The structured manual, reports on the effect of waterproof membrane, due to blocked surface water drainage and leaking expansion joints , are all means by which will put the structure at risk from alkali -aggregate reaction; a common defect.
Information on the background and the application of detailing of reinforced concrete under EC2 is published and supports BS EN 1992-1-2:2004 in a one piece manual edited by Mosley and Bungey (2012) and new editions by Calavera (2014).
Following publications from the Design Manual for Road and Bridges (Department of Transport) :
- BD 54/15 Part 5: Inspection and Maintenance of Concrete Highway Structures – Maintenance
- BA 35/ 90 : Inspection and Maintenance of Concrete Highway Structures – Repair
The design application of Vehicle restrain in multi-storey car park must realte to :
- BD 37/88
- BD 52/93
- BD 50/94
- Code of Practice BS 6779:Part 1:1998 and Eurocode 1: Part 2.7: Accidental actiotions due to impact and explosions.
The (current) literature on [X] abounds with examples of..SUMMARY
Chapter 3 METHODOLOGY OVERVIEW
3.0 Content Overview
Thus far this dissertation has discussed the importance of concrete deteroation
The approach taken for this report was firstly to review relevant material to carry out a literature research which ranged from identifying the properties of reinforced concrete, to understanding the associated factors contributing. To set a fundamental understanding on this , there is a rapidly growing literature on defects of concrete structures and the problems that has led to detroaition..
With sufficient amount of data and content to b
There are number of readily available literature on defects of concrete structures, Existing literature was interpreted and used as material in three of the four objective and was the main source for the poin
Various tools were explored in depth to meet the objectives to address the issues of concrete defects. The scope of the project only covers the general assessment of defects of concrete buildings where the main limitation is presented in the remaining chapters to consider for further guidance for engineers and building surveyors on how to assess and successfully carry out inspections for defect prevention.
Chapter 4 INSPECTION PROCEDURE
This chapter will provide a discussion review of the chosen research methodology used to evaluate the main points to meet Objective 3 of this study. The methods applied to locate defects for this research is discussed, as well as the limitations of the adapted research method. The steps considered for this project outlines the identification of main factors affecting the performance, and general maintenance of existing concrete structures. Upon this, it is only then acceptable to reference appropriate recommendation on relevant repair works.
To successfully execute this point of discussion, three site investigations were carried out by applying the principal methods of condition survey, through visual inspections. Every site visited were conducted in the same manner and interpreted, where a site recording sheet was used to report any remarks related to the defects identified. The survey included photographs and measurements of the visible evidence of the defected area of the buildings. This is done to illustrate the prominent causes that affects the overall condition, in which further analysis can be made.
4.1 Inspection Regime
The procedure for undertaking the inspections involved site trips, to observe the structure to identify any defects. The fundamental requirement of carrying out the inspections is to develop, review, update and improve previous and present surveys, to ensure that the best method is developed for repair and maintenance.
This then can progress to support the identification, planning and programming of improvement activities necessary to achieve the functional requirements. It is also done to ensure public safety by bringing immediate attention to the defects having safety implication.
Although there are many concrete structures that could have been assessed, Multi Storey carparks and Precast Concrete Culverts are subjected to many problems that has led to early deterioration and structural defects considering its age, history, form, constriction and vulnerable detailing through poor design, which may require temporary closures for costly repairs and rehabilitation.
Management of Highway Structures: Code of Practice 1 states that: ‘The overall purpose of inspection, testing and monitoring is to check that the particular structure it is safe for use and fit for purpose and to provide the data required to support the Good Management Practice identified in this Code’.
The aim for the methodology can be classified into simple steps to address the issues and make final agreements for repair. The American Concrete institute, Report ACI 224.1R-93‘Causes, Evaluation and Repair of Cracks’, provides the basic guidelines that should be followed once conducting a survey and the additional steps required thereafter. The following stages are acknowledged within the methodology steps for inspections to meet the objectives of this dissertation.
- Identifying an ‘EFFECT’.
- Capturing the defect – Camera.
- Determining the CAUSE.
- Deciding whether the problem needs to be repaired.
- Conducting some form of condition survey to quantify problems.
- Non-destructive test- half/cells, chloride profiles.
- Dealing with repair analysis and the related engineering issues in the repair.
- Determine repair strategies that includes techniques and repair materials for further recommendations.
- Finally, prepare a strategic plan for repair.
4.1.1 Condition Survey
The site inspections were supported with conditions surveys. The steps acquired for a Condition Survey provides an assessment of the physical condition of the buildings. The survey outlines the key points of the identified defects and the maintenance issues including, but not limited to structural aspects.
Although the site inspections were performed without any guidance from the local authorities, the overall condition of the operating system of the building were not recognised. The three structures inspected were observed to determine whether the results showed a recurring problem, and what can be done for improvement.
The sites were observed extensively to outline the associated patterns on the distress areas of the building, in relation to expansion joints, environmental exposure, surface distress, metal corrosion, water/moisture content level, and column lines. The observations and photographic documentation were then used for reporting the inspection to generalise and develop sample plan to consider for further testing and to provide a maintenance proposal for the property owners.
|Structure Type||Location||Overall Structure Condition Rating||Element Type
Table 3.1 : Condition Analysis for inspection of sites
To configure with the site inspections, a BCI (Bridge Condition Indicator) rating system is used to review the condition of the structures, to meet the principles of condition survey. The Bridge Condition Indicator was primarily used to examine the structure of the Culvert, to provide a specific statement as they are listed under the bridge categories of the Charter Institution of Highway and Transportation. The colour coordinated indicator of the system ranges from green to red to indicate the poor to good relation of the conditions of the surveyed piece.
Completed condition surveys and reports can be found in Appendix 2
Table 3.2 : Bridge Condition Indicator; London Bridges Engineering Group
4.2 Specific Areas of Inspection
It is essential to record defects that requires immediate attention. However, not all concrete associated defects were at present therefore, certain types where only recorded. Common defects within Multi-Storey carparks are originated from the roof deck elevation with presence of cracks, allowing rainwater to penetrate through therefore, such common defects are important to be reviewed.
By applying the principals of Condition Survey, the following general defect types where concentrated on during these inspections:
- Rust, Stains and Cracks in concrete, especially on soffits walls, and surfaces.
- Evidence of corrosion of steel reinforcement.
- Spalling of the concrete.
- Wet / damp areas, especially ponding on decks and leakage due to poor drainage and alignments.
- Delaminated Concrete surfaces.
4.3 Health and Safety
Basic health and safety measures were made available during the site inspections, to minimise further factors affecting the time and management considered while recording the defects.
The following personal protective equipment were worn while undertaking the inspection when accessing hazardous zones of the area, this includes;
- Hives – for visibility purpose
- Steel Cap Boots
- Wellington boots when accessing wet zones.
- Hard Hat -particularly when low headroom presents risks of injury to head.
While visually accessing the two Multi- Storey car parks, safe walking routes including fire exits around the carpark were acknowledged before progressing to the top tier. The safety aspects of the Culvert were also assessed, mainly on the surroundings and the floor surface, as it carries an open drain under the road structure above. The wet conditions meant careful approach for the inspection, and at an event of adverse weather conditions, the correct PPE is worn.
4.3.1 Risk Review
The methodology process that were applied to identify the risks are very much associated with the defects. It was crucial to identify the risks to enable future selection of the appropriate management tools for prevention material over the life of the structure.
The result in risks while undertaking inspection of the carparks can arise from moving vehicles driven from the car park users, and the limited headroom within a confined area of the culvert.
To support this, risk assessment forms were completed during the site inspections, to evaluate any potential risks during the activity of the investigation and associated with the structure. A rating system was derived through the risk assessment ranging from low too high to access the level of vulnerability and the likelihood of the factors to occur.
The scale of risks identified during the inspections; the precautions considered is mentioned to obtain the outlined evidence to apply in the role for recommendation, in which the property owners and local authorities should consider to. This is done to ensure that it meets the correct requirement for the life care plan of the structures.
Attached copy of the risk assessment sheets can be found in Appendix C.
a BCI Socing range system was used to estabilis the consition survru..
Limitation , explain few points, discussion can go in that, that you did not have c;ear access
both methods were implied, however not all were achieved due to some imitations.
Also in methodology/ what areas , why top deck and look at phone notes, mnaybe useful
Hanley-Wood, LLC, “Chemical Attack on Hardened Concrete,” Concrete Construction, August, 1975, pages 328 to 333.
Mehta, P. Kumar, “Sulfate Attack on Concrete: Separating Myth from Reality,” Concrete International, Farmington Hills, Michigan, August 2000, pages 57 to 61.
Verbeck, G. J., Carbonation of Hydrated Portland Cement, RX087, Portland Cement Association, http://www.portcement.org/pdf_files/RX087.pdf, 1958.
Clear, K.C., and Hay, R.E., “Time-to-Corrosion of Reinforcing Steel in Concrete Slabe, V.1: Effect of Mix Design and Construction Parameters,” Report No. FHWA-RD-73-32, Federal Highway Administration, Washington, DC, April, 1973, 103 pages.
Clear K.C., “Time-to-Corrosion of Reinforcing Steel in Concrete Slabs,” Federal Highway Administration, PB 258 446, Vol. 3, April, 1976.
RECOMMENDATION AND MAINTENACRE
The report encourages engineers to intprudce new techniques to tackle theses situation with new design speicaication on whaat actions shall be
Poor design loss of concrete/ cover depth………..
Verbeck, G. J (1958)
Verbeck, G. J., Carbonation of Hydrated Portland Cement, RX087, Portland Cement Association, http://www.portcement.org/pdf_files/RX087.pdf, 1958
A great deal has been written on the subject of the carbonation of concrete and its effect on the rustion of rebars
- Concrete Repair
Schabowiczs’ (2013) book, ‘Methodology for non-destructive identification of thickness of unilaterally ‘, the author
accessible concrete elements
Azari H, Nazarian S, Yuan D. Assessing sensitivity of impact echo and ultrasonic surface
waves methods for non-destructive evaluation of concrete structures. Construction and
Building Materials 2014; 71: 384-391.
Schabowicz K. Methodology for non-destructive identification of thickness of unilaterally
accessible concrete elements by means of state-of-the-art acoustic techniques, Journal of
Civil Engineering and Management 2013; 19(3): 325-334.
BRE (2000) BRE Digest 444–Corrosion of Steel in Concrete, Building Reseearch establishment, Watford, Uk ∑ Bungey J H, Millard S and Grantham M (2006), Testing of Concrete Structures (4th edn), Taylor & Francis, Oxford, Uk, and New York ∑ Carper k (2000), Forensic Engineering (2nd edn), CRC, Boca Raton, Fl ∑ Feld J and Carper K L (1997), Construction Failure (2nd edn), Wiley, New York
Camera…. Cover meter …..carbonation depth thingy
Inspection is great …. Blah blah balh
Waterproof memberatre of decks and roofs- perkins….. Decks from the page of ICE>….
Mehta and all that details the application off…., two graphs….
PAPER FOR CULVERT
LIFE CARE PLAN
Cause from theat sentence, inspections…… remember to put in aims and obijectove..
Cover from that link , Main caue of carbonation…..
|Project Activity Log|
|LSBU -School of Built Environment and Architecture :BSc Civil Engineering|
|Project Title: Causes, Prevention and Repair of Defects in Concrete Buildings|
|Name of Student: Akshay Singh Parmar – 3305626
Project Supervisor: Mr. Stephen Vary
|Meeting 1-Discussed Project outline|
|Site Reording Sheet|
|LSBU -School of Built Environment and Architecture :BSc Civil Engineering|
|Project Title: Causes, Prevention and Repair of Defects in Concrete Buildings|
|Name of Student: Akshay Singh Parmar – 3305626
Project Supervisor: Mr. Stephen Vary
|Location||Time of Log||Remarks|
|Meeting 1-Discussed Project outline|