Non-Destructive Evaluation of Reinforced Concrete Structures

Deterioration Processes and Standard Test Methods

Christiane Maierhofer, Hans-Wolf Reinhardt, Gerd Dobmann

• Publisher: Woodhead Publishing
• Year: 2010
• ISBN:
  9781845699536
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Many concrete structures and elements of concrete infrastructure have exceeded their original design lives and are deteriorating to an extent where they are becoming dangerous. The deterioration can be internal or not obvious and therefore only shows up with detailed testing. Non-destructive evaluation of reinforced concrete structures, Volume 1: Deterioration processes and standard test methods reviews the processes of deterioration and classical and standard test methods.Part one discusses deterioration of reinforced concrete and testing problems with chapters on topics such as key issues in the non-destructive testing of concrete structures, when to use non-destructive testing of reinforced concrete structures, deterioration processes in reinforced concrete, modelling ageing and corrosion processes in reinforced concrete structures, components in concrete and their impact on quality, and predicting the service life of reinforced concrete structures. Part two reviews classical and standard testing methods including microscopic examination of deteriorated concrete, the analysis of solid components and their ratios in reinforced concrete structures, the determination of chlorides in concrete structures, and investigating the original water content of reinforced concrete structures.With its distinguished editors and international team of contributors, Non-destructive evaluation of reinforced concrete structures, Volume 1: Deterioration processes and standard test methods will be a standard reference for civil and structural engineers as well as those concerned with making decisions regarding the safety of reinforced concrete structures.

• Provides a comprehensive discussion from examination of the components in concrete and their affect on quality through to the role of and tools required for lifetime management
• Experts in the field identify the testing problems associated with infrastructure considering design, build and maintenance stages
• Presents a guide for when to use non-destructive testing of reinforced concrete structures including the role of time in testing

Part I

Deterioration of reinforced concrete and testing problems

1

Introduction: key issues in the non-destructive testing of concrete structures

M. Soutsos

J. Bungey, University of Liverpool, UK

Abstract:

In-place testing of concrete structures to assess durability performance plays an important role in establishing long-term infrastructure maintenance strategies. This role is considered in detail, together with the development of relevant non-destructive test methods and associated ‘Standards’ over the past 40 years. Examples of driving factors are given together with illustrative industrial case studies, including maintenance strategies, based on UK experience over that period. Particular attention is given to the role of international organisations and national industrial bodies in development and dissemination of authoritative guidance documentation, including recently introduced European Standards.

Key words

infrastructure

structural concrete

in-place testing

durability performance

standards

1.1 Introduction

Infrastructure is what supports our daily life: roads and harbours, railways and airports, hospitals, sports stadiums and schools, access to drinking water and shelter from the weather. Infrastructure adds to our quality of life, and because it works, we take it for granted. Only when parts of it fail, or are taken away, do we realise its value.¹

1.2 Design, build and maintain

Concrete is, because of its versatility, comparative cheapness and energy efficiency, of great and increasing importance for all types of construction throughout the world. Concrete structures can be durable and long lasting but to be so, due consideration needs to be given at the design stage to the effect that the environment to which the structure will be exposed will have on the concrete. Degradation can result from either that environment, for example frost damage, or from internal causes within the concrete as in alkali–aggregate reaction. It is also necessary to distinguish between degradation of the concrete itself and loss of protection and subsequent corrosion of the steel reinforcement. The ACI Committee 201² defines concrete durability as: ‘its resistance to deteriorating influences which may through inadvertence or ignorance reside in the concrete itself, or which are inherent in the environment to which it is exposed’.

Initially, concrete was regarded as having an inherently high durability, but more recent experiences have shown that this is not necessarily the case unless durability design forms an integral part of the design and construction process. There is a need to consider all potential deterioration mechanisms at the design stage in order to select and specify an appropriate concrete mixture from a durability perspective.³ The prescriptive specification for concrete based on permissible maximum water–cement ratio and minimum cement content has received much criticism in recent years. It may even have inadvertently allowed designers and contractors to avoid having to consider or implement all the available information required for a sound design for durable construction. This includes careful attention to drainage and detailing to minimise the effects of water, which is a key transportation and fuelling agent, upon materials. Unexpected maintenance and repairs arising very early in the specified service life of structures has caused enormous financial burdens to clients. The expectation of the owner of a structure is that it will only require very little or no maintenance during its design life. The owners have realised that the cheapest option for constructing a structure may work out to be an expensive option in the long run.

Owners have sought ways of minimising project risks to themselves. The design–bid–build delivery system was the norm where the owner contracted separately the design and construction of a project. However, they then adopted design/build delivery systems where from inception to completion only one organisation is liable to the owner for defects, delays, and losses. Streamlining the delivery system reduced the delivery time of the completed project by forcing consultancy/design teams and contractors/construction companies to form collaborations and complete the separate tasks at the same time, i.e. working in parallel. This system is used to minimise the project risk for an owner and to reduce the delivery schedule by overlapping the design phase and construction phase of a project.

However, this approach does not take ‘life cycle costing’ into account. The benefits of ‘life cycle costing’ are particularly important, as most infrastructure owners spend more money maintaining their systems than on expansion. In addition, the life-cycle approach removes important maintenance issues from the political vagaries affecting many maintenance budgets, with owners often not knowing how much funding will be available to them from year to year. In such cases, they are often forced to spend what money they do have on the most pressing maintenance needs rather than a more rational and cost-effective, preventive approach. Major infrastructure projects have now moved to design–build–operate (maintain) or ‘turnkey’ procurement, e.g., the US Department of Transportation – Federal Highway Administration⁴ defines it as an integrated partnership that combines the design and construction responsibilities of design–build procurements with operations and maintenance, see Fig. 1.1.

1.1 Design–build–operate (maintain).⁴

The advantage of the design–build–operate (maintain) (DBOM) approach is that it combines responsibility for usually disparate functions (design, construction, and maintenance) under a single entity. This allows the private partners to take advantage of a number of efficiencies. The project design can be tailored to the construction equipment and materials that will be used. In addition, the DBOM team is also required to establish a long-term maintenance programme up front, together with estimates of the associated costs. The team’s detailed knowledge of the project design and the materials utilised allows it to develop a tailored maintenance plan that anticipates and addresses needs as they occur, thereby reducing the risk that issues will go unnoticed or unattended and then deteriorate into much more costly problems.

Few structures collapse in the UK but when they do the consequences and ramifications are huge. ‘Avoid the complacency which leads to tragedy’, was the central theme of the Standing Committee on Structural Safety’s 12th bi-annual report.⁵ However, lack of attention to due consideration of durability criteria in the design and specification of structures in the past has led to a thriving and expanding repair industry in recent years, see Fig. 1.2,⁶ and design for ease of inspection and maintenance should be regarded as an important issue.

1.2 Thriving and expanding repair industry in the UK.⁶

1.3 Role of in-place testing

The principal driving force for the numerous developments of nondestructive testing (NDT) methods and equipment has, of cou...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Preface
• Part I: Deterioration of reinforced concrete and testing problems
• Part II: Conventional/standard testing methods for concrete
• Index