Maintenance of Brick and Stone Masonry Structures

A.M. Sowden

• Publisher: CRC Press
• Year: 2020
• Print ISBN: 9780419149309
• eBook ISBN: 9781000143867
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

This book deals with all the tasks related to brick and stone masonry structures, from the initial identification of defects and their diagnosis to their treatment and monitoring of its cost-effectiveness. It is written in the context of bridges and their associated retaining walls in the U.K.

Part One Introduction

Chapter one The approach to maintenance

A.M. Sowden

1. 1.1 Maintenance - a neglected art
2. 1.2 Maintenance in context
3. 1.3 Brick and stone masonry in context
4. 1.4 The management of maintenance
5. 1.5 Financial considerations
6. 1.6 Environmental considerations
7. 1.7 The achievement of effective maintenance
8. 1.8 References and further reading

Inevitably, inexorably, all structures deteriorate towards a state of unserviceability and collapse. Maintenance is the art of controlling the rate at which they do so. Its objective is to ensure that, throughout their required life span, they are preserved in a satisfactorily functional condition with a proper regard for safety and economy. Proficiency in this field relies upon the exercise of skills and judgement derived from experience rather than theory; above all, it calls for an understanding of the long-term behaviour of structures and materials and for ingenuity based on a knowledge of a wide range of remedial techniques.

1.1 Maintenance - a neglected art

Maintenance rarely seems to receive the attention it deserves. Structure owners are preoccupied with the initial capital costs of their assets, usually without sufficient appreciation of the implications of ill-judged economies at this stage. There is a common failure to recognize the extent to which a structure represents an investment requiring protection throughout its life. The fact that expenditure on maintaining structural fabric can often be deferred without apparent loss or harm leads to a lack of concern for signs of incipient deterioration, with the result that available finance is diverted from preventive maintenance to activities with greater obvious, but only cosmetic, impact. Yet neglect in the early stages is likely to lead to costs which will escalate rapidly the longer action is deferred until a stage is reached where essential remedial works make irresistibly urgent demands on resources; this rarely allows the best or most economic use of those resources.

As a result, the maintenance function has tended to be an under-rated activity - unsung and unappreciated, disregarded until some failure occurs (and then damned as mis-managed!). To engineers, it lacks the attraction and glamour of new construction, which is esteemed as exciting and innovative with visible results; there is little apparent appeal in a task which is seen as a tedious struggle against deterioration and decay, achieving no more than the perpetuation of what already exists. Too often it is taken for granted.

In reality, maintenance involves technical and managerial skills as great and as varied as those required for any other civil engineering activity and can be more challenging, demanding and fulfilling than most. Maintenance Engineers probably need a wider appreciation of the behaviour of a greater range of structures than do many designers; the materials they deal with have less reliable characteristics than their modern equivalents; there is more frequent need for the exercise of engineering judgement in fields where there are no established codes of practice and little authoritative guidance. The successful repair of an operational structure with minimal interference with its normal use may call for resourcefulness and ingenuity unmatched in new construction.

Maintenance practitioners cannot therefore be regarded as second-class engineers, with lower skills, for whom professional qualifications are irrelevant and who can be remunerated accordingly. The expenditure for which they are responsible is massive (even if, in practice, inadequate) and there is vast scope for its inefficient or wasteful application on inappropriate, ineffective or even unnecessary repairs.

There is therefore a critical need for a better appreciation of the importance of maintenance as an essential and integral part of sustaining infrastructure assets and for establishing appropriate policies for the care of those assets. This must involve suitable recognition of the role of its practitioners - professional, technician and artisan - and the provision of adequate resources to enable them to discharge that role properly. There is currently a general perception that levels of financing and resourcing of maintenance activities in the United Kingdom are inadequate, albeit to a degree on which there is little consensus. Whatever may be the extent of such shortfall, it is unquestionable that available resources could be used more effectively and efficiently if maintenance efforts were given more regard and attention and more purposeful direction by more experienced engineers, better provided with appropriate information and support.

In the latter respect, there is a dearth of printed material giving positive maintenance advice and guidance; what exists is generally of a fairly basic and limited nature, scattered over various publications and often hard to find. The published work of researchers on long-term performance is largely restricted to reports on accelerated ageing tests on materials, which may not accurately reflect the real interaction of natural and human agents of deterioration. Few textbooks or codes of practice deal with the interrelationship between cost, reliability and durability under practical conditions of exposure and use. The training given to aspiring engineers at most academic institutions fails to imbue even an awareness of the importance of maintenance or of the principles of exercising control over it; the qualification requirements of the professional institutions are only just beginning to encourage a different approach. Pleas for a more formal recognition of professional maintenance management as an integral part of the province of the civil engineer (e.g. Robertson, 1969) have gone largely unheeded.

In respect of techniques and equipment, maintenance has generally used traditional labour-intensive methods, with little mechanization. Maintainers' requirements differ in many respects from those of their designer colleagues, and their problems have tended to be neglected by development organizations and manufacturers. In many cases it has been left to Maintenance Engineers themselves to devise and develop their own solutions, as occurred, for example, in the technique of the mechanical pointing of masonry. There are still unfulfilled requirements for more effective and more economic methods in most fields of maintenance, and not least in that of brick and stone masonry.

To focus attention and efforts on such problems, Maintenance Engineers must make their needs better known and may well have to work together more closely to demonstrate to potential innovators and suppliers that there is a worth-while market for cost-effective solutions.

1.2 Maintenance in context

Deterioration of a structure starts as soon as it is built; consideration of its maintenance should be - but seldom is - invoked long before that.

For the conceptual design of a new structure, the engineer needs to establish what is the sponsor's policy (if indeed he has one) with regard to that structure's maintenance. What is its role in securing the objectives of the business? What is its required life expectation? How soon can it become obsolescent and require modification? What standard of maintenance can be regarded as acceptable and economically viable? What are the criteria or limits for the assessment of serviceability? To what extent can the disruption and indirect costs arising from maintenance operations be tolerated? It is probable that such considerations will not have occurred to the sponsor, and so the engineer may well have to convince him of their relevance and make him realize their economic implications. He must give appropriate advice and information. He must then ensure that the decisions he receives exert their proper influence on his basic design proposals. He should now be drawing on his knowledge of the long-term behaviour of different materials and structural forms and making design decisions in the light of the treatment they are likely to receive in the particular service for which they are intended; he must select them and arrange for their application in a manner appropriate to their individual characteristics and to the environment, in its widest sense, in which they will be used. He must be constantly aware that the maintenance performance of a structure, throughout its life, will be a reflection of his original design decisions.

In the detailed design stage such considerations continue to apply with equal force. The basic materials may have been settled, but it is still necessary to determine and define the appropriate qualities or grades of each and to ensure that incompatible materials are not placed in juxtaposition. There may be a case for the adoption of a 'mendable' design, in which elements likely to have a relatively short life or to be vulnerable to damage are arranged so as to be readily renewable, possibly in some pre-assembled form; for parts which could be difficult or costly to repair or replace, a degree of overdesign could well be viable. There must be constant awareness of the risk of introducing features which will adversely affect durability or long-term appearance or which will restrict the required usage. In particular, since moisture, especially if charged with aggressive chemicals, is the greatest single cause of deterioration of most structural materials, there must be effective provision of waterproofing and/or drainage to ensure that water is shed quickly and led away in a controlled manner; ledges and crevices where moisture can lie and dirt accumulate should be ruthlessly designed out. The effects of weathering and surface staining on appearance must be carefully considered, as must the possibility of differential or thermal movement. A great deal of experience is needed to foresee the many factors which may accelerate deterioration. Equally, considerable expertise is required to counter them without increasing costs.

It is just as important, at this stage, to ensure ready access to all parts of the structure, initially to allow it to be properly examined and any defects observed, and subsequently to facilitate remedial operations. Not only does this mean the avoidance of inaccessible gaps between elements and fixtures (such as cladding and advertisement hoardings) which would obscure signs of trouble, but also it means the provision of safe means of reaching all parts of the structure - access platforms, manholes, catwalks and/or permanent fixing points for the attachment of ladders, scaffolds or safety lines. Masonry structures built by the Romans were frequently provided with stones which protruded from the face to accommodate scaffolding; it is curious that, 2000 years later, this lesson seems so often to have been forgotten!

At the construction stage the quality of materials and workmanship will have a major effect on subsequent maintenance. It is therefore necessary to define acceptable standards clearly and precisely and to ensure adherence to them by the employment of a reliable workforce, competently monitored and supervised. In weighing up the advantages of different methods of construction, the effect of each upon ageing characteristics ranks high among the relevant factors. Thus, durability might be improved by maximizing the amount of off-site construction, which can be undertaken under the more controlled and protected conditions of a factory rather than on a site exposed to the vagaries of weather; however, offsetting this could be a susceptibility to leakages at site joints. Even the programming of the work can have an effect; it is regrettably common to fail to allow adequate time for waterproofing operations to be undertaken with the care and thoroughness which they need if troublesome and unsightly leaks are to be avoided.

In support of the foregoing arguments, it is relevant that investigations of 510 defective buildings by the Building Research Establishment (1975) revealed that almo...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Contributors
• Preface
• Glossary
• PART ONE Introduction
• PART TWO Inspection, investigation and assessment
• PART THREE Deterioration: causes, characteristics and counter measures
• PART FOUR Remedial techniques
• PART FIVE Special types of structure
• Index