Site Control of Materials. Handling, Storage and Protection

143 Pages·1981·4.022 MB·English

by  John E Johnston (Auth.)

Site Control of Materials
Handling, storage and protection
John Å Johnston
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First published 1981
©John E.Johnston 1981
British Library Cataloguing in Publication Data
Johnston, John
Site control of materials.
1. Materials handling 2. Building sites
3. Building materials
I. Title
658.7'81 TH438
ISBN 0-408-00377-4
Typeset by Butterworths Litho Preparation Department
Printed in England by Billing & Sons Ltd., Guildford, London
and Worcester
Preface
It is generally accepted that the initial selection of materials plays a major
part in achieving a satisfactory building. Unfortunately, it is not always so
easily recognised that the methods adopted on site for handling and storing
these materials are equally important. Manufacturers and suppliers go to
great lengths to provide commodities which comply with recognised
standards, but much of their effort can be eroded if the same importance is
not attached to the product when it is transferred to the care of the
contruction team.
Construction sites are not ideal places for storing valuable or fragile
materials. Traditionally, construction materials were robust so that certain
liberties could be taken during construction without serious consequences.
Heavier demands on available stocks, stimulated by urgent construction
programmes, have resulted in alternatives being sought, with more uses
required from traditional sources. This produced redesigned clay products,
reduced timber sections, thinner lead pipes and subsequently thinner
copper pipes, concrete products instead of brick and tile, plastic in place of
timber and cast iron, glass instead of brickwork or stonework, and bitumen
felt in lieu of asphalt.
It also resulted in more fragile components on site, requiring more
sophisticated methods for storing and handling. However, these did not
automatically follow, so that wastage problems increased. On small one-off
contracts the percentage of waste might not have produced much reaction,
but mass housing development increased wastage so much that it could not
be ignored.
Complex control systems can easily be introduced to site, but in general
attitudes must change before such systems are seen to be necessary and
then successfully applied. General management do not always accept the
responsibility here, and claim that the problems arise because sites are
remote from head office. However, much of the blame can be attributed to
a lack of understanding of site control problems in the pre-planning stages
of the contract. Pre-planning will take care of purchasing, deliveries and
bulk storage, but the details of handling, storing and distributing materials
on site are always assumed to be the responsibility of site management.
This approach is only really suitable if support and guidance are offered
to site management when work begins on site. One way to achieve this is to
appoint a materials controller, with all the responsibilities that implies, so
that planned materials handling and distribution can proceed from the
outset of the contract. An efficient materials controller not only reduces
waste on site, but also relieves general site supervision from many tasks,
allowing them more time to concentrate on workmanship and treatment of
materials. A materials controller can ensure that deliveries are thoroughly
checked and recorded; carelessness at this stage can account for much
waste or faulty components. Mishandling and excessive handling create
further waste or defective components, and close control is the only way to
Preface
avoid such problems. Materials control can only be applied effectively by
directing the attention of all operative levels on site to it - craftsmen,
supervisors and management groups.
Supervision always contributes to quality on a construction project, but
it is a joint responsibility, and not the prerogative of any single person.
Increased consideration of craft skills and personal responsibility might
contribute significantly to reducing materials waste, but it needs better
methods of rewarding such attributes. Site accounting is an obvious means
of detecting excess waste, at least where the accounting is thorough and
efficient. However, while major losses will become apparent through
normal accounting methods, the small, cumulative losses can add up to
something equally serious, and these are not always readily apparent to the
accountant.
The overall objective in planning and controlling materials at delivery
stage, in storage, or in site distribution, must be to obtain the most efficient
use of those materials while reducing waste to the minimum. So far as
actual quantities are concerned, waste materials must be seen as a total loss
and subsequent replacements an added cost to the contract, apart from the
possible consequence of delays.
Materials waste can be classified as loss through poor site security,
inefficient handling, inadequate storage, and misuse in construction or
manufacture, all of which point to poor management. Where the losses
occur at site level then it is site controls which must be improved, and this
will be more effective where support is available from head office
management. Plans can be made at head office or at site management
level, but implementation can only be achieved by general cooperation at
site level.
The construction industry does not always enjoy a very good public
image. This could be due to a lack of understanding of the problems which
beset the construction team on almost any site. However, untidy sites
usually indicate careless site controls, and certainly provide a warning that
material waste is likely to be excessive. Improving site controls will restrict
waste, provide a better image for the industry as a whole, and reduce the
financial loss ultimately reflected within the income of everyone concerned
with construction today.
Acknowledgements
I wish to record my appreciation to the following for their contribution to
this book: Brian Williams, for his help in research and processing the
photographs; Ron Boyd and Roy Williams, for some of the photographs;
Walter Godson and Roy Wall, for reading the original draft and offering
valuable advice; and Arthur Kelly for many useful comments in the early
stages of the book. My thanks are also due to Mrs Linda Carmen for her
assistance, particularly in typing the final draft. Finally I would also thank
my editor Lionel Browne, of Butterworths, for his assistance throughout
and in bringing the book to its final presentation.
J. E. J.
Helsby, Cheshire
1981
1
The need for site controls
It is no secret that large quantities of building materials are allowed to be
buried or burnt each year as a result of inadequate controls on site
(Figure 1).
Figure 1 Large quantities of materials are allowed to be buried or burnt each year
through inadequate site controls
The problem is vast. In 1976 the UK's Building Research Establishment
reported that 10-20% of all materials delivered to site either ended up as
waste or were illegally removed during the contract*. This is probably a
conservative estimate compared with the waste on many sites, particularly
large scattered contracts such as housing development.
The size of the problem can be put in its true perspective by converting
these percentages into actual figures. Using UK Government statistics for
1976, it appears that more than 6 million tonnes of sand, and an equal
*"E. R. Skoyles and H. J. Hussey, 'Wastage of materials on building sites,' BRE Current
Paper CP/44/74.
1
2 The need for site controls
amount of aggregate, were lost in that year! No doubt some of this was
removed illegally, but most of it was probably finally buried during the
construction of external works on site (Figure 3).
In the same year, 7 million square metres of concrete blocks either
disappeared or were unaccounted for in site valuations; and losses of
plasterboard amounted to more than 11 million square metres! A mere 1%
of timber lost in 1976 would have been worth £4.3 million. The actual
losses for that year were far in excess of 1%: yet another indication of just
how serious the situation really is.
Figure 2 More consideration must be applied to materials management,
particularly at site level
Figure 3 Most of the sand and aggregate lost each year (6 million tonnes each in
1976) was probably buried during construction of external works
Changing patterns of supply and demand 3
The potential effect on the national economy is frightening, but it is
unlikely that positive action will be taken to remedy the situation until
construction management fully appreciate that materials waste means lost
profits and/or unnecessary increases in contract prices. In fact waste is,
either directly or indirectly, a financial loss to client, contractor and
operative alike. Moreover, one cannot ignore the fact that it also repre-
sents a deprivation of resources for future generations.
Changing patterns of supply and demand
The construction industry has changed considerably in recent years,
influencing production rates, construction techniques and the total quanti-
ty of materials used each year. Individual contracts have increased
substantially in size and value, necessitating more sophisticated manage-
ment techniques and increased mechanisation of the construction process.
All this has increased the demand for materials beyond the capacity of the
traditional sources of supply. New materials are being introduced, and
traditional materials are being processed and manufactured into new
products. This increase in the total quantity of materials used has in turn
led to an increase in the amount of waste.
Figure 4 The present emphasis on timber-frame construction has contributed to
the increase in timber imports
Many of the materials used by the UK construction industry have to be
imported, sometimes as raw materials which are then processed and
re-exported. Imports include copper, asbestos, asphalt and timber.
Current UK imports of timber amount to 92% of the total used in
construction. The main sources of softwood are North America, Canada,
Russia and Scandinavia; together, these countries provide 79% of UK
requirements. The current emphasis on timber-frame construction has
4 The need for site controls
contributed to an increase in timber imports, which in 1975 were worth
£260 million; in 1976 this figure almost doubled to £429 million. Timber is
graded for all construction purposes to comply with the UK Building
Regulations. Most of it is shipped into the country in standard sizes, and
these should be borne in mind at the design stage. Timber supplied for
frame construction is usually treated with preservative before being
exported, using impregnation methods which affect the moisture content
on delivery.
Two World Wars and indiscriminate commercial felling reduced timber
resources for a while, and though quick-growing timbers like spruce and
pine can be replaced with minimum disturbance to the industry, trees
which require maturity to reach their prime are more difficult to replace.
This applies particularly to hardwoods such as mahogany and teak. These
are found mainly in the Far East, and following the last World War a
shortage created interest in many lesser-known timbers, such as obeche,
ciroko, and makore. Laminated timbers are now used for purposes where
the natural product would be unsuitable, while chipboard and similar
reconstituted timber has replaced much natural timber for sheeting pur-
poses.
The clay and shale used in the manufacture of bricks are fairly abundant
in the UK, while aggregates for concrete production remain available in
sufficient quantity, for the present at least. Supplies of clay and shale bricks
have been augmented with bricks manufactured from calcium silicates as
well as from concrete, and in some cases brick has been displaced by
building blocks manufactured from concrete, clay, and lightweight mate-
rials. During 1967 production of concrete blocks in the UK amounted to 49
million m2, but by the end of 1976 this had increased to 70 million m 2.
The roofing industry was dominated by slates and clay tiles before the
Second World War, but the quality of concrete roofing tiles has improved
significantly. As they were more economical they were adopted after the
War as standard roofing materials for mass housing projects, and they still
retain a firm hold over this particular market. Flat-roof design provided an
alternative which produced a variety of roof decking in timber, asbestos,
and metal. This sheeting is covered with a layer of insulation board and
sealed by applying two or three thicknesses of bitumen-impregnated felt
laid in hot bitumen; a layer of light-reflecting aggregates laid in hot or cold
bitumen provides solar protection.
Pre-cast concrete, produced in the form of large panels with various
forms of surface treatment, has replaced much traditional brickwork,
particularly on high-rise development. Concrete has also been used
extensively in conjunction with glass to create the typically modern
buildings found in almost every country in the world. Pre-cast beams and
slabs are produced in greater quantities today for use in suspended floors
and roofs, while pre-cast blocks manufactured with crushed stone as the
aggregate and termed 'reconstituted stone' have replaced much natural
stone on modern buildings.
During the 1950s lead pipe was superseded by drawn copper tube, but
this material has rapidly given way to polythene and other forms of plastics
tubing, which is available in various diameters and can be used for both
internal and external services installations. Earthenware drainage has to
Design 5
compete with plastics and pitch-fibre products which are much lighter to
handle than the traditional product, and sometimes quicker to install.
The urge to speed up internal operations to keep pace with progress in
shell construction received a tremendous boost when traditional plastering
techniques were overtaken by dry lining. This not only reduced the quantity
of water introduced into buildings during construction, but also provided
better insulation values and economised on plaster use. Over 75 million m 2
of plaster board were produced in 1967, and this figure had increased to
117 million by 1976, illustrating once again the success of a traditional
material produced in a modern form.
Trends in building design continually call for new materials, and the
demand has been met with many innovations, not all of which have been
successful. Until recently production of materials for the construction
industry had been increasing each year to meet current building program-
mes, but there had been an even bigger increase in the proportion
produced as manufactured materials and components, such as ready-mixed
concrete and mortar, pre-cast concrete units, structural timber frames,
trussed rafters, plasterboard, pre-formed partitions, ceiling panels, and
door sets. Unfortunately this apparent wealth of materials convinced many
people in the industry that unlimited resources were available for all time.
Such views must be discouraged.
In recent years temporary shortages of materials have indicated the
problems that could be caused by more serious shortages. Shortages in
other industries can affect supplies to the construction industry. This was
evident in the fuel crisis of 1973-1974, when many sites were brought to a
halt because there was no energy to produce materials; and even when
stocks were available at the factory, there was no way of transporting them
to the site.
So long as alternatives to traditional materials remain acceptable to the
construction industry the problem will probably be regarded as a limited
one, but it should be remembered that most alternative materials still rely
on traditional sources.
Many experts have experienced serious doubts about the long-term
availability of our present natural resources, and this must concern
everyone in the industry. Research into alternative sources of supply has
centred on waste products from other industries. Some success has been
achieved in producing lightweight aggregates from fly-ash, a by-product of
power-station fuel. Research continues with plastics waste, wood chips,
cereal straw, rice, glass, and phenolic resins. However, there is a long way
to go before we can be sure the problem will be solved.
The construction industry may continue to use present-day resources for
many years; but the problem of resource availability was not even
conceivable to the industry less than four decades ago!
Design
When the designer is researching materials for construction he consults
various sources, but in particular the literature circulated by manufactur-
ers. Most products comply with current standards (although variations do
6 The need for site controls
occasionally occur), but the designer will check this information before
including his selected products in the specification. Unfortunately, the
literature in hand is not always up to date, and this can create complica-
tions when work actually commences on site. The designer includes a
description in the specification for each type of material or component
required in the contract, but often he only quotes the number of the
relevant British Standard, together with some general comments. For
more detailed and accurate information the contractor is expected to refer
to current BS documents, but these standard specifications can sometimes
be inconclusive.
Materials that have been carefully selected by the designer may be
unavailable by the time they are actually required on site, either through
delays in production or because increased prices make them too expensive.
Replacement materials have then to be specified, but contract pressures
may restrict the amount of time available for researching the product;
hence alternatives often lack the qualities or characteristics of the original
choice. Unless the designer allows for the difference in quality, increased
supervision is necessary on site to maintain standards. The product is
usually blamed if it fails and yet it might have met the requirements if used
correctly.
The selection of components and materials is as important as both design
and workmanship in achieving successful results. If selected materials do
not always stand up to the conditions expected of them, the cause may be
conflict between aesthetic values and practical requirements, and this can
be influenced by the designer's professional training. Architects are very
conscious of aesthetic values; for example, in selecting a facing brick the
colour will be considered first, and then the texture, before the porosity is
considered. Given the same choice the engineer examines the porosity and
the density of the material, before considering the final shape of the brick
after firing. Much modern design omits any projecting features on brick
facades, so that this question of porosity can be fundamental to the success
of modern brickwork; there are numerous examples of brickwork that has
failed because of this.
If the problems associated with waste are to be resolved, designers must
take more account of the actual construction procedures applied on site.
Once work has commenced, variations to drawings should be kept to an
absolute minimum, and all information connected with construction should
be made available at an early stage, rather than when the programme has
been finalised. The application of materials and the amount of waste are
highly dependent on good design and, in particular, on how the details are
prepared.
Waste
Waste occurs on site for a number of reasons, most of which can be
prevented. Some of the more obvious ones are:
Φ misinterpretation of drawings;
• overestimating the quantity required;
Φ faulty workmanship;
Φ careless handling of materials.