Preface
Concrete and steel are the two most commonly
used structural materials. They sometimes complement
one another, and sometimes compete with
one another so that structures of a similar type and
function can be built in either of these materials.
And yet, the engineer often knows less about the
concrete of which the structure is made than about
the steel.
Steel is manufactured under carefully controlled
conditions; its properties are determined in
a laboratory and described in a manufacturer’s certificate.
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Thus, the designer need only specify the
steel as complying with a relevant standard, and
the site engineer’s supervision is limited to the
workmanship of the connections between the individual
steel members.
On a concrete building site, the situation is
totally different. It is true that the quality of cement
is guaranteed by the manufacturer in a manner
similar to that of steel and, provided suitable cementitious
materials are chosen, it is hardly ever
a cause of faults in a concrete structure. But it
is concrete, and not cement, that is the building
material. The structural members are more often
than not made in situ, and their quality is almost
exclusively dependent on the workmanship of
concrete making and placing.
The disparity in the methods of steel and concrete
making is, therefore, clear, and the importance
of the control of the quality of concrete work
on the site is apparent. Furthermore, as the trade
of a concretor has not yet the training and the tradition
of some of the other building trades, an engineer’s
supervision on the site is essential. These
facts must be borne in mind by the designer, as
careful and intricate design can be easily vitiated
if the properties of the actual concrete differ from
those assumed in the design calculations. Structural
design is only as good as the materials used.
From the above it must not be concluded that
making good concrete is difficult. ‘Bad’ concrete
– often a substance of unsuitable consistency,
hardening into a honeycombed, non-homogeneous
mass – is made simply by mixing cement,
aggregate and water. Surprisingly, the ingredients
of a good concrete are exactly the same, and it is
only the ‘know-how’, backed up by understanding,
that is responsible for the difference.
What, then, is good concrete? There are two
overall criteria: the concrete has to be satisfactory
in its hardened state, and also in its fresh state
while being transported from the mixer and
placed in the formwork. The requirements in the
fresh state are that the consistency of the mix be
such that it can be compacted by the means desired
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without excessive effort, and also that the
mix be cohesive enough for the methods of transporting
and placing used so as not to produce segregation
with a consequent lack of homogeneity
of the finished product. The primary requirements
of a good concrete in its hardened state
are a satisfactory compressive strength and an adequate
durability.
All this has been valid since the first edition
of this book appeared in 1963. In its three editions
and the 12 languages in which translations
have been published, the book seems to have
served well those involved in concrete, which
continues to be the most important and widespread
construction material. However, very significant
changes in knowledge and in practice
have taken place in recent years, and this is why
a fourth edition needed to be written. The extent
of these changes has been such that a ‘bolt-on’
approach was not appropriate and, except for its
fundamental core, this is, therefore, a new book.
Its coverage has been greatly widened, and it
gives a broad as well as a detailed view of concrete
as a construction material. But there has
been no change for change’s sake. The form,
style, approach, and organization of the material
in the previous editions have been maintained so
that those readers who are familiar with the earlier
versions will have no difficulty in finding their
way in the new book.
The fourth edition contains much new material
on cementitious materials, some of which were
not used, or were little used, in the past. Knowledge
of these materials should now form part of
the engineer’s stock-in-trade. Durability of concrete
under various conditions of exposure, including
carbonation and alkali–silica reaction, is
treated fully. In particular, the behaviour of concrete
under the extreme conditions existing in
coastal areas of the hot parts of the world, where a
great deal of construction nowadays takes place,
is discussed. Other new topics are: high performance
concrete, recently introduced admixtures,
concrete under cryogenic conditions, and properties
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of the aggregate–matrix interface, to mention
but the main ones.
It has to be admitted that the treatment of the
various cementitious materials presented quite a
challenge which has provoked the following digression.
A very large number of papers on these
materials and some other topics were published
in the 1980s and continue in the 1990s. Many
worthwhile papers have elucidated the behaviour
of the various materials and their influence on
the properties of concrete. But many more reported
narrowly construed investigations which described
the influence of a single parameter, with
some other conditions kept unrealistically constant.
Sometimes it is forgotten that, in a concrete
mix, it is usually not possible to change one ingredient
without altering some other property of
the mix.
Generalized inferences from such piecemeal
research are at best difficult and at worst dangerous.
We do not need more of these little research
projects, each one chalking up a ‘publication’
in the author’s curriculum vitae. Nor do we
need an endless succession of formulae, each derived
from a small set of data. Some, seemingly
impressive, analyses show an excellent correlation
with the experimental data fed into the pool
from which the expressions were derived in the
first place: such correlation is not surprising. But
then it should not be surprising either if the expressions
fail dismally when used to predict the
behaviour in untried circumstances where there
exist factors ignored in the original analysis.
A further comment can be made about the influences
of various factors on the behaviour of
concrete which have been determined by statistical
analyses. While the use of statistics in the
evaluation of test results and in establishing relationships
is valuable, and often essential, a statistical
relation alone, without a physical explanation,
is not a sound basis for claiming that a true
relation exists between two or more factors. Likewise,
extrapolation of a valid relationship must
not be assumed to be automatically valid. This is
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obvious but sometimes forgotten by an enthusiastic
author who is under the impression that he
or she has discovered a general ‘rule’.
Whereas we must consider available research,
there is little value in collecting together a mass
of research findings or giving a general review
of each topic of research. Rather, this book has
striven to integrate the various topics so as to
show their interdependence in the making and using
of concrete. An understanding of the physical
and chemical phenomena involved is an essential
basis for tackling the unfamiliar, in contrast
to the
ad hoc
approach for picking up clues from
past experience, which will work only so far, and
sometimes may result in a catastrophe. Concrete
is a patient material but, even so, avoidable flaws
in the selection and proportioning of the mix ingredients
should be avoided.
It has to be remembered that the various concrete
mixes now used are derivatives and developments
of the traditional concrete, so that knowledge
of the basic properties of concrete continues
to be essential. In consequence, a large part
of the book is devoted to these fundamentals. The
original work of the pioneers of the knowledge
of concrete which explains the underlying behaviour
of concrete on a scientific basis and the
classical references have been retained: they allow
us to have a proper perspective of our knowledge.
The ultimate purpose of this book is to facilitate
better construction in concrete. To achieve
this, it is necessary to understand, to master, and
to control the behaviour of concrete not only in
the laboratory but also in actual structures. It is
in this respect that an author with a structural
background is at an advantage. Furthermore, experience
in construction and in investigations of
lack of durability and serviceability has been exploited.
Because the book is used in so many countries,
it was thought best to use both the SI and
the Imperial units of measurement, now paradoxically
known as American. All the data, diagrams
and tables are, therefore, conveniently presented
for readers, progressive or traditionalist, in all
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countries.
This book was written in its entirety during
the period of one year and it should therefore
present a closely-knit explanation of the behaviour
of concrete, rather than a series of somewhat
disconnected chapters. This cohesion may
be of benefit to readers who have often been obliged
to consult collections of uncoordinated articles
in a ‘book’ with a nominal editor or editors.
In a single volume, it is not possible to cover
the whole field of concrete: specialized materials,
such as fibre reinforced concrete, polymer concrete,
or sulfur concrete, albeit useful, are not
dealt with. Inevitably, the author selects what he
considers most important or most interesting, or
simply what he knows most about, even though
the scope of his knowledge increases with age
and experience. The emphasis in this book is on
an integrated view of the properties of concrete
and on underlying scientific reasons, for, as Henri
Poincaré said, an accumulation of facts is no
more a science than a heap of stones is a house.
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