G NIEDERWANGER The structure of rubble walls of old bell towers is comparable with the structure of concrete with large aggregates—of course the strength of the mortar of limestone masonry is much smaller than cement stone of lowest quality. Nevertheless it is possible to compare the results of dynamic measurements on towers built by the named kinds of masonry with empirical results of concrete technology and In this connection the measured data of the dynamic response of a building under shock loadings and periodical loading by shakers before, during and after a stabilization are: the lowest natural frequency; the damping ratio of Lehr; and the horizontal displacements of the tower during bell ringing. The observed masonries showed clear perceptible systems of macrocracks before reconstruction; whose direction deviates only from the perpendicular line. The big pores and cracks in the masonry could clearly be recognized by TV-observation of the interior of boreholes of diameter mm.
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Concrete and steel are the two most commonly used structural materials. They sometimes comple- ment 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 con- trolled conditions; its properties are determined in a laboratory and described in a manufacturers cer- tificate.
Thus, the designer need only specify the steel as complying with a relevant standard, and the site engineers supervision is limited to the workmanship of the connections between the indi- vidual 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 ce- mentitious 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 con- crete making is, therefore, clear, and the import- ance 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 tra- dition of some of the other building trades, an en- gineers 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.
Struc- tural 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-homogen- eous 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 understand- ing, 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 de- sired without excessive effort, and also that the mix be cohesive enough for the methods of trans- porting and placing used so as not to produce se- gregation with a consequent lack of homogen- eity of the finished product.
The primary require- ments of a good concrete in its hardened state are a satisfactory compressive strength and an ad- equate durability. All this has been valid since the first edition of this book appeared in In its three edi- tions 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 wide- spread construction material.
However, very sig- nificant 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 con- crete as a construction material. But there has been no change for changes 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 earli- er versions will have no difficulty in finding their way in the new book.
The fourth edition contains much new materi- al on cementitious materials, some of which were not used, or were little used, in the past. Know- ledge of these materials should now form part of the engineers stock-in-trade. Durability of con- crete under various conditions of exposure, in- cluding carbonation and alkalisilica reaction, is treated fully.
In particular, the behaviour of con- crete 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 perform- ance concrete, recently introduced admixtures, concrete under cryogenic conditions, and proper- ties of the aggregatematrix 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 di- gression.
A very large number of papers on these materials and some other topics were published in the s and continue in the s. Many worthwhile papers have elucidated the behaviour of the various materials and their influence on the properties of concrete. But many more repor- ted narrowly construed investigations which de- scribed the influence of a single parameter, with some other conditions kept unrealistically con- stant.
Sometimes it is forgotten that, in a concrete mix, it is usually not possible to change one in- gredient without altering some other property of the mix. Generalized inferences from such piecemeal research are at best difficult and at worst dan- gerous. We do not need more of these little re- search projects, each one chalking up a publica- tion in the authors curriculum vitae.
Nor do we need an endless succession of formulae, each de- rived from a small set of data. Some, seemingly impressive, analyses show an excellent correla- tion 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 ex- pressions 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 in- fluences of various factors on the behaviour of concrete which have been determined by statist- ical analyses. While the use of statistics in the evaluation of test results and in establishing rela- tionships is valuable, and often essential, a stat- istical relation alone, without a physical explana- tion, is not a sound basis for claiming that a true relation exists between two or more factors. Like- wise, extrapolation of a valid relationship must not be assumed to be automatically valid.
This is obvious but sometimes forgotten by an enthusi- astic 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 us- ing of concrete. An understanding of the physic- al and chemical phenomena involved is an essen- tial 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 in- gredients should be avoided. It has to be remembered that the various con- crete mixes now used are derivatives and devel- opments of the traditional concrete, so that know- ledge of the basic properties of concrete contin- ues 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 beha- viour of concrete on a scientific basis and the classical references have been retained: they al- low us to have a proper perspective of our know- ledge.
The ultimate purpose of this book is to facil- itate 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, ex- perience in construction and in investigations of lack of durability and serviceability has been ex- ploited.
Because the book is used in so many coun- tries, it was thought best to use both the SI and the Imperial units of measurement, now paradox- ically known as American. All the data, diagrams and tables are, therefore, conveniently presented for readers, progressive or traditionalist, in all 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 beha- viour of concrete, rather than a series of some- what disconnected chapters. This cohesion may be of benefit to readers who have often been ob- liged to consult collections of uncoordinated art- icles 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 con- crete, 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 Poincar said, an accumulation of facts is no more a science than a heap of stones is a house.
The copyright of the following illustrations and tables rests with the Crown and my thanks are due to the Controller of HM Stationery Office for per- mission to reproduce: Figures 2. The following have made material from their publications available to me, for which I thank them: National Bureau of Standards Washington, D. The late Pro- fessor J. Kirkaldy kindly provided the data of Table 3. The full details of the sources can be found at the end of each chapter; the reference numbers appear with the captions to the illustrations and the headings to the tables.
I am grateful to my various clients in litigation and arbitration, and equally to their opposing parties, who enabled me to achieve a better un- derstanding of the behaviour of concrete in ser- vice, often by way of observing its misbeha- viour.
Very considerable help in finding references was provided by the staff of the Library of the In- stitution of Civil Engineers, and especially by Mr Robert Thomas who was indefatigable in track- ing down the various sources. Finally, I wish to put on record the enormous effort and achieve- ment of Mary Hallam Neville in cementing the sources and references into a cohesive manuscript culminating in a concrete book.
Without her prompting a much better word than nagging this book may not have anteceded the Authors de- cease. Cement, in the general sense of the word, can be described as a material with adhesive and co- hesive properties which make it capable of bond- ing mineral fragments into a compact whole. This definition embraces a large variety of cementing materials. For constructional purposes, the meaning of the term cement is restricted to the bonding ma- terials used with stones, sand, bricks, building blocks, etc.
The principal constituents of this type of cement are compounds of lime, so that in building and civil engineering we are concerned with calcareous cement.
The cements of interest in the making of concrete have the property of setting and hardening under water by virtue of a chemical reaction with it and are, therefore, called hydraulic cements. Hydraulic cements consist mainly of silicates and aluminates of lime, and can be classified broadly as natural cements, Portland cements, and high-alumina cements. The present chapter deals with the manufacture of Portland cement and its structure and properties, both when un- hydrated and in a hardened state.
The different types of Portland and other cements are con- sidered in Chapter 2. The use of cementing materials is very old. The ancient Egyptians used calcined impure gypsum.
The Greeks and the Romans used calcined lime- stone and later learned to add to lime and water, sand and crushed stone or brick and broken tiles. This was the first concrete in history. Lime mor- tar does not harden under water, and for con- struction under water the Romans ground togeth- er lime and a volcanic ash or finely ground burnt clay tiles.
The active silica and alumina in the ash and the tiles combined with the lime to produce what became known as pozzolanic cement from the name of the village of Pozzuoli, near Vesuvi- us, where the volcanic ash was first found. The name pozzolanic cement is used to this day to describe cements obtained simply by the grinding of natural materials at normal temperature.
Some of the Roman structures in which masonry was bonded by mortar, such as the Coliseum in Rome and the Pont du Gard near Nmes, and concrete structures such as the Pantheon in Rome, have survived to this day, with the cementitious mater- ial still hard and firm.
In the ruins at Pompeii, the mortar is often less weathered than the rather soft stone. The Middle Ages brought a general decline in the quality and use of cement, and it was only in the eighteenth century that an advance in the knowledge of cements occurred. John Smeaton, commissioned in to rebuild the Eddystone Lighthouse, off the Cornish coast, found that the best mortar was produced when pozzolana was mixed with limestone containing a considerable proportion of clayey matter.
By recognizing the role of the clay, hitherto considered undesirable, Smeaton was the first to understand the chemical properties of hydraulic lime, that is a material ob- tained by burning a mixture of lime and clay. There followed a development of other hy- draulic cements, such as the Roman cement ob- tained by James Parker by calcining nodules of argillaceous limestone, culminating in the patent for Portland cement taken out by Joseph Asp- din, a Leeds bricklayer, stonemason, and builder, in This cement was prepared by heating a mixture of finely-divided clay and hard limestone in a furnace until CO2 had been driven off; this temperature was much lower than that necessary for clinkering.
The prototype of modern cement was made in by Isaac Johnson, who burnt a mixture of clay and chalk until clinkering, so that the reactions necessary for the formation of strongly cementitious compounds took place. The name Portland cement, given originally due to the resemblance of the colour and quality of the hardened cement to Portland stone a limestone quarried in Dorset has remained throughout the world to this day to describe a cement obtained by intimately mixing together calcareous and argillaceous, or other silica-, alumina-, and iron oxide-bearing materials, burn- ing them at a clinkering temperature, and grind- ing the resulting clinker.
The definition of Port- land cement in various standards is on these lines, recognizing that gypsum is added after burning; nowadays, other materials may also be added or blended see p. From the definition of Portland cement given above, it can be seen that it is made primarly from a calcareous material, such as limestone or chalk, and from alumina and silica found as clay or shale.
Properties of Concrete
Concrete and steel are the two most commonly used structural materials. They sometimes comple- ment 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 con- trolled conditions; its properties are determined in a laboratory and described in a manufacturers cer- tificate. Thus, the designer need only specify the steel as complying with a relevant standard, and the site engineers supervision is limited to the workmanship of the connections between the indi- vidual steel members. On a concrete building site, the situation is totally different.
Concrete Technology by A M Neville
Advanced, 8th ed Christopher Kitcher. The overall effect is to give an integrated view of the properties of concrete so as to enable the reader to achieve the best possible construction in concrete. User Review — Flag as inappropriate very good. Concretes with particular properties Properties of aggregate 4.
Properties of Concrete