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Blended cements ASTM special technical publication STP 897
Book reviews
Book reviews Strength Evaluation of Existing Concrete Bridges Edited by Tony C. Liu Published by the American Concrete Institute, PO Box 19150, Redford Station, 22400 W. Seven Mile Road, Detroit, Michigan 48219, USA, 1985. Library of Congress Catalog Card Number 85-72286, Price: Members $31.50, Non-members $41.25, V + 262pp. The bridges of a nation are its valuable assets and need to be preserved and maintained for their load capacity, and strengthened if necessary for continued satisfactory performance. Strength evaluation of existing concrete bridges is thus a vital component of this process of ensuring that bridge structures continue to carry their design loads with adequate strength and safety. The papers in this publication contribute a great deal of new information and cover a wide range of subjects on the strength evaluation of existing concrete bridge structures. The papers were presented at two Symposia organised by the American Concrete Institute-- the first in Washington in November 1979 and the second in New York in November 1984. In spite of the time lag between the two Symposia, all the papers are not only very relevant to the overall theme but also very interrelated to each other. The 12 papers included in this volume discuss a wide range of techniques to evaluate the strength and serviceability conditions of bridge structures. Load testing provides an inexpensive and effective means of assessing the behaviour of bridge structures, and is particularly suited to multi-girder bridge systems; this technique is discussed in five of the papers in this volume. For both tee beam decks and pseudo box decks, the results of load tests are shown to be adequate for design purposes, although for good correlation, the torsional stiffness of the transverse grillage members has to be increased substantially. Tests reported from Japan, on the other hand, emphasise the differences between field tests and isolated beam bending tests. The rigidity of a beam that is part of an existing bridge is much higher than that expected from an isolated beam test. Similarly, in spite of highly deteriorated appearance of concrete, no significant losses in strength were observed. This is confirmed by other load tests which showed no differences in bridge behaviour due to concrete condition. Analytical methods can also be used for structural investigations. Finite element models often provide simple tools to analyse structural actions; and one paper shows how this technique is used to examine possible causes of existing cracks in bridge piers. Cracking and inadequate shear strength are perennial problems in bridge structures (apart from steel corrosion and consequent loss of steel area). The latter is particularly relevant to AASHTO design specifications which prior to the 1970's permitted much greater shear stress in concrete
than allowed by current codes. Shear strength assessment of bridge beams is therefore very critical to many existing bridges. Shear strength evaluation is discussed in two papers, and it is gratifying to note that the modified compression field theory, currently incorporated in the Canadian Concrete Code, is capable of predicting the shear behaviour of reinforced and prestressed concrete beams. Field testing is reported in two papers. Deflection measurement methods and thermal infrared and ground penetrating radar remote sensing technologies have been applied to the non-destructive evaluation of existing concrete bridge decks. Several case histories are presented - - like the strength evaluation of Nelson Street bridge in Atlanta, Georgia, built in 1906 and clearly structurally deficient for today's traffic loads. An interesting observation arising from load testing is that precast deck panel systems act more like simple spans compared to conventional cast-in-place bridge decks which act as continuous systems. Full scale structural testing can thus show up some of the basic deficiencies in design assumptions, and the need for closer understanding between design and structural performance. A unique value of this Symposium volume is the many case histories reported, and the relationship between analysis, design and construction.
Blended Cements ASTM Special Technical Publication STP 897 Edited by Geoffrey Frohnsdorff Published by The American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103, USA, 1986. ISBN 0 8034 0453 7, Price: Members $20.80, List Price: $26.00. Available from ASTM or in Europe from American Technical Publishers Ltd., 68a Wilbury Way, Hitchin, Herts SG4 0TP, U.K. (Price £26.00). It is now universally recognised that from economic, technological and ecological considerations, cement replacement materials have an im!5ortant role to play in the construction industry. Small amounts of inert fillers have always been acceptable as cement replacements, but if the fillers are pozzolanic, they impart not only technical benefits to the resulting concrete, but also enable larger quantities of cement replacement to be achieved. From energy considerations, the case for the use of pozzolanic admixtures is overwhelming. This publication is therefore not only timely but also much needed to help to create a better understanding of the role and function of blended cements, and also thereby facilitate the development of new standards. The volume contains nine papers which were presented at a Symposium held in Denver in June 1984. Of the nine papers, four discuss portland blast furnace slag cements, one, portland fly ash cement, and three, blended cements with slag and pozzolans. The last paper is devoted to the present status of cement standardisation in Europe. The four papers on slags confirm without doubt that when used as an admixture or as a blended cement, it
57
Book reviews
can yield satisfactory concretes with respect to both strength development and durability. The data show that there are differences in performance between slags, and that tests on individual slag and cement mixtures are necessary to establish and characterise slag performance. Both compressive strength and heat of hydration are controlled by a large number of manufacture parameters such as glass content of the slag, grinding fineness and amount of gypsum. On the other hand, resistance to sulphate attack and alkali aggregate reaction is found to be high irrespective of the glass and gypsum contents of the slag and the fineness of the blended cement. It is a pity that with the large amounts of fly ash currently available in the world, there is only one paper devoted to fly ash. Nevertheless, this paper confirms the pozzolanic nature of fly ash. However, it is reported that the addition of fly ash increases the total porosity at early ages whilst after 3 months hydration, both total porosity and pore size distribution are similar to that of OPC paste. Three papers are devoted to blended cements with slag and pozzolans. It is shown that with sufficient cement replacement, the ultimate permeability of a sulphate resistant portland cement paste is greatly reduced. Silica fume was found to be most effective in reducing permeability at early ages. Silica fume was also the most effective in reducing calcium hydroxide contents while slag was the least effective. The results showed no clear correlation between permeability and porosity or pore size parameters alone. Blended cements with controlled particlesize distribution were able to develop properties similar to those of normal concrete. The last paper presents a timely review of cement standardisation in Europe. The author predicts that by the year 2000, the use of blended cements will increase all over the world, and portland cements will eventually come to be regarded as special cements for use where exceptional performance is required. With increasing interest in blended cements the world over, this publication would be of great value to cement producers, concrete technologists~ researchers and students alike. The extensive data on recent research should enable the wider use of mineral admixtures, and the development of appropriate standards for their use to be achieved:
Corrosion of Rebars in Concrete A S T M Special Technical Publication STP 906 Edited by Victor Chaker Published by The American Society for Testing and Materials, 1916 Race Street, Philadelphia PA 19103, USA, 1986. ISBN 0 8031 0468 5, Price: Members £23.00, Others £29.00. Available from A S T M or in Europe from American Technical Publishers Ltd., 68a Wilbury Way, Hitchin, Herts SG4 0TP, U.K. European price £29.00. Corrosion of steel bars in reinforced and prestressed concrete members has become a major world problem.
58
The structures most widely affected are highway bridges exposed to ice, snow and chlorides but others such as prestressed concrete pipes, large span structures and car garages are also equally involved. A great deal of research during the last 2 decades has led to a better understanding of the mechanism of steel corrosion, and particularly to develop monitoring methods and protection of steel bars. This publication makes a distinct and valuable contribution to further this understanding. It contains the papers presented at an ASTM Symposium organised by Committee G-1 on Corrosion of Metals and held in November 1984. The Symposium concentrated on two areas - - Corrosion Effects of Stray Currents and Techniques for Evaluating Rebar Corrosion. On these two subject areas, this volume comprises a unique collection of excellent papers which no engineer, designer and researcher can afford to ignore. Apart from a historical background to the work of Committee G-1 and a summary, there are nine papers included in this volume. An excellent state-of-the-art paper on fundamental studies related to steel corrosion sets the scene for the volume. There are four papers devoted to evaluating steel corrosion. The use of polarisation resistance and impedance methods to determine the corrosion rate of steel embedded in concrete is reported. Reinforced earth systems are also susceptible to corrosion since they contain steel bars, fibres or nets. The results of a field survey concerning corrosion susceptibility of the metallic elements in such systems are described. These data show that both environment and backfill characteristics are of great importance. Marine environments are highly corrosive, for example, and the use of inert materials or materials coated with corrosion resistant substances is recommended. Recently high tensile polymer grids have come into wide use as soil reinforcing elements and their major advantage in being corrosion resistant cannot be over-emphasised. The corrosion problems associated with concrete pipes is reported and the detection of corrosion discussed. Extreme care is shown to be necessary when applying cathodic protection because of the electrical discontinuity between the different segments of the pipes, as well as the different metallic elements that need to be made continuous. The last paper in this group discusses the use of X-ray as a measure of prediction of concrete cracking. Four papers are devoted to protection systems and the effects of stray currents. Tests show that lightning conductor connections influence the corrosion rate, and that artificial lightning and the use of radioactive lightning conductions also accelerate corrosion. An interesting application using the atmospheric charges to protect the rebars from corrosion is reported. A cathodic protection system using a mesh of polymeric anodes to protect the reinforcing steel in a concrete substructure is also described. Chloride-induced corrosion of steel reinforcement is widespread in the construction industry. The addition of a corrosion inhibitor to the concrete mix is reported to offer a practical solution to this problem, and calcium nitrite is shown to be very effective in this way. Tests reported from Greece show that two additives - -
Book reviews Strength Evaluation of Existing Concrete Bridges Edited by Tony C. Liu Published by the American Concrete Institute, PO Box 19150, Redford Station, 22400 W. Seven Mile Road, Detroit, Michigan 48219, USA, 1985. Library of Congress Catalog Card Number 85-72286, Price: Members $31.50, Non-members $41.25, V + 262pp. The bridges of a nation are its valuable assets and need to be preserved and maintained for their load capacity, and strengthened if necessary for continued satisfactory performance. Strength evaluation of existing concrete bridges is thus a vital component of this process of ensuring that bridge structures continue to carry their design loads with adequate strength and safety. The papers in this publication contribute a great deal of new information and cover a wide range of subjects on the strength evaluation of existing concrete bridge structures. The papers were presented at two Symposia organised by the American Concrete Institute-- the first in Washington in November 1979 and the second in New York in November 1984. In spite of the time lag between the two Symposia, all the papers are not only very relevant to the overall theme but also very interrelated to each other. The 12 papers included in this volume discuss a wide range of techniques to evaluate the strength and serviceability conditions of bridge structures. Load testing provides an inexpensive and effective means of assessing the behaviour of bridge structures, and is particularly suited to multi-girder bridge systems; this technique is discussed in five of the papers in this volume. For both tee beam decks and pseudo box decks, the results of load tests are shown to be adequate for design purposes, although for good correlation, the torsional stiffness of the transverse grillage members has to be increased substantially. Tests reported from Japan, on the other hand, emphasise the differences between field tests and isolated beam bending tests. The rigidity of a beam that is part of an existing bridge is much higher than that expected from an isolated beam test. Similarly, in spite of highly deteriorated appearance of concrete, no significant losses in strength were observed. This is confirmed by other load tests which showed no differences in bridge behaviour due to concrete condition. Analytical methods can also be used for structural investigations. Finite element models often provide simple tools to analyse structural actions; and one paper shows how this technique is used to examine possible causes of existing cracks in bridge piers. Cracking and inadequate shear strength are perennial problems in bridge structures (apart from steel corrosion and consequent loss of steel area). The latter is particularly relevant to AASHTO design specifications which prior to the 1970's permitted much greater shear stress in concrete
than allowed by current codes. Shear strength assessment of bridge beams is therefore very critical to many existing bridges. Shear strength evaluation is discussed in two papers, and it is gratifying to note that the modified compression field theory, currently incorporated in the Canadian Concrete Code, is capable of predicting the shear behaviour of reinforced and prestressed concrete beams. Field testing is reported in two papers. Deflection measurement methods and thermal infrared and ground penetrating radar remote sensing technologies have been applied to the non-destructive evaluation of existing concrete bridge decks. Several case histories are presented - - like the strength evaluation of Nelson Street bridge in Atlanta, Georgia, built in 1906 and clearly structurally deficient for today's traffic loads. An interesting observation arising from load testing is that precast deck panel systems act more like simple spans compared to conventional cast-in-place bridge decks which act as continuous systems. Full scale structural testing can thus show up some of the basic deficiencies in design assumptions, and the need for closer understanding between design and structural performance. A unique value of this Symposium volume is the many case histories reported, and the relationship between analysis, design and construction.
Blended Cements ASTM Special Technical Publication STP 897 Edited by Geoffrey Frohnsdorff Published by The American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103, USA, 1986. ISBN 0 8034 0453 7, Price: Members $20.80, List Price: $26.00. Available from ASTM or in Europe from American Technical Publishers Ltd., 68a Wilbury Way, Hitchin, Herts SG4 0TP, U.K. (Price £26.00). It is now universally recognised that from economic, technological and ecological considerations, cement replacement materials have an im!5ortant role to play in the construction industry. Small amounts of inert fillers have always been acceptable as cement replacements, but if the fillers are pozzolanic, they impart not only technical benefits to the resulting concrete, but also enable larger quantities of cement replacement to be achieved. From energy considerations, the case for the use of pozzolanic admixtures is overwhelming. This publication is therefore not only timely but also much needed to help to create a better understanding of the role and function of blended cements, and also thereby facilitate the development of new standards. The volume contains nine papers which were presented at a Symposium held in Denver in June 1984. Of the nine papers, four discuss portland blast furnace slag cements, one, portland fly ash cement, and three, blended cements with slag and pozzolans. The last paper is devoted to the present status of cement standardisation in Europe. The four papers on slags confirm without doubt that when used as an admixture or as a blended cement, it
57
Book reviews
can yield satisfactory concretes with respect to both strength development and durability. The data show that there are differences in performance between slags, and that tests on individual slag and cement mixtures are necessary to establish and characterise slag performance. Both compressive strength and heat of hydration are controlled by a large number of manufacture parameters such as glass content of the slag, grinding fineness and amount of gypsum. On the other hand, resistance to sulphate attack and alkali aggregate reaction is found to be high irrespective of the glass and gypsum contents of the slag and the fineness of the blended cement. It is a pity that with the large amounts of fly ash currently available in the world, there is only one paper devoted to fly ash. Nevertheless, this paper confirms the pozzolanic nature of fly ash. However, it is reported that the addition of fly ash increases the total porosity at early ages whilst after 3 months hydration, both total porosity and pore size distribution are similar to that of OPC paste. Three papers are devoted to blended cements with slag and pozzolans. It is shown that with sufficient cement replacement, the ultimate permeability of a sulphate resistant portland cement paste is greatly reduced. Silica fume was found to be most effective in reducing permeability at early ages. Silica fume was also the most effective in reducing calcium hydroxide contents while slag was the least effective. The results showed no clear correlation between permeability and porosity or pore size parameters alone. Blended cements with controlled particlesize distribution were able to develop properties similar to those of normal concrete. The last paper presents a timely review of cement standardisation in Europe. The author predicts that by the year 2000, the use of blended cements will increase all over the world, and portland cements will eventually come to be regarded as special cements for use where exceptional performance is required. With increasing interest in blended cements the world over, this publication would be of great value to cement producers, concrete technologists~ researchers and students alike. The extensive data on recent research should enable the wider use of mineral admixtures, and the development of appropriate standards for their use to be achieved:
Corrosion of Rebars in Concrete A S T M Special Technical Publication STP 906 Edited by Victor Chaker Published by The American Society for Testing and Materials, 1916 Race Street, Philadelphia PA 19103, USA, 1986. ISBN 0 8031 0468 5, Price: Members £23.00, Others £29.00. Available from A S T M or in Europe from American Technical Publishers Ltd., 68a Wilbury Way, Hitchin, Herts SG4 0TP, U.K. European price £29.00. Corrosion of steel bars in reinforced and prestressed concrete members has become a major world problem.
58
The structures most widely affected are highway bridges exposed to ice, snow and chlorides but others such as prestressed concrete pipes, large span structures and car garages are also equally involved. A great deal of research during the last 2 decades has led to a better understanding of the mechanism of steel corrosion, and particularly to develop monitoring methods and protection of steel bars. This publication makes a distinct and valuable contribution to further this understanding. It contains the papers presented at an ASTM Symposium organised by Committee G-1 on Corrosion of Metals and held in November 1984. The Symposium concentrated on two areas - - Corrosion Effects of Stray Currents and Techniques for Evaluating Rebar Corrosion. On these two subject areas, this volume comprises a unique collection of excellent papers which no engineer, designer and researcher can afford to ignore. Apart from a historical background to the work of Committee G-1 and a summary, there are nine papers included in this volume. An excellent state-of-the-art paper on fundamental studies related to steel corrosion sets the scene for the volume. There are four papers devoted to evaluating steel corrosion. The use of polarisation resistance and impedance methods to determine the corrosion rate of steel embedded in concrete is reported. Reinforced earth systems are also susceptible to corrosion since they contain steel bars, fibres or nets. The results of a field survey concerning corrosion susceptibility of the metallic elements in such systems are described. These data show that both environment and backfill characteristics are of great importance. Marine environments are highly corrosive, for example, and the use of inert materials or materials coated with corrosion resistant substances is recommended. Recently high tensile polymer grids have come into wide use as soil reinforcing elements and their major advantage in being corrosion resistant cannot be over-emphasised. The corrosion problems associated with concrete pipes is reported and the detection of corrosion discussed. Extreme care is shown to be necessary when applying cathodic protection because of the electrical discontinuity between the different segments of the pipes, as well as the different metallic elements that need to be made continuous. The last paper in this group discusses the use of X-ray as a measure of prediction of concrete cracking. Four papers are devoted to protection systems and the effects of stray currents. Tests show that lightning conductor connections influence the corrosion rate, and that artificial lightning and the use of radioactive lightning conductions also accelerate corrosion. An interesting application using the atmospheric charges to protect the rebars from corrosion is reported. A cathodic protection system using a mesh of polymeric anodes to protect the reinforcing steel in a concrete substructure is also described. Chloride-induced corrosion of steel reinforcement is widespread in the construction industry. The addition of a corrosion inhibitor to the concrete mix is reported to offer a practical solution to this problem, and calcium nitrite is shown to be very effective in this way. Tests reported from Greece show that two additives - -