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Production of Portland cement is responsible for about seven percent of the world's greenhouse gas emissions. The pressure to make the production of concrete more sustainable, or \"greener\", is considerable and increasing. This requires a wholesale shift in processes, materials and methods in the concrete industry. Pure Portland cement will need to be replaced by more complex binary, tertiary or even quaternary binders, including other types of cementitious materials. We can expect an increasing use of high performance concrete, primarily because of its high sustainability and durability. Much more attention will have to be paid to the proper curing of the concrete if we want to improve its life expectancy. Presenting the latest advances in the science of concrete, this book focuses particularly on sustainability, durability, and economy. It explores the potential for increased sustainability in concrete from the initial mixing right through to its behaviour in complex structures exposed to different types of loads and aggressive environments.

Science and Technology of Concrete Admixtures presents admixtures from both a theoretical and practical point-of-view.The authors emphasize key concepts that can be used to better understand the working mechanisms of these products by presenting a concise overview on the fundamental behavior of Portland cement and hydraulic binders as well as.

It is suggested that high performance concrete is not fundamentally different from the concrete used in the past, although it usually contains fly ash, ground granulated blastfurnace slag and silica fume, as well as superplasticizer. The cost aspects of the use of silica fume are considered. The content of cementitious material is high and the water/cement ratio is low; the maximum size of aggregate is small. Although ordinary Portland cement is used, it must be compatible with a given superplasticizer; the causes of incompatibility are discussed. The distinct shrinkage behaviour of high performance concrete is considered and the reasons for an absolute necessity of wet curing are given. Some uses of high performance concrete are mentioned. A 'prediction' of the future of high performance concrete and of concrete in general is offered.[PUBLICATION ABSTRACT]

Internal curing is promoted as a way to mitigate autogenous shrinkage in high-performance concrete having a low water-binder ratio (w/b). Different methods of internal curing have been proposed. In this study, the effect of substituting 20% of normalweight sand by an equal mass of lightweight sand on the development of shrinkage was investigated on a 0.35 w/b high-performance concrete. Shrinkage was monitored using vibrating wire gauges cast at the center of 100 × 100 × 400 mm (4 × 4 × 16 in.) concrete samples. Two samples were sealed with self-adhesive aluminum foil to represent a closed curing system without any exchange of humidity between the concrete and its environment. After demolding at the age of 23 to 25 hours, two other samples were cured under water for 6 days. Thereafter, these two samples were removed from water and maintained at 23 °C (73 °F) and a 50% relative humidity (RH) environment. Experimental results clearly demonstrate the efficiency of a 20% substitution of normalweight by a lightweight sand to reduce autogenous and drying shrinkage. The incorporation of 20% lightweight sand did not significantly affect the 28-day compressive strength. The cementitious matrix presented low chloride ion permeability. Internal curing through the use of partial replacement of normalweight sand by lightweight sand definitely represents an efficient method to diminish autogenous and drying shrinkage in low w/b concretes where external water curing does not allow in-depth curing of concrete. [PUBLICATION ABSTRACT]

To lower the carbon footprint of concrete structures, blended cements are increasingly replacing ordinary portland cements in North America. The environmental gains are significant, as the substitution of each kilogram of portland cement clinker results in a decrease of about 0.8 kg (1.8 lb) of CO2 emissions associated with cement production. Blended cements (binders) contain fillers or supplementary cementitious materials (SCMs), which are less reactive than the portland cement, change the hydration process, and thus reduce the early compressive strengths. There are at least two different ways to increase the early compressive strength of blended cements. The chemical approach consists of increasing the fineness of the cement and the content of C3S and C3A in the clinker. This approach solves the short-term strength problem, but it does not improve the long-term strength of blended cements; it may also lead to less durable concretes.

For each tonne of cement used, the cement industry emits an average of 0.9 t of CO sub(2), which contributes to the greenhouse effect. To satisfy the demands of the concrete industry for cementing materials, new environmental requirements, and the implementation of a sustainable development policy, the use of supplementary cementitious material as a replacement of part of the Portland cement has proven to be an interesting avenue that has not yet been fully explored. Granulated blast-furnace slag has been and is being used as a supplementary cementitious material in replacement of cement in many countries. In Canada, its proportion is usually limited to 20-25% of cement replacement owing to a significant decrease in early age compressive strength as well as a lower scaling resistance. In this study, we have tried to show that by reducing the water:cement ratio we can increase cement replacement by slag up to 50% without harming its short-term compressive strength and scaling resistance. The concretes that were prepared had a workability comparable to that of the reference concrete without slag, sufficient compressive strength to allow demoulding after 24 h, very low chloride ion permeability even at 28 d, as well as very good freeze-thaw and scaling resistance, as long as it is water-cured for a slightly longer period.Original Abstract: A chaque tonne de ciment produite, une cimenterie moderne emet en moyenne 0,9 t de CO sub(2). Pour satisfaire les besoins en beton et les nouvelles exigences environnementales resultant de la mise en application du Protocole de Kyoto, tout en mettant en oeuvre une politique de developpement durable, l'utilisation d'ajouts mineraux s'avere une avenue interessante qui n'a pas ete encore exploitee a son plein potentiel. le laitier de haut fourneau broye a deja ete et est utilise comme ajout mineral dans de nombreux pays, et au Canada ou son dosage est habituellement limite a entre 20 et 25 % en remplacement de ciment a cause d'une diminution significative de la resistance initiale et de la resistance a l'ecaillage. Nous avons voulu montrer qu'en abaissant le rapport eau/liant (E/L) du beton, nous pouvons augmenter le taux de remplacement du ciment par du laitier jusqu'a 50 %, sans nuire a la resistance a court terme du beton et a sa resistance a l'ecail lage. Les betons que nous avons prepares avaient une maniabilite comparable a celle d'un beton de reference qui ne contenait pas de laitier, une resistance en compression suffisante pour permettre leur decoffrage a 24 h, une tres faible permeabilite aux ions chlore, ainsi qu'une bonne resistance au gel-degel et a l'ecaillage a condition d'etre muris a l'eau un peu plus longtemps.

The binder is one of the two most important components of concrete because, along with water, through the w/b ratio, it influences essentially all of the mechanical properties of both fresh and hardened concrete, and its durability. Since the sustainability of concrete must now be improved, it is no longer possible to continue to produce concrete as was done during the twentieth century, when short-term profit was the only driving force. It is essential to put into practice all of the knowledge available to minimize the waste of materials and the emission of greenhouse gases, mainly CO2 associated with the production and use of concrete.

In most text books, creep is associated with shrinkage, creep being the volumetric contraction associated with the application of a constant load, while shrinkage is the volumetric contraction associated with a non-loaded specimen of concrete.We have deliberately excluded creep from this chapter, in spite of its great importance in practical applications in pre-stressed and post-tensioned structural elements because:• This book is essentially a “materials” book and not a “structures” book. • The physico-chemical phenomena that explain creep are still the subjectof considerable scientific debate. However, nano-indentation tests (Acker et al., 2004) have clearly shown that the movement of water in C-S-H under the application of a constant load is somehow involved in creep.

Those who have already read the book High Performance Concrete (Aïtcin, 1998) will think that it is madness for us to start this book as well with a chapter devoted to terminology and definitions. In 1998, Aïtcin wrote:Discussions on terminology are tricky and can be endless but it must be admitted that often the quality of the information in a technical book is diminished by the lack of consensus on the exact meaning of the terms used. The author makes no claim for the superiority of the terminology he uses; he wants only to make clear the exact meaning of the terms he employs. The reader is free to disagree with the pertinence and the validity of the proposed terminology but, by accepting it momentarily, he will better understand the concepts and values expressed in this book. The acceptance of these definitions is essential to make the most of reading this book. As stated by A.M. Neville “The choice of one term over another is purely a personal preference and does not imply a greater accuracy of definition”.

In recent years, we have learned how to produce a remarkable range of concrete products: ultra-high strength concrete, self-compacting concretes, corrosion inhibiting concretes, “tough” concretes (with the addition of fibres), and now even sustainable concretes. In fact, we can now largely “tailor-make” concretes for virtually any project. However, in our approach to mixture proportioning, we still rely largely on prescriptive specifications, such as those described in Chapter 14. That is, specifications that generally include requirements such as maximum w/b ratios, minimum cement contents, cement types, limitations on the types and/or amounts of both chemical and mineral admixtures, on the amount of filler material in the cement, and so on. These types of specifications have served us reasonably well in the past, when the cement and concrete industries as a whole were much less sophisticated than they are now. However, such specifications also tend to inhibit the most efficient use of the materials now available to make up a concrete mixture.