Self-Compacting Concrete


Introduction

Self-compacting concretes (SCCs), highly fluid concretes placed without vibration, were introduced into French construction works towards the end of the 1990s. The concept came into being a decade earlier in Prof. Okumara’s laboratory [OKA 00] in Japan. The high seismicity of this geographical region requires the use of high levels of steel reinforcement in construction. The use of “self-compacting” concretes appeared as a solution to improve the filling up of zones which are not very accessible to conventional methods of concrete compaction. This solution also has the advantage of overcoming the gradual decline in the number of workers qualified to handle and place concrete.




In France, SCC was initially of interest to the precast concrete and ready mix concrete industries, and in the construction industry, well before project managers and contracting authorities became interested in it [CIM 03]. The use of SCC enables improvements in productivity through reductions in manpower and placing delays. It also improves quality through a better filling of the formwork, better coating of the steel reinforcement, even a better facing. Finally, and undeniably their best asset, SCCs reduce the difficulty of the work. By preventing vibration, the health effects of concrete construction disappear (white hand syndrome, hearing loss, noise disturbances for the

x Self-Compacting Concrete

neighbors). Little by little, SCCs have also won over architects by offering them the possibility of playing with complex volumes.


Even though SCCs have established their position in the prefabrication industry (around half of the volume produced), SCCs used in situ are struggling to make an impact on construction sites, in France as well as in other countries [SHA 07]. Despite their numerous advantages, SCCs represent less than 3% of ready mix concrete produced in France [BTP 07]. Several factors lend themselves to explaining this slow expansion of SCCs [CUS 07]. Firstly, making SCCs is somewhat difficult, since the components must be of a good quality and have little variation in their properties. While the properties of fresh vibrated concretes are affected relatively little by normal variations in the components (size distribution, water content, etc.), SCCs, on the other hand, are much more sensitive. Secondly, the production tool is not always precise enough for making concretes which are strongly affected by errors in the mixture proportions. Thirdly, the formworks must be well prepared, properly waterproofed and must, above all, be able to withstand pressures that are a priori higher than those involved in handling vibrated concretes.


However, SCCs have the potential of continuing to expand. To begin with, the standardizing framework, which had previously been vague in Europe, was enforced in June 2010 with the release of the EN 206-9 standard which brought in rules for production, handling, and specific controls for SCC, complementing EN 206-1. SCCs are becoming widespread elsewhere by strengthening the dialog – which is truly indispensable – between construction agents, owners, project managers, architects, businesses and suppliers, and also research laboratories. SCCs, complex and innovating materials, have been the object of a real infatuation by researchers the world over. As a witness to this success, international conferences have been dedicated

to SCCs since 1999 [SCC 99]. Today the extent of the research allows us to have a better understanding of the behavior of these concretes.


The objective of this book is therefore to disseminate knowledge acquired by recent research in order to enable the student, the technician, or the engineer who reads it, to develop an understanding of the formulation of these materials. The composition of SCCs must satisfy several criteria. In addition, different authors have endeavored to reply to each of the questions posed in the following chapters, without losing sight of the global objective of techno-economical optimization.


Chapter 1 is dedicated to rheology and concrete casting. Theoretical concepts are presented and useful experimental tools for characterizing the behavior of these complex mixtures are described. Experimental data also shows the range of variability and the influence of the principal formulation parameters.


Chapter 2 enables the reader to understand the specifics of the behavior of SCCs at early ages. This behavior, which is strongly influenced by the particular formulations of SCCs, is characterized by vulnerability to desiccation and the resultant strains.

Chapter 3 focuses on the mechanical and delayed behaviors of SCCs in comparison with ordinary derivative concretes. This aspect is crucial for designing selfcompacting

concrete pieces.


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