Nanotechnology and Cementitious Materials K.L. Scrivener 1 Abstract. The relevance of nanotechnology and more specifically nanoscience to cementitious materials is discussed. Some examples are given of the influence of nanosciences on our understanding of cementitious materials and its impact on the applications of these materials. 1 Introduction In recent years notechnology has become THE buzz word. In this article I discuss the relevance of nanotechnology to cementitious materials – the most used materi- als on the planet. To start with some definition – everyone now knows that nano means very small and more specifically phenomena in the range below 100 nm. We can be perhaps identify 3 main strands of nanotechnology: 1. Top-down approaches - seek to create smaller devices by using larger ones to direct their assembly. This applies mainly to technologies descended from conventional solid-state silicon methods for fabricating microprocessors, which are now capable of creating features smaller than 100 nm 2. Bottom-up approaches - seek to arrange smaller components into more complex assemblies. Sophisticated examples include the manipulation of base pairs to construct structures out of DNA, but extend to approaches from the field of "classical" chemical synthesis aimed at designing molecules with well-defined shape. [1] 3. Nanoscience – the term nanotechnology is also used to refer simply to the study of materials at the nanoscale, usually referring to the use of advanced characterization techniques and atomistic or molecular level modeling. Therefore it is clear that “nanotechnology” is becoming a catch all phrase to re- fer to studies which would previous have been considered as branches of chemis- try of materials science. In this respect nanotechnology (strands 2 & 3) has an K.L. Scrivener Ecole Polytechnique Féderale de Lausanne, EPFL, Switzerland e-mail : karen.scrivener@epfl.ch