3D experimental investigation of the microstructure of cement pastes using synchrotron X-ray microtomography (μCT) E. Gallucci a, ⁎ , K. Scrivener a , A. Groso b , M. Stampanoni b , G. Margaritondo c a Laboratory of Construction Materials, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Switzerland b Swiss Light Source, Paul Sherrer Institute, CH-5232-Villigen, Switzerland c Laboratoire de Spectroscopie Electronique, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Switzerland Received 3 May 2005; accepted 23 October 2006 Abstract Cement pastes aged from 1 to 60 days were studied using synchrotron microtomography on the MS-X04SA beam line at the Swiss Light Source. This allowed three dimensional images to be obtained with a resolution approaching that of backscattered electron images in the SEM. From these images, several features can be extracted and studied, both quantitatively and morphologically. In this study, attention was focused on the reacting anhydrous cement grains and porosity. Three dimensional imaging of capillary porosity allowed the connectivity and tortuosity of the pore network to be studied. It is shown that the degree of connectivity of the pore network is very sensitive to both the spatial resolution of the images and the evolution of contrast resolution during ageing of the cement. © 2006 Elsevier Ltd. All rights reserved. Keywords: D—cement paste; B—microstructure; B—synchrotron microtomography; B—image analysis 1. Introduction The performance of cement pastes and concretes is controlled by their microstructure, in particular the pore network plays a critical role in determining mechanical properties and interactions with the environment which determine durability. This latter aspect is the focus of considerable research effort. The challenge is to predict the performance of concrete over the lifetime of a structure which is a minimum of several decades and increasingly over a century for the most important struc- tures. For other applications, such as waste disposal, time scales of more than one thousand years must be considered. In order to extrapolate from short term laboratory testing, models of performance must be underpinned by a detailed understanding of the transport mechanisms whereby species from the environment (e.g. Cl - , SO 4 2- ions, CO 2 ) penetrate into the con- crete. In this regard the connectivity of the capillary pore struc- ture is central. The porosity of cement extends over a wide range of length scales, classically this is divided into: – so-called ‘gel-pores’ which are intrinsic to the C-S-H product. This porosity lies in the range of a few nanometres and due to this small size plays only a minor role in transport processes affecting durability and other aspects of performance. – capillary pores corresponding to the originally water filled spaces not filled by hydration products, the size of these ranges from a few nanometres to tens of micrometers, i.e. more than 4 orders of magnitude, – air voids, from tens of μm to mm in size are heterogeneities of the original mix. They are a small fraction of the whole porosity and as they are isolated have a minor role on overall transport processes. The voids in hollow shells or the gaps between unreacted grains and C-S-H shells that are observed in cement pastes may also be considered as porosity although it is not clear to what extent these voids are connected to the capillary pore network [1]. Hence capillary porosity of cement pastes is the main factor affecting the performance of cementitious materials. A large, Cement and Concrete Research 37 (2007) 360 – 368 ⁎ Corresponding author. E-mail address: emmanuel.gallucci@epfl.ch (E. Gallucci). 0008-8846/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2006.10.012