Cement and Concrete Research 29 (1999) 1299–1304 0008-8846/99/$ – see front matter © 1999 Elsevier Science Ltd. All rights reserved. PII: S0008-8846(99)00077-0 SPACE system for simulation of aggregated matter application to cement hydration Martijn Stroeven*, Piet Stroeven Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevin Laboratory, Stevinweg 4, 2628 GA Delft, The Netherlands Received 7 January 1999; accepted 10 March 1999 Abstract This paper presents the basic features of the Software Package for the Assessment of Compositional Evolution (SPACE). SPACE consists of a two-stage simulation strategy, providing successively for the three-dimensional packing of a particulate system and the struc- tural evolution, the latter representing a sintering, foaming, or hydrating particulate system. Hence, SPACE has versatile potentialities. The initial distribution results from a generation process in which a predefined number of particles are dynamically mixed using a Newto- nian motion model. Bulk material and interfaces can be simulated. The results obtained have been demonstrated to be realistic. Next, this paper deals with the simulation of cement hydration as an illustrative application of the SPACE system. The model starts with a simulated spatial distribution of anhydrous cement particles in a water-filled volume and simulates the hydration process through a series of rela- tively simple growth rules, which are iterated many times. The kinetic hydration model used here is similar to one used by van Breugel. The chemical reaction between cement and water results in expansion of the particle and in the formation of multiple contacts with other hydrating particles. The effects of this interparticle contact as well as the effect of water consumption on the hydration and expansion rate have been explicitly accounted for, with the aid of a surface sampling method that can efficiently evaluate the degree of contact between particles. Results from various numerical experiments will show the microstructural development in bulk and in the interfacial zone. © 1999 Elsevier Science Ltd. All rights reserved. Keywords: Hydration; Kinetics; Interfacial transition zone; Microstructure; Particle size distribution 1. Introduction The interest in particle packing arises in different areas in engineering. This interest can be explained in that a large proportion of natural and manufactured materials we deal with are, or contain, aggregates of several shapes and sizes. “Particles” are conceived in these fields as aggregate grains, minerals, metal or chemical powders, soils, molecules, pores, or rocks. The behaviour of such materials depends partly on the properties of the composing parts of the mate- rial body and partly on their interaction pattern. Some com- posite properties are structure insensitive, but most proper- ties are structure sensitive, thereby reflecting the underlying internal particulate structure. For example, in concrete, damage evolution as observed at a mesoscale is governed to a large extent by the granular aggregate structure. It is generally accepted that the zone around aggregates in the cementitious matrix is the weakest in the mechanical system. Because the aggregate constitutes a dense random packing, it yields as a consequence a dense network of weak interfaces. Obviously, loading the material body results in a cracking behaviour that is governed by the aggregate skeleton. At the same time, on a microscale, fresh cement paste can be considered a granular mixture of cement particles in water. Evaluation of the cement structure and hydration pro- cess in the interfacial zone (ITZ) around aggregates can lead to an improved understanding of the material behaviour, not only at a microlevel but on higher levels as well. For opaque materials such as concrete, it would require some effort to acquire this sort of structural information in an experimental way, such as by using microtomography [1]. The approach that aims to simulate the hydration of ce- ment paste is presented in this paper. A model is introduced that simulates the granular structure of fresh cement at the microlevel as a spatial distribution of spherical (cement) particles diluted in an aqueous matrix. An iterative algo- rithm simulates the mixing process of the ingredients by specifying the mechanical behaviour of each element when contact occurs with other objects and by relating the ele- ment’s dynamic behaviour with respect to external forces. Until a desired distribution has been obtained the elements are presumed chemically inactive. When the hydration pro- * Corresponding author. fax: 31-15-2611465. E-mail address: m.stroeven@ct.tudelft.nl (M. Stroeven)