Assessment of packing characteristics by computer simulation

Most relevant engineering mechanical properties of normal concretes such as compressive strength are to a large extent governed by the density and the uniformity of the aggregate packing as the load-bearing structure. Nevertheless, the integrity of this skeleton will gradually break down under increased loadings. In cementitious materials this is due to debonding of particle-matrix interfaces, which leads to crack initiation and propagation in the so-called interfacial transition zone. The strength of the interfacial transition zone on a structural level is also governed by the density and the uniformity of the packing of (blended) cement particles in the neighbourhood of aggregate surfaces. However, particularly structure-sensitive properties like cracking and tensile strength are also, and to a disproportional degree, influenced by the nonuniformity of the particle packing. This is true for microcracking that results from packing discontinuities in the binder near particle interfaces, as well as for engineering cracking at the concrete element's surfaces due to aggregate-packing discontinuities near the mould. The SPACE system (Software Package for the Assessment of Compositional Evolution) has been developed to assess the characteristics of dense random-packing situations in opaque materials by a "realistic" structural simulation. This paper presents a short introduction to the system and deals only with the essential design features. Next, an application addressing the particle-packing problems demonstrates the system's capabilities. (C) 1999 Elsevier Science Ltd. All rights reserved.