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. Neverth eless, the integrity of this skeleton will gradually break down under incre ased loadings. In cementitious materials this is due to debonding of partic le-matrix interfaces, which leads to crack initiation and propagation in th e so-called interfacial transition zone. The strength of the interfacial tr ansition zone on a structural level is also governed by the density and the uniformity of the packing of (blended) cement particles in the neighbourho od of aggregate surfaces. However, particularly structure-sensitive propert ies like cracking and tensile strength are also, and to a disproportional d egree, influenced by the nonuniformity of the particle packing. This is tru e for microcracking that results from packing discontinuities in the binder near particle interfaces, as well as for engineering cracking at the concr ete element's surfaces due to aggregate-packing discontinuities near the mo uld. The SPACE system (Software Package for the Assessment of Compositional Evolution) has been developed to assess the characteristics of dense rando m-packing situations in opaque materials by a "realistic" structural simula tion. This paper presents a short introduction to the system and deals only with the essential design features. Next, an application addressing the pa rticle-packing problems demonstrates the system's capabilities. (C) 1999 El sevier Science Ltd. All rights reserved.