A package of computer programs for simulating the microstructure of a three-dimensional cubic volume of concrete has been developed. A three-dimensional representation of microstructure is necessary for the computation of percolation and physical properties for comparison to experiment. Concrete nominally consists of air voids and aggregates (rocks and sand) dispersed in cement paste (cement + water + admixtures). However, its microstructure is complicated by the presence of an interfacial transition zone (ITZ) present at each aggregate (air void)-cement paste interface. The ITZ cement paste generally has a different microstructure and different material properties than the bulk paste. Fortunately, the literature contains a composite material model, the so-called hard core/soft shell (HCSS) core particles located in a homogeneous matrix, each particle being surrounded by a concentric soft shell (equivalent to the ITZ regions). The hard core particles can not overlap one another, but the soft shells are allowed to overlap each other and the hard core particles.
At NIST, we have developed a set of computer programs to simulate the microstructure of a 3-D cubic volume of hard core/soft shell particles randomly placed in a bulk matrix. While developed specifically to model the microstructure of concrete, these programs have also found ready application to macro-defect-free cements, analysis of air void distributions in concrete, and nanometer-scale modelling of the calcium silicate hydrate gel present in cement paste. These programs are described in detail in section 2 of the user's manual provided on the right.