CELLULAR AUTOMATION SIMULATIONS OF CEMENT HYDRATION AND MICROSTRUCTURE DEVELOPMENT

Cellular automaton algorithms, which operate on a starting digital ima ge of a water-cement suspension, are described. The algorithms simulat e the microstructure development process due to hydration reactions th at occur between cement and water. This paper describes the evolution of the cement model from a simple model, which treated the cement part icles as single-phase materials, with a greatly simplified hydration c hemistry, into a model which has many more chemical species and includ es numerous reactions which eventually convert the viscous water-cemen t suspension into a rigid porous solid. Methods are presented for gene rating two- and three-dimensional images representing suspension initi al conditions; these are derived from both micrographs of real cements and computer-based algorithms. The 2D initial images are based on the processing of backscattered electron and x-ray images of real cement suspensions. The 3D images employ either spheres to represent cement p articles, or more realistic randomly shaped particles via an algorithm which smooths and thresholds a 3D lattice whose sites are initially p opulated with random white noise. A convenient measure of the point at which the initial paste turns into a solid material is the percolatio n threshold of the solids. Consideration of these models has already l ed to the prediction and subsequent experimental observation of a shar ply defined onset of shear wave propagation, from ultrasonic measureme nts through hydrating cement slurries. The amount of hydration needed to reach the percolation threshold can be determined in the present si mulations, and our results are compared with time of shear wave onset in actual cement slurries. Variants of the basic model provide insight into both early-time behaviour that is of primary interest to oil wel l cementing and the later-time microstructural properties that are of interest in the construction industry.