I thank H. Saleh for supplying the x-ray tomographic image from which the real aggregate images were taken, and K. Snyder for generating the visualizations of the two particles in Figs. 12 and 13. Useful conversations are acknowledged with M. Taylor, N. Martys, R. Livingston, and J. Douglas. I also acknowledge the partial support of the Virtual Cement and Concrete Testing Laboratory industrial consortium.