Concrete is a mixture of cement, water, fine and coarse aggregate (sand and gravel) and chemical additives. Changing the proportion of ingredients in the concrete recipe can add strength or durability but also can increase costs or reduce workability. The National Institute of Standards and Technology set up the Virtual Cement and Concrete Testing Laboratory to predict the behavior of concrete using computer models and visualizations like this one.
National Institute of Standards and Technology: W.L. George, N.S. Martys, J. Lancien, S.G. Satterfield, M. Olano, E. Garboczi and J. Terrill