Next: Acknowledgements Up: Main Previous: Expansive aggregate
When different parts of the microstructure of a concrete undergo expansive growth, different kinds of stress and displacement patterns result. Many scenarios can be studied with the equations developed in this paper, since eqs. (1)-(7) are completely general for linear, isotropic elastic materials. Viscoelastic effects have been ignored in this paper, though they do play a major role in these kinds of deleterious processes [12,13]. In this paper, the shell phase was not thought of as the interfacial transition zone, but it could be, allowing the interplay between interfacial zone cement paste, bulk cement paste, and aggregate to be studied .
Under the assumptions of this paper, it is clear that uniform, on average, matrix expansion, followed by circumferential cracking between aggregate and matrix due to radial stress in the matrix, will lead to open gaps surrounding the aggregates, whose width is proportional to the aggregate radius. If this circumferential cracking was caused by the expansion of a thin layer located at the interface, like in some models of delayed ettringite formation-induced damage, then the widths of the gaps observed would be proportional to the layer thickness, and not the aggregate radii. Aggregate expansion leads to radial cracking, and so no gaps will appear at all. All these results are of course subject to some modification due to the many aggregates that appear in a real, non-dilute concrete, but the major qualitative differences between the kinds of cracking produced by expansion of different parts of the microstructure will remain the same as those predicted by this simple dilute model . This makes the results of this paper useful for interpreting cracks produced by unknown deleterious processes in field concretes observed under the microscope. Non-spherical aggregate shapes will also not change the qualitative aspects of the problem studied in this paper.