Do Crushing Operations Influence the Results of Accelerated Expansion Laboratory Tests?

The most common standards ruling the assessment of the potential reactivity of aggregates consider that the petrographic analysis should be followed, in the first step, by accelerated mortar-bar tests and, in case of a positive result, by concrete-prism tests. However, experience has shown that these different approaches often provide contradictory results in the classification of an aggregate as innocuous or potentially reactive. Discussion about the inaccuracy of the accelerated mortar-bar test for some slow reactive aggregates has been puzzling the scientific community and some explanations have been suggested to explain this fact. In the present work, deformed rocks used as aggregates, previously submitted to accelerated mortar-bar tests and to concrete-prism tests, are analyzed regarding different grain sizes. The research aims to define the role of crushing mechanisms in the destruction of crystals originated from sub-graining, due to tectonic deformation, during the production of the smaller particles requested by the mortar-bar test. With this purpose, the petrographic analysis of the rocks selected, and their correspondent sand size aggregates has been done using the image-based open software JMicrovision.