Multi-technique and multi-scale approach applied to study the structural behavior of heterogeneous materials: natural SiO₂ case

Abstract

A multi-technique and multi-scale approach have been initiated to study the structural properties of a natural heterogeneous material. This approach has led us to introduce the concepts of long-range order LRO and short-range order SRO. The correlation between these concepts has enabled us to advance in the comprehension of the mechanisms of degradation of natural SiO₂ aggregate submitted to the process of the alkali–silica reaction (ASR). On LRO scale, the structural changes of the aggregate are revealed by the reduction of the size of grains, which means that the attack starts by affecting amorphous and poorly crystallized zones. This phenomenon generates the formation of very unstable amorphous and nanocrystallized products, which take part in the degradation of the aggregate. On SRO scale tetrahedral environment of silicon atoms is preserved in spite of the introduction of OH^- ions with a relaxation phenomenon. The second layer of coordination around silicon remains almost unchanged. These results add new information showing that ASR must be considered as a multi-scale process. The methodology itself may be extended to other problems.