Migmatitic gneiss aggregates: Compositional, mechanical, and morphological responses to innate heterogeneity

Abstract

Abstract Migmatites are hybrid rocks composed of a mixture of metamorphic and igneous lithotypes. This feature can induce marked physical and mechanical variability in aggregates' technological properties, which may affect the performance and durability of structures constructed using these aggregate rocks. However, previous studies have not addressed the technological properties of the migmatite components. This pioneering study explores heterogenous migmatitic gneiss aggregates including their composition, petrography, mechanical degradation, strength, and particle morphology. After stockpile sampling, five distinct lithotypes were identified in addition to the migmatitic gneiss itself: paleosome, melanosome, leucosome, granitoid, and pegmatite. Subsequently, the aggregates were subjected to a geological evaluation and were characterized based on their physical and mechanical properties. A morphological evaluation was conducted via digital image processing of aggregates before and after Los Angeles and micro-Deval tests. The proportion of igneous materials (leucosome, pegmatite, and granitoid) varied according to the aggregate particle size, suggesting that the suitability of these aggregates may vary depending on their intended application. Melanosome and leucosome lithotypes presented antagonistic compositional, physical, mechanical, and morphological behavior. Among particle morphological parameters, surface texture best described the migmatite gneiss heterogeneity, which was closely related to intrinsic rock properties. The degradation analysis associated with digital image processing allowed to evaluate the main degradation mechanism to which aggregates are exposed in each test. Thus, this research highlights the need to determine the composition of aggregates produced from migmatites and the characteristics of their components to properly evaluate their behavior in construction applications.