Unveiling nanomechanical and pore-structural evolution of bio-precipitate arrays in heterogeneous granular media

Abstract

Biologically induced reactions in granular media (geomaterials) often rely on precipitates from enzymes or microbes to promote the formation of mineral precipitate crystals in its pores. However, there is a major knowledge gap in understanding the hypotheses behind the mechanisms of how, where, and when these biomineralization reactions influence the microbial or enzymatic precipitate growth in heterogeneous granular media, and its impact on its material properties at the pore scale. In this regard, we propose to identify the complex spatio-temporal mechanisms controlling enzymatic (EP) and microbial (MP) precipitates, the temporal distribution patterns (arrays) in heterogeneous granular media (rocks), and quantify the resultant alterations in its nanomechanical signatures due to enzymatic- or microbial-induced reactions. The rock material specimens were incubated with enzymes and microbial species followed by quantitatively analyzing their modified nanomechanical properties (Young's modulus, E; fracture toughness, KIC; hardness, H) and pore volume in addition to characterizing the nano-to-micro-structure. Analysis of the results reveals that bio-precipitates can occlude the nano-and-micro-pores in specimens with reduced pore volume (MP:12.4 %; EP:48.8 %), thereby yielding beneficial nanomechanical alterations (MP: +21.2 % H, +16 % E, +41.3 % KIC; EP: +38.5 % H, +17 % E, +22.2 % KIC) depending on distinct conditions of the bio-precipitated reactions. Looking forward, this work provides a blueprint for the rational design of inherently-heterogeneous granular media with further enhanced biomimicry toward more innovative and environmentally friendly solutions in natural and built infrastructure.