Interplay between FIB processing, microstructure, and micromechanics in cement pastes

This article investigates the interplay between microstructure, focused ion beam (FIB) micro-beam preparation, and micromechanical properties of cement pastes derived from Portland cement CEM I-42.5R. It identifies and quantifies the effects of gallium FIB processing on individual cement phases, including inner and outer hydration products, Portlandite, and residual clinker. A detailed methodology is presented for preparing cantilever micro-beams, emphasizing critical steps such as phase selection, imaging, ion milling, transport, and mechanical testing. Several adverse factors are identified: continuous electron beam imaging increases surface roughness and reduces tensile strength; high ion beam currents ( > 1 nA under the given experimental configuration and FIB settings) cause local heating, leading to water evaporation, densification, and phase transformations in C–S–H gels and Portlandite. Additional challenges include ion beam drift, which distorts beam geometry, and vacuum-induced moisture cycling, which promotes micro-cracking. Best practices are proposed to mitigate these issues, including the use of low ion beam currents (0.2–1 nA), minimized electron beam exposure, stable environmental control to prevent moisture cycling, and careful phase selection. The article provides examples of both good and incorrect practices, offering practical guidelines for reliable FIB-based micromechanical testing of cement pastes. • FIB enables precise micro-beam fabrication for cement micromechanics. • Improper FIB settings cause surface damage and change in phase properties. • Drift, high electron or ion load, degrade micro-beam geometry and tensile strength. • Best practices provided mitigate errors in bending and fracture tests.