The micro-mechanical reinforcement mechanism of alkali-activated cement by CLDH seeding: a cross-scale investigation

Blast furnace slag-based alkali-activated cements (AACs) can develop low stiffness and significant deformation compared to Portland cement due to amorphous nature of its reaction products. This study evaluates the effectiveness of a calcined layered double hydroxide (CLDH) as a seeding material to regulate the phase assemblage and micromechanical performance of AACs composites. Results demonstrate that CLDH particles act as nucleation seeds accelerating reacting kinetics inducing the formation of an aluminum substituted calcium silicate hydrate gel (C-A-S-H gel) highly intermixed with a Mg-Al LDH type phase (Ht). This composite phase presents higher elastic modulus compared to samples without CLDH. The addition of CLDH led to microstructure densification and improved homogeneity, and reduced adhesion forces. These microstructure features led to higher compressive strength and enhanced volume stability in CLDH-composite AACs, demonstrating a strong link between microstructural refinement and macroscopic behavior. This study reveals that phase engineering via the addition of CLDH seeding is an effective approach for tailoring the nanostructure and micromechanical performance of AACs. By establishing a clear mechanistic link between CLDH seeding, C-A-S-H/Ht nanocomposite formation, and the resulting improvements in micromechanical properties, and macroscopic performance, this study provides both a viable strategy for enhancing the volume stability of alkali-activated materials and a transferable methodological framework for evaluating nanoscale seeding effects in cementitious systems.