Layered double hydroxides-based binders: Performance, reaction mechanism, and thermodynamic modelling

The commercial viability of alkali-activated materials remains fundamentally constrained by the high variability and limited availability of traditional aluminosilicate precursors. Addressing this critical barrier requires the utilization of widely accessible, consistent feedstocks. Herein, we report the development of a novel layered double hydroxide (LDH)-based binder utilizing limestone powder (LP) as the primary precursor . This study presents the first systematic, year-long comparative investigation of binders incorporating monocarboaluminate (MCA-LDH) versus hydrotalcite (HT-LDH). An LP activated with sodium aluminate (NaAlO 2 ) solution produced an MCA-LDH binder with compressive strengths ranging from 23 to 78 MPa after one year, depending on the alkali dosage. Crucially, the substitution of 30 vol% of LP with reactive magnesia fundamentally altered the phase assemblage, suppressing MCA-LDH formation and promoting the development of the stable HT-LDH phase, a finding consistent with thermodynamic predictions and microstructural analysis. The long-term performance data reveal significant structural degradation in the MCA-LDH crystalline lattice over time, contrasting sharply with the superior stability of HT-LDH. It was found that the formation of pirssonite (Na 2 CO 3 ⋅CaCO 3 ⋅2H 2 O) is the primary mechanism driving the detrimental decrease in water availability and subsequent MCA-LDH crystalline deformation. This work, supported by integrated thermodynamic modeling, establishes a robust theoretical framework for elucidating the long-term phase transformation kinetics, and provides essential guidance for the design of durable LP-based alkali-activated systems.