Role of meso-porous MgAl-LDH nanorods in the hydrothermal alkali activation of slag binders: Mechanical integrity and thermal stability

This study investigates the role of structurally tailored MgAl–CO 3 layered double hydroxide (LDH) nanorods, synthesized through a cost-efficient coprecipitation method, in enhancing the performance of alkali-activated slag (AAS) under severe curing and thermal conditions. The synthesized LDH nanorods exhibited ultrafine size (∼5 nm), high surface area (63.1 m 2 /g), and low crystallinity, features that have not been previously combined in LDHs used for AAS modification. LDH additions (0–2 wt.%) were incorporated into AAS activated with 5 wt% NaOH to evaluate effects on setting behavior, compressive strength, pore structure, phase evolution, and thermal resistance. Increasing LDH content prolonged final setting time by 20–75 min. A 1 wt% dosage produced the best mechanical response, raising compressive strength from 32 to 40 MPa at 1 day and from 56 to 72 MPa at 28 days. Hydrothermal curing at 145 °C for 4 h yielded high-strength composites, reaching 80 MPa for the 1 wt% LDH mixture. This mixture also retained the highest residual strengths after heating to 250, 500, and 750 °C. Characterization results (XRD, FTIR, SEM/EDX, BET/BJH) confirmed that LDH nanorods significantly refined the mesoporous network and promoted the formation of well-crystallized CSH, CAH, CASH, zeolitic phases, and Mg-modified hydrates, collectively explaining the improved mechanical and thermal performance. The findings highlight that introducing engineered LDH nanorods with controlled morphology and low crystallinity offers a novel strategy to optimize AAS matrices, especially for precast or thermally stressed applications.