MgO-Based Expansive Agents in Cementitious Materials

Magnesium oxide (MgO)-based expansive agents have emerged as a strategic means to mitigate shrinkage and cracking in cementitious systems by generating controlled volumetric expansion during hydration. Upon addition to Portland or blended cements, reactive MgO hydrates to brucite (Mg(OH)₂), inducing internal stress that offsets tensile strains arising from drying and thermal variations. The expansion kinetics are governed by the intrinsic reactivity of MgO, particle size distribution and dosage, which together determine the timing and magnitude of volume change. High-reactivity MgO yields early expansion beneficial for countering plastic shrinkage, whereas lower-reactivity forms impart long-term compensation against autogenous and drying shrinkage. The interplay between MgO hydration and pore structure evolution also influences mechanical performance and durability, with optimal dosages refining microstructural connectivity and reducing permeability without unduly compromising strength. Practical applications span mass concrete in dams, bridge decks and high-performance hydraulic structures, where tailored MgO formulations can be blended or combined with fibres and supplementary cementitious materials to achieve self-compacting, crack-resistant composites. The global impetus to reduce lifecycle carbon emissions further underscores the appeal of MgO as a dual-function additive, offering both expansion control and potential carbonation uptake over service life.

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MgO-Based Expansive Agents in Cementitious Materials publication trend

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Technical terms

Cementitious materials: Mixtures that harden by hydration, encompassing Portland cement, supplementary binders and additives.

Reactive MgO: Magnesium oxide with high surface area and low calcination temperature, prone to rapid hydration and early expansion.

Hydration: Chemical reaction between cementitious phases and water, forming binding products such as calcium-silicate-hydrate and brucite.

Brucite: The crystalline product Mg(OH)₂ formed during MgO hydration, whose growth exerts expansion pressure.

Pore structure: Distribution and connectivity of capillary and gel pores within hardened cement paste, influencing strength and transport.

Autogenous shrinkage: Volume reduction caused by self-desiccation in low-water-to-cement systems, mitigated by MgO expansion.

References

1. Influence of MgO on the Hydration and Shrinkage Behavior of Low Heat Portland Cement-Based Materials via Pore Structural and Fractal Analysis. Fractal and Fractional (2022).
2. Pore Structural and Fractal Analysis of the Effects of MgO Reactivity and Dosage on Permeability and F–T Resistance of Concrete. Fractal and Fractional (2022).
3. Hydration and durability of low-heat cementitious composites for dam concrete: Thermodynamic modeling and experiments. Frontiers in Materials (2023).