Al-driven cement functionality by manifold structuring & disorder

doi:10.1039/D5MA00244C

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Al-driven cement functionality by manifold structuring & disorder

2025-10-16

DOI：10.1039/D5MA00244C

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Cementitious calcium–silicate–hydrate (C–S–H) gel structures with differing aluminium (Al) content and structuring were characterised by a series of ab initio molecular dynamics (AIMD) experiments. Differing Al-binding modes and coordinations (4; 5; 6) were incorporated into dynamic simulations of various C–S–H bulk structures (layered; non-layered; anhydrous porous; hydrated porous) to resolve Al's configurational preference as well as any effects on Si/Al chain structure; including Lowenstein type ‘Al-avoidance’ (preference for non-neighbouring Al atoms) and Pore sizes. Emphasis was placed on modelling fault lines in C–(A–)S–H structures; where local order is thought to be lost. These regions tend to have high concentrations of micro stresses that potentially induce crack propagation and would thus possibly benefit from Al-toughening. Principal aspects of Loewenstein's Al avoidance are not operative in the majority of cases; with alternating Al atoms increasing chain length and branching giving rise to larger pores. O–Al–O and Al–O–Al bond angles were shown to be more flexible than their Si counterparts (O–Si–O; Si–O–Si); the former Al-units effectively acting as atomic hinge points. Al-coordination was shown to shift dynamically throughout each simulation; generally occupying tetrahedral Al-IV geometry with some preference for penta-coordinated Al-V at Q2 and Q3 sites. Loewenstein's principle of opposite coordination modes for adjacent Al are observed; specifically; Al neighbours will seldom hold the same coordination geometry. Through this approach we have demonstrated structuring of C–(A–)S–H containing stable hydrated pores; in agreement with experimental trends arising from empirical NMR and small angle neutron scattering (SANS) measurements in established works.

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