Revealing the Effect of Irradiation on Cement Hydrates: Evidence of a Topological Self-Organization
Abstract
Reactive MD in LAMMPS with iterative neutron-collision cascades (300 eV PKA, ReaxFF + Manzano parameters) on Pellenq C–S–H models shows radiation-induced self-organization and optimal damage resistance near isostatic Ca/Si ≈ 1.5.
Summary¶
C–S–H models across Ca/Si ratios are prepared from tobermorite-based workflows (GCMC water, ReaxFF relaxation for hydroxylation—see Methods in paper) so that initial silicate chain statistics and pore water content reflect composition before irradiation. Irradiation is modeled with iterative reactive MD in LAMMPS: choose primary knock-on atoms weighted by neutron cross sections (Table 1), impart 300 eV, evolve ballistic cascade with NVE in a 10 Å sphere (variable timestep, max displacement 0.0001 Å per step) and 0.5 fs otherwise for 20 ps; outer shell Berendsen 300 K; post-cascade NPT 300 K, 0 bar for 5 ps; repeat until enthalpy/density saturate. Systems ~6000 atoms with box sizes chosen to avoid cascade self-interaction. ReaxFF parameters from Manzano et al.; ZBL short-range corrections noted unnecessary at this incident energy. Topological constraint theory enumerates rigidity metrics vs composition to connect network connectivity changes to mechanical eigenstress release under damage accumulation.
Methods¶
Force-field training / fitting. Manzano et al. C–S–H ReaxFF with EEM-style charge treatment is used as published (no new QM refit in this ACS Appl. Mater. Interfaces article).
MD application (atomistic dynamics). Engine / code: LAMMPS integrates iterative collision cascades on Pellenq-type C–S–H models prepared with GCMC water and prior ReaxFF relaxation (see article Methods). System size & composition: ~6000-atom cells whose periodic extents are chosen ≥2× the maximum PKA travel distance (per the “avoid self-interaction under periodic boundary conditions” criterion stated in the article). PKA selection: weighted by neutron cross sections (Table 1). Cascade energy: 300 eV per primary knock-on. Spatial partitioning: 10 Å spherical hot core treated in microcanonical (NVE) dynamics with variable timestep (max displacement 0.0001 Å per step) switching to fixed Δt = 0.5 fs outside the high-collision regime; 20 ps ballistic segment. Shell thermostat: atoms outside the sphere held at 300 K with a Berendsen thermostat. Post-cascade relaxation: NPT at 300 K, 0 bar, for 5 ps to allow density adjustment. Iteration: repeat with new PKAs until enthalpy and density saturate. Barostat: N/A — applied only during the short NPT relaxation windows, not during the NVE core cascade. Electric field: N/A — not applied. Enhanced sampling: N/A — direct cascade protocol.
Static QM / DFT. N/A — DFT is not the cascade integrator; DFT enters only indirectly via the Manzano ReaxFF training lineage referenced in the paper.
Review / non-simulation framing. N/A — primary application article (not a review).
Findings¶
Outcomes & mechanisms. C–S–H reorders under accumulated radiation: silicate chain statistics, pore water, and medium-range order shift even though the gel is comparatively radiation-tolerant versus crystalline silicates in their comparison. Topological constraint theory (TCT) links network rigidity changes to stress release; mobile water is argued to facilitate eigenstress relaxation during self-organization.
Comparisons. The manuscript contrasts irradiated vs pristine structures across Ca/Si and against crystalline silicate benchmarks as summarized in the article.
Sensitivity & design levers. Damage resistance vs Ca/Si is non-monotonic, with a highlighted optimum near Ca/Si ≈ 1.5 tied to isostatic rigidity in their TCT analysis.
Limitations & outlook (as authored). 300 eV PKA energy is a modeling choice; C–S–H construction inherits Pellenq-model limitations noted in the article.
Corpus / KB honesty. Protocol details above follow the indexed PDF; use DOI-linked tables for quantitative TCT metrics.
Limitations¶
Model C–S–H construction inherits known limitations of the Pellenq approach; cascade energy fixed at 300 eV.
Relevance to group¶
Uses ReaxFF cement parametrizations central to group-related cement simulations.
Citations and evidence anchors¶
- DOI:
10.1021/acsami.7b09405