Hydrated Calcium Silicate Erosion in Sulfate Environments a Molecular Dynamics Simulation Study

Area of Science:

• Materials Science
• Chemistry
• Geochemistry

Background:

• Hydrated calcium silicate (C-S-H gel) is a key component in cementitious materials.
• Sulfate attack is a major degradation mechanism for concrete and other silicate-based materials.
• Understanding the micro-mechanism of C-S-H gel erosion in sulfate environments is crucial for material durability.

Purpose of the Study:

• To investigate the micro-mechanism of C-S-H gel erosion in sodium sulfate solutions.
• To elucidate the interaction mechanism between sulfate ions and C-S-H gel at the molecular level.
• To correlate ion transport and C-S-H gel structural changes with erosion progression.

Main Methods:

• Development of a solid-liquid molecular dynamics model for C-S-H gel/sodium sulfate.
• Simulation of ion transport at varying sodium sulfate concentrations (5%, 8%, 10%).
• Scanning electron microscopy (SEM) to analyze micro-morphology of eroded samples.

Main Results:

• Increased Na2SO4 concentration enhances C-S-H ion adsorption capacity.
• Sulfate ions promote C-S-H decalcification, forming gypsum and ettringite (AFt).
• Sulfate attack accelerates C-S-H hydrolysis, increasing Na+ and Ca2+ diffusion and exacerbating erosion.
• Na+ exhibits strong, stable adsorption on C-S-H pore surfaces via Na-Os bonds.
• Sulfate ions migrate faster with water molecules, intensifying corrosion.

Conclusions:

• Sulfate ion ingress and adsorption are key drivers of C-S-H gel erosion.
• The formation of gypsum and ettringite, coupled with accelerated hydrolysis, significantly degrades C-S-H structure.
• Molecular dynamics simulations provide valuable insights into the complex interactions governing sulfate attack on C-S-H gel.