A multi-scale approach for percolation transition and its application to cement setting.

Area of Science:

• Materials Science
• Chemical Engineering
• Physics

Background:

• Cement setting is a critical phenomenon in construction materials.
• It involves the formation of nanoscale hydration products (calcium-silicate-hydrates) that bridge cement grains.
• The transition from a fluid paste to a solid is understood as a percolation process, but bridging micro- and nano-scales has been challenging.

Purpose of the Study:

• To develop a multi-scale model that bridges the gap between cement grain (micron) and nano-hydrate (nanoscale) levels.
• To investigate cement setting as an off-lattice bond percolation process.
• To determine the critical threshold for cement setting and the role of nano-texture.

Main Methods:

• Development of a multi-scale model integrating micron-scale cement grains and nanoscale hydration products.
• Modeling cement setting as an off-lattice bond percolation process.
• Utilizing a kinetic Monte Carlo Nucleation and Growth model to simulate nano-hydrate formation within local observation windows.

Main Results:

• The study identifies cement setting as a percolation phenomenon requiring only a small fraction (~12%) of bonds between cement grains.
• This finding highlights the crucial role of nano-texture in achieving macroscopic setting.
• Simulations indicate that this low hydrate amount is minimally affected by water-to-cement ratio and nonreactive fillers.

Conclusions:

• A predictive theory of cement setting is now feasible by integrating multi-scale information.
• The nano-texture of hydration products is essential for understanding and predicting cement setting.
• Experimental verification supports the model's counter-intuitive predictions regarding the low bond requirement for setting.