# Freezing point depression and freeze-thaw damage by nano-fuidic salt trapping

## TL;DR

This paper introduces a nanofluidic salt trapping mechanism that explains freeze-thaw damage in concrete and biological cryo-tolerance, emphasizing ion confinement and pressure effects over traditional expansion models.

## Contribution

It proposes a novel nanofluidic salt trapping theory that accounts for freeze-thaw damage and cryo-tolerance, challenging existing explanations based on water expansion.

## Key findings

- Salt trapping lowers freezing point but causes high disjoining pressures.
- Ice nucleation in charged pores leads to pressure buildup until salt removal occurs.
- The model predicts non-monotonic damage dependence on salt concentration.

## Abstract

A remarkable variety of organisms and wet materials are able to endure temperatures far below the freezing point of bulk water. Cryo-tolerance in biology is usually attributed to "anti-freeze" proteins, and yet massive supercooling ($< -40^\circ$C) is also possible in porous media containing only simple aqueous electrolytes. For concrete pavements, the common wisdom is that freeze-thaw damage results from the expansion of water upon freezing, but this cannot explain the large pressures ($> 10$~MPa) required to damage concrete, the observed correlation between pavement damage and de-icing salts, or the damage of cement paste loaded with benzene (which contracts upon freezing). In this Letter, we propose a different mechanism -- nanofluidic salt trapping -- which can explain the observations, using simple mathematical models of dissolved ions confined to thin liquid films between growing ice and charged surfaces. Although trapped salt lowers the freezing point, ice nucleation in charged pores causes enormous disjoining pressures via the rejected ions, until their removal by precipitation or surface adsorption at a lower temperatures releases the pressure and allows complete freezing. The theory is able to predict the non-monotonic salt-concentration dependence of freeze-thaw damage in concreter and provides a general framework to understand the origins of cryo-tolerance.