Pore damage in cementitious binders caused by deicer salt frost exposure

• Deicer salt scaling is a result of excessive ice-growth in capillary pores.
• Ice-growth causes a substantial apparent pore volume increase in scaled materials.
• A conceptual scaling model is proposed.
• A mathematical description of sorptivity is derived from pore size distribution.

Pore structure measurements on scaled-off materials from concrete specimens subjected to deicer salt frost exposure and on the control mortar samples were undertaken in order to better understand the causes for deicer salt scaling. Nitrogen sorption isotherms were obtained and the results clearly demonstrate that pore damage is severe with an increase in apparent capillary porosity of over 50%. This is strong evidence of excessive pore pressure due to ice-growth within the surface region, which is promoted by the additional liquid present in the salt solution on concrete surface. The 3-D pore stresses in the surface zone result in residual compressive stresses within the two confined directions (length and width) and a net tensile stress in the unconfined direction. This stress state causes “popout” of the cement paste. Ice nucleation and associated growth is controlled by paste pore structure that governs the rate of liquid transport by suction. Effective means of mitigating deicer salt scaling are: reduction in paste porosity by lowering water-binder (w/b) ratio or by means of pozzolanic reactions; utilization of hydrophobic surface treatment using silanes. A refined sorptivity model is presented to evaluate the scaling resistance of concrete.