Any mechanism for salt scaling must account for the many characteristics elucidated by hundreds of experimental and field investigations over the last 60 years. A number of experimental procedures have been employed to gauge the ability of a concrete mixture to resist salt scaling. Fortunately, the differences in the three main techniques are negligible. Therefore, data from all procedures are used to identify underlying trends. The basic technique for quantifying resistance to salt scaling consists of pooling a moderately concentrated salt solution on the surface of a cementitious slab. The depth of the solution, and thickness of the slab are roughly 6 mm and >75 mm, respectively. This system is then subjected to daily freeze thaw cycles, where the temperature is lowered to -20°C over a period of 4 - 8 hr., then held at this minimum temperature for a period of 3 - 6 hr., and finally thawed at room temperature. The amount of damage is quantified periodically by monitoring a change in the dynamic elastic modulus of the slab as well as measuring the mass of material removed from the surface. The mass loss is normalized by the area of the surface tested.
Figure 1 - Schematic of the ASTM C672 Procedure for determining the ability of a concrete mixture to resist damage from salt
Chapter 2 (Request this document) of my Ph. D thesis consists of a survey of the Salt Scaling studies performed over the past 60 years. This extensive review elucidated the following characteristics of salt scaling
- 1) Salt Scaling consists of the progressive removal of small flakes or chips of binder
- 2) A pessimum exists at a solute concentration of ~ 3%, independent of the solute used.
- 3) No scaling occurs when the pool of solution is missing from the concrete surface.
- 4) No damage occurs when the minimum temperature is held above -10°C; the amount of damage increases as the minimum temperature decreases below -10°C and with longer time at the minimum temperature.
- 5) Air entrainment improves salt scaling resistance.
- 6) The salt concentration of the pool on the surface is more important than the salt concentration in the pore solution.
- 7) Susceptibility to salt scaling is not correlated with susceptibility to internal frost action.
- 8) The strength of the surface governs the ability of a cementitious body to resist salt scaling.