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As a consequence of the spatial evolution of the freezing temperature, the
top layer and a more inward layer of the concrete can be frozen, while in
an intermediate layer the water (salt solution) will still be liquid. When the
temperature further drops, this intermediate layer can also start freezing.
However, following the hydraulic pressure theory, at this stage the hydraulic pressure cannot be relaxed because the water cannot enter the already
frozen top and bottom layers. As a result, the already frozen top layer will
be (locally) pushed off, causing a scaling damage pattern.
5.2.2.1.2 Glue spall theory
By compiling a critical review of the research concerning salt frost scaling,
Valenza and Scherer (2007a) concluded that the salt concentration of the
salty water layer on the concrete surface is more important than the salt
concentration in the pore solution. Furthermore, a pessimum exists at a
solute concentration of about 3% and no scaling occurs when the pool of
solution is missing from the concrete surface. Valenza and Scherer (2007a)
also conclude that the susceptibility to salt scaling is not correlated with
the susceptibility to internal frost action, and that the ability to resist salt
scaling is rather determined by the strength of the concrete surface. These
findings cannot be explained by previously mentioned theories. As a result,
the glue spall mechanism was proposed as the primary cause of salt scaling
(Valenza 2005, Valenza and Scherer 2007b, Sun and Scherer 2010).
Due to the application of de-icing salts, a small layer of salt solution is
formed on the horizontal concrete surface. When this solution layer freezes, it
turns into a solid material. Upon further cooling, the thermal contraction of
the ice layer is about five times higher than the thermal contraction of the concrete due to the large difference in the thermal expansion coefficient between
ice (about 50.10 −6 /°C) and concrete (about 10.10 −6 /°C). The larger thermal
contraction of the ice layer is restrained by the concrete substrate, causing tensile stresses within the ice layer. Depending on the salt concentration, cracks
will occur in the ice layer. Following the principles of fracture mechanics, it
can be shown that the cracks in the ice layer can penetrate into the concrete
substrate, where they will bifurcate into a path parallel to the concrete surface
(see Figure 5.10). As a result, small flakes will be removed from the concrete
surface, leading to the well-known salt scaling damage pattern.
Following the glue spalling theory, salt scaling is an almost purely
mechanical phenomenon involving issues of restraint (the thermal deformations of the ice layer are restrained by the concrete substrate) and fracture
mechanics (cracks will occur in the ice layer, will propagate into the concrete substrate, and will bifurcate into a path parallel to the surface). Some
physical issues also play a role, because the freezing temperature and the
mechanical properties of the frozen solution depend on the salt concentration. Pure water ice is not expected to crack, brine ice formed from solutions
As a consequence of the spatial evolution of the freezing temperature, the
top layer and a more inward layer of the concrete can be frozen, while in
an intermediate layer the water (salt solution) will still be liquid. When the
temperature further drops, this intermediate layer can also start freezing.
However, following the hydraulic pressure theory, at this stage the hydraulic pressure cannot be relaxed because the water cannot enter the already
frozen top and bottom layers. As a result, the already frozen top layer will
be (locally) pushed off, causing a scaling damage pattern.
5.2.2.1.2 Glue spall theory
By compiling a critical review of the research concerning salt frost scaling,
Valenza and Scherer (2007a) concluded that the salt concentration of the
salty water layer on the concrete surface is more important than the salt
concentration in the pore solution. Furthermore, a pessimum exists at a
solute concentration of about 3% and no scaling occurs when the pool of
solution is missing from the concrete surface. Valenza and Scherer (2007a)
also conclude that the susceptibility to salt scaling is not correlated with
the susceptibility to internal frost action, and that the ability to resist salt
scaling is rather determined by the strength of the concrete surface. These
findings cannot be explained by previously mentioned theories. As a result,
the glue spall mechanism was proposed as the primary cause of salt scaling
(Valenza 2005, Valenza and Scherer 2007b, Sun and Scherer 2010).
Due to the application of de-icing salts, a small layer of salt solution is
formed on the horizontal concrete surface. When this solution layer freezes, it
turns into a solid material. Upon further cooling, the thermal contraction of
the ice layer is about five times higher than the thermal contraction of the concrete due to the large difference in the thermal expansion coefficient between
ice (about 50.10 −6 /°C) and concrete (about 10.10 −6 /°C). The larger thermal
contraction of the ice layer is restrained by the concrete substrate, causing tensile stresses within the ice layer. Depending on the salt concentration, cracks
will occur in the ice layer. Following the principles of fracture mechanics, it
can be shown that the cracks in the ice layer can penetrate into the concrete
substrate, where they will bifurcate into a path parallel to the concrete surface
(see Figure 5.10). As a result, small flakes will be removed from the concrete
surface, leading to the well-known salt scaling damage pattern.
Following the glue spalling theory, salt scaling is an almost purely
mechanical phenomenon involving issues of restraint (the thermal deformations of the ice layer are restrained by the concrete substrate) and fracture
mechanics (cracks will occur in the ice layer, will propagate into the concrete substrate, and will bifurcate into a path parallel to the surface). Some
physical issues also play a role, because the freezing temperature and the
mechanical properties of the frozen solution depend on the salt concentration. Pure water ice is not expected to crack, brine ice formed from solutions