Actions during service 117
(ITZ) contribute to cavitation damage. As soon as cavitation erosion has
been initiated, the erosion rate will increase due to the increasing roughness
of the surface and thus the increased promotion of cavitation. Significant
damage can occur, possibly leading to complete failure of the structure as
illustrated by the 1983 spillway tunnel failure at the Glen Canyon Dam in
Arizona.
Increasing the concrete strength will increase the resistance against cavitation erosion. However, a strong concrete surface is not necessarily sufficient to mitigate cavitation damage, because even steel is typically damaged
by this phenomenon (as clearly noticeable on pumps and marine propellers). Avoidance of cavitation erosion can be best obtained by an adequate
design of the hydraulic structure, keeping pressures high and fluid velocities low. More detailed information can be found in the report of ACI
Committee 210 (2003).
5.2.4.2 Erosion by abrasion
In order to clean concrete surfaces, e.g. in view of some rehabilitation activities, sand blasting is a very popular technique. Sand particles are projected
onto the concrete surface, either in dry form or in suspension. Their abrasive action removes a thin layer of material including dirt particles, leaving
a very clean and nice concrete surface. Abrasion is a very efficient cleaning
technique when performed in a controlled way. However, the same abrasive action can severely damage concrete structures when performed in a
non-controlled way: erosion by abrasion. Not only sand particles can cause
abrasion. As mentioned in the definition, all solids, whether in dry state or
in suspension, can contribute to abrasion. This includes traffic on roads and
even pedestrians on walkways or in corridors (see Figure 5.13).
Besides roads, walkways, and stairs which are typical cases showing
dry abrasion erosion, spillways, basins, sluiceways, drainage conduits, and
tunnel linings are typical hydraulic structures showing abrasion by waterborne solids. In the case of hydraulic structures, abrasion erosion can be
combined with cavitation erosion (see Section 5.2.4.1). In severe cases, the
abrasion erosion can range in depth from a few centimetres to a few metres,
depending on the flow conditions. Some remarkable examples are shown in
the report of ACI Committee 210 (2003).
The abrasive erosion rate is influenced by several parameters. A first list of
parameters relates to the eroding particles: size, shape, quantity, hardness,
and velocity. A second list relates to the concrete quality: strength, porosity, water content, aggregate content, aggregate type, and curing. Papenfus
(2003) schematically gives a very detailed list of the various influencing factors. More practically, several authors mention that a minimum compressive strength of 28 MPa (400 psi) should be considered to obtain abrasion
resistant concrete surfaces (Mehta and Monteiro 2006). Liu et al. (2006)
(ITZ) contribute to cavitation damage. As soon as cavitation erosion has
been initiated, the erosion rate will increase due to the increasing roughness
of the surface and thus the increased promotion of cavitation. Significant
damage can occur, possibly leading to complete failure of the structure as
illustrated by the 1983 spillway tunnel failure at the Glen Canyon Dam in
Arizona.
Increasing the concrete strength will increase the resistance against cavitation erosion. However, a strong concrete surface is not necessarily sufficient to mitigate cavitation damage, because even steel is typically damaged
by this phenomenon (as clearly noticeable on pumps and marine propellers). Avoidance of cavitation erosion can be best obtained by an adequate
design of the hydraulic structure, keeping pressures high and fluid velocities low. More detailed information can be found in the report of ACI
Committee 210 (2003).
5.2.4.2 Erosion by abrasion
In order to clean concrete surfaces, e.g. in view of some rehabilitation activities, sand blasting is a very popular technique. Sand particles are projected
onto the concrete surface, either in dry form or in suspension. Their abrasive action removes a thin layer of material including dirt particles, leaving
a very clean and nice concrete surface. Abrasion is a very efficient cleaning
technique when performed in a controlled way. However, the same abrasive action can severely damage concrete structures when performed in a
non-controlled way: erosion by abrasion. Not only sand particles can cause
abrasion. As mentioned in the definition, all solids, whether in dry state or
in suspension, can contribute to abrasion. This includes traffic on roads and
even pedestrians on walkways or in corridors (see Figure 5.13).
Besides roads, walkways, and stairs which are typical cases showing
dry abrasion erosion, spillways, basins, sluiceways, drainage conduits, and
tunnel linings are typical hydraulic structures showing abrasion by waterborne solids. In the case of hydraulic structures, abrasion erosion can be
combined with cavitation erosion (see Section 5.2.4.1). In severe cases, the
abrasion erosion can range in depth from a few centimetres to a few metres,
depending on the flow conditions. Some remarkable examples are shown in
the report of ACI Committee 210 (2003).
The abrasive erosion rate is influenced by several parameters. A first list of
parameters relates to the eroding particles: size, shape, quantity, hardness,
and velocity. A second list relates to the concrete quality: strength, porosity, water content, aggregate content, aggregate type, and curing. Papenfus
(2003) schematically gives a very detailed list of the various influencing factors. More practically, several authors mention that a minimum compressive strength of 28 MPa (400 psi) should be considered to obtain abrasion
resistant concrete surfaces (Mehta and Monteiro 2006). Liu et al. (2006)