116 Damage to concrete structures
that the degree of carbonation can reach values of 60% after 30 years
(Matsushita et al. 2004a), which explains why carbonation is one of the
most harmful factors affecting the durability of AAC.
5.2.4 erosion
ACI Committee 210 (2003) defines erosion as the progressive disintegration of a solid by cavitation, abrasion, or chemical action. The committeee
further explains that cavitation erosion results from the collapse of vapour
bubbles formed by pressure changes within a high-velocity water flow,
while abrasion erosion is caused by water-transported silt, sand, gravel, ice,
or debris. Mehta and Monteiro (2006) consider the general term surface
wear for the progressive loss of mass from a concrete surface due to abrasion, erosion, and cavitation. With abrasion, they refer to dry addition as
in the case of wear on pavements and industrial floors by vehicular traffic.
The term erosion is used to describe wear by the abrasive action of fluids containing solid particles in suspension. While the definitions of abrasion and erosion seem to be different in these two references, Mehta and
Monteiro (2006) follow the same meaning of cavitation as given by ACI
Committee 210 (2003).
In this book, we will consider erosion as the progressive loss of mass
from a concrete surface due to cavitation or abrasion. Chemical actions will
be considered separately (see Section 5.3). With abrasion, we understand
the erosive action by solids, whether in dry state or in suspension. Both
forms of erosion considered here, namely cavitation and abrasion, will be
further explained in the following sub-sections.
5.2.4.1 Erosion by cavitation
According to Moskvin (1978), ‘cavitation takes place in a fast fluid as a
consequence of a decrease in pressure. Disturbance of the continuity in
a stream of water is accompanied by the formation of small and then of
larger vapour-filled cavities. Upon sudden collapse of these cavities as a
result of a rapid change in external pressure, a large impact pressure is
created. If a collapse of the cavities occurs on or near the surface of a solid
body, the forces are transmitted to it, which if frequently recurring, can
cause pitting of the surface material’. Two main parameters seem to influence the problem of cavitation; namely the velocity of the fluid and the
roughness of the surface. A higher roughness promotes cavitation, as is the
case for a higher fluid velocity.
Since the aggregate particles are typically harder than the mortar matrix,
cavitation erosion initially shows a clear tendency to follow the mortar
matrix, after which the aggregate particles are undermined (ACI Committee
210, 2003). Microcracks in the matrix and in the interfacial transition zone
that the degree of carbonation can reach values of 60% after 30 years
(Matsushita et al. 2004a), which explains why carbonation is one of the
most harmful factors affecting the durability of AAC.
5.2.4 erosion
ACI Committee 210 (2003) defines erosion as the progressive disintegration of a solid by cavitation, abrasion, or chemical action. The committeee
further explains that cavitation erosion results from the collapse of vapour
bubbles formed by pressure changes within a high-velocity water flow,
while abrasion erosion is caused by water-transported silt, sand, gravel, ice,
or debris. Mehta and Monteiro (2006) consider the general term surface
wear for the progressive loss of mass from a concrete surface due to abrasion, erosion, and cavitation. With abrasion, they refer to dry addition as
in the case of wear on pavements and industrial floors by vehicular traffic.
The term erosion is used to describe wear by the abrasive action of fluids containing solid particles in suspension. While the definitions of abrasion and erosion seem to be different in these two references, Mehta and
Monteiro (2006) follow the same meaning of cavitation as given by ACI
Committee 210 (2003).
In this book, we will consider erosion as the progressive loss of mass
from a concrete surface due to cavitation or abrasion. Chemical actions will
be considered separately (see Section 5.3). With abrasion, we understand
the erosive action by solids, whether in dry state or in suspension. Both
forms of erosion considered here, namely cavitation and abrasion, will be
further explained in the following sub-sections.
5.2.4.1 Erosion by cavitation
According to Moskvin (1978), ‘cavitation takes place in a fast fluid as a
consequence of a decrease in pressure. Disturbance of the continuity in
a stream of water is accompanied by the formation of small and then of
larger vapour-filled cavities. Upon sudden collapse of these cavities as a
result of a rapid change in external pressure, a large impact pressure is
created. If a collapse of the cavities occurs on or near the surface of a solid
body, the forces are transmitted to it, which if frequently recurring, can
cause pitting of the surface material’. Two main parameters seem to influence the problem of cavitation; namely the velocity of the fluid and the
roughness of the surface. A higher roughness promotes cavitation, as is the
case for a higher fluid velocity.
Since the aggregate particles are typically harder than the mortar matrix,
cavitation erosion initially shows a clear tendency to follow the mortar
matrix, after which the aggregate particles are undermined (ACI Committee
210, 2003). Microcracks in the matrix and in the interfacial transition zone