MATERIALS ENGINEERING CONCEPTS - Materials for Civil and Construction Engineers - page 25

1.3.3 Surface Characteristics
The surface properties of materials of interest to civil engineers include cor-
rosion and degradation, the ability of the material to resist abrasion and
wear, and surface texture.

Corrosion and Degradation Nearly all materials deteriorate over their service
lives. The mechanisms contributing to the deterioration of a material differ
depending on the characteristics of the material and the environment. Crys-
talline materials, such as metals and ceramics, deteriorate through a corrosion
process in which there is a loss of material, either by dissolution or by the
formation of nonmetallic scale or film. Polymers, such as asphalt, deterio-
rate by degradation of the material, including the effects of solvent and ul-
traviolet radiation on the material.
The protection of materials from environmental degradation is an im-
portant design concern, especially when the implications of deterioration
and degradation on the life and maintenance costs of the structure are con-
sidered. The selection of a material should consider both how the material
will react with the environment and the cost of preventing the resulting
degradation.

Abrasion and Wear Resistance Since most structures in civil engineering are
static, the abrasion or wear resistance is of less importance than in other
fields of engineering. For example, mechanical engineers must be concerned
with the wear of parts in the design of machinery. This is not to say that
wear resistance can be totally ignored in civil engineering. Pavements must
be designed to resist the wear and polishing from vehicle tires in order to
provide adequate skid resistance for braking and turning. Resistance to
abrasion and wear is, therefore, an important property of aggregates used in
pavements.

Surface Texture The surface texture of some materials and structures is of
importance to civil engineers. For example, smooth texture of aggregate par-
ticles is needed in portland cement concrete to improve workability during
mixing and placing. In contrast, rough texture of aggregate particles is need-
ed in asphalt concrete mixtures to provide a stable pavement layer that re-
sists deformation under the action of load. Also, a certain level of surface
texture is needed in the pavement surface to provide adequate friction re-
sistance and prevent skidding of vehicles when the pavement is wet.

1.4 Production and Construction

Even if a material is well suited to a specific application, production and
construction considerations may block the selection of the material. Produc-
tion considerations include the availability of the material and the ability