Sound barriers are constructed to protect noise sensitive areas from noise pollution.  The most common application of sound barrier walls is to insulate residential communities from highway noise, although they are also installed along railways and around industrial work areas for similar reasons. They can also be used outside specific building locations to dampen the sounds of pad-mounted mechanical equipment, such as air conditioners.  Sound barrier walls and noise pollution regulations came with increased vehicle traffic and greater public awareness in the 1970’s.  Today, for example, the National Environmental Policy Act of 1970 still requires a noise analysis and barrier wall construction effort, if necessary, as part of federally funded highway projects.   A more recent concern of sound barrier walls is that they be aesthetically pleasing and blend well within existing landscapes and communities.

Retaining walls contain soils and hold them in place behind the inside face of a vertical (wall) structure. Retaining walls are installed when a large shift in a site’s grade elevation is desired in a very short distance, in some cases for aesthetic reasons. Since the soils contained behind the wall are trapped at a nearly vertical angle, depending on the height of the wall and the soils there can be tremendous soil pressures present which must be carefully designed for. Additionally, any loads on top of the soils contained behind the wall (known as a surcharge), such as paving or other site improvements, will contribute to an even greater loading on a retaining wall structure. Moisture content and adequate drainage of the retained soils is also an important consideration.

Brick unit paving offers an aesthetically pleasing alternative to traditional concrete and asphalt materials, when moderate traffic loads allow its use.  In the most common brick unit paving construction method, individual bricks are abutted on a bed of compacted sand over a granular base course.  These layers (or courses) are constructed upon prepared foundational soils known as the subgrade, and are contained within a framework of edge restraints.

Portland cement concrete paving is also referred to as rigid paving. Concrete pavement is supported by a base layer of compacted aggregates or treated soils, which is in turn placed upon the foundational subgrade soils of the prepared roadbed. If two base layers are utilized, they are referred to as the base and sub-base layers (or courses). Rigid (concrete) pavement differs from flexible (asphalt) pavement in that rigid pavement is designed to carry traffic loads within the pavement layer itself.

The main objective of concrete base courses is to regulate moisture, preventing the types of damage common to rigid pavement systems. Load transfer concerns, which can necessitate some base course applications, is less of an issue for rigid pavement.  Aggregate base courses for rigid (concrete) and flexible (asphalt) pavements are discussed in article 32.11.23.

An aggregate base course is the layer of soil installed between the surface pavement layer and subgrade (foundation soils) of either flexible (asphalt) or rigid (concrete) pavement. Their purpose is to help transition surface loads from the pavement to the subgrade, evenly support the pavement surface profile, and protect the overall pavement system from water intrusion and deformation. While these objectives of base course layers are applicable to both types of pavements, load transfer is a more focused design consideration for flexible pavement, while moisture control is a priority for rigid pavement designs. Concrete base courses are further discussed in Article 32.11.36.

Asphalt surface treatments refer to the reconditioning of the wearing (surface) course of older existing asphalt pavements. The term may also be applied to the final phases of new asphalt pavement construction. (Article 32.12.16 discusses Asphalt Paving).

Surface treatments provide enhanced waterproofing of the pavement, prevent the raveling (detachment and loss) of the fine aggregates (i.e. sand) from within the surface course of the pavement, smooth out existing surface imperfections, and provide improved skid resistance for vehicle traffic. Asphalt surface treatments are nominally less than an inch thick.