This section identifies best practices in materials selection that may be influenced by coastal processes. The material guidance included in this section would apply to various TxDOT infrastructure projects, including pavements, facilities, ferries, drainage structures, bridges, etc. Besides typical design factors such as traffic loading and subgrade soil characteristics, infrastructure located within coastal areas can be subject to additional effects such as saltwater intrusion, uplift from storm surges, and rapid drawdowns.

Infrastructure’s exposure to saltwater can lead to serious damage and drastically reduce the design life of infrastructure if not considered in the design. It is recommended the designer consult guidance on material selection for infrastructure that could encounter this environment.

Infrastructure including, but not limited to, drainage structures, bridge piles, and guard rails may need to consider saltwater influence when choosing the most appropriate material. For example, for bridge piles located in saltwater environments, marine grade steel is recommended (USACE New Orleans District, 2012).

The U.S. Army Corps of Engineers provides guidance on materials selection for various infrastructure and coastal conditions.

Similar to all typical pavements, coastal pavements can be categorized into rigid and flexible pavement types. Rigid pavements are composed of a stiff Portland Cement Concrete (PCC) surface, while flexible pavements consist of bendable surfaces, such as asphalt. Common to both pavement types are base courses and subbase courses, consisting typically of aggregate materials. All pavement sections are supported by a subgrade, which usually entails the existing ground formation. Pavement type, including future maintenance (of joints, materials, etc.), will primarily be determined by the transportation design (e.g., loading, traffic), but coastal impacts should also be considered.

The general impact of saltwater intrusion on pavements is the effect of corrosion, and pavement materials must be selected to counteract this factor. For PCC pavements, the primary element susceptible to corrosion is any steel reinforcement contained within, as well as any steel dowels used at the joints. One way to afford corrosion protection is by using corrosion-resistant materials for reinforcement and dowels. Alternatively, plastic fiber reinforcement, which is not subject to oxidation, may be used as a form of reinforcement. Improvements to the PCC mix design itself can also provide enhanced protection from saltwater, such as by using sulfate resistant cement and by reducing the permeability of concrete through the use pozzolans, including fly ash, slag cements, and silica fume. Another consideration during pavement design is increasing the concrete thickness over reinforcing bars to provide additional protection.

Asphalt surfaces are not significantly affected by saltwater corrosion. Generally, a dense-graded asphalt mixture with low porosity is recommended for pavement construction. A soft asphalt binder is preferred so that a longer service life to hardening under saline attack is obtained. Additionally, eliminating the use of moisture-susceptible aggregates and anti-stripping agents can minimize moisture damage of the asphalt mixture in general.