Long-Term Thinking Yields Innovative Wharf Topping

Typically wharves and piers handling container and break bulk cargo utilize asphalt pavement for the wearing surface. Top picks, RTGs, straddle carriers, and Taylor Lifts typically wear out these asphalt surfaces with surprising speed. It is not uncommon to see rutting and potholes developing within the first year of a new terminal's operation, especially in the rain saturated Pacific Northwest. The Port of Tacoma typically spends an estimated $400,000 on annual maintenance for asphalt paved cargo facilities. In some cases due to repetitive loading from cargo handling equipment, resurfacing is required every five to seven years on wharf and pier facilities. This activity is not only costly, but creates significant disruption to the busy terminal's operations. When designing the new East Blair One Wharf facility, the Port of Tacoma was interested in comparing the life-cycle cost of asphalt versus concrete wearing surfaces. Initial studies were conducted comparing the costs and expected life cycles of the two materials. The Port evaluated the alternatives and decided to design the new wharf structure to accommodate an asphalt topping surface with a bid alternate of a concrete topping surface. Once the bids were received and the contractor was selected, the Port ultimately decided to pay the higher initial up-front cost and install a concrete topping for the wharf's wearing surface. This paper will discuss the following aspects of the topping slab: • Costs — Comparing initial estimates to final construction costs and expected life-cycle costs. • Technical Aspects — Discussion of design criteria to mitigate shrinkage cracking, minimize damage due to heavy equipment loads and adhesion to precast concrete structural deck panels. • Constructability — Implementation of the contractor's work plan in conformance with the design requirements.