Materials Performance

OCT 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 104 of 138

OCTOBER 2018 WWW.MATERIALSPERFORMANCE.COM 16 The VDOT system calls for the use of SS on bridges with higher volumes of traffic, and other corrosion-resistant alloys on bridges with lower volumes of traffic. Primarily the main urban bridges, which are high-volume traffic bridges, are constructed of materials with the highest corrosion resistance because these bridges are exposed to more deicing salts. In the more rural areas, the steel used is always alloyed for corrosion resistance, but is not as corrosion resistant. If a contractor is doing design work for VDOT, Sharp comments, they can look at the VDOT road and bridge specifications and determine which corro- sion-resistant materials should be used for components depending on the functional classification of the bridge being built. For example, Class III cor- rosion-resistant reinforcing steel is used for bridges on freeways as well as principal arterial roads in both urban and rural locations, while Class I corro- sion-resistant reinforcing steel is specified for local roads and streets in both urban and rural areas. The VDOT also started using carbon fiber reinforced polymer (CFRP) high- strength strand for some reinforced concrete structures, such as beams and piles. "If a pile is going to be placed in salt or brackish water, that is where we moved toward using materials such as CFRP, which is considered to be corro- sion free," Sharp explains. "It's increasing the cost of building that element, but the additional initial cost will be recaptured in time as now you have a high-quality material there." Additionally, VDOT uses supplementary cementitious materials such as fly ash, granulated blast-furnace slag, and silica fume—compared to some of the older concretes used that were standard cement mixtures—to increase the durability of the concrete as well as decrease the permeability of the concrete to curb the ingress of chlorides. Since future corrosion can be a significant problem and present a great expense for new structures, FDOT focuses on corrosion prevention by using materials and construction methods that will significantly delay the onset of corrosion on any portion of the bridge. This includes using high-performance concrete and increasing the concrete cover over the rebar so that it will take longer for chlorides to penetrate to the depth of the rebar, as well as using innovative materials. On many new structures being built in corrosive envi- ronments, FDOT is using highly corrosion-resistant rebar such as SS, GFRP, and CFRP to ensure that it attains at least 75 years of corrosion-free service from its structures and most probably 100 years. CFRP is placed in a precast beam before concrete is added. Photo courtesy of Stephen Sharp, VDOT. Corrosion-resistant ASTM A1035 steel has been placed in the deck of Route 123 Bridge over the Occoquan River in Virginia and the construction crew is placing concrete. Photo courtesy of Stephen Sharp, VDOT.

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