Steel deck corrosion

Steel Deck Corrosion under Phenolic Roof Insulation. Phenolic foam roof insulation (PFRI) was hailed as the next panacea of roofing in the 1980s, as it had all the desired qualities of ideal roof insulation. It exhibited exceptional insulation with no thermal drift, great dimensional stability and easily passed fire resistance tests [1]. However, severe steel deck corrosion was observed as soon as three years after commercial PFRI was installed on some steel decks. 

PLATE 8 Corrosion is a chemical process whose results are easy to see in the world around us. In this picture, corrosion of reinforcing steel has caused the conerete pillars to spall, weakening the bridge and forcing the installation of wooden joists to temporarily support the bridge deck structure. The results of corrosion impose significant economic costs on society—in 1982, these eosts were estimated at about 120 billion. Courtesy, Robert Baboian, Texas Instruments, Inc. 

The screen deck may be made from woven or welded steel wire mesh with square apertures. Such decks have a high proportion of open area and are relatively inexpensive. However, they have a low resistance to wear and corrosion and produce high noise levels when vibrated. Woven wire decks with rectangular apertures are sometimes used to reduce pegging. 

Punched steel plates are very robust, but have a low proportion of open area. They are often used for screening larger sizes of stone and in trommel screens (see section 5.5.2.3), where robustness is important. Increasingly, moulded decks made from rubber or polymers (e.g. polyurethane) are used because of their resistance to wear and corrosion, and their surface properties which reduce blinding and noise emission. Their disadvantages are higher initial cost and a lower proportion of open area. 

Minimum deck thickness is usually 14 gage (0.0747 in) for corrosion-resistant alloys and 10 gage (0.1345 in) for carbon steel (88, 137, 211, 399). The latter typically provides a corrosion allowance of 64 in for the top side or bottom side (137). A corrosion allowance of Vie in is recommended for major support beams constructed from carbon steel none is usually required for alloy construction (399). 

Linear polarization resistance (LPR). These measurements allow the actual corrosion rate of embedded probes or of the reinforcing bars to be monitored over time. The measurement principle is described in Section 16.2.3. In addition to the reference electrode a counter-electrode of a corrosion resistant material (e. g. stainless steel or activated titanium) has to be embedded. Several compact LPR sensor systems were developed and installed in structures such as precast deck elements in a road tunnel [6,20]. When existing structures have to be monitored for corrosion rate, a corroding piece of rebar can be isolated (by cutting) to get... 

McDonald et al. studied the performance of solid stainless steel rebars (types 304 and 316) and found that they performed well while ferritic stainless steels (types 405 and 430) developed pitting (15). Studies by McDonald et al. reported investigations on a 10-year exposure of 304 stainless steel in Michigan and Type 304 stainless steel clad rebar in a bridge deck in New Jersey and found no corrosion (15). In a study by Virmani and Clemena, the type 316 stainless steel-clad rebar extended the estimated time to the cracking of the concrete beyond 50 years, but not as much as solid types 304 and 316 stainless steels (100 years) (16). 

In addition, McDonald et al. (15) reported on two highway structures constructed with stainless steel rebar. No corrosion was observed for solid 304 stainless steel rebar in a bridge deck in Michigan as well as in New Jersey. The chloride levels in both bridge decks were below or at the threshold level for corrosion initiation in black steel rebars. It is estimated that the use of solid stainless steel rebar provides an expected life of 75-100 years (15, 16). McDonald et al. estimated the costs, at three installations, of the use of solid stainless steel and found the overall cost to be 6-16% higher than black steel (17). 

To provide longer service life to the concrete decks of the order of 75-120 years without the need to repair corrosion-induced concrete damage, a number of solid and clad corrosion-resistant 304 and 316 stainless steel rebars have been developed. Both alloys provide excellent corrosion protection but at higher cost. Type 316 stainless rebar requires more detailed studies. 

There are 543,019 concrete and steel bridges of which 78,448 are structurally deficient, leaving 464,571 bridges to be maintained for estimating purposes it is assumed that all these bridges have a conventionally reinforced concrete deck. The annualized life-cycle direct cost of original construction, routine maintenance, patching and rehabilitation for a black steel rebar deck costs between 18,000 and 22,000. These costs are both corrosion- and non-corrosion related. 

The objective is to predict corrosion initiation time for various cases using SimCorr . In this simulation, chloride is assumed present at the surface at aU times. The model simulations are used to determine corrosion initiation time and reinforcing steel rebar life in the deck and cap beam of the bridge. SimCorr can be used to predict corrosion initiation time as a function of stmctural and environmental parameters, estimate structure life, design concrete mixes, and geometry based on Hfetime calculations and optimize corrosion protection system as a function of surrounding conditions. SimCorr also serves as a tool for evaluation of chloride transport and underlying concrete corrosion. The simulation software is based on the first principles model described in [77]. 

Since those first systems were applied in the 1970s, systems have been developed and applied to bridge decks, substructures and other elements, buildings, wharves and every conceivable type of reinforced concrete structure suffering from corrosion of the reinforcing steel. More recently systems have also been applied to steel in mortar in stone brick and terracotta clad structures. 

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