Deicing reinforcement

In the modem age, a highly developed infrastructure is essential for economic growth and prosperity. Many stmctures essential to this infrastmcture, especially those made of reinforced concrete, have suffered severe degradation since their construction due to the combined effects of deicing salts, freeze-thaw cycles, aggressive environments, and drastically increased live loads. One of the major problems facing the civil engineers of today is to preserve, maintain, and retrofit these structures [1],... 

Bridge decks, parking structures, and other reinforced concrete structures lend themselves to cathodic protection, particularly when the concrete is contaminated with cathodic chlorides from deicing salts or a marine environment. Special techniques are required as described by Rog and Swait [71] NACE [72, 73] and Morgan [74]. 

In nonmarine applications, the percent of surface area deteriorated because of corrosion of reinforcing steel is much less and often is limited to area beneath expansion joints and drains, which are exposed to deicing salt runoff. 

Structural collapses of reinforced concrete structures due to corrosion are rare. The author knows of two multi-storey parking structures in North America which have collapsed due to deicing salt induced corrosion (Simon, 2004). A prestressed concrete bridge collapsed in Wales dne to deicing salt attack on the strands hidden from investigation (Woodward and Williams, 1988), and another one in Enrope. Usually concrete damage would have to be well advanced before a strncture is at risk. 

Figure 3.7 The M4 elevated section in West London showing exposed reinforcement due to concrete spalling induced by reinforcement corrosion. Corrosion was caused deicing salt leakage from the deck above.

Thare are several reasons for FBECR becoming the protective system of choice in the USA and Canada for reinforcing steel exposed to chloride attack. One is the reluctance to use waterproof membranes on bridge decks as they are difficult to install properly and to monitor both for correct installation and for performance after installation. The preference for a very low maintenance bridge deck led most state DOTs and the Federal Highway Administration (FHWA) to look for alternative protective systems on all bridges exposed to chlorides from the sea or from deicing salt. 

Normally, reinforcing steel is in a passive state due to the formation of a tenacious passive oxide coating called gamma ferric oxide on the steel surface created by the highly alkaline environment (pH > 12.5) of concrete. However, the presence of chloride ions at the concrete/steel interface in excess of the reaction threshold level 0.5 kg to 1.0 kg of chloride ions/meter concrete (1.0-2.0 lb of chloride ions/yard ) depassivates the steel, and corrosion will initiate. On bridges, the source of the chloride ion is usually deicing chemicals applied in the snow-belt areas in winter or salt spray with seawater in coastal areas. 

J2 Corrosion of steel reinforcing ban (reban) in a concrete bridge head, (a) The corrosion cell which arises due to water penetration and chloride pick-up from the concrete or from deicing salts, (b) The expansive corrosion products may cause cracking of the concrete. Tn severe cases, delamination results, (c) Impressed current, cathodic protection may be applied, (d) A flexible anode mesh may be installed (which is then covered with a concrete overlay)i Power usage is < 10 Wm" of the concrete surface. (Courtesy Raychem Ltd.)... 

Reinforced concrete electrochemical protection methods used against corrosion caused by contamination with chlorides or the carbonization process may be used for new structures, as well as those already used in soil, water, and atmospheric environments. The first practical CP application was realized in the U.S. A. for the protection of a bridge contaminated with deicing salts (Stratfull, 1974). 

Concrete is a widely used structural material that is frequently reinforced with carhon steel reinforcing rods, post-tensioning cable or prestressing wires. The steel is necessary to maintain the strength of the structure, but it is subject to corrosion. The cracking associated with corrosion in concrete is a major concern in areas with marine environments and in areas which use deicing salts. 

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