Prestressing Process

Construction materials for the plant include prestressed brick linings, Hastelloys B and C, tantalum, Kynar, and Teflon. All these materials have been successfully tested under process conditions. 

A third issue is hydrogen evolution. This is inevitable with ECE and so this process must not be used on prestressing steel. 

The problem of hydrogen embrittlement and prestressing steel has been discussed in Section 7.8 for cathodic protection, and Section 7.11.5 for realkalization. The realkalization process applies 20-50 V DC between the anode and the steel. It must therefore send the steel potential well beyond the level needed for hydrogen evolution. 

Chloride removal cannot be applied to prestressed structures due to the risk of hydrogen embrittlement. The use of lithium-based electrolytes suggests that ASR can be controlled. As stated earlier for impressed current cathodic protection, there must be electrical continuity within the reinforcement network for any of the electrochemical techniques to be applied. We do not know how long the treatment process will last but a range of 5-20 years is likely, depending upon conditions. 

Maracaibo Lake Bridge is 9 km long, situated in the southern part of Maracaibo city and spans Maracaibo Lake at one of its narrowest parts. The maximum height of the bridge table is 50 m above lake level. The bridge is a prestressed concrete structure the beams of 46.6-m length were prefabricated on shore and later incorporated in the construction process. A total of 544 beams were constructed. For the foundations prestressed cylinder piles were sunk to a maximum depth of 60 m. The bridge has 137 piers with spans of 235, 85, 46.6, and 36.6 m. 

VG 400 reactor plant was intended for both electricity production and process heat. The heat is transferred to a methane steam reformer and hydrogen gained is used for ammonia production. The reactor plant parameters are given in Table 3. The key components of the reactor plant are housed in the prestressed concrete reactor vessel (Fig 1). 

There are three known side effects of ECE. The first is the acceleration of alkali silica reactivity (ASR), another is reduction in bond at the steel concrete interface. A third issue is hydrogen evolution. Hydrogen evolution is inevitable with ECE and so this process must not be used on steel used for prestressing. 

The two major problems are ASR and prestressing. Careful studies should be carried out if ASR is a risk. This was discussed in the previous chapter as a problem for cathodic protection (Section 6,9), chloride removal (Section 6.10.6) and realkalization (6.11,5), Although the electrical current density and charge levels are lower than for chloride removal, there is still a risk that the hydroxyl ions generated at the steel will increase the alkalinity around the aggregate particles and cause ASR, This can be tested in the laboratory by taking cores and subjecting them to the current levels to be used in the realkalization process. 

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