Reinforcing steel

Si, A1,0 and H)). Steel reinforcing can be easily detected and studied in detail in concrete 1000 mm thick and more. For this purpose it is possible to use rapid medical x-ray film, requiring exposure times of 6 to 26 minutes for concrete tliicknesses of 600 and 900 mm respeetively. 

Steelmaking dust Steel mtridation Steel quenching Steel Recycling Institute Steel reinforcing Steel RG-H process H steels Steels... 

In concrete, triethanolamine accelerates set time and increases early set strength (41—43). These ate often formulated as admixtures (44), for later addition to the concrete mixtures. Compared to calcium chloride, another common set accelerator, triethanolamine is less corrosive to steel-reinforcing materials, and gives a concrete that is more resistant to creep under stress (45). Triethanolamine can also neutralize any acid in the concrete and forms a salt with chlorides. Improvement of mechanical properties, whiteness, and more even distribution of iron impurities in the mixture of portland cements, can be effected by addition of 2% triethanolamine (46). Triethanolamine bottoms and alkanolamine soaps can also be used in these type appUcations. Waterproofing or sealing concrete can be accompUshed by using formulations containing triethanolamine (47,48). 

Corrosion Inhibitors. Steel-reinforcing wire and rods embedded in concrete containing quinoline or quinoline chromate are less susceptible to corrosion (72) (see Corrosion and corrosion control). Treating the surface of metals with 8-hydroxyquinoline [148-24-3] makes them resistant to tarnishing and corrosion (73). Ethylene glycol-type antifreeze may contain quinoline, 2-chloro-, 4-amino-, 8-nitro-, or 8-hydroxyquinoline to prevent corrosion (74). 

There are less exotic ways of increasing the strength of cement and concrete. One is to impregnate it with a polymer, which fills the pores and increases the fracture toughness a little. Another is by fibre reinforcement (Chapter 25). Steel-reinforced concrete is a sort of fibre-reinforced composite the reinforcement carries tensile loads and, if prestressed, keeps the concrete in compression. Cement can be reinforced with fine steel wire, or with glass fibres. But these refinements, though simple, greatly increase the cost and mean that they are only viable in special applications. Plain Portland cement is probably the world s cheapest and most successful material. 

In the case of higher protection current densities and protection currents, interference can occur on nearby installations not covered by the protection. The danger of anodic interference must be investigated by making measurements and prevented by taking appropriate measures [7] (see Section 9.2). For the same reasons, anode systems should not be installed near steel-reinforced concrete foundations. 

The danger of corrosion is in general greater for pipelines in industrial installations than in long-distance pipelines because in most cases cell formation occurs with steel-reinforced concrete foundations (see Section 4.3). This danger of corrosion can be overcome by local cathodic protection in areas of distinct industrial installations. The method resembles that of local cathodic protection [1]. The protected area is not limited, i.e., the pipelines are not electrically isolated from continuing and branching pipelines. 

Fig. 12-1 Danger of corrosion caused by cell formation with steel-reinforced structures and of the pipe/soil potential.

For efficient current distribution, steel-reinforced concrete walls should be provided at the wall entrance of pipes and at least 1 m around them and up to the soil surface with at least 2 mm thick electrically insulating layers of plastic or bitumen. This is also recommended if the pipelines are laid in soil parallel to steel-reinforced concrete foundations and the closest spacing is smaller than twice the pipe diameter or smaller than 0.5 m [2]. 

Fig. 12-5 Voltage cone AU and pipe/soil potentials at a wall entrance in a steel-reinforced concrete foundation.

Installations with Small Steel-Reinforced Concrete Foundations... 

Pumping or compressor stations are necessary for the transport of material in pipelines. These stations are usually electrically separated from the cathodically protected long-distance pipeline. The concrete foundations are much smaller than in power stations and refineries. Since the station piping is endangered by cell formation with the steel-reinforced concrete foundations, local cathodic protection is recommended. 

Structures or pits for water lines are mostly of steel-reinforced concrete. At the wall entrance, contact can easily arise between the pipeline and the reinforcement. In the immediate vicinity of the pit, insufficient lowering of the potential occurs despite the cathodic protection of the pipeline. Figure 12-7 shows that voltage cones caused by equalizing currents are present up to a few meters from the shaft. With protection current densities of 5 mA mr for the concrete surfaces, even for a small pit of 150 m surface area, 0.75 A is necessary. A larger distribution pit of 500 m requires 2.5 A. Such large protection currents can only be obtained with additional impressed current anodes which are installed in the immediate vicinity of the pipe entry into the concrete. The local cathodic protection is a necessary completion of the conventional protection of the pipeline, which would otherwise be lacking in the pit. 

Considerable stray currents can, of course, be caused by dc-driven cranes that load and unload ships where the rails act as the return conductor for the current. The rails run parallel to the harbor basin, quay walls of steel-reinforced concrete or steel piling walls. These can take up a large part of the stray current and conduct it further because of their small longitudinal resistance. Noticeable stray current inter-... 

Very often steel sheet pilings exist in conjunction with steel-reinforced concrete structures in harbors or locks. If cathodic protection is not necessary for the reinforced concrete structure, there is no hindrance to the ingress of the protection current due to the connection with the steel surfaces to be protected. The concrete surface has to be partly considered at the design stage. An example is the base of the ferry harbor at Puttgarden, which consists of reinforced concrete and is electrically connected to the uncoated steel sheet piling. 

Ferry harbor, Puttgarden None 8500 and ca. 5500 steel-reinforced concrete 160 PtTi 360 20 X 100 >10... 

Harbor structures are very accessible and can be investigated without the effects of wave motion. Grounding of steel pilings presents no problems and the work can be carried out from the quay (see the left-hand side of Fig. 16-13). With steel-reinforced concrete structures, measurements have to be made from a boat if no reliable contact has been provided in their eonstruction (see the right-hand side of Fig. 16-13). 

Cathodic protection of reinforcing steel with impressed current is a relatively new protection method. It was used experimentally at the end of the 1950s [21,22] for renovating steel-reinforced concrete structures damaged by corrosion, but not pursued further because of a lack of suitable anode materials so that driving voltages of 15 to 200 V had to be applied. Also, from previous experience [23-26], loss of adhesion between the steel and concrete due to cathodic alkalinity [see Eqs. (2-17) and (2-19)] was feared, which discouraged further technical development. 

Cathodic protection can be used as a renovation measure for steel-reinforced concrete structures (see Chapter 19). Although material costs of from 100 DM m" (particularly with preparation, erection, and spray coating costs) up to 300 DM m are quite high, they do not compare with the costs of demolition or partial replacement. ... 

Since stray current corrosion damage can occur after only a few years, the economy of stray current protection measures is obviously not questionable [12], In Fig. 22-3 the effect of stray currents is shown by curve 2 [14]. Without there being firm evidence, it is apparent that the shape of the corrosion damage curve in steel-reinforced concrete (see Sections 10.3.6 and 4.3) is similar to that for stray current corrosion [15]. 

Considerable alterations have been made in the chapters concerned with technical applications which are the result of advances in electrochemical corrosion protection in general practice. Here also, abbreviation and omission of less relevant parts of the older editions have had to be made to create space for more recent information. Recent applications in the chemical industry have necessitated a complete rewriting of the industrial chapter. A new chapter is included on the cathodic protection of steel reinforcement in concrete. 

Ammonium salts Slow to rapid disintegration If cement is porous, corrosion of steel reinforcement may occur... 

Fabricating - Steel sections are cut, welded and otherwise prepared to form the steel frame of a building. Rods and bars are similarly cut and shaped to form the steel reinforcement for concrete buildings. 

Numerous multiphase composite materials exhibit more than one characteristic of the various classes, fibrous, laminated, or particulate composite materials, just discussed. For example, reinforced concrete is both particulate (because the concrete is composed of gravel in a cement-paste binder) and fibrous (because of the steel reinforcement). 

Spread Foundations. The purpose of the spread foundation is to distribute loads over a large enough area so that soil can support the loads safely and without excessive settlement. Such foundations are made of steel-reinforced concrete. When concrete is used for a foundation, it should be placed on undisturbed soil. All vegetation should be removed from the surface therefore, the upper few inches of soil should be removed before concrete is laid down. The area of the foundation must be large enough to ensure that the bearing capacity of the soil is not exceeded or that maximum settlement is within acceptable limits. If details are known of the subsurface soil conditions, the foundation must be sized so that differential settlement will not be excessive. For... 

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