Concrete steels

By varying molecular weight and functionaUty of the castor polyols and the type of isocyanate, a variety of clear and pigmented urethane coatings can be prepared. Copolymers of vinyl and castor-based urethane have also been reported for use as exterior coatings for plywood and flexible substrates (90) and for appHcation over steel, concrete, and wood substrates (91). 

The way in which materials are used in a developed nation is fairly standard. All consume steel, concrete and wood in construction steel and aluminium in general engineering copper in electrical conductors polymers in appliances, and so forth and roughly in the same proportions. Among metals, steel is used in the greatest quantities by far 90% of all the metal produced in the world is steel. But the non-metals wood and concrete beat steel - they are used in even greater volume. 

The anodically produced acid is neutralized by the alkaline mortar (CaO). Corrosion is then possible only if the supply of alkali at the steel surface is consumed and the steel becomes active. This process is possible only under certain circumstances after a very long incubation period. Apparently in steel-concrete foundations the possible current densities are so small that this case never arises. The possibility of danger has to be verified with thin outer coatings where deliming has been noticed on the steel surface. 

A similar danger of corrosion lies in cell formation in steel-concrete foundations (see Section 4.3). Such steel-concrete cells are today the most frequent cause of the increasing amount of premature damage at defects in the coating of new steel pipelines. The incidence of this type of cell formation is increased by the connection of potential-equalizing conductors in internal gas pipelines and domestic water pipelines [25], as well as by the increased use of reinforcing steel in concrete foundations for grounding electrical installations [26]. 

Figure 10-10 shows the voltage cones for four different steel-concrete foundations [27]. Pipelines in the vicinity of such foundations are affected by these voltage cones (see Section 9.2), which can quickly lead to corrosion damage, particularly in pipelines that have some defects in their coatings. 

Factors that affect cell formation are the type of cement, the water/cement ratio and the aeration of the concrete [6]. Figure 12-1 shows schematically the cell action and the variation of the pipe/soil potential where there is contact with a steel-concrete structure. The cell current density is determined by the large area of the cathode [see Fig. 2-6 and Eq. (2-44)]. In industrial installations the area of steel surface in concrete is usually greater than lO m ... 

In the local cathodic protection of the bottoms of flat-bottomed tanks, cell formation with steel-concrete foundations is of little importance since the surfaces are relatively small, in contrast to the installations in Sections 12.2 to 12.5. On the other hand, connected components of the installation, such as cables and grounds, take up considerable protection current. On account of the large foundations of flat-bottomed tanks, which are often bare or only poorly coated, polarization to the protection potential is only possible with very negative on potentials. In tank foundations with the... 

The passivating action of an aqueous solution within porous concrete can be changed by various factors (see Section 5.3.2). The passive film can be destroyed by penetration of chloride ions to the reinforcing steel if a critical concentration of ions is reached. In damp concrete, local corrosion can occur even in the presence of the alkaline water absorbed in the porous concrete (see Section 2.3.2). The Cl content is limited to 0.4% of the cement mass in steel-concrete structures [6] and to 0.2% in prestressed concrete structures [7]. 

The information in Sections 2.2, 2.4 and 3.3 is relevant for protection criteria. Investigations [43] with steel-concrete test bodies have shown that even in unfavorable conditions with aerated large-area cathodes and small-area damp anodes in Cl -rich alkaline environments, or in decalcified (neutral) surroundings with additions of CU at test potentials of (/f.y.cuso4 = -0.75 and -0.85 V, cell formation is suppressed. After the experiments had proceeded for 6 months, the demounted specimens showed no recognizable corrosive attack. 

Fig. 19-1 Experimental setup for the cathodic protection of an active steel concrete-passive steel cell.

Drainage tests and initial measurements should not be made before 28 days have elapsed after the anodes are embedded in the artificial concrete system in order to allow the hydration of the concrete and to ensure moisture equilibrium, which can affect the potentials. The protection current density is limited to 20 mA ra"-(at the steel surface) to avoid possible reduction in the steel-concrete bond. Usual current densities lie in the range 1 to 15 mA 129-33]. 

Corrosion likelihood (depassivation) Steel/concrete potential Uccso, (V)... 

Fig. 19-8 Steel/concrete potentials (two records) and temperature as a function of the time of year. (The protection installation was switched on in June 1986.)...

Pressure vessel Material steel steel steel concrete... 

OR IF L KNOWN AND MATERIAL SELECTED FROM STEEL, CONCRETE, WOOD, AND ALUMINUM,... 

Both our new chemistry building and the science of thermodynamics are functional, but beautiful. The building is a very modern combination of glass, steel, concrete, and brick, set on the edge of a hill, where it projects an image of strength, stability, and beauty. The aesthetic beauty of thermodynamics results from the rigor of the discipline. Thermodynamics is one of the pre-eminent... 

In all blast-resistant structures (steel, concrete, or masonry) special attention should be given to the integrity of connections between structural elements up to the point of maximum response. For example, it is important to prevent premature brittle failure of welded connections to avoid stress concentrations or notches at joints in steel structures and to provide ductile reinforcement detailing in concrete/masonry structure connections. For all materials, it is recommended that connections be designed to be stronger than the connected structural members such that the more ductile member will govern the design over the more brittle connection. 

Type of Stress Reinforcing Steel Concrete Ultimate... 

Measures to reduce the impact of fire include active and passive systems. Active systems include automatic sprinkler, water deluge, water mist, gaseous agent, dry chemical, foam, and standpipe handle systems. Passive protection is provided by fire resistive construction, including spray-applied or cementitious fireproofing of steel, concrete/masonry construction, and water-filled steel columns. Chapter 7 provides details on the design of fire protection systems. 

The protection of steel reinforcements. Concrete produces a layer of passivity at the steel/concrete interface and any breakdown of this can increase the chance of reinforcement corrosion. In addition, it is important that concrete be maintained in a state of low permeability to minimize the passage of moisture and air to the steel. 

The presence of calcium chloride at concentrations greater than about 1.5% by weight of cement can lead to breakdown of the passive layer of Fe203 normally present at the steel/concrete interface, rendering the... 

Fig. 5.31 Typical circuit for recording the potential of a steel/concrete electrode relative to that of a saturated calomel electrode (Gouda).

Munroe-Neumann effect is the property of explosive charges detonated in contact with objects of steel, concrete etc, to produce much deeper holes in the objects when the charge contains a cavity than when the explosive is solid. According to Birkhoff et al, (Ref 28) this property of explosives has been known for at least 150 years, the earliest reference to it being in 1792. 

Large and medium size piping and valves require rubber or rubber lined construction whereas smaller ones are constructed with mild steel, concrete or stainless steel of suitable grade. 

When an explosive detonates, tremendous pressure is released practically instantaneously in a shock wave which exists only a fraction of a second at any given place. The subsequent expansion of gases performs work but the sudden pressure thus created will shatter rather than displace any object in its path. The ability of an expl to demolish(fragment, shatter) a solid object (such as steel, concrete, stone) when fired in direct contact with it or in its vicinity is called brisance (from the French "briser = to break or shatter). 

Fig. 14. (a) Pictorial representation of 2-dimensional metal depicting the coexistence of COVALENT bond, () and isotropic free electrons (shaded)., (b) Pictorial representation of 2-dimensional steel concrete showing the coexistence of steel rod (straight lines) surrounded by isotropic concrete (shaded). 

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