Steel concrete reinforcement

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]. 

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]. 

In the middle of the last century, the tensile properties of concrete were improved by the introduction of steel to reinforce the concrete. This practice has developed since then to such an extent that reinforced concrete is now one of the major structural materials used in construction. In general it has proved to be a good durable material with some of the structures erected at the turn of the century still providing satisfactory service in the late 1970s. 

Treadaway, K. W. J., Cox, R. N. and Brown, B. L., Durability of corrosion resisting steels for reinforced concrete. Proceedings of the Institute of Civil Engineers (in press)... 

Since blast-resistant design is based on structural response beyond elastic limits into the inelastic range, buildings should be carefully designed in a manner that minimizes stress concentrations, brittle behavior, and abrupt failures. Some of the significant design considerations for steel and reinforced concrete blast-resistant structures are briefly summarized in this section. 

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. 

Results of value can also be obtained by firing the explosive in a steel vessel reinforced with concrete. Care must be taken that by the use of lead tube or similar method the explosive is adequately confined, as unconfined explosives can produce abnormal fumes. 

Type of Stress Reinforcing Steel Concrete Ultimate... 

This chapter provides material properties and response criteria necessary to design facilities constructed of reinforced concrete, reinforced masonry, structural stcc and cold formed steel. Static and dynamic properties are covered for the materials used in these facilities. Allowable response criteria are covered for both... 

The stability of the concrete mix can be considered in terms of its cohesion , which is a subjective term used to describe its ability to maintain a homogeneous appearance when subjected to applied stress. Lack of cohesion leads to segregation of the mix components into layers relevant to their densities. A further term associated with mix stability is that of bleeding , which is the movement of water to the surface of the fresh concrete. This phenomenon can occur either in isolation or as a manifestation of segregation. Bleeding in excess is normally considered to be undesirable because of the dangers of water runs at the shutter/concrete interface and cracking due to plastic settlements, and there is also the possibility of adverse effect on the concrete-reinforcement bond due to the collection of water beneath the steel. 

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 formation of the passive layer at the concrete/reinforcement interface referred to earlier (Section 1.4) is due to the alkaline nature of the concrete. The alkalinity is due to calcium, sodium and potassium hydroxides which, over a period of time, react with atmospheric carbon dioxide to form carbonates. This reduction in alkalinity in reflected in a diminished protective capacity towards the steel reinforcement. 

Ferroconcrete. One of the names for concrete reinforced by steel in various forms, usually rods... 

The liquid waste is stored for at least 6 y prior to solidification to reduce the decay heat (Fig. 16.8) by a factor of 10 or more. The first U.S. military fuel reprocessing wastes were stored as neutralized waste in mild steel tanks at the Hanford reservation in eastern Washington. These steel-lined, reinforced-concrete tanks were 500,000-1,000,000 gal in capacity with provisions for removal of waste heat and radiolysis products. Corrosion of several tanks occurred with the release of waste. Fortunately, the soil around these tanks retarded nuclide transport. A better (and more expensive) design for storage tanks was implemented at the Savannah River site in South Carolina consisting of a second steel tank inside of a Hanford-style tank. The storage of acid waste in these tanks has not encountered the corrosion problems seen with the Hanford tanks. 

The Bessemer process is relatively less expensive but does not produce a product of high quality. It is not possible to exercise control over the composition of the product because the conversion occurs so quickly. Furthermore, this process does not effect the removal of phosphorus. The phosphorus pentoxide that is formed during the blow is reduced to phosphorus upon addition of carbon and hence remains as an impurity in the final product. Provision for the removal of phosphorus may be made by the use of the so-called basic Bessemer process, which employs a converter lined with magnesia (MgO), but this practice entails other disadvantages. In the United States, the acid Bessemer process is used exclusively and accounts for about 15% of the steel produced in this country. Steel so produced is used largely as structural steel, as reinforcement for concrete, and in the tinplate industries. 

ASTM Standard A 955-96, Standard Specification for Deformed and Plain Stainless Steel Bars for Concrete Reinforcement (Type 304, 304L, 316, 316L, 316 LN and duplex 2205)... 

Kilworth, S.R., J. Fallon, Stainless Steels for Reinforcement, Concrete Durability in the Arabian Gulf, 2nd Regional Concrete Conference, Bahrain, 19-21 March 1995. 

Chloride contents must be kept low to avoid corrosion of steel in reinforced concrete (Section 12.3) and formation of kiln rings and preheater deposits. Contents below 0.02% are preferred, though higher ones can be acceptable if a sufficient proportion of the kiln gases is bypassed or in less energy-efficient (e.g. wet process) plants. 

---