Concrete, corrosion resistance

The effect of mineral additions (slag, fly ash, pozzolanic materials) on the same properties of concrete has been also determined. However, there are still some problems to be resolved as yet. Amongst them, the role of cement phases as concrete corrosion resistance controlUng factors has been pointed out by Bombled [3], though... 

The gas distribution system can be composed of a network of perforated pipe, slotted or vented concrete block, or metal grating. When there are no space hmitations, single-level filters are used. In regions where footprint space is hmited, hke Japan, multiple-deck filter beds have become commonplace. If inorganic compounds are being treated, corrosion-resistant materials of construc tion are used due to the acidic by-products of the bioreaction. 

Cement and Concrete Concrete is an aggregate of inert reinforcing particles in an amorphous matrix of hardened cement paste. Concrete made of portland cement has limited resistance to acids and bases and will fail mechanically following absorption of crystalforming solutions such as brines and various organics. Concretes made of corrosion-resistant cements (such as calcium aluminate) can be selected for specific chemical exposures. 

Epoxy resin cements are specifically intended for resistance to caustic alkalis and organic solvents, but they also have fair acid resistance. They have excellent bond strength to other materials including ceramic and concrete. The corrosion resistances of the cements described above are given in Table 3.40. 

Sulfur can replace 30-50% of the asphalt in the hlends used for road construction. Road surfaces made from asphalt-sulfur hlends have nearly double the strength of conventional pavement, and it has been claimed that such roads are more resistant to climatic conditions. The impregnation of concrete with molten sulfur is another potential large sulfur use. Concretes impregnated with sulfur have better tensile strength and corrosion resistance than conventional concretes. Sulfur is also used to produce phosphorous pentasulfide, a precursor for zinc dithiophosphates used as corrosion inhibitors. 

Normally concrete is reinforced with plain carbon steel, but under conditions where rapid carbonation can occur or there is a risk of chloride contamination, corrosion-protected or more corrosion-resistant reinforcing steels may be necessary. Currently there are three reinforcing bars which have enhanced corrosion resistance ... 

Galvanised steel provides increased corrosion resistance in carbonated concrete. In concrete with more than 0.4% chloride ion with respect to the cement content, there is an increased risk of corrosion and at high chloride contents the rate of corrosion approaches that of plain carbon steel. In test conditions the rate of corrosion is greater in the presence of sodium chloride than calcium chloride. Fusion-bonded epoxy-coated steel performs well in chloride-contaminated concrete up to about 3.9% chloride ion in content. 

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 the 1930s, the TP pipe industry continues to expand its use worldwide. It now represents over 30% of the dollar share compared to other materials (iron/steel at 45%, copper at 12%, concrete at 8%, aluminum at 4%, etc.). Although RP TS pipe represents a small portion of the market, it is a product of choice for many special high performance applications. Corrosion resistance, toughness, and strength contribute to its growing acceptance. 

Concrete exposed to deicer salts, or to a marine environment is subjected to chloride and sodium loading. The ability of concrete to resist the penetration of chlorides and sodium is a primary design consideration in marine or cold environments. The ingress of chlorides into concrete is a major problem due to chloride-induced corrosion of the reinforcing steel and deicer salt scaling [a process by which a thin layer (< 1 mm) of concrete deteriorates from the surface of the concrete]. The penetration of sodium from sea water or deicer salts is generally... 

Admixture formulations containing two or more compounds (multicomponent) in which each component plays a specific role or compliments the corrosion resistance capacities of the other are also used. For example, a mixture of calcium nitrite and calcium formate is used to both accelerate strength of the concrete and inhibit corrosion of the steel during steam curing. 

Sulphur concretes appear well suited for use in environments corrosive to Portland cement concretes. The extensive work by the U.S. Bureau of Mines shows their material performs admirably in such environments. When used as a lining, the initial stress-strain behaviour will allow the material to adapt to the main structural element and relieve internal stresses without cracking. Corrosion resistance will be maintained by the material thereafter, even though the stress strain behaviour alters. On its own, the material retains sufficient strength to withstand typical loads involved in this type of application (eg. liquid container). Sudicrete has not been tested much in this area, although laboratory tests show similar promise. 

Sulfur concretes (SC) are basically simple materials, made by mixing sulfur plus certain additives with heated mineral aggregates. On cooling, SC sets to give a high-strength material with superb corrosion resistance. 

Sulfur concretes can be designed to have compressive and tensile strengths twice or more those of comparable Portland cement concretes (PCC), and full strength is reached in hours rather then weeks. Sulfur concretes are extremely corrosion resistant to many chemicals, including most acids and salts. The metallurgical and fertilizer industries have shown interest in using SC in corrosive enviornments where PCC has a very short lifetime. 

A wide range of applications for sulfur concrete such as SUDICRETE provide many advantages. Included are industrial flooring, electrolytic vats, sumps, catch basins, tanks, sewage and waste impoundment ponds, bridge decks, pipes, etc., all of which can benefit from its extreme corrosion resistance. Rapid... 

Part of Chevrons program has focused on the use of composites as liners for earthen structures. Their durability, strength, and ease of application offer important advantages over concrete and other lining materials for certain uses. Another phase of the program has emphasized the use of composites as protective coatings for concrete. In this application, their durability, weatherability, and corrosion resistance can extend the... 

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