Concrete prestressed

Concrete Products. Limestone aggregate is used competitively with other aggregate in the manufacture of molded, reinforced, and prestressed concrete products in the form of block, brick, pipe, panels, beams, etc. 

For high, heavy tanks, a foundation ring may be needed. Prestressed concrete tanks are sufficiently heavy to require foundation rings. Foundations must extend below the frost line. Some tanks that are not flat-bottomed may also be supported by soil if it is suitably... 

Concrete pressure vessels may be used in applications that require large sizes. Such vessels, if made of steel, would be too large and heavy to ship. Through the use of posttensioned (prestressed) concrete, the vessel is fabricated on the site. In this construc tion, the reinforcing steel is placed in tubes or plastic covers, which are cast into the concrete. Tension is applied to the steel after the concrete has acquired most of its strength. 

LNG is stored in metal double-wall or prestressed concrete tanks, frozen earth, or mined quarries or caverns. 

Cathodic protection cannot work with prestressed concrete structures that have electrically insulated, coated pipes. There is positive experience in the case of a direct connection without coated pipes this is protection of buried prestressed concrete pipelines by zinc anodes [38], Stability against H-induced stress corrosion in high-strength steels with impressed current has to be tested (see Section 2.3.4). 

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]. 

For prestressed concrete, either high-tensile steel wires or occasionally bars of steel alloy containing manganese and silicon, can be used. Galvanised wires may also be used for prestressed concrete, but it is recommended that they be chromated before use. 

There are many specialty cements including reinforced concrete, lightweight concrete, prestressed concrete, gypsium, and heavy glass. 

Table 5.5 Effect of CaCI2 on corrosion of high tensiie steei wires in normaiiy cured prestressed concrete specimens stored outdoors...

The most widely used anodic inhibitors are calcium and sodium nitrite, sodium benzoate and sodium chromate. With the exception of calcium nitrite, no other chemical is available in North America as a proprietary product. Nitrites have been used in the USA for more than 14 years and for nearly 40 years in Europe. Calcium nitrite is marketed as a non-chloride accelerator, as well as a corrosion inhibitor. For 25-30% solids in solution, dosage rates range from 2 to 4% by weight of cement depending on the application [50]. Calcium nitrite has been used in bridges, parking and roof decks, marine and other prestressed concrete structures that are exposed to chloride attack. 

High Range Water-Reducer Committee Recommended Practice. (1980). Draft of the Prestressed Concrete Institute. 

For example, creep has an adverse effect on the behaviour of a prestressed concrete member but is irrelevant when considering curbs and gutters since these are subjected to very small sustained stresses. 

Demolition of prestressed concrete bridge beams with expls 3 D62... 

Prestressed concrete elements for use in construction has increased severalfold since World War I. The concrete block industry also has expanded greatly during the same period, replacing brickwork and stonework for many applications because of economy and speed. In addition lo the usual cement, sand, and gravel, concrete blocks arc also available with several other ingredients to lower Ihe weight and density of the blocks, increase thermal insulative qualities, and lo add color. See also Ceramics. 

Demolition of Prestressed Concrete Bridge Beams with Explosives is discussed by J.A. Dennis in Engineer Research and Development Labs Rept 1830, Fort Belvoir, Va (Sept 1965)... 

The volume includes 37 papers. Discussions cover the verification of flat plate analyses by model studies long-term behavior of small composite prestressed concrete bridge beams studies of a prestressed concrete girder with web openings the structural behavior of a hyperbolic cooling tower under static loadings models of shear wall structures ... 

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