Concrete mechanical properties

Keywords biopolymer, chitosan, latex, concrete, mechanical properties, SEM, XRD, performance. 

The insulating value and mechanical properties of rigid plastic foams have led to the development of several novel methods of buUding constmction. Polyurethane foam panels may be used as unit stmctural components (220) and expanded polystyrene is employed as a concrete base in thin-sheU constmction (221). 

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). 

Abdelrazig, B. E. I., Sharp, J. H. El-Jazairi, B. (1989). Microstructure and mechanical properties of mortars made from magnesia-phosphate cement. Cement Concrete Research, 19, 247-58. 

Beaudoin, J. J. Feldman, R. F. (1975). Mechanical properties of autoclaved calcium silicate systems. Cement and Concrete Research, 5 (2), 103-18. 

Table 6.9 Mechanical properties of concrete containing calcium nitrite (Berke and Weil)...

The method of placement makes shoterete potentially more variable and more anisotropic than normal concrete. Consequently, the development of the physical and mechanical properties such as strength, shrinkage, permeability and durability is drastically different from those of normal concrete. The effects are particularly noticeable during the very early and later ages [107, 109, 117]. 

Durable concrete is typically characterized by low porosity because the fundamental porosity of concrete influences all of its material properties. For this reason, most of our standard practices for the construction of concrete structures have as their objective the minimization of paste porosity, which consequently increases both strength and durability. Although low water-cement ratio (W/C) is responsible for improved mechanical properties and enhanced durability, attaining a low W/C necessitates either a sacrifice in workability, or the use of high cement content, neither a desirable consequence. A more advantagious alternative is the use of water-reducing admixtures (WRAs). 

Table 7.19 Typical mechanical properties of high-volume fly ash concrete made with ASTM Type I and Type III cements (Maihotra [69]) ...

The admixture may remain in a free state as a solid, in solution, interact at the surface, or chemically combine with the hydrates. Physicochemical and mechanical properties of the concrete may be influenced by the type and extent of the interaction. Thus, the early hydration reactions of cement may be affected in diverse ways and it is possible that more than one effect occurs at the same time. These are sununarized below [125]. 

In sulphur concretes, the mechanical properties of the sulphur binder are usually altered from those of the "pure crystalline (orthorhombic) element - the thermodynamically stable form of sulphur at room temperatures. The property alteration is... 

The hardened state at a relatively early age (usually 28 days) where mechanical properties are determined as a basis of structural requirements. The later hardened state during its in place life when the concrete should fulfill its structural or aesthetic role without deterioration under the service conditions. 

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