دانلود رایگان مقاله لاتین خواص مکانیکی کامپوزیت سیمان از سایت الزویر
عنوان فارسی مقاله:
خواص مکانیکی کامپوزیت سیمان فوق العاده سبک و در دماهای پایین از 0 تا -60 ° C
عنوان انگلیسی مقاله:
Mechanical properties of ultra-lightweight cement composite at low temperatures of 0 to −60 °C
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
After the discovery of oil and gas reservoirs in the Arctic region in the last century, productions and explorations continue to this day, contributing to the growth of oil and gas industry. A type of ultra lightweight cement composite (ULCC) was developed [9] to tailor the offshore structural applications in the Arctic areas, in particular for offshore floating structures and liquefied natural gas (LNG) storage tanks. For floating structures, it is desirable that these structures are of low self-weight. In construction of offshore structures such as oil platforms, most base structures are floated out to sites by tugboats and then completed on site. The low selfweight improves deployment and on-site installation of the structures. The ULCC generally has a unit weight of at least 40% less than that of conventional concrete and compressive strength of up to about 65 MPa with low permeability [23]. The ULCC has lower densities and higher specific strengths (compressive strength/ density) compared with lightweight concrete (LWC). In addition, the permeability of ULCC is significantly lower than that of the LWC [22,23]. Thus, the ULCC is more suitable for floating structures in offshore environment with potentially reduced maintenance costs due to reduced permeability. According to Danish Meteorological Institute (Dmi) Centre for Ocean and Ice, the daily mean temperatures for the Arctic area north of the 80th parallel ranged from - 40 C to 2 C from the period of 1958e2014 [13]. This raises the question about the possibility of using the ULCC in such environments, since low temperatures could affect the mechanical properties of the ULCC as a structural material and in steel-ULCC composite structural members. However, no information on the mechanical properties of the ULCC under subzero temperatures of 0 to 60 C is currently available. This initiates the research described in this paper. For normal weight concrete (NWC), mechanical properties of the concrete are improved when concrete is cooled down to subzero temperatures [21,24,27,31,34]. Compressive strength, modulus of elasticity, Poisson's ratio, tensile strength, and flexural strength of concrete generally increase with decreasing temperature (below 0 C). The aforementioned improvements are attributed to the * C freezing of water and formation of ice in pores and microcracks inside the concrete. Therefore, the behavior of concrete at low temperatures is governed by moisture content in pores and freezing temperature of pore solution. It was found, for example, that dry concrete is little affected by such low temperature and not much affected at 50% RH [24]. Miura [29] found that the increase in the compressive strength is nearly proportional to the moisture content of the NWC, and a relationship between the compressive strength and the moisture content and low temperature was proposed. When concrete is cooled to 0 C, most of the water in the concrete does not freeze immediately. The freezing point of water in capillary pores is affected by the pore size and salt concentration in pores. Lower temperatures are required to freeze water in smaller pores or in pores with salt solutions. Skapski et al. [35] presented an equation [Eq (1)] that co-relates the ice crystal radius (g) which is assumed to be close to the true pore radius (gp) to temperature (T) at which water freezes, and the relationship is illustrated in Fig. 1.
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کلمات کلیدی:
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