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Lime, cement and concrete
Published in Arthur Lyons, Materials for Architects and Builders, 2019
Weak, permeable concrete is particularly vulnerable to the absorption of water into capillary pores and cracks. On freezing, the ice formed will expand, causing frost damage. The use of air-entraining agents, which produce discontinuous pores within concrete, reduces the risk of surface frost damage. Concrete is particularly vulnerable to frost damage during the first two days of early hardening. Where new concrete is at risk, frost precautions are necessary to ensure that the mix temperature does not fall below 5°C until a strength of 2 MPa is achieved. Eurocode 2 (BS EN 1992-1-1: 2004 + A1: 2014) refers to four levels of exposure class (XF1 to XF4) with respect to freeze/thaw deterioration (Table 3.19, p. 104).
New Techniques to Produce Functional Materials: Chemical Vapour Deposition
Published in Shintaro Furusaki, John Garside, L.S. Fan, The Expanding World of Chemical Engineering, 2019
Frost formation is a sort of CVD process; gas phase water molecules diffuse to a surface and are deposited and frozen there. Snow however comprises ice crystals or powder and deposits much more rapidly than frost. If snow, or powder formation, is an inevitable consequence of the high temperatures and concentrations necessary to speed up the CVD process, is it possible to collect the clusters and powders together on the substrate and so greatly increase the rate at which deposition takes place? This might then give us a way of using CVD processes for bulk ceramics where production requires a rate at least two orders of magnitude greater than conventional CVD processes. Although this might sound a rather crude idea, it was the basis of the developments that we made in my research group.
Assessment of the Service Life of Materials Exposed to Frost
Published in Christer Sjöström, Durability of Building Materials and Components 7, 2018
Pure frost attack is treated in this paper. By this is meant freeze-thaw in pure water and with “pure” water in the pore system. Thus, salt scaling is not considered. Frost damage will only occur when the internal stresses in the material, occurring as a consequence of transformation of water into ice, exceeds the tensile strength of the material. In a small piece of the material, completely moisture isolated from the surroundings, the stresses at a certain freezing temperature θ will only be a function of the rate of freezing of the pore water, and of the amount of freezable water. σθ=fdwf/dtθ;wfθ where σθ [Pa] is the internal stress at temperature θ [°C], (dw f/dt)θ [m3/(m3•s)] is the rate of freezing of pore water at temperature θ, and (wf)θ [m3/m3] is the amount of freezable water.
Experimental and Artificial Neural Network Evaluation of Frost Formation on Square Finned Tube under Natural Convection
Published in Heat Transfer Engineering, 2023
Soroush Abadi Iranagh, Ali Reza Tahavvor, Mahmood Yaghoubi, Mohammad Mehdi Tavakol
Fins are utilized for various purposes such as air conditioning operations, heating systems, refrigeration, finned-heat exchangers, ventilation, solar processes, electric cooling, electrical systems, etc. The frost layer forming on the tubes and fins causes heat and performance loss by impacting variables such as air properties, wall temperature, and air humidity. Frost forms when the surface temperature is lower than the freezing point of water and the dew point of the air. This exchanging phenomenon limits the airflow area by obstructing the flow channel, raising thermal resistance, and subsequently lowering the heat transfer rate of the system. Fins are widely used in various heating, ventilation, and air conditioning applications due to their geometrical properties such as evaporators in cooling systems, oil coolers, refrigerators, and heat exchangers. Also, fins are available in a wide range of shapes. The square-finned tube is specially used in incinerating devices, economizing systems, and air conditioners.
Automated image segmentation of air voids in hardened concrete surface using photometric stereo method
Published in International Journal of Pavement Engineering, 2022
Jueqiang Tao, Haitao Gong, Feng Wang, Xiaohua Luo, Xin Qiu, Yaxiong Huang
The concrete transportation infrastructures in cold regions such as pavements, bridge decks, airports, and sidewalks are exposed to frost penetration and freezing conditions. Freezing water expands by 9% in volume and produces pressure in the pores of the concrete (Yeon and Kim 2018). The accumulative effects of successive freeze-thaw cycles and traffic loads could eventually lead to cracking, scaling, and spalling on concrete pavements and then cause deterioration of pavement performance (Adkins and Christiansen 1989). The entrained air voids in hardened concrete are formed mainly through the folding actions of the concrete mixer and can improve concrete freeze-thawing performance. The entrained air voids can help mitigate the internal pore pressure during freeze-thaw cycles whereby water escapes into empty air voids (Song et al. 2017). The air-void system with uniformly dispersed small air voids shortens the distance between any point in cement paste and an air void and helps the concrete release the pressure built-up under freezing conditions (Walker 1997). However, densely dispersed air voids or large air voids should be avoided since air voids could weaken the strength of hardened concrete.
Numerical investigation and design of reinforced concrete beams with non-uniform frost damage on the compression and tension sides
Published in Structure and Infrastructure Engineering, 2019
Mingqian Ren, Fuyuan Gong, Koichi Maekawa
The cracks driven by external loading are almost perpendicular to the longitudinal direction and mainly concentrated around the mid-span, within a region of approximately 30 cm. The distribution of large cracks under flexural loads can be affected by frost damage. For example, when the number of FTCs is small (C5-10, C10-10, and C15-10), the large strains in the tension area are symmetrically distributed around the span centre. However, when the number of FTCs increases (200 and 300), the distribution of tensile strains is no longer symmetrical but appears on one side of the nearby mid-span. This is because the frost expansion is non-uniform, and its induced cracks are randomly orientated. As a result, the major cracks may initiate under flexural loads and propagate rather randomly. In other words, the broken symmetry of coupled damage by the FTCs and mechanistic actions is successfully reproduced computationally.