Electric heating – Heating devices – Combined with diverse-type art device
Reexamination Certificate
2001-10-29
2004-11-30
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
Combined with diverse-type art device
C219S541000, C014S073000, C404S071000, C404S079000, C392S432000
Reexamination Certificate
active
06825444
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a system for removing snow and ice accumulation from concrete surfaces, and, more particularly, to a heated bridge deck system and the materials and method of fabrication and use.
BACKGROUND OF THE INVENTION
Paved surfaces are prone to ice accumulation in winter weather. Concrete bridge decks are particularly vulnerable to icing in these conditions and also to frost formation in moderate temperatures since they are completely exposed to the air. Bridge decks generally freeze before the roads approaching them. Even slight ice accumulation on roadways can make driving treacherous. Statistics indicate that 10 to 15 percent of all roadway accidents are directly related to the roadway and its environment. This percentage alone represents thousands of human injuries and deaths and millions of dollars in property damage each year. Ice accumulation on paved surfaces is not merely a concern for motorists; icing of pedestrian walkways accounts for countless personal injuries, some potentially serious, due to slipping and falling.
In addition to natural melting and traffic movement, approaches to removing ice from paved roads and walkways traditionally involve mechanical treatments such as plowing. However, as the bond between ice and pavement can be quite strong, plowing alone may not be completely effective. In the alternative, road salts and chemicals for deicing are commonly applied to roadway ice accumulation. These chemicals melt into the ice and spread under the ice layer to help break the bond between the ice and the pavement. This can be rather effective, especially in conjunction with subsequent mechanical removal.
The most common deicing chemical used by highway agencies is sodium chloride (NaCl), commonly referred to as road salt. Road salt is also used to deice pedestrian walkways. It is usually used alone or mixed with fine granular particles such as sand. The temperature for effectively using road salt in deicing applications ranges from −10° C. to 1° C. (14° F. to 34° F.).
Another chemical frequently used in deicing operations is calcium chloride (CaCl
2
). Calcium chloride has qualities preferable to road salt in that it adheres better to paved surfaces at lower temperatures and has a freezing point below that of sodium chloride. One of the drawbacks of calcium chloride, however, is that it is more expensive than road salt. Therefore, rather than utilizing calcium chloride alone, it is often used in combination with road salt in low temperature (i.e., temperatures below −10° C.) deicing operations. A further drawback is that the residual calcium chloride remains wet on the road surface, causing slick pavement. It also causes melted snow to re-freeze into ice when the temperature decreases.
The primary problems with using chloride salts as deicing agents involve the corrosive effects of the chloride ions present in the aforementioned chemicals. The use of chloride salts causes damage to concrete, corrosive damage to reinforcing steel in concrete bridge decks and other roadway structures, corrosive damage to automobile bodies, and pollution of roadside soils due to concentrations of sodium and chloride in water runoff. Furthermore, the use of salt produces osmotic pressure causing water to move toward the top layer of the pavement where freezing takes place. This action is more severe than ordinary seasonal freezing and thawing and causes greater stress to the surface of the pavement. These problems are a major concern to transportation officials and public works due to rapid degradation of existing concrete roadways and bridge decks.
Alternative chemicals which seek to replace chloride salts have been developed. Calcium magnesium acetate (CMA) is one alternative. Studies indicate that, unlike chloride salts, CMA is not likely to have an adverse effect on the environment. However, CMA is slower acting and less effective than chloride salts at lower temperatures, in freezing rain, in dry snow, and in light traffic. The application of CMA to the road surface also requires a larger truck capacity and larger enclosed storage space than chloride salts. Thus, CMA is a more expensive and less effective alternative to chloride salts.
Other deicing chemicals have been tested by various highway agencies with mixed results. Urea (CO(NH
2
)
2
, a soluble nitrogenous compound, is commonly used by airports as an ice control chemical due to it low corrosivity. However, urea is only effective at temperatures above −9° C. (15° F.) and is less effective and more expensive than road salt. Magnesium chloride (MgCl
2
) is sometimes used as a substitute for calcium chloride because it is less expensive and works at similarly low temperatures. But, while it is effective in melting dry snow, magnesium chloride is less effective in melting ice. Formamide (NCONH
2
) is a less corrosive alternative to chloride salts but is much more expensive, and has a higher freezing point which lessens its effectiveness in colder temperatures. Finally, tetrapotassium pyrophosphate (TKPP) is an effective alternative for temperatures above −4° C. (25° F.). TKPP has no corrosive effects on concrete and cannot penetrate concrete to affect reinforcing steel. However, it is corrosive to exposed steel (e.g., automobile chassis and brakes) and costs approximately 15 times as much as road salt.
In light of the drawbacks associated with road salts and chemicals for deicing, a significant amount of prior research has been directed toward developing a system for effectively preventing or removing roadway ice accumulation from paved surfaces without the detrimental effects associated with the use of chemical agents. This prior research primarily has centered on the use of both insulation materials for preventing ice accumulation and electric or thermal heating for deicing, but met only limited success.
Insulation of roadway structures and bridge decks is one method currently used to prevent frost and ice formation by reducing heat loss from the surface of the roadway or structure. As bridge decks are particularly prone to ice and frost formation, the underside of bridge decks have been insulated with materials such as urethane foam, plastic foam and polystyrene foam. A similar practice has been used in the subgrade of highway pavements and airfield runways. In addition to reducing heat loss from the surface and preventing ice and frost formation, insulation also seeks to decrease the number of seasonal freeze-thaw cycles to which the roadway or structure is subjected and also to decrease the amount of chemical deicing agent used to deice the roadway or structure.
Polystyrene foam insulation has been used in Michigan, Iowa, Minnesota and Alaska in the United States as well as Britain, Sweden and Canada. Results have shown that polystyrene effectively prevented frost formation in the subgrade of the roadways. Tests with urethane foam have been conducted in Missouri and Nebraska in the United States with mixed results. The urethane foam did help reduce the severity of frost and ice formation on roadways and bridge decks. However, it generally was not effective in achieving a reduction in the number of seasonal freeze-thaw cycles nor in reducing the amount of salt used in deicing applications thereon. Furthermore, there was a significant problem related to the bonding of urethane foam to the concrete.
Overall, insulation is only a partial solution to the deicing problem. Insulation is primarily used as a preventive measure, and can only prevent ice formation at certain temperatures. Once ice does accumulate on the roadway or structure, the insulation cannot be relied upon to remove the ice accumulation.
One viable solution to the remaining problem of removing ice accumulation involves the development of heating systems for roadways and structures. Obviously, by heating the surface of the roadway, structure, or bridge deck to a temperature above the freezing point of water (0° C., 32° F.), the snow and ice thereon will melt, alleviating the need for mechanic
Chen Bing
Nguyen Lim
Tuan Christopher Y.
Yehia Sherif
Board of Regents of University of Nebraska
Jeffery John A.
Shook Hardy & Bacon L.L.P.
LandOfFree
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