Elsevier

Applied Thermal Engineering

Volume 199, 25 November 2021, 117549
Applied Thermal Engineering

Application of dehumidification as anti-corrosion technology on suspension bridges: A review

https://doi.org/10.1016/j.applthermaleng.2021.117549Get rights and content

Highlights

  • Dehumidification is a proactive corrosion protection for suspension bridges’ main cable.

  • A review on different dehumidification systems on suspension bridges.

  • Discussion on limitations and adaptations for main cable anti-corrosion application.

  • Identifying future scenarios and challenges of dehumidification on suspension bridges.

Abstract

The moisture from residual droplets during construction and infiltration of wet air during operation can cause metal corrosion of main cables on suspension bridges. Main cable dehumidification, emerged as a prospective corrosion protection approach, which provides an internal environment of relative humidity below 60%, would significantly mitigate the corrosion. This paper presents a state-of-the-art listicle review of existing dehumidification systems implemented on 47 suspension bridges (e.g., the Akashi Kaikyo Bridge, the Runyang Yangtze River Bridge). Dehumidification methods adopted in suspension bridges, including solid desiccant dehumidification, condensing dehumidification and integrated dehumidification, are elaborated. Based on that, crucial limitations and adaptations of various systems for main cable applications are discussed. Then, technical suggestions concerning the moisture load matching, sensor configurations, full-bridge sealings, dehumidification equipment placement and system division, are given to realize system sustainability and energy efficiency. Finally, this paper examined one potential development of a multi-stage dehumidification system that uses condensing dehumidification and solid desiccant dehumidification, which facilitates cascade utilization of the waste energy and enhances the system efficiency.

Introduction

The suspension bridge is one of the types of bridge structures with the most extended spanning capacity. It is composed of suspension cables, pylons, anchors, suspenders, and bridge deck systems [1], [2]. Among these, the main cable of the suspension bridge is the essential component during the bridge’s design life cycle, which is the main load-bearing structure of the suspension bridge. The functioning of main cables is directly related to the service life of the bridge. The suspension cable, which mainly bears the tensile force, is generally made of steel (steel wire, steel cable, etc.) with high tensile strength. Therefore, the life of the suspension bridge depends largely on the integrity of the irreplaceable main cable. In previous times, the key to prolonging the effective life of the suspension bridge is the inspection, maintenance, and repair of the main cable after the service of the suspension bridge.

The suspension bridges are usually exposed to sulfides, chlorides, soot, dust and other impurities, which can lead to severe metal corrosion. For more than a decade, various countries have being conducting research on anti-corrosion of main cables and other parts on the suspension bridge [3], [4]. It is estimated that the metal loss caused by atmospheric corrosion accounts for more than half of the total corrosion loss in a suspension bridge [5], [6]. Tabatabai [7] detailed reported corrosion status of suspension bridges using both short-term and long-term inspection techniques. Furuya et al. [8] performed a wide field investigation on cable corrosion of several Japanese suspension bridges and found that the lower part and side parts of cables were suffered from severe corrosion due to high humidity. Suzumura and Nakamura [9], [10] performed accelerated corrosion test on suspension cable wires and reported that the life index was less than 10 years when wires were kept in the wet or soaked environments, and 34 years with a Relative Humidity (RH) of 100%. Guo et al. [11] reviewed the corrosion development and some passive rust removal techniques used for corroded steel bridges and identified potential environmental impacts.

The main influence factors of the external corrosive environment on the main cable and other components mainly include humidity, temperature, and local atmospheric composition. First of all, the water vapor in the main cable might be caused by rainwater remaining in the open air before the installation; or it might penetrate into the main cable due to cracks in the coating interfaces or gaps during use. Eventually, a water film would be formed on the surface of the metal wire. The moisture inside cables would be one of the critical elements as a matter of fact that the level of corrosion in steel on the coast is approximately 400–500 times higher than that in the desert [12]. Secondly, as the temperature increases, the steel wire corrosion of the main cable will be accelerated. In addition, the drastic temperature change will result in rupture and exposure of the formed oxide passivation film on the surface of the steel wire [13]. This phenomenon would make the internal metal suffered to the corrosive environment recurrently, thereby creating a new corrosion interface. The higher the temperature and humidity inside the main cable, the faster the chemical and electrochemical corrosion will occur. Thirdly, the severity of corrosion is significantly different in different atmospheric environments. Suspension bridges were mostly installed near water bodies or urban industrial areas. In these areas, the high content of MgCl2 and NaCl solid particles in the air and gases such as CO, CO2, NOX, SO2 and H2S could contribute to a higher degree of chemical and electrochemical corrosion of the main cable [5], [9]. When the main cable steel wire undergoes chemical corrosion, metal oxides, sulfides, halides, hydroxides and other impurities would be generated [14]. What is worse, the corrosion process continues to occur due to the unstable corrosion product films, and the steel wire structure would be permanently destroyed [15].

After continuous efforts and explorations by various countries, an effective suspension bridge corrosion protection method using the dehumidification system has been put forward [16]. Since traditional rust preventive methods were inefficient in Japan due to its weather conditions with high humidity and large temperature changes, a dehumidification system was adopted in the maintenance of Akashi Kaikyo Bridge [17]. Over a six-month operation, the RH in the main cable decreased to the target level, which is 40% and the galvanized steel wires were generally corrosion resistant [18]. In 2012, Taizhou Yangtze River Bridge has employed the dehumidification system in the construction stage and after one year operation of dehumidification system with fluorinated polyurethane paint, the internal RH of main cable was reduced to 55% [19].

As demonstrated in Fig. 1, the dehumidification process is mainly composed of three phases: evaporation of water retained in the cable void, evaporation of water retained at the bottom of the cable, and evaporation of water accumulated on the bottom plate. Compared with traditional passive corrosion protection methods, including plastic and neoprene wrappings, elastomeric painting and oil painting, the dehumidification method would tackle the internal moisture more enduringly and efficiently, either retaining water from past or penetrating water due to the wind forces and seasonal temperature fluctuation. Existing studies have demonstrated that controlling the humidity of the main cable can effectively prevent the formation of a liquid film on the surface of the steel wire, and the chemical reaction process of iron ionization will also be restricted[[5], [20]]. Thus, the corrosion rate of the steel wire would be significantly reduced. Additionally, the inspection and assessment of the main cables of several suspension bridges showed unbalanced water accumulation in the main cables to a certain degree [21]; that is, the lower wire strands would trap more moisture than the upper wire [22], [23]. Also, there is a certain difference in the humidity of the strand surface and the inner wire. The proposed proactive anti-corrosion technology would be the only path to mitigate these dilemmas.

Recent interest in desiccant-based air dehumidification systems has increased considerably due to its promising energy-saving dehumidification capabilities [24], [25], [26]. Sultan et al. [27] comprehensively reviewed desiccant air-conditioning (DAC) systems in various environmental conditions and revealed their economic feasibility. Chua et al. [28] presented recent developments in air-control strategies, including dehumidification in both residents and industrial processes. Zheng et al. [29] provided a scheme for selecting desiccant coated heat exchanger (DCHE)-based air according to different climates and building types. Moreover, regeneration of desiccant-based dehumidification could be realized with solar energy or other low-grade waste heat to further improve efficiency. Shukla and Modi [30] have concluded that a hybrid solar system for liquid desiccant air-conditioning system would consume less than 30–50% of energy of a conventional system. A variety of studies have been conducted in the area of dehumidification concerning desiccant and substrate materials [31], [32], system constructions [33], [34] and application scenarios [35], [36], [37], [38]. However, most studies focused on dehumidification in buildings, rather than on bridges. Outdoor climates, such as temperature and humidity of more severe and rapidly changing patterns, differ from indoor conditions, as do the air dehumidification requirements. To remedy this situation, efforts shall be made to ameliorate the performance of currently available dehumidification technologies towards a specially designed system for suspension bridges.

Apart from the gaps in application scenarios of dehumidification, most previous studies on this proactive anti-corrosion technology were focusing on engineering-wise recordings of the individual bridge. There is a lack of a comprehensive review on main cable dehumidification technology. This paper first introduces the historical development and state-of-art status of dehumidification applied in suspension bridge anti-corrosion systems worldwide. A detailed listing of the adopted dehumidification corrosion protection systems for representative suspension bridges is demonstrated for the first time in this field. Subsequently, several current main active dehumidification methods are introduced systematically. From the perspectives of principles and equipment, the advantages and disadvantages, and applicable conditions of different dehumidification methods are compared and used to provide a reference for the exercising of proactive dehumidification and anti-corrosion systems on suspension bridges. Multiple authentic and verified cases are introduced as the illustration of the air treatment in the main cables of the suspension bridge. Moreover, novel potential energy-conservation dehumidification systems is elaborated. Lastly, after a comprehensive feasibility analysis of the proposed proactive corrosion protection technology, future scenarios and challenges in the application are briefly discussed. Fig. 2 shows an overview of this work. Starting from the methods, principles and equipment of active dehumidification, this paper provides a reference for the design and operation of the dehumidification systems for suspension bridges. It envisages guiding the development of proactive bridge anti-corrosion systems henceforward.

Section snippets

Developments of proactive anti-corrosion in suspension bridges retrofits and constructions

Researchers have spent decades researching corrosion and anti-corrosion problems that have plagued steel wire in main cables and other parts of suspension bridges, with principal components demonstrated in Fig. 3, throughout the history of construction[5].

The traditional main cable protection system of protective paste/winding steel wire/outer protective coating has been serving for anti-corrosion coating on the main cable’s surface, presently and widely[12]. In the middle of the 19th century,

Dehumidification systems design scheme for suspension bridge

As shown in Fig. 7, an established main cable proactive corrosion protection system is mainly composed of a filter unit to remove coarse and fine particles, a dehumidifier to remove moisture from the air, a blower that supplies air to the air clamp, and regularly an aftercooler unit to chill the dry air[2]. More recent systems employed a plenum chamber to create a buffer for the dehumidified air [58], [62], which eliminates the need for an aftercooler. The fully treated air is delivered to the

Feasibility considerations and cost analysis of proactive corrosion protection methodologies

Following the analyses of detailed components, Fig. 19 outlines a general technology roadmap for applying dehumidification systems as corrosion protection when applied to suspension bridges.

In addition to the well-established principle of proactive corrosion prevention of maintaining a dry environment by means of dehumidification technology, a few considerations and clarification must be made for each specific case in order to ensure the feasibility of using this method on suspension bridges.

Future scenarios and challenges in the application of dehumidification system on suspension bridge

Compared with the previous passive anti-corrosion methods, the dehumidification system made it transformed into active anti-corrosion, which achieved good performance in delaying the corrosion of the main cable. However, this system also has its shortcomings. First of all, the cost of the entire system at the stage of installation is relatively high. In addition, it is necessary to continuously provide dry air for the main cable throughout its life cycle, which consumes much energy. Secondly,

Concluding remarks

Considering that metal corrosion would cease when RH is below 60%, dehumidification offers an innovative and potentially beneficial corrosion protection process for suspension bridge. A dehumidification system, providing a dry air protection cover for main cables, can either be incorporated into the bridge’s design or retrofitted during maintenance process. After years of engineering applications, this paper comprehensively reviewed the developments, dehumidification techniques, systematic

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The research described in this paper is supported by the Key R & D Program of Jiangsu province (No.BE2018118), the National Natural Science Foundation of China (No.51520105009), the China Postdoctoral Science Foundation (No.2020M681452) and the Fundamental Research Funds for the Central Universities (No.2242021R20018). The first author would also like to acknowledge the scholarship from China Scholarship Council (Grant No.202006090149).

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