Materials Performance

NOV 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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40 NOVEMBER 2018 W W W.MATERIALSPERFORMANCE.COM MATERIALS SELECTION & DESIGN M Several factors contribute to degra- dation of concrete power poles and significant funds are expended to replace them. In this article, the effects of mechanical activity and cor- rosion in the degradation of the con- crete poles were investigated. To increase the corrosion resistance, a concrete mix design was selected through laboratory tests in such a way that it has minimum penetrability to corrosive agents. The concrete cover was also increased in the lower por- tion of the pole. To reduce mechani- cal bending of the poles, prestressing and change of reinforcement design were employed. Many factors can play a role in early d egrad ation of c oncret e p ower p o l e s, including damage from corrosion and mechanical forces. Corrosive agents and water penetrate through the soil into the buried part of the concrete pole. This can produce a wicking effect where the pene- trating groundwater begins to evaporate after reaching a height above the atmo- spheric-buried interface of the pole. This leads to an increase in concentration of corrosive agents in the lower part of the pole and the occurrence of color changes in this location. The wicking ultimately leads to reinforcement corrosion and as a result, Control of Environmental Degradation of Concrete Power Poles a bba S a ghajani, Subsea R&D Center, Isfahan University of Technology, Isfahan, Iran b ehnaz a ghajani, Department of Civil Engineering, Isfahan University of Technology, Isfahan, Iran cracking and spal ling of th e c oncret e cover. 1 The weight of electrical cables attached to the pole and wind forces can bend the pole. These loads can produce cracks in the concrete in both atmospheric and buried portions. These cracks can accelerate the penetration of corrosive agents into con- crete and as a result, accelerate degrada- tion of the pole. In some cases, moisture, air pollution, and corrosion of the concrete poles in the lower part can result in conditions of leak- ing electrical current from the high-voltage electrical wires through the insulators, to the concrete pole, and then to the ground, w hi ch a c c el erat e s d eg ra d ation of th e pole. 1-4 As shown in Figure 1, there are two dif- ferent types of concrete power poles typi- cally constructed in Iran. The first type has a round section (O poles) and the second has an H-shaped section (H poles). The O poles are prestressed, so they exhibit less bending vs. the cable weight and wind force. Also, a centrifugal method is used in their construction , so centrifugal force helps remove excess water from the con- crete prior to curing. Thus, a high-strength, low-permeability concrete with a minimum water-to-cement ratio is formed. The poles have high durability in normal environ- mental exposure and therefore there is not a mechanical degradation problem in using them in Iran. In contrast to the O poles, the

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